LM Calibration BoreholeLoggingMethods
LM Calibration BoreholeLoggingMethods
LM Calibration BoreholeLoggingMethods
rej~rinkttlfnlm
Mining and Groundwater Geophysiall967
Borehole logging methods for exploration
and evaluation of uranium deposits
Philip H. Dodd, Robert F. Droullard
and Carl P. Lathan
US.Atomic Energy Commhwn
GmrPd Jtinct&n, Colorado
Abstract, M o l e -1 i s thc geophysical methad mast exten&@ RkmB. La dipgraphie tks sondagas eat fa rnithode &pftytgquw la pLfS
wrt in the Udtrrd States for exploratio~md edwtim of wanhi dpandue aux Ems-Unis pour l'expbfrrtim e t 1'6duatlm dei gimnents
&pod&. dammow lop, C o r n r n d j suppkrnentd with a singbz-pobt d'wmiurn. X&s diagmnmas de rayons gamma, mrsmmeat compl&tegar
msfstailee log, m t l y supply about 80 percent of the bask data for om wt m n u m &e r&gfivi& P point unique, fwmissmtt 3Jmkment
regerve c W t i o R a d mu& of the w ~ k r 6 . p
&ngk
~ inf~nnatio~ environ 80 p, 100 des d o n n h de hnse pour k cdcul des &saw de
Tmck-mounted 'rotmy eqnipmcnt i s EMhmody emphy&& r n b a i rst une b o r n parti des rewignernents g6ologiquss des mucites
holes usually hwre a nominai b e t u of 4 112 inches range from 22 t~ sou+&-ntes.
2500 k t in depth, are seldom d, and may be f&d with ais at water. Ott u t i h BR g b 6 M w e foreuse mr un m i o n ; lea emus ont
aCaBbraBw and quantkitive analysis o f ths grass natural mma-ray lw un d i n m h de 4 112 po., urn prafgndkur Be 25 i 25QOpi,, sont t a r a n t
to obtain equhplmrt @a& aad thichess of om hesections m b d m tubgs et sont soit vlC &it rempk d b a .
&ha prtrpathallty between the w a un&r the log curve and the praduct La oallbratbn at i'malyse qurtrrtihtive d'en@strement bnat mmrd de
of the moan Wujvflen t mde and thickness dl?a mdiwtive layer. wens g m f f l a effect& paw &tamher, la qadi& iquivnlente st
R-k density md idaced paramekrs arc d l a t e d from gamma- l'&&smr &.s.inkcsecti~nsde mhefai.sont fondis sw.la pxqaortionaaiIt6
gsmma &-A diremnt technique permits canpllation of natural enhe la stlhee WSe. sws.la mark du diagromme et Itr pra&it I
fadfoactivity to obtain density data from ore zone. Calibration and l'&paimuret dc la qu9th kquivatentes may ennes d'une ccwche radioactive.
mmctian Factors for nonstandard E.onditians an demmrtnwl for e&
p m b in fuU-scale mbdd ha%% GAB- arid RHOLOG, Computer
h &a des r o d = et les p m i t r e s cmnmei sont caleul6s & pa&
ilcs emgistremeats $ammqanm Use technique & tUf&ncu m e t
progrnms wdtten in FORTRAN JI for the 1BM TO90 computar, are wed to d'mulsr In radbactiud naftrrelle paw o b h i r ks d m & dnnstmiefques
qumtltativel~ analyze p m m w a d mrnagamma I* t o obtain des zunes min&&kr#& Les fackurs de &bra& et da e b t r e d m pour des
cquivdent &ad%, tttlcew and bulk den~ty. eonditi~afmormdes 5wt diterminds pour c h y r WnUage- daw les tmus
mreat hvestiptfwls indie& that mtud gamma-ray spec- l P 3 &dIe rk#U?re- Lzs pr-es
ds'PesE CAMLOG et MOWQ
oEws significant additional techniqum for expt0ma"on and evahution. en FORTRAN II pour k caluhldce fsh4 7090 servent P&w
S o ~ i o d i d detectors
e mQ sinde w rnulikharmet p u k beigbt m1y;tcis quantitative das di-es de rayray p m a et dea diagrammes gamma-
ukd in canjunction 4 th the hsic signJ conditioning and &&I pulse gamma afm d'obfenbh qualid,l'ipalsreur eZ la den&& brute iquivdata&
counting systcm, supplemented with automatic gain or spe#um stw La r e c h e t c b en m r s indiquent que la spectrosopie u x rayons
bikers, to make in&m or diffeientd meastuemenb of the - m y gamma nsturels offre de nouveUes Wmiqws supplhsntnires gpilr
aneigizs. Germ Ehawcte~ikticphoto paks of hUium208, bismutb214, llexploration et I'&dwdon d~ g k n m k Dm d6t~~tr.w d7Mm &
and potassium4 m b adeqwu4 d i E e m t b d h spite bf extensive dim et Qs appareiIs b'analyse de tendun d'imputsion i ~ ~ n a simples ux
Wtedng in the formation md bomholrt. oti multiples smt u4iliks ~ ~ n j o m t m u anvtw vn sys6m de con-nm-
ment des signaux & hse et de d c u l num6nlque par Lnpuldon m p 1 b
par une 8mpW1anaukatique w des.slatriltsafews I qatn arm de
pouvoit effemer des mestires int&@es ou didirenWlss des beq@&s
mans mma. ceriaines paintes phowgraphiqw mmt&stiqtw du
Ldiurn-208, #u bismuth-224 et du potmiw-40 peumt etie Men
difsirenciles en dipit d'urte diffhsirm p r ~ n g n c kdans la f o n n a h et dans
le mdage.
Natural gamma-my logging ta debut uranium ore ws fmt Borehale measuterhents, though fraught with problems and
investigated in 1945. Subsequent improvements in methods and pitfdh, offer more than campensating technical md economic
equipment by government and industry have established geo- ndvantages. These indude reduced coring, sampling and analytical
physical logging as a major part of most exploration and costs; continuous dara from which a rnulti~udeof sample intwvds
evaluation programs. Some 80 percent or more of the basic may be d e c t e d and statistically investigated; rdatively larger
engineering and gedcrgid information used by the uranium sample volume; c e r h h data may be obtained Prom previwsIy
mining industry and the Atamic Energy Commission to calculate drilled and casd holes; samples are relatively undisturbed; and
are reserves, prsdict ex tensions of depositsand for mine planning analog records, free of subjective observations, are immediately
is derived from logs of noncoted holes. With the resurgenee of available for qualitative evaluation and correlation.
exploration, particularly as d-r, more widely spaced and Contemporaty Io@g p r o p s for uranium evaluation and
costly holes are drilled, the capabilities to extract m m informa- exptoratioa commmfy include anatog records of naturd gross
tion from the hole w l l significantly assist in the economic search gamma-ray, single-paint resistance, spontaneous potential (SP)
for new dktricts, new favorable environments, and the r a m s and directional measurements. Thm tecords ,are produced by
and resources required by the growing demands of the nuclear tmckmounted units operated by mining or sewice companies
fuel industry. Some major companies and individuals elect to log with semi-
portable equipment, without powered winches and often without mplontioa holes per day or as many as SO shallow holes in the,
benefd of chart mcorders. It is p d b i u to obtain adequate results case of open-pit d i n g sites. Portable equipment, if properly
for many applications with portabh-instruments if these are wdi &signed and operated, can meet many of the I~ggingrequihs-
M i d and &&fully opemted, However, much offie p0rhb18 merits, and hdeed may be necessary for certain rugged terrain or
hstmmmCation is poor and operated by untrained persomet forundergroundlong-hole l o w .
wkich d t s in less than adequate data for qumtibtivu analysis, The holes may be air-Eilled, water-med, ar partially water-
Though not in general USBat this time, suitable caliper tools fdIed; md the inledace is seldurn encounkredatthe same depth
are avabbie a d the caliper 1% b paobbly the b e t method for m w ~ ~ s i measurements
v e in the same hole. Heavy muds are
obtaining the hole-siza corrections required for quantitative log seldom used, mud cake is generally thb, mvaion by ftesh ddlling
mdy&i Although the feasibhi of gamma-gamma l o w for water m y be pronounced, anand the f o m t i o d waters are usually
radioactive minerals, includiing om zones, has been dsmoastrated fresb to slightly saiine. Hence fluid densiQ may be a s k e d to be
by Do& and DmuZtard (13651, den&y~orosity measurements 1.0. T ~ intensity
E of mturd gamma dinti00 ~angesfrom the
haw not hen adopted by industry. Resigtivity and induced equivalent of a few ppm uranium from the intrindc utmium,
pohrbtion [IF) logs are being tested in rhe field but are nut yet thorium and patawium in the rocks, throu* several hundred
routine or dwelopd to full cspabitiky. equivalent ppm in momalous and minetalized rock, to extreme
-tic sucegtibility, neutron-neubn, induction and high-grade zones oonWng several pacent W u m and its
perhaps wen neutron actiwtion or photon fluorescence log&% ~ammaiemitthg decay products. This great range in natural
apperrr to warrant research 'aad development for the radioactive $ m a activity causes revere problem in irrrstrumentationd&gn
miaeral industry. and lagging prmedures.
This p q e r presents a review of a current multipurpose loggins A range in magnitude of g m m s activity of 10s cannot be
sy%m, the principles and m&& for calibration, and quan- adequately spanned by a &I& detector. To resolve slight
titative d y s i s of natural grm gamma-ray md gmmqamma miatinmi of tirhology or to quantitatively aadyze dight
aensiZy logs anomalies equivalent to a few ppm uranium requirts a wisitive
Some pralimhury observations and ~ o p e n t salso are in- detector, yielding at least SO to 1Oll counts per second [cps) to
tr&hced conaexnfng current mlts from a small project recently achieve adequate statistical precision at ~eawnablelagging speck
initiated by the Grand Junctim 0%- of the U,S. Atomio Energy This same detmor would generate several hundredthuusndcps
CoRunissbn to inveswte techniques aad applications of in-hole In a high-grab ore zone of appreciable thickness, which signG
mtud g a m m ~ a yspectmscupy to tsplofation and e v h t i o n of cantly exceeds the capability o f current logging instrumentation.
mmhm resources. Conversely, a detector with adequate sensitivity to maamre
ore-grade materials without averloEtding the pulse-trand&on
General ~onditionsand problems which and counting i n s m k t i o n at perhaps 50,000 or even 106,000
cps would yield too low a count rate from normal IWolo&cunits
iirfluence fogging '
tr, achieve an adequate contrast and statistical precision at
The majorily af producing u d k deposits in ttre United Rate%
, an8 hence the current exploration targ~ts,have relatively d o p e r a t i d logging speeds.
dimnttnuous substratified confiptions and occur in sdhent- A shilar grbb1gn exists ts p n m ~ m density a to-. I
ary r o c k which are ofkn poorly indurated. Orebodiesare found an optimum combination of detector mnaifMty, source strength
a m , below md sttide the water-t9ble. Lihdogic unit3must be
and spacing is selected far adequate statistical accuracy in
defined for correlation and om zones for economic evatution, counting, then if signilkant additional gamma radiatron is
which mge from a few bcbs to tens of feet in thickness. encountered in an ore zam, the total count rate may well tax or
Rotary seismic-shot-hole type dgs are mst cornmanly em exceed the lineat response capbdity d the system. The
ploy& for dritling. The drilling media may be air, water or baak-scattefd rachti'on from the source 51 the probe is obscured
natural mud. The holm have nominal diameters of about 4 112 by the natural gamma radiation from rhinerdhd and oee zones,
inches but may range from 2 to 9 iaches. In most ass the hdes and special logging techniques are n e c q to m e m the
k h t e From the vertical, are ather crooked, and often rough-
density of ore zones.
w d d because of cavinb urahout8, and swelling clay ~ s . Also, though it may be tmpting to use hqx wnsitive crystals
Beeaur of these conditions the probes tend to ride the side and
for gammaray spe~tralmeasurements, it is even mom imperative
hdes have a short H e for I-. Not infrequently pmba not to exceed the gros eount rate which the system can aahiev&
without distorting the puls+hight infomation.
bemm lodged and must b abandoned. Multiplepurpase probes
are -ble to save time in the hole, but excepivt1y complex
and costly probes may not be ecoaomic. Equipment and instrumentation
AZthough recently aplomtion drilling has WQ gettbg Tnrek-mounred gsaphysimt unit m W A D-1A
deeper, the holes seIdom exceed 2500 fact and rrsudy are 200 to Lqrj-&g unit. Figure 1 showti a hck-mounted geophysical unit
$00 k t Qep. Cmsequently, temperatuFe and preww con&- developed by the Grand J ~ t i o nOfka of the U.S. Atomic
tiow are not severe. M a h e probes, large cables and powerful Energy Commission for mearch and development in the field of
winch%, w h as used fa mast petroleum log&& are nat borehole I* a3 appUed to the search for and evaluation of
optimum far urmium logging requbmertts. This permits the we radioactive mineral deposits. The system is more wphissicated
of nnaiter and more mmmverable vehicles for lagging units than required for routine logging and is much more complex than
w h i i must negotiate steep and mmw hill+idi tmih and mall units now in mutine operation by lhe rrlluing and service
drin sibs. Often a logging unit $ expected to service mveraI deep wqanies. Tt is used to make natural gtwumray, neutron,
Dodd, Oroullard and l a t h ~ n
Nuclm &s#mmtati~a
. - > M m t d sodium iDdide crystals, mn- h &afiom
lj2 X lLJ2to 5 X 4 W e s , ate &for the ~ a r h t a p of m
xtmsudng gmma rays i n WmbIas, Tkn c r y d s = opticdiy
mypled 0,vpropriate pfi6b&dtipUw We$, and the w$ut
pules &e d0u@&i 'to the hgging cabla by m e w of m~ampl%se'ra
ad mBIe &ym.
d k .A ,doubl+amored, thff:emnducmt cable of
the 3HO tgpe.is used Fo~i n t m o ~ d n g the prnbe md the
wu$me~k
~wfmt~ equi$mM @t&1 d@m ~
comrhgJv Thec
at&& sad ~ ; f4.e 3HO 10- cable is wnra$cted to an
L ~ n r s uqt ~ dees a m~dmode$hear
o which
fie$ ( & b ~mudel 4J'E))-The mpN&p M d e s a e m . q ad
pulse $hapi= fur the inpets of a s i x f % W la d p e r
'~wiett-%obtd mDdel 5583A) wd utn an&&, spectnun
&biker @amner m&I NC-20). The &I&. &met a&per is
w d ia all thm of its operating modes far vdms appkatiims.
Its QUQW pubes m fed KO B gamg -it whidh ~ , ~by t
a:qstal: clock, TMs unit estabIishq the &ad t$me of the ,sy&em
a i d prw&ks wle@de +@ad timesI in ineremw d 1 micro-
4, ,from 3 tP 13d mkosemds; and its oulput pukes rn
used to driw t h e andug and * t M a t a readout shcuit&
Figure I. 8 0 - t A rnu@upm loggi unit h l w d by US.
Atomic Emrsy' E e r m n h ta support m, materiala prqpqms.
Dowmhale p m b is a m to lwing &!a and 'l- d e k i o r
b r 9 u f i e b qmzraal m ~ r m m th'm
s theirwhd. Figuq 2. SIo& d m , USAEC mqide!
RD-1A geaphydallQgging unit.
F m w s i W i o d v e and 0 t h m S d s
Ptrfse rate is measured with a sder-timer (Hewlett-Packard viewed on arl oscilloscope (Tektronix model RM47) and
modal 5202L) operating as 3 d i a l ratemar. Bimq<aded readout is by an X-.T"point plotter (Houston OmniIpaphic model
decimal data from this unit are converted to an analog mal by 6550).
means of a digital-twnalbg convertex (Hewlett-Pachrd model A resolver-inteator (TMC model 522RA) is used to p m e s
W A ) , which drives a dusrl-chaand s t r i p h a recnrder (West- analyzer-memory dataJ and digital output is recorded on a
r ~ & smodel GS-11-AIU). decimal printer ( F m W m&Ilu)O).
Fulae-rate data for the digital readout are fed to an irrtegxating
di@d voltmeter (Dymec model 240lB) apmting in the fie- Ancilfq instrumtatfan
qmcy made. An extend c.~~1b'matiori pmcalex and time base Slrrfae .equ&ment [~Lcrricbgingg). PoPotentid and cnmt
prorides muntsrper-second output which can be comcted for logs are made with an electric logging unit (Mount Sapris model
dea&time loss by meant of a livpthbq section contrafled by 6464). Eithet spontanehus potential or induced pdarimtion 1 % ~
gating signals from the dead-the unit. The 3CD output of the can be made on the potentid &el while the current hannel
digital vo1tmfer is mhpl~dto a (Hewlett-Packard model 562AR) provides sither singie-point resistance or short-nod resistiv*
decimal printer far digitaldata output. - lags. Analog output from this unit is coupled to the Westrmics
1 n W control signals for $he digital readout are developed dud-channe1 stripchart recorder.
in the synchrudriven depth-mawring system thr~ugba Ii&t- Surfdm equipment (caliper tog&)- Signah f ~ o mthe caliper
activated puke generator. Intewals of 0.1, 0.25, 0.90, or 1.W $rob am.coupled to the digital vobeter (Iaymc mo&124018)
foof may be dected by a switclk ,operatingin the voliagwneasuw mde. The borehole diameter
Surfce eequipment @ec&mmpyj. G m a q a y is curwetted to a voltage which is recorded on the digital printer.
puIses from the various detectors are routed either directly tq a Analog output is generated by measuring the voltag8tc-frequency
1024 channel analyzer (TMC model 1.001) m are conditlonwi converter ogtput of the diital vdbneter b u g h the scaler-timer
thf~tghthe Ortec 410 m p u e r followed by a bias ampUf~er md digitd-to-analog eowarter combinatiun ussd innuclear pulse
(TMC model 343) and a pule sbetcher (arb martel 41 1) prior comtinp
to height mslysis. A digital stabilieer @%4C model 23'OA) controls Test equipment in the Model RD-I A geophysicd 1- unit
both ihe gain and ths bb8ehe of the d y z u r . h c l u d ~the aforementioned digital voltmeter and oscilhmpe,
A d a & output fm the mmorg section of the aadyzer is and a m p pulse generator t%rWey Nucleonics model GL3).
2 so the response will be half that of a full sample volume, Fur this
U sinitple ease, t h e bed boundary is indicated by'the half+mplitude
rr 20 point on the log trace. This is also the i n k tion point on the lag
P curve rep~essntiq~a decrease in the mte of increase in response of
f lo the detector to the material in the are zone.
0 If the sample volume is not spherical, if the boundary is
I0 20 gradational (or the zaae is not homogeneous) and if the zone is
True Ccwnt Rate "N*-l@cps less than one radius thiQ, the mehod cannot rigomsly defme
the bo~ndary.The thickness is, therefom, an empirid!y detep
Figure 7. Nmlinea~iw caused by in* mined estimate which is remarkably good for thicknesses of 2 or
strument dsad time for typ'kal logging mbre feet; iewr thicknews tend t o be ovepimated. Fortuna@
warns ussd by the uranium industry. ly this does not affect determination d %T, which represents
the quantity of radioactive materid; it may caw &@it 'flution'
PrincfpEe of moiysig From h' dibwtion equation (I), gTZ' is and hen* underestimation 6f he average g a l oithe zone. For
determined by numerical integmtian of the response at re- practical mining and reserve calculation this errot ia thickness,
i n t e r ~ & from background to background, fie values to be which is @mafIy small, can be tolerated or ignored because
integrated depend on the logging system and may be the thicknesses les than 2 feet can seldom be economicdIy extiacted
deflection af the andog reeocdat regular interrats or, fura diiid withw t diution. Perhaps future theoretical work will devslop a
systumt the values recorded at agdq intarvds while loBging. The figorow technique.
predsi~nof the integmtion, and therefa= of the analysis, is Cwmtion* VaM quantitative analyses, based M Equatioa 1
dependent on the inWd and number of the values befng
integrated. ' h e average radbnetric or equivalent gmde cT is described in the preteding skction, depend on the proper
dculated by dividing the grade-thickness product GTT by the application of wrrecflans for nonlinearity ia the logging system
t h i e b s T. The thickness is the dimm between t h e ore or bad and for variations of the logging environment from the standard
eonditims of calibration.
bmndatiesnnd may be Wimakd fmm thelog.
A somewhat empirical method has been devised to estimate Dead t h comction. Assuming that adequate instmentation is
the thickness T from the lag. The method is based on a employed, the only sWc:mt tronllnearity in the logging systerp
hypothetical spherical sample volume, which is only a convenient is caused by instrument dead time. If compenotionfordead ttme
rppr&mtion. Figure 6 illuakabs the method. X i shows a is not provided in the logging system, such as -the crystal ch& -
homogeneous ore zone having shp boundaries, several prnitiow dead t i module of the FUTlA system, then each numer@i
Dodd. Droulhrrl and Lathan
I I
PROBE A- S1eeI shell 4.0 inchrl O.D., W a l l 0.237 inch lhick
+31,, inch t h i c k Inn4r ~ h m l l , Ha1 datmctor %x inch v4
a 1.40
0
-
I
1 1
t PROBE 8- STebI #hell 1.0 in!h#8 O.D., wall 0.065 inch thick
I NnI dmtmotor % x $ inch
A
3r
u 1.30
41
a
m
0
C1
*W
t
;q r.20 ----
W
J
P
W B
K
2 1.m -.
1.0
t.0 2.0 sn 10 6.n 8.0 7.0 8.0
anRLnoLt D I A Y ~ T E R IH IHtnts
N=- n .A
2 ' eeo
1 -nf
'.
I 4:
absorber OF @mna rays, such iu water or natural mud, thm F h r a 9. Comction factors for wall4hickneo of canhg wing
r fluid and size are nerrrrary. Correction typical natural gammaray logging prbber
major corrections f ~ hole
InEergmula~fluids and unwud abundana of dements of high
atomic:number in the rocks,
The eHect af free water in the formation is illustrated by the
two la@ in Figure 10. With Um exception d tha 36 percent by
weat of water h model P-W, these models contain essentirrIly
the* same materhls. Hmever, the Jog of the water-sshrattd
m d e l has a distinctly 1- amplitude md areaunder the cum.
F m empirical investigation and qerience, it appl"s &at a
factor derived from the rehtiomhip .
of natural gamma radiation obxuns the scatrered gamma rays noncon d d h g acrd 10- methods, and the density 1 ; i cm
fmm the density probe. supply the otherwise mvdab1e ba-density meawemenL Dry
To overcome this pmbiemr a methud of density lo@% h3ls bulk density pd may be used in geologic investigations and to
been developed wMGh caa~eIsthe bwkgtound of fiamd gamma evaluate mining problms, For a particular ruck typo, such as
mdjatioa and m e m ~ s the. wet bulk &nsity ( h d d and D m l - saadt#one, the d e p e of induration or cementatian, which is
lard, 1965). Wlues for dry density, porosity and water cmkot of indicated by the demity, directly afbcts its competence under
the m&, which are mquired to evaluate uranium depmits, a ~ e mining stresses and its frqnm&tioa.
derived from the wet density measurement. A digital recording Fxactiond porosity # (Equation 61,is mq&d to edmhte pd
system a d a computer program for automatic processing of the and tb water content of the rock. Pofosi~data mppIemcnt
&a contribute sigifhntly to h a ptactid application of ais WoIogic interpretations from other logs, support geolpgia
lag. studies of ore ~ontmlsand genesis, and may be wed to evaluate
water probterns encountered ia mining. A correction for wabr
- Principle of scattered gammst.my dmsity logging content of the host rack is fieeded to determine om grade from
Ektmn densfly rehtPd to bulk densiq. The probe used to natud gmm-ray logs.
measure buLk densiq ph In the borehole contains a c ~ l h a t e d Saturation S, h e fraction of the pore space occupied by
s a w of gamma rays which is separated fmm the detector. water, Is r q i h d to establish the fluid density pf sad 6 cdcutata
Gamma rays from the souroe penetrate the m k and are scatted the water content. Below the water-table 100 pemnt saturation
b a k to the ibtector. Titman and WW (1969, C-Lubek and n a y be assumed, at lest in the case of r& &ing intercon-
&itton (19651, and Ceubeh (1965) have shown that by wing a nected pore space. Above the water-table stturntion may bs
suitable detector and gammaray mew the response i s prowr- measured with a neutron lag or a t i m a t d k r n expmitmce. ,
tianal to the Conyrtrrn scatterfng which is tontro1Ld by the Me.thwf for dsminittg defisiq ~f uuratlklm ore rmw. The
electron density p, of the medium. I f following method and cdculations am used to detemrine the
dry bulk densiw of uranium-bearing -.
mad t h e mwactims. As in the case of natural gamma-ray or
when N, = Avgadro's niirrtber and Z{A is the ratio of atomic other nuclear pulse counting methods, &e response uf the density
number 1o atomic weight, then h? response is also pmpodionaI logging system must be corrected for instrument d e d tinre. If no$
to the bulk density. Tittmm md Wahl(1 %S), and Danes (1960) comctod by the logging system it is made by the computer
have also shown that, with the aecqtion of hydrogen, Z/d of rhe p r o m u&g Equation 2 a d the correctiua B~comesvery
common rock-fom& e1emenb is matly constmi. Themfore, by sign'fitant at the high count rates generated by the cambiied
applying co$wctions for nonstandard Z/A , the -pons of the radiation from the. souroe and urallim om,
s y s m may be cahirated iEl terms of &. Drference method urhg diid spacing The intensity of the
B o ~ P ~Fractional
. porosity # is cdcvfated from the mlationshig scattered gamma wdiadon s& the detector is, witbin certa& limits,
a function of the sourwtdetector spacing. Therefore for a @en
dmsit)r, the response of a probe having a short spacing is r r a~ d
I n f o m d ~ nsought from density logit@ Dry bulk density, Figum 13. Cwnpariwn of density logs of
tather than wet Wty,is uxtd in the volume-to-weight conver- an ore zone. using single spa~ing and
sion for OR reserve ~rrlcubtions.Many dupasits are evaluated by diffetenee msrhods.
Dodd, DrouHard and Latbn
&rewn&arbn of comctiom for h h u i e efficts. k model of The density and caliper - IQB. ipctuding mandty entmd
knifom deadty.which c o n @ h7 holes,r-g in diameter from idenMeation data; im recorded tin perforated tape by the
235 ka 8.50 *chest is used to &ternbe correotbn factors for 1g- system. These are cotlvrrted to p u d e d cardsby an tBM
bo~holeeffects. Whh the pro'ba held stationary agaiast the w d . 047 tape-tq-card convener and additional identihkion md
the c w n t rates far siT-EUed,andwater-mod holes are mewred cmrml data m supplied an manually punched c a d Tfre data
for'short aaB long spacing M d the rates comcted fpr dead time. Cards &R listed for e d i before being submiffad to the
hrreati~msaye computed to noma&$ the FWE sets of data to cemgu tar.
the standard ak-flll~dhole, 4.5 W h e s h diamekr. Cumes
ahowing th@cso@cth for diameter in air- and wate~med holes
for sh& and long spacing Figure 16) w hted by WRAP which
mmputes the coefficients and applicable terns of four pdy-
nomid earrectjon equations similar to Equasion 11. ltttroduction and history. As part of its p t ~ g ~ i ht ol alppart
fndusuy wit11 rescarch md dtvel~prnentof new or improved
Cbrrectlon,& Murca detnjl. TI12 half-life of the Cobdt-dO source explasatiun and evaluation todr, the Grand Junction Office of
is 5.3 years and a comction factor for mum demy a1 the rime the U.S. Atomic Emrm Commrbicn wceatly initiated a smaU
of l o w g is applied by the computer to mahibin the calibration projeet to develop ~plkationsof gamma-my speclrnslropy to
--
equation. field Wesligations. The following cmarmts and obwwrrtions an
CdhriOn of cpdipw p d e . The caliper system is Iinear t h u g h JnAole specud rnearaernents are the result of preriminary and
the operating range md a singI+point mlihmtian is mada by expbrarory studies.
pIachg the p b e in a metd dew of known diarbeter imd As early as 1948 and 1949 hoftadter published on the
adjwtin8 the voltagz in t b divider circuit to obtain the e a m t applkatfon of Nsl(T0 crystah to detect gamma energies from
measurement, law-intensity swrces- The technique ' sona b e m e standard
labamtory practice. DiGiwamd, er d.,[1952), h b%scbbinga
prmeo& Automasic data processing contributes scintillation 1-g unit designed for umnium exploration stated,
mtly to the p k tical application of me dmgitjr logghgmethod "A further advantage i s the fact that he sodium iodide mystat
W u s m y routint maniplatioris are required to interrelate sciniillation intensity k directly proportiond 'to the &orbed
the data fmm the several types oE logs sad to corrw the data ro energy af the iacident gamma ph~tan.T l h makes it pmstble to
standad talibration mnditium. AdditiW mmlpuhtio~~ are obtain gamma enew spectra frPm the material in h e hole
needed to 4cuIate the dry -ty, porosity and wakes content (which is extrtmely useful for rfetemhing the nahttt of the
ar elddy s p d intervals. radioactive marerid thereiay
RHOIBG*, a computer p m written in FORTRAN II fur Laborabry, surface and ftbome n~~asuremeob of gamma
fhe IBM 7090, lms been developed to prams tfie data fmm &a spectra being aapted to the search for ndfoactiue mir.amb
density and caliper log. The computzr cslwlrlbs wd prints out (A.dtrms, 194+ A b m s md Frylr, 1964; Pzrntpeflon and Saigei,
up to 2OC4 densicy and m c b t e d values in a single hale and 1965; Foote, 1967)~
determines the average density or Zones of special interest. An In spite o f numerous fifefences to spectral m~suremwbin
error code is printed at the gpmpdate deph if data from she literature, especially since about 1960, the uranium mining
associated 10sm not available or have been interpolated from industry in the Unibd S taies has made no cme~rtedeffort to
adjacent readings, or if they we dettrmided to be invdid for adopt this potentially valuable tool for expforation and e d w -
mraain portions of the hok. C q s from a given hole may be tion. Possibly the lack of ininrest stas stemmed ftom the
discontinuous, top and bottom depths of as~ciatedlogs need not ~ernporarily restricted market Tor urmium, possibly bec3use
match and, in the absence of specific data, cstimities uf mrrtiin reliable and stable Instrumeflta ti011 w lttr spectral capability was
parametersmay be used. bntb expensive dnd unproven, aad possibly because the open-
tional staffs generally considered the whole aubjecJas 'black bm'
? h e R H O b m p r ~ u a mW. &doped c C. d e ~ e ~ ~i c r wd k - h c d t . In my event, the advantages of down-hole spwtml
~unetionO P ~ CUS.
~. ~turnict'natgy ~gmmtsston. measurements largely remain to be developed and demonsfWed.
Dodd, Oroullard and Lathan
Nahlralgamma-my spectra. Gamma rays are emitted by at least 24 thickness gradustly o b s w ~ speaks until, for a 1-foot thiaknes,
of the 37 common natural radiaisotope of the dtu6~unand those peaks represenfing energies less than one mev we little more
uranium series and potassium Several rmatural garnrna-emitters, than bmIy diwm'ible shoulders along the spectntm. The~eM,
such as bismuth-214, emit gamma photons at m y energies. Well spectrampy in inthe borebde based on nadution of photopeaks
over a hundmd primary energies have been recagnWd, and with is restricted to the enecl5y region genera& above 1 mev. Even
improved resolution in instrumentation the numbr is increasing. above 1 mev the spectra from Zarge samples measured by the hole
Compton scatter bf the p+aq photons within the sample probes contain a larger scattered comp~nentthan 500 to 1000
pmduces a more-or-less continuaus spectnnn of phqtotls with grn laboratory samples: However, photopeaks can be adeqrakly
energies below the photopea of all pairnary energies in the solved by a good logging system to be ofpractical value.
muree. The gamma-rw emitters of major si~*ficmce in borehole In the low-enew region below 0 5 mev, not only ate the
measuremen ki shown .onthe decay sesies diagram ofFigure 3. photopeaks abmted by scatter, but photmlectric absorptioa by
Figure 17 &QWS the high-enqy portion of a spectrllm fora high Z elemenfs, particularly of photoas l e s than 6.1 xnev,
natural soil sample containing peta&siurn, and uranium and distorts the primary s p e m m ; the lawenergy spectrum is
Thorium series. The more prominent photopeaks, i d e n s ~ d in the sensitive to composition {Kartashm, 1961). In fsct, Czubek
Eg!us. am ~ e n e n l l yI~lievedmost useful in down-hole measure- (1965) md dthdrs proposed to measure this absorption of :he
ments, Tlrese include the peak of thallium-208 at 2,62 mev, lawenergy photons from a monoenergetic source ta calculate
which i used to indicate natural thoxium-232; a bismuth-214 effective 2 numbers. and evaluate composition.
pe& nt 1.76 mev, uxd to indicate ntdium-umnium; and the Problem, with instrumentation for quaofitatiw spectral
pohssium-40 peak ai 1.46 mev, used to measure total potassium, measurements dow-hole lrre formidabte compared t o lnbmto~y
'Problems in downhole spectrosopy. Good down-hole spectral and surface work The proportionality be tween. photon energy
measuremen& are mom difficult to achiwe than those at the and pulse height must be nadtaidtd while mmsmitting the signal
sttrface or in the laboratory. The large sample volume 'seen' by ~ s to the ampliEier
through hundreds of feet of I o g g i n ~ cables
the probg wuss the photopeaks ~f the primary energies, md analyzer. Both pndtivtty and e%c@acy for high-energy
y low-enetgy region below .S mev, to be
p ~ r & i c u ~i ~n l the photons increase with crystd volume. StatktiaUy relhhle count-
obscumd by fill-in from Cqmptoon scatter of alI hi&er energies. ing of the wfeated energy bwds is achi~vedin less time with Iarge
As noted by Gregory and Horwood (19611, in~reasingsample crysf&: Hawever, the supporting electronics system must be
capable of linear- response at the resulting high gras courit rate. should be alert to and capable of evduathg data pnerated whge
No sin* detector is optimum fqr a wide range of intensity. exploeg far mare conventiorral deposits. Certainly when quaa-
Environmental factm m o h rigoraus. Temperature, in titatively evaluating deposits containing 8,05 percent uranlum or
prticular, may change rather severeky and rapidly. ScintiIlation- less by radiometric methods, it becornes advIsab1e to eliminate
type deiectori; employing photomultiplier tubes are particularly any bias imposed by p m a rays from 0th than the uranium
susceptible to changes in gain with temperatme. wctral series. Kartashou (1961) d$cusses the nece~ityfor such h-hoL
measurements preclude open- the system on the @inplateau analyses and the probable analytical ems when using a 50 gm
w&h overcomes the pfobbm when gross countins The extended Nal(TI') detector atid iPrrlinute counting time on n maU
t h e requiaetl to obtain a series of stationary or long dynamic a n d y cofitSning about 50 ppm u m b m , 13 ppm thorium and
mmuanients in a deep hole, particularly with fluctuating 2.6 percent potassium. The estimated analytical emn were 4,8
amb3ent temperatures, appears to ~ q u systemb gain sbbilhe percent for utanitlm, 12.7 percenr Tor thorium and 29.2 pemnt
tion. for poYdum. For thw measurements extreme sensitivity is not
Sample geameky and environment cannot be contmHsd in required, and may indad be un&sirabl@at Iigher concentrations;
the borehole. Small deviations from Oalzbratiorl conditions may but excellent precision and accuracy in absolute concentmtion is
not seriously chanp the ratio of photons at the energies desltable.
earnonly selected far spectral analysis of uranium, thorium h d Under favorable conditions certain types of disequilibrium in
potassium; but such deviations wilI affect detemhtions of uranium ops may be detected. The Iow-entrgy photons fom
absolute eonentratitsns. thorim234, prot&tinium-W4 axtd uxani~m-235,a i ~ may h be
differentiated in the laboratury sample, are relatidy mora
Applications to exploration and evabatian. The mast obvious #mpor~i~naI to the uranium tontent than the total spwtrurn if
and simplest appli~atian of gamma spectrosco,pyis to qu&tattv+ the uranium-radium series are not in equilibrium. However, these
ly identie the source of gmmn radiation. A gross gamma-my diagnostic photons are busied in a continuum of wattend
anomaly, whether det-ed From the air, from a vehic.k, on ths g m a s in the lowenew re@n and cannot 'be selectively
outcrop, or from a bow hole log, is unlabeled as to adgin and may measured in fhe borehole. Lyubavin and O v c ~ i k o v(1961)
not indicate the element of interest. In the seardh for uranium proprrsd a merhod based on the relative fraction of gamma
deposits in sandstone it b not uncomman to find anomalies radiation of uranium and its decay products prior to radium and
gemrated by minor concentrations of thotiurnbearing heavy the total gamma radiatim of the uranium-radium series, Blake
W r d s or po$dm-xieh @wcanitie zones. Relatively un- (196 5 ) reported encouraging results from similar preliminary Reid
sophisticated queJ3tative spectmopy will um&y identify the inyegti@tions based on simple Wiss between the hard and total
source(s) of gamma f l y s. spectrum, which were meast~red by enclosing one af two
Radium haloes are, of course, importmi guides In uranium detectors in tbe prok with a physical energy filter.
exp bration. Btoad but low&kmity radiaar;tfve anomaUes, Electronic disfirnination can &arpen the differentiation
equbbalentto only I 0 m f 5 ppm uranium, are potential targets b~tweensoft and hard portions of the spectntm. T h w ratios,
far widwpaced preliminary explora~ondrilling. Homvas, m y which a t best yield small percentage chanss with dkquiIibrim,
sudi appawnt ~ ~ a t hdws m t represent fades changes involv- are extremely musenstv ie tQ tfie individual memternenf ;and the
ing intrinsic potassium or thorium m i n e d . Mbor variations, two measurements, to be valid, must repmsent @e same m p le
sither endchment or depletion, of perhaps 5 ppm in the and, to be reliiabte, require instwentatian wjth almost perfect
uranium-radium goneentratiort, which can be readily obscured by stability. Minor c h ~ g e sin borehole mvironmeat drasticdy
c b p r in gross radioactivity, may be s&ni&ant ggides to affect the bw-energy spectrum and, if not adequate1y corrected.
fmrable areas for detailed expioration. Similarly Moxham, ct d., will cause variation in ratios unrelated f o &@&durn h spite
(1%5), found spectral r n e m m n t s of uranium, tharium and of these problemq inhole disequilibrium rneasuremenh would be
pot&&wn: thorium mtios could be applied to alteration studies immengely valuable and therefore intensive investiga60m axe
as poskble halo-like guides to certain copper and copper-lead-ainc wmmkd to dwelop reliable operatima1 procedums for dis
depasibJn A rimna. equilibrium logging. Closely spaced or continuous re~ordscould
Geolagicf-geochemical environments ,may be 'fi~rprinted' be integrated to ubtain disequiiibdumcometion factors which, if
by cham&ristlc ratim or cWging ratios of uranium: thorium: applied to the gms gamma log of ore zones, would mom
potassium. Eath ofthese elements reacts somewhat dieteatly to accurately indicate the uranium cancentmtian. Even iC the
& m p s in pH, eH. and to common ion concentmtinns. For disquilibriam is only qualitatively indicated, the 103s would be
exmpte. because of the increased mobility of the uranyl ions, a valuable in studying the disequilibrium problem; and a s e k s of
depletion in uranium relathe to thorium or potasdim may measurements might well indicate the position of the s9mpld
indicate a cument ox paleooxidgtian environment (Adams and zone relative to solution roll fronts described by King and Austin
Wmver, 1958). For these studies the absolute conoentration need (1966).
not be determined with extreme accuracy, but the mialive values
require hi& precision and sensitivity.
If low-grade dcpos& of uranium, containing perhaps 100 Summary
pprn, become economically simificant if will become mcessaTy to The uranium mining industry increasingly relies on analysis of
q u a titauveiy distinguish betwen the gamma rays emitted by the Lugs to obtain most of the geologicd and engineering data from
uranium &cay series and those originating in the potassium or exploration and devalapment drtlting.
thorium minerats uf the host rock. This has already become a Na t u d gamma-ray logs can be qumtttafively analywd by the
problem in evdua lion of poteatid m m e s . The mining &dustry CAMLOG compubr pchgram to determine depth, thickness and
PREREG IS TRANTS
Azher A n s a r i P e t e r Dellimore
U n i v e r s i t y of Minnesota U.S. Bureau of Mines
Department of Geology and Geophysics BuiLding 20
310 P i l l s b u r y Drive SE Denver F e d e r a l C e n t e r
Minneapolis, MN 55455 Denver, CO 80225
D. D. Snyder A. D. White
Mount S o p r i s I n s t r u m e n t Co. EG&G Ortec
P.O. Box 449 100 Midland Road
D e l t a , CO 81416 Oak Ridge, TN 37830
Gary Wilson
Utah Power and L i g h t
P.O. Box 340
Moab, U t 84532
William A. Woolson
S c i e n c e A p p l i c a t i o n s , Inc.
P.O. Box 2351
La J o l l a , CA 92037
E r n i e Young
Mount S o p r i s I n s t r u m e n t s Co
P.O. Box 449
D e l t a , CO 81416
John Young
Century Geophysical C o r p o r a t i o n
6650 E. Apache
T u l s a , OK 74115
PREREGISTRANTS
Larry Ball
M e r l e Crew
P h i l i p Dodd
Jack E l l i s
Donald E v e r h a r t
Carl Lathan
C a r l Roach
Fundamentals of
Gamma-Ray Logging
FUNDAXENTALS OF GAMMA-RAY LOGGING
R o b e r t D. Wilson
Bendix F i e l d E n g i n e e r i n g C o r p o r a t i o n
INTRODUCTION
The t e c h n i q u e of p a s s i v e l y o b s e r v i n g t h e gamma r a d i a t i o n e n i t t e d by t h e
n a t u r a l l y o c c u r r i n g r a d i o i s o t o p e s w i c h i n e a r t h f o r n a t i o n s h a s been i n u s e f o r
over t h i r t y years. I n r e c e n t y e a r s , however, t h e r e have been i m p o r t a n t
a d v a n c e s i n b o t h t h e t e c h n o l o g y and methodology of gamma-ray l o g g i n g
techniques. In a d d i t i o n , a c t i v e techniques a r e being developed t h a t s t i m u l a t e
gamma-ray e m i s s i o n from o t h e r w i s e s t a b l e e l e m e n t s .
t h r o u g h a c o m p l i c a t e d decay s e r i e s t o a s t a b l e l e a d i s o t o p e . Dozens of
d i f f e r e n t e n e r g y gamma r a y s a r e e m i t t e d d u r i n g t h e decay of b o t h uranium and LT \
thorium. The most i n t e n s e of t h e s e gamma r a y s a r e e m i t t e d by d a u g h t e r L
, \(-A
F i g u r e 1 shows t h e r e l a t i v e i n t e n s i t i e s f o r t h e ganma-ray e n e r g i e s
e m i t t e d by t h e t h r e e n a t u r a l l y o c c u r r i n g e l e m e n t s p o t a s s i u m , uranium, and
thorium. Each s o u r c e s p e c t r u m i s n o r n a l i z e d t o u n i t t o t a l i n t e n s i t y . Macy of
t h e v e r y l o w - i n t e n s i t y gamma r a y s a r e o m i t t e d from t h e uranium and thorium
s p e c t r a ; y e t t h e c o m p l e x i t y of t h e s e s o u r c e s a s shown i n F i g u r e 1 c o n t r a s t s
s h a r p l y w i t h t h e s i n g l e - s o u r c e e n e r g y from potassium.
When t h e s e s o u r c e s a r e u n i f o r m l y d i s t r i b u t e d t h r o u g h o u t a n e a r t h
f o r m a t i o n , and when a b o r e h o l e probe i s i n t r o d u c e d as shown i n F i g u r e 2, t h e
gamma-ray e n e r g y s p e c t r a i n c i d e n t on t h e probe w i l l a p p e a r a s shown i n
Figure 3 . (These f l u x e s were c a l c u l a t e d by Mike Evans of t h e Los Alamos
S c i e n t i f i c L a b o r a t o r y u s i n g r a d i a t i o n t r a n s p o r t t h e o r y . The s e s s i o n e n t i t l e d
"Gamma-Ray T r a n s p o r t C a l c u l a t i o n s " s c h e d u l e d f o r Wednesday morning w i l l be
l a r g e l y d e v o t e d t o t h e d e t a i l s of s u c h c a l c u l a t i o n s . )
I n t h e p r o c e s s of t r a n s p o r t i n g from e a c h s o u r c e l o c a t i o n i n t h e f o r m a t i o n
t o t h e probe l o c a t i o n w i t h i 2 t h e b o r e h o l e , t h e gamma r a y s undergo b o t h
s c a t t e r i n g and a b s o r p t i o n i n t e r a c t i o n s . The s c a t t e r i n g i n t e r a c t i o n s have t h e
e f f e c t of i n t r o d u c i n g a continuum component t o t h e spectrum t h a t becomes
i n c r e a s i n g l y prominenr a t low e n e r g i e s . T h i s f e a t u r e i s a p p a r e n t i n a l l t h r e e
s p e c t r a of F i g u r e 3 .
LOGGING TRUCK
INSTRUMENTATION
AND
DRAW WORKS
- ,I
FIGURE 3
Sodium I o d i d e D e t e c t o r Response
A b o r e h o l e l o g g i n g s y s t e m l i k e t h e one shown s c h e m a t i c a l l y i n F i g u r e 2 i s
used t o a c q u i r e gamma-ray s p e c t r a a s a f u n c t i o n of d e p t h . The d e t e c t o r
p u l s e - h e i g h t d i s t r i b u t i o n f o r e a c h d e p t h i n t e r v a l must be e n e r g y a n a l y z e d
e i t h e r w i t h i n t h e probe o r w i t h t h e s u r f a c e i n s t r u m e n t a t i o n . The r e s u l t i n g
gross-count o r s p e c t r a l d a t a must t h e n be c o n v e r t e d t 3 r a d i o e l e m e n t
c o n c e n t r a t i o n u s i n g c a l i b r a t i o n c o n s t a n t s t h a t a r e deduced f r o m a c a l i h r a r i q z
Gross-Count Log C a l i b r a t i o n Method
WIOACTIVE DISEQUILIBRIIM L
?SD ITS EFFECT ON GAPMA-RAY LOGS
CONCLUDING XEMARKS
I
RESPONSE
Calibration Standards
Spectral Hardware
/15'2//0*L ->--71* . F . . .. W
B E N D I W D O E SPECTRAL PROBES
PHYSICAL
ELECTRONICS
Voltage 'Regulator
H. V. Supply
Amplifier/Line Driver
DETECTORS
Nal (TI), Ruggedized
Dual Detectors
1.5 x 12 inches
1 x 6 inches (shielded)
Resolution: 9-1 1 %
Spectral Calibrat~onand
Correction Methods
CALIBRATION AND DATA CORRECTION TECHNIQUES
David C. Stromswold
B o b e r t D. Wilson
Bendix F i e l d E n g i n e e r i n g C o r p o r a t i o n
INTRODUCTION
T a b l e 1. S p e c t r a l Energy Windows.
Potassiuui
Uranium
Thorium
MODELS
The c o u n t i n g e f f i c i e n c y of a d e t e c t o r i s d e t e r m i n e d by r e c o r d i n g c o u n t s
i n t h e p o t a s s i u m (K), uranium ( U ) , and t h o r i u m (Th) models a t a d e t e c t o r d e p t h
o f 5.5 f e e t . The K model p r o v i d e s t h e l o w e s t c o u n t r a t e s of a l l t h e models,
and t h u s i t r e q u i r e s l o n g e r c o u n t i n g t i m e s t h a n b o t h t h e U and Th models i n
o r d e r t o o b t a i n e q u i v a l e n t c o u n t i n g s t a t i s t i c s . Background c o u n t s a r e ob-
t a i n e d by p l a c i n g t h e probe i n a l a r g e w a t e r t a n k w i t h t h e d e t e c t o r a t a d e p t h
of 5.5 f e e t . The t i m e s needed f o r c o l l e c t i o n of a d e q u a t e d a t a a l s o v a r y w i t h
d e t e c t o r volume and s h i e l d i n g ( f i l t e r s ) . Counting t i m e s used i n c a l i b r a t i n g a
Bendix/DOE s p e c t r a l p r o b e i n t h e models a r e g i v e n i n T a b l e 3.
T a b l e 3. C a l i b r a t i o n Counting T i n e s .
where
R = AC (1)
R= 3 x 3 matrix of observed count rates in K, U, and Th models after
background has been subtracted
C= 3 x 3 matrix of concentrations of calibration models
A = 3 x 3 matrix of proportionality determined from R
and C.
The elements of the three matrices are defined as follows:
= count rate in ith energy window in the j'th calibration model after
'i j background subtraction;
1 = Potassium
2 = Uranium
3 = Thorium.
C = AmlR
where
where
C,i = concentration of ith radioactive element
A = 2 matrix element of A-1
Water
Water correction factors are deterinined from the ratio of the calculated
concentrations for the wet and dry holes:
Separate correction factors are determined for K, U, and Th and they are used
to multiply the (uncorrected) concentrations of these elements calculated from
field logging data:
Elements
Potassium
Uranium
Thorium
The water correction data for a 1.5 x 12-inch NaI(TL) detector in a 2.1-inch,
centralized probe (Figure 4) have been fitted to the exponential curve
where
Elements c d
Potassium 0.9912 0.0872
Uranium 1.0116 0.0737
Thorium 1.0031 0.0688
Steel Casing
The presence of steel casing reduces the number of formation gamma rays
reaching a detector in a borehole, and corrections must be made to obtain
correct concentrations from the logging data obtained in cased holes. Steel
casings of thickness 0.06-inch to 0.5-inch are available at Grand Junction for
determining casing corrections experimentally. These casings have an inside
diameter of 3 inches and they are 4.5 feet long. They are hung individually
over a detector and counts are recorded in the K, U, and Th calibration
models. In this way, a separate calibration is obtained for each casing
thickness, and changes in both sensitivities and stripping ratios can be
calculated.
Fi - erp ( fi,. x )
where
Parameter Value
Background S u b t r a c t i o n
Conclusion
Logging d a t a c o l l e c t e d i n h o l e s t h a t a r e c a s e d o r have d i a m e t e r s
d i f f e r e n t from t h e s t a n d a r d 4.5 i n c h e s of t h e c a l i b r a t i o n models m g s t be
c o r r e c t e d t o g i v e p r o p e r a s s a y s . The c o r r e c t i o n s c a n be d e t e r m i n e d
e x p e r i m e n t a l i y u s i n g t h e c a l i b r a t i o n f a c i l i t i e s a t Grand J u n c t i o n .
GAMMA-RAY SPECTROMETRIC CALIBRATION FACILITIES -A PRELIMINARY REPORT
P r o j e c t 720085
P.G. Killeen
Resource Geophysics and Geochemistry Dlvision
Abstract
Killeen, P.G., Gamma-ray spectrometric calibration facilities - a preliminary report; Current
Research, Part A, Geol. Surv. Can., Paper 78-lA, p. 243-247, 1978.
In order to make quantitative measurements of radioelement concentrations with a gamma-ray
spectrometer the spectrometer must be calibrated using sources having (1) known radioelement
contents, and (2) geometry similar to that in which the measurement will be made. In the case of
portable gamma-ray spectrometers the measurement in the field will generally be made on relatively
flat outcrop surfaces. This may be simulated using a flat concrete pad approximately flush with the
ground surface. In the case of gamma-ray spectral logging, the measurement geometry is, of course,
a borehole. In this case model boreholes including appropriate "ore" zones can be constructed in
concrete.
Figure 47.1. Location of t h e Geological Survey calibration facilities for portable gamma-ray
s p e c t r o m e t e r s and g a m m a - r a y s p e c t r a l logging equipment.
243
\\ G.S.C. CALIBRATION
2
2
Introduction
In October 1971, t h e G e o l o g ~ c a l Survey of Canada
completed t h e constructlon near O t t a w a of extensive callbra- FACILITIES
tlon f a c l l ~ t i e s for gamma-ray s p e c t r o m e t r y e q u ~ p m e n t a s
mentioned above. They m e e t or e x c e e d t h e recommendatlons
of t h e IAEA (1976). Thls paper comprises a p r e l l m ~ n a r y
report on t h e new f a c l l l t ~ e s : thelr locatlon, d e s c r ~ p t l o n ,
prellmlnary analyses of samples taken during constructlon,
HOLES
and t h e procedure f o r obtaining a c c e s s t o t h e calibratlon
facllltles, and p r e l ~ m l n a r y recommended procedures for
carrylng o u t t h e callbratlon measurements.
/
Location of the Calibration Facilities
The new c a l ~ b r a t l o n f a c l l l t ~ e s a r e located on t h e
QUAR
property of t h e CANMET (E.M.R.) laboratory complex a t PADS 4
Bells Corners approximately l 0 k m west of Ottawa.
Flgure 47.1 shows t h e locatlon. The c a l ~ b r a t ~ o fna c l l l t ~ e s
conslst of a s e t of 10 c a l ~ b r a t l o npads for portable spec- ROAD
t r o m e t e r s , located along a gravel road leadlng t o a n
abandoned quarry In which nine t e s t columns contalnlng t h e
model boreholes a r e c o n s t r u c t e d ( s e e Fig. 47.2). I - 100
O Metres
Calibration Pads for Portable Gamma-Ray Spectrometers
The callbration pads a r e c o n c r e t e cyilnders, 60 c m thick
and 3 m In diameter, maklng e f f e c t ~ v e l ylnflnlte sources ~f
t h e d e t e c t o r of t h e portable gamma-ray s p e c t r o m e t e r 1s
centrally located on and w ~ t h i na f e w inches of t h e s u r f a c e of
t h e pad. Three pads contain d l f f e r e n t potasslum c o n c e n t r a -
tlons, t h r e e contaln d ~ f f e r e n t uranlum concentratlons and
t h r e e contaln d l f f e r e n t thorlum concentratlons. The
dlfferent radloelement concentratlons w e r e obtained by
adding t o t h e c o n c r e t e appropriate a m o u n t s of uranlum ore,
t h o r ~ u m oxide, or nephellne syenlte f o r U, Th, and K Figure 47.2. Detailed locations of t h e 10 c a l l b r a t ~ o npads
respectively. A t e n t h pad, r e f e r r e d t o a s t h e blank pad, was and t h e model holes on t h e property of t h e
constructed wlth n~ , l d ~ o e l e m e n taddltlves. The p r e l l m ~ n a r y CANMET laboratory complex a t Bells Corners.
mean values of t n e radloelement c o n t e n t s of s o m e of t h e
samples taken durlng constructlon a r e glven In
Table 47.1. At t h e t ~ m eof t h ~ swrltlng, not all
o f t h e samples h a v e been analyzed. Thus,
although subject t o revlslon, t h e s e p r e l ~ m i n a r y
values indlcate t h e range of concentratlons
available for calibratlon purposes. The flve
pads a t Uplands A ~ r p o r t , whlch had p r e v ~ o u s l y
been used for callbratlon of portable lnstru-
ments, have a very llmlted range of radlo-
e l e m e n t concentratlons slnce they were
d e s ~ g n e d for c a l ~ b r a t ~ n airborne
g gamma-ray
s p e c t r o m e t e r s (Grasty and Darnley, 197 1) and
wlll continue t o b e used for t h a t purpose. The
new callbratlon pads should greatly Improve t h e
a c c u r a c y and r e p e a t l b ~ l l t yof determinations of
callbratlon factors.
The recommended procedure for carrylng
o u t c a l ~ b r a t ~ o measurements
n IS explained In
g r e a t e r detall on handout s h e e t s provided t o
users of t h e callbratlon f a c l l l t ~ e s . These
Include a d e t a ~ l e dl o c a t ~ o nmap, a t a b l e of pad
numbers wlth thelr radloelement concenrra-
tlOns, and lnformatlon obtaining F ~ g u r e47.3. The nlne c o n c r e t e t e s t columns viewed f r o m inside t h e quarrv
c l e a r a n c e for a c c e s s t o t h e c a l i b r a t ~ o n site. showing t h e "ore zones" and a logglng truck parked above In t h e
Thls lnformatlon may b e obtalned by contacting worklngareaforcallbratlnglogg~ngsystems.(GSC photo 203254-0).
t h e R a d ~ a t ~ o nMethods Sectlon, Resource
Geophysics and G e o c h e m ~ s t r y Dlvlsion of t h e
G e o l o g ~ c a lSurvey of Canada.
Basically t b e callbration procedure for portable g a m m a - If t h e s e d a t a , along wlth the types and serlal numbers of
ray s p e c t r o m e t e r s conslsts of taklng s e v e r a l readings on each t h e s p e c t r o m e t e r s and d e t e c t o r s a r e glven t o t h e G e o i o g ~ c a l
pad In order t o obtaln good counting s t a t l s t l c s , with t h e Survey, t h e c a l ~ b r a t ~ oconstants
n will b e computed; t h e r r
d e t e c t o r a t a sllghtly d ~ f f e r e n t locatlon near t h e c e n t r e of no c h a r g e f o r this service. The use of t h e calibra
t h e pad for e a c h reading. Countlng t i m e s will depend on constants for computing In sltu assays w a s described .
d e t e c t o r slze. K ~ l l e e nand C a m e r o n (1977).
PULLEY
Table 47.1
Pre!in~inary mean radioelement concentrations
for calibration pads
GAMMA - WINCH
Qad Number -
K% e U ppm eTh ppm
BOREHOLE
PK-1-OT 0.88
PK-2-OT 1.48
PK-3-OT 2.87 METRES
PU-4-OT
PU-5-OT
PU-6-OT
PT-7-OT
PT-8-OT
PT-9-OT
PB-10-OT 0.24 0.16
Figure 47.6.
Comparison of unstrlpped and
stripped gamma-ray s p e c t r a l logs
showing a n o m a l i e s caused by K,
U, and Th respectively.
Table 47.2 units of K, then, a r e pprn s/count. The r a w field log IS then
multiplied by K t o give t h e o r e grades in c a s e s of uniform o r e
Preliminary m e a n radioelement c o n c e n t r a t i o n s z o n e s approximately I m or m o r e in thickness (i.e. infinitely
f o r t e s t columns thick). The g r a d e values obtained for thinner zones will b e
lower than t h e a c t u a l grade.
Column Number -
K% e U ppm e T h ppm
In order t o e n h a n c e t h e a c c u r a c y and resolution of o r e
BK-I-OT g r a d e d e t e r m i n a t i o n s in thin beds and complex sequences, '
I High Resolution
. - 5 ~ ~ d ~ & . i 6 6 &
J
~ ~
Spectroscopy
e d /
Gamma-Ray Transport
Calculations
TITLE: A Computer Plodel f o r Calcul a t i n g Gamma-Ray Pul s e - H e i g h t
S p e c t r a f o r Logging A p p l i c a t i o n s
klichael L. Evans
AESTRACT
The response of any instrument is perhaps best the aetector. In aaoition, spectral energy resolu-
unoerstooa in terms of a mathematical mcdel that ticn requirements may greatly accentuate the prob-
spproxirates the measurement process. The spectral lem of cbtaining high-resolution, high-precision
ineasurement of radiation fields with scintillation pulse-height spectra. Hence, an alternate tecn-
counters involves the transpcrt of rzdiation from niqce has been chosen to describe the measurement
its emission in the source, through various inter- of raaiation fielas.
posed media, to the detector. Interactions of the The count rate calculation methoa to be
raciation in the media result in bcth scattereo ana described is strai~htforwara an0 very fiexible In
unscattered flux components impinging on the its application. The methoo can yielo photon
aetector. The pulse-hei~ht spectrum arising from and/or neutron pulse-height distributions for gen-
the incident flux spectrum aepends on the ranaom eral geometries and various types ci aetectors
nature of the scinti 1 laticn process ano the photo- incluaing orcanic and inor~anic scintillators,
sultiplier respcnse. sol ia-state cetectcrs, ano Gas prcportlcr8ai
This Teasurerent process ctfi be rioae!eo by the ccunters. The pulse-hei~nt spectrw c(rc,n;
"cnt? Carlo rethcd. Eoqtiever, scne mocei ~ecmetries observe0 in a ceteczor in a raoiation fjela ~ i v f n
result in Jerj wezs rzciatian fluxes incicsnc on
- -
by i(r,:,Ej can te computia 6s:
300-channel inacrix is neeoea to aescrioe the
response of tne detector to garrma rays incident on
tne aetector at a single point ; ,dith a sing12
-L
A
angle of inciaence G . Clearly, then, certain
hhere' c(rd,h) is the nufiber of events in simplifying assumptions must be aade ~f tiign-
pulse-height channel h (cnts/s/PieV) when the aetec- resolution, nigh-precision response function maps
t3r is located at point Td in the model geometry. are to Se generatea in reasonaoie computer execu-
The angular flux ?(T,$,E) (particles/cm2 /s/sr/ tion times.
MeV) is the number of particles passing through Radiometric logging is pertorfiea in scurcel
point ? in the direction 5 having energy E. The detector ~eometries that frequently result in
anaular flux is computed for all points t in the radiation fields that vary only slokl:, in niasnituae
model by usin9 a one-, two-, or three-dimensional and direction over the detectcr surface. This is
discrete ordinates code. The number of independent true of airborne and surface surveys for which the
spatial variables modeled aepends on the symmetry source is large compareo hith the survey height.
of the problem geometry. The CNETRAN' and In borehole logging, the variation in the raaiati~n
TNOTRAN' codes are currently being used to com- field is small for both centralizes ana siaewallea
pute angular fluxes of interest in the NURE pro- gecmetr ies, provided the ore-bearing forn:ation is
cram. Use of these codes results in angular fluxes large comparea with the detector length. however,
-
that are ccsputea only for discrete values cf the
variables ;, 2 , and E. That is, values
the radiation fielo can vary si~nificantlj in mag-
independent
- - nitude ana cirection over the aetsctor s ~ r f a c ekhen
of Y(r,O,E) are available only at the spatial and logging throuch thin, ore-bear ins zones. In
angular mesh points specifies in the discrete particular, the polar Gepenaence or the fieio can
ordinates transport prcb'iem. The energy oomain is vary consiaerably as a function of aistance from
also subdivided into groups of finite wiath. Thus, the ore zone.
Eq. (1) can be written as sunis over aiscrete values; ;i. good approximation to the pulse-neight ois-
-
-
E r 7
-
+
.
dnepe ji?,?,:) = T ( i - ' , < , i ) d3 is the current at
p i n t 7 in the dlrectlcn 2 . Tne r~nctlonR ( : ,l,i,hj
4
c -. r = ~l [XI
E Q 1 ;
R~;.Q,G.E.~)
I (3
for tne discrete values at which ! is computed. resulting from r3diation inclcent on the cletectcr
-
Tnis greatly reauces the computing effort required surface at ai l pointj r snc azitiiutnai angles 6.
to aeterrnine (or map) trle response function for a The effective detector response is c3mputea at eacn
;I ;en G?iectOr. Even ss, ~(Y,$,i,h) can sti i i be a angie ac for wnich the discrete orcinates c3ae
very larse matrix, depending especially on the proviaes ancjuiar flux values. The secona tsrm is
cpso;;~til;nr?qi;i:.?j in tne energy (E) a d puise- a11 ?quivaient inc1,ierlt c;r:-ent impinsing on t h e
n?ignt , % ~ariacl;es. TIP 2ngu;ir flux s ~ e c t r a 3 i
-
oetector surtace 31 points r frcnr Sne airect;crs
the z ~ : * z ~ ~ -i:c:cE suojuriirce gamma-ray tr~nsport P. it tnis eqbivalent current iaequat?iy Cescr:ctj
i'.,i;;-.i i:l ii;? iri ?nee;.:! it!.tiCtiiTf cont3lnfng 355 zhe aver?,? ,T~;'~IIU;S cc; azi:ilittiai a: v?c:ion ,i
;<s~ss i - 1 u - s:tc'.ra na.jirl.3 :!;e in-lcent rllrr.=:i:. ~ r i z l i t~ie ,j?t2.:'.0:. r'ES2911S
. .
, -,,
"<Svj.,3.31.
-,')'"S. ~SJ-::ns~n~i 3 LA" Je ~,~-ur~~~,-i a
2---.--*- . L C 2 . j 5.'3.. :
y i e l d a c c e p t a b l e e s t i m a t e s of the r e s u l t i n g pulse- The f o l d i n g e x p r e s s i o n i n Eq. (3) hill be bsea
ieignt distribution. These assumptions are t o obtain estimates o f the pulse-height aistribu-
c r i t i c a l t o g r a c t i c a l e v a l u a t i o n o f Eq. (1). If a t i o n s observed i n b o t h t h e a i r b o r n e ana s u b s u r f a c e
separate detector respons? f u n c t i o n were requirea geometries. khile other foloing techniques niay
tc all jossible points of
..
~ n c i d e n c e r , angles o f y i e l a &ore accurate estimates tor certain cjeon:e-
incidence 4 and 6, ana r a a i a t i o n energy E, an tries ana a e t e c t o r s , preliminary results inaicate
i n t r a c t a ~ l e computer ~ r o b l e n would r e . A that iq. ( 3 ) w i l l y i e i a aaequate p u l s e - h e i ~ ; t ~ spec-
t
t r a c c a o l e s o l u t i o n i s o o t a i n e d by assuming t h a t t h e t r a for t h e l o g g i n g cjeometries o f i n t e r e s t . Like-
puise-heignt o i s t r i b ~ t : o n GeJenas s t r o n g l y on o n l y wise, t h e use of a broao p a r a l l e l bean f o r response
+
5 and 4, i n a i s ~ e a k l ydependent on 3 aria r. Using function deternlination may be ififerior to otner
t n i s scnerne, t h e o e t e c t o r response need be e x p l i c - bearnldetector configurations for certain aetectar
i i i y aete:.x:necl f o r o n l y E and Q, l r h i l e an i m p l i c i t sizes ana shapes. However, t h e agreement between
sum o v e r 7 ana @ i s deernea s u f f i c i e n t t o describe ccmputea ana measurea p u l s e - h e i g h t spectra f o r the
t n e d e t e c t o r response f o r geometries i n which t h e a i r b o r n e and subsurface geometries has t e e n gooa i n
and $ aepenaence o f t h e i n c i d e n t p a r t i c l e c u r r e n t t h e i n i t i a l comparisons.
i s 'weak and can be r e p l a i e a by an e q u i v a l e n t sum as The scheme for calculating pulse-height ais-
weii. tributions c(Td,n) using iq. (3) is summarizea
Accurate estimates of the effective detector schematically i n Fig. 3. The one-airnensional ais-
responses Re can be computed for c y l i n d r i c a l 1y C r e t e o r d i n a t e s t r a n s p o r t code ONETRAN i s used t o
A
s;mir?tric detectors by mapping with broad par- compute t h e a n g u l a r flux values Y(r,,:,E) for tne
r ~ l l e i ,earns inciaent it the polar angles ec. l o g g i n g geometry of interest, wnile :he anaiogue
Detectors not having c y l i n a r i c a i symmetry w i l l , in t4onte C a r l o t r a n s p o r t coae GAbIRES i s usea t o d e t e r -
ge!ierl, ? x n i ~ i t s i g n i f i c a n t v a r i a t j o n i n response mine the effective ~etector response
. u ~ t h the 3zinuthal a n ~ l eo f incidence. Sinc? t h e Re;~=oc,E,h). Values of 'e [?,G,E) for different
cietector response code S A F R E S ~ usea in these geometries ana Ke(e=ec,E,n) for aifierent
sT~oies presently treats only aetectors tnat are detectors are stored i n separate f i l e s tnat serve
r i ? h t circular cjlinaers, NE , , d i l l r e s t r i c t t h e f o l - as input to t h e f o l d i n g code ENFOLD. This coae
1 sl.vlng d i s c u s s j c n t o C e t e c t o r s h a v i n g t h a t shape. perform tne sunlmations indicates i n Eq. (33 to
,:jns erati ti on of aetectors having other snapes determine tne t h e o r e t i c a l pulse-height aistrlbuti~n
A
wculd entai 1 g o d ~i fc a t i o n of both tne response c(<,h) fcr a given detector iocation r,.
f u n c t i o n coae as w e l l as the foiding Eq. (3) to Thus, tnis generalized proc2aure permits easy
expi i c i t l y include the effects of aetector azi- calculation of pulse-heiynt spectra for different
mutnal response. ;n practice, the r e s t r i c t i o n ts aetectors \ v a r y i n g i n type, shape, End s i z e ) an0
cy i i n a r i c a l o e t e c t o r cjeometry i j o f 1 it t l e concern, aifferent logging configurations (varyins in
s i n c ? most d e t e c t o r s use0 f o r radionietric logging geometry, c o m p o s i t i o n , and s i z e ) .
anc s u r v e y s a r e r i g n t c i r c u l a r c y l i n a e r s . ixamples of pulse-neight distrioutions gener-
;he zifective d e t e c t o r rosponse R (e=e,,E,nj a t e a i n t h i s day a r e shown beiow. The f l u x s p e c t r a
e L
-
has oeen coixputed f a r a ?-in. Dy ? - i n . NaI c r y s t a l ? j r = O,E,n) observed a t t h e c e n t e r o i an 11.43-cx
u s i n g a broad p a r a l l e l b e a of garma r a y s i n c i a e n t . - i n . ) aiam, air-filled, unczsea, infir!lt+ly
on the en0 face of tne crystal ( oC= o n ) . That l o n g b o r e h o l e a r e shown i n Figs. 4-6 f o r a K, IJ,
response f u n c t i o n Rap i s snown i n Fiss. 1 and 2, and Th source spectrulil, respectiveij. Tne source
~ ~ h : c na r e three-aimensicnal perspective plots of was distrloutea h o m o g e n e o u ~ l ~i n toe formatisn
3
xhe energy vs p d l s e - n e i ~ n c c u r f a c e . Sotn p l o L s use (C = 2.i33 j / c m , P = 0.3, S = 1.0) surrounuing
1
, -, ~ ~ i r i : ? , m i c (cast? :I!, ressonse s c a i s s 53 tnat the t h e b o r e n o i e and corresponoea t~ a ~ r y - ~ e l ~c lnn -t
,c~lir-es o f t::. s ~ : - < 3 c e 3z r,i._;n e n e r g i e s silch as centration of 16.43 per ccnt i, 4.37-opin i, .ins
.~.! - e;! i f T y
f 2 - -
Lne f 22.h 2nc int! first and secorid 1_1.4-?pm ;n, ressctiveiy. cui st-neisnt ;I;s:r.;:;-
RESPCYSE
Fig. 2 The response function map of Fig. 1 viewed from a different perspec-
tive. The map has been rotated clockwise about the response axis
relative to Fig. 1.
I
ONETRAN
ENFOLD
POTASS I UM SPECTRUM
CENTRALIZED GEOMETRY
probe diameter 5 225" BOREHOLE PARAhlElTiLS
crystal size = 15'' x 7" diameter = 4.Y
fluid = air
casing = none
I
02 a4 ob od LO u 14 UI
GAMMA-RAY ENERGY (MeV)
05 la Id 20 Y
CAMYA-RAY EXERCY (MeV)
1
THORI Uit SPECTRCht
CENTRAL] ZED CEOY ETRY
probe diameter = 225" BOREHOLE PARAUETERS
crystal s u e = 1 . 5 x 7(( diameter = 4-51.
fluid = air
casing = none
i
CAYMA-RAYENERGY (MeV)
s l m u j a t e d c e t e r t o r r e s s i u t ~ o n:no 10niinsar:;j.
POTASS 1CY SPECTRUM
Centralized Geometry
pro& diameter = 223' BOREHOLE PARAMFTEX
crystal size = LS' x T' diameter = 4.5"
fluid = air
i
01 0s oa LO 12 14 ~a
GAMMA-RAY PVLSE HEIGHT (MeV)
210'1~ 03 1
10 W -a Zd 50
GAMMA-RAY PULSE HEIGHT (MeV)
?.
- I ?. 2 lse-hei~hr sFecrruK CCCli.L~ltcf o r a ~ r z n i u r ,scbrce cry-v,elcnC c c r c e r -
P,.
trzticn o f 4.37 i ; ~ i - . "1 parmetors, c t b e r thcn ttie sclirce, heC*
icer,t:cal tc thcse fcr Fic. 7.
05 w W w U 30
GAMMA-RAY P C U E HEIGHT (MeV)
i
K MODEL
I Sidewalled Geometry
I
.. .
"lfll', & b L $ ro
Pulse Height (MeV)
a+ t
F i c . 10 Ccrnparison of theoretical and experimental puiie-heisat spectra
observea in the K rodel at the DCE Grana J ~ n c t i o n caiioration
facility. The ccmputec spectrum has synthesized iron n, U, ih spectra
s'milar to those of F i o s . 7 - 9 , assuming radicelement c~ncentr3tions
ceterminea frcm sarpling the K mooel ana ;eriorning chemlcai analysis.
U MODEL
Sidewalled Ceomet ry
oa 0.4 OE 12 1.6 zo rr
I
28
Pulse iieight (MeV)
1 T MODEL
i Sidewalled Ceome try
ular, t h e 3-in. b y 3-in. NaI a e c e c t o r was modeled 2. K. D. L a t h r o p and F. rJ. b r i n k l e y , "TkOTii*N 11:
wrli w i t h r e g a r d t o enerGy resolution and p u l s e - An I n t e r f a c e d , E x p o r t a b l e V e r s i o n o f t h e TkOTRAN
Code f o r Two-Dimensional T r a n s p o r t , " i o s A lamos
height nonlinearity. N a t i o n a l L a b o r a t o r y r e p o r t LA-6848-MS (July
The t h e o r e t i c a l KUT window s e n s i t i v i t i e s agree 1973).
very well ~ i t n tne experimentai vaiues. The 3. 41. L. Evans, "FIDA Technology f o r Uranilim
Resource E v a l u a t i o n , " Los Aiainos Natiorial
poorsst agreement occurs for the thorium sensi-
L a o o r a t o r y r e p o r t LA-6996-PK (Octooer 1977 j,
t i v i t y , where t h e t h e o r e t i c a l v a l u e i s 7.7 p e r c e n t 24-32.
srnal 1 e r than t h e experiinental value. Data t a k e n
4. M. A. Wathews, C a r i . J. Koizumi, ana H i l ~ o nB.
n o r 2 r e c e n z l y by Lqvoorg ( b u t as y e t u n p u b i i s n e d ) Evans, "DOE-Grana J u n c t i o n Logging Noael Gata
Synopsis ," DOE r e p o r t GJBX-76(78).
i n a k o r l d w i d ? round r o b i n s t u d y a t many c a l i b r a -
t'cn facilities, suggests tnat a sensitivity of 5. L. Lovoorg, L. Yotter-Jensen, P. X i r k e g a a r d , and
E. N. C h r i s t i a n s e n , N ~ c l . i n s t r u . and i.l*tn.,
aoout 3.31 f o r p o t a s s i u m 3no 0.125 f o r thorium are
more a c c d r a t e average v a l u e s . I f t n i s i s so, then
-
167 (19791, 341.
KUT Window Sensitivities
Airborne Geometry
Experiment
(Lovborg) 3.17
Theory
(Evans) 3.38
David C . Stromswold
R o b e r t D. V i l s o n
Bendix F i e l d E n g i n e e r i n g C o r p o r a t i o n
The p r o c e s s of l o g g i n g a f o r m a t i o n o f t e n p r o v i d e s a n i n a c c u r a t e r e p r e s e n -
t a t i o n of t h e s p a t i a l d i s t r i b u t i o n of r a d i o a c t i v e m a t e r i a l s , e s p e c i a l l y when
t h e f o r m a t i o n c o n t a i n s t h i n zones of o r e . The l o g shows a g e n e r a l r e p r e s e n t a -
t i o n of t h e o r e ' s d i s t r i b u t i o n , b u t s h a r p zone changes a r e washed o u t and
a p p e a r on t h e l o g a s g r a d u a l t r a n s i t i o n s . The d a t a c a n be deconvolved
s p a t i a l l y t o produce a b e t t e r r e p r e s e n t a t i o n of t h e f o r m a t i o n i f t h e r e s p o n s e
of t h e d e t e c t o r t o t h i n zones i s known. T h i s r e s p o n s e can be measured
d i r e c t l y i n c a l i b r a t i o n models s u c h a s t h e thin-bed models, o r i t can b e
c a l c u l a t e d from l o g g i n g d a t a c o l l e c t e d i n t h i c k - z o n e models which have a s h a r p
t r a n s i t i o n between a n o r e zone and a b a r r e n zone.
I n t h e GAhiLOG t e c h n i q u e ( S c o t t , 1 9 6 3 ) , an i t e r a t i l r e p r o c e d u r e i s used t o
c a l c u l a t e a s e r i e s of 0 . 5 - f o o t - t h i c k a n o m a l i e s . Weighting f a c t o r s f o r 0 . 5 - f o o t
i n t e r v a l s c c m p r i s e a symmetric 5-point f i l t e r which i s p a s s e d o v e r t h e
l o g g i n g d a t a t o s h a r p e n t h e l o g ' s t r a n s i t i o n s between zones of d i f f e r i n g o r e
g r a d e s . The w e i g h t i n g f a c t o r s c a n be d e t e r m i n e d e x p e r i m e n t a l l y f o r t h e
uranium e n e r g y window u s i n g t h e 90" bed of t h e thin-bed c a l i b r a t i o n model.
The s i m u l a t e d h a l f - f o o t anomaly needed f o r GAXLOG c a n b e o b t a i n e d from t h e
2-inch-thick zone d a t a from t h e thin-bed model by summing l o g g i n g d a t a from
t h r e e a d j a c e n t 2-inch zones. !&en t h i s was done f o r a 1.5-inch x 12-inch
d e t e c t o r , t h e d a t a i n F i g u r e 1 were o b t a i n e d f o r a s i m u l a t e d h a l f - f o o t
anomaly. The d a t a i n t h e f i g u r e have a l r e a d y had background s u b t r a c t e d as
d e t e r m i n e d i n t h e b a r r e n p o r t i o n of t h e model f a r from t h e o r e zone. The
c u r v e drawn t h r o u g h t h e d a t a i s a v i s u a l f i t t o t h e p o i n t s . GAMLOG w e i g h t i n g
c o e f f i c i e n t s c a n be d e t e r m i n e d from t h e r e l a t i v e c o u n t i n g r a t e s a t 0.5-foot
i n t e r v a l s from t h e peak a t t h e c e n t e r of t h e s i s u l a t e d o r e zone. R e s u l t i n g
c o e f f i c i e n t s a r e l i s t e d i n T a b l e i f o r t h e c a s e w i t h t h e b o r e h o l e d r y and
w a t e r f i l l e d ( a s i n F i g u r e 1 ) . Weighting c o e f f i c i e n t s a r e a l s o l i s t e d f o r t h e
f i l t e r e d 1-inch x 6-inch d e t e c t o r w i t h t h e b o r e h o i e d r y . N o t i c e t h a t the
c o e f f i c i e n t s f o r t h e 1-inch x 6-inch d e t e c t o r f a l l o f f n o r e r s 2 F d l y from t h e
c e n t e r v a l u e t h a n do t h e o n e s f o r t h e 1.5-inch x 12-inch d e t e c t o r . T h i s i s i n
agreement w i t h e x p e c t a t i o n s t h a t a l o n g d e t e c t o r w i l l have a more s p r e a d o u t
FIGURE 1
URANIUM WINDOW THIN ZONE RESPONSE
I I I I I I
s p a t i a l r e s p o n s e t o a t h i n zone t h a n w i l l a s h o r t d e t e c t o r . The a d d i t i o n of
w a t e r t o t h e 4.5-inch b o r e h o l e had l i t t l e e f f e c t on t h e w e i g h t i n g c o e f f i c i e n t s
f o r t h e 1.5-inch x 12-inch d e t e c t o r .
Hole Distance ( f e e t )
Detector (4.5-inch) 0.0 0.5 1.O 1.5
Inverse F i l t e r
The c o n s t a n t a l p h a ( a ) depends on s e v e r a l f a c t o r s i n c l u d i n g b o r e h o l e d i a i a e t e r
and f l u i d c o n t e n t . The i n v e r s e f i l t e r used t o deconvolve a ganna-ray l o g con-
s i s t s of t h r e e c o e f f i c i e n t s :
where L z i s t h e d i g i t a l sampling i n t e r v a l a l o n g t h e b o r e h o l e .
Hole Alpha
Detector (4.5-inch) i n -1 cm-1
ALPHA PARAMETER
VERSUS
\
BOREHOLE DIAMETER
David C. Stromswold
Bendix F i e l d E n g i n e e r i n g C o r p o r a t i o n
The p r o c e s s of o b t a i n i n g a gamma-ray l o g of a f o r m a t i o n o f t e n p r o v i d e s a n
i n a c c u r a t e r e p r e s e n t a t i o n of t h e s p a t i a l d i s t r i b u t i o n of r a d i o a c t i v e
m a t e r i a l s , e s p e c i a l l y when t h e f o r m a t i o n c o n t a i n s t h i n zones of o r e . The l o g
shows a g e n e r a l r e p r e s e n t a t i o n of t h e o r e ' s d i s t r i b u t i o n , b u t s h a r p zone
changes a r e washed o u t and a p p e a r on t h e l o g a s g r a d u a l t r a n s i t i o n s . The
l o g g i n g s p e e d , gamma-ray p a t h l e n g t h t h r o u g h t h e f o r m a t i o n , and t h e l e n g t h of
t h e d e t e c t o r c o n t r i b u t e t o t h e c r e a t i o n of t h e g r a d u a l t r a n s i t i o n s r a t h e r t h a n
t h e s h a r p b o u n d a r i e s which may a c t u a l l y be p r e s e n t . T h i s smearing does n o t
a f f e c t t h e t o t a l g r a d e - t h i c k n e s s p r o d u c t , b u t i t i s o f t e n d e s i r a b l e t o know
t h e g r a d e s and t h i c k n e s s e s of t h e o r e l a y e r s s e p a r a t e l y .
GAMLOG P a r a m e t e r s
The w e i g h t i n g f a c t o r s c a n be d e t e r m i n e d e x p e r i m e n t a l l y by l o g g i n g t h r o u g h
a n o r e z o n e / b a r r e n zone i n t e r f a c e i n a c a l i b r a t i o n model. The r e s p o n s e of t h e
probe t o a h y p o t h e t i c a l h a l f - f o o t anomaly p o s i t i o n e d a t t h e i n t e r f a c e b e t x e e n
t h e two t h i c k zones can b e c a l c u l a t e d from t h e l o g g i n g d a t a by s u b t r a c t i n g
count r a t e s s e p a r a t e d by h a l f - f o o t i n t e r v a l s i n t h e o r i g i n a l l o g ( S c o t t ,
1 9 6 3 ) . Then t h e c o u n t r a t e d i f f e r e n c e s a r a p l o t t e d , a c u r v e i s o b t a i n e d which
peaks a t t h e l o c a t i o n of t h e i n t e r f a c e and f a l l s o f f on each s i d e . From t h e
magnitude of t h e c u r v e a t t h e peak and a t s u c c e s s i v e h a l f - f o o t i n t e r v a l s on
each s i d e of t h e peak, t h e w e i g h t i n g f a c t o r s a r e o b t a i n e d . For e a s e of
comparison, t h e w e i g h t i n g f a c t o r f o r t h e peak i s g e n e r a l l y a s s i g n e d t h e v a l u e
1.00 and t h e o t h e r w e i g h t i n g f a c t o r s a r e e x p r e s s e d a s f r a c t i o n s of t h i s peak
h e i g h t ( e . g . , 0 . 2 3 f o r t h e 0 . 5 - f o o t p o i n t s , 0.04 f o r t h e 1.0-foot p o l n t s , a n d
0.01 f o r t h e 1;s-foot p o i n t s ) . Khen t h e w e i g h t i n g f a c t o r s a r e a p p l i e d t o
l o g g i n g d a t a , t h e y a r e n o r m a l i z e d t o g i v e a t o t a l weight of u n i t y s o t h a t t h e
g r a d e - t h i c k n e s s p r o d u c t i s n o t d i s t u r b e d . Thus e a c h w e i g h t i n g f a c t o r i s
d i v i d e d by t h e s u n of a l l t h e w e i g h t i n g f a c t o r s [ e . g . , t h e y a r e d i v i d e d by
1.00 + 2(0.28) + 2(0.04) + 2(0.01) = 1.661. T h i s d i v i s i o n w i l l n o t be
i n c l u d e d i n t h e r e s u l t s p r e s e n t e d h e r e , however, because i t c o m p l i c a t e s
comparison of w e i g h t i n g f a c t o r s d e t e r m i n e d f o r d i f f e r e n t b o r e h o l e c o n d i t i o n s .
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*Estimated u n c e r t a i n t y i n w e i g h t i n g f a c t o r s i s -
M.01.
. . , . - - -
- . - . . . . . - . . -.-......... - .-
..... .. .....
. . -
ORE ZONE
- . . . . . . . - - - -- - - - - -
. .- . .-.. -- -- - ---
- . . . - - . . . . .- .... -. .
-- - -- . --.
. - .-- -- ..
----
I
. . . . .- . . - -~ -- . . .
9
- . . . . . . . . . .
- --a +- ---
I
. . . . . -- - . --.-.. .- -.- - -- ---- --.-- - -
-
.
-
--
-
- - -- -- --- -
- . . . - s ...... --
-.. -.-- .
. -. . . -. -
---ap--
.- -.
-
~ . - -- . . -
..
.. . . . . -. - . . . - . -- .... A -..- -
.- . . . - -- - .- -. . . . - . -- . -. -. .-. .- . -.- - ..& ..- - . -- .-. .. -- -- - -- -
i e
~. . . . . . . . . ... -
- 0
. . . - - .- . . - -- - . . . . - .. - -- ..- -. . . . . - -. -- -- - ...... -. 8 -
-.
8 0
9 8
. - . -ap.
0
1 I 1 I I 1 I 1
FIGUPE 2
COWU RATE DIFEFElCE FOR
W-FCOT SEPARATIONS
vs' m
8
-
loco -
I00 - 0
-
Li
!u
k
*s
EI
9
9
d
\ 49
5
0
10 -
\ e
-
@
8
1-
-
I
1 1 1 1 I
3 50 70 90 110 130
CEPM (INCHES)
f o r t h e 4.5-inch h o l e . The same w e i g h t i n g f a c t o r v a r i e s by 38 p e r c e n t when
t h e h o l e s a r e f i l l e d w i t h w a t e r . The g r e a t e r v a r i a t i o n i n t h e a i r - f i l l e d
h o l e s i s e x p l a i n e d by t h e i n c r e a s e d r a n g e of t h e ganma-rays t h r o u g h a i r .
T a b l e 2. Weighting F a c t o r s f o r Century
Model !/go55 P r o b e
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" E s t i m a t e d u n c e r t a i n t y 13 w e i g h t i n g f a c t o r s i s i-O.01.
I n v e r s e F i l t e r Alpha P a r a m e t e r s
A s e c o n d method f o r s p a t i a l l y d e c o n v o l v i n g gamma-ray l o g s i s t h e i n v e r s e
f i l t e r t e c h n i q u e e s ~ o u s e dby Conaway a n d K i l l e e n ( 1 9 7 8 ) of t h e G e o p h y s i c a l
S u r v e y o f Canada. T h i s i s a n o n - i t e r a t i v e t e c h n i q u e t h a t assumes t h e r e s p o n s 2
of a p o i n t - s i z e d d e t e c t o r t o a n i n f i n i t e s i m a l l y t h i n zone i s t h e d o u b l e - s i d e d
exponential
The c o n s t a n t a l p h a (ci) d e p e n d s on s e v e r a l f a c t o r s i n c l u d i n g b o r e h o l e d i a m e t e r
a n d f l u i d c o n t e n t , a n d z i s t h e d i s t a n c e o f t h e d e t e c t o r from t h e t h i n z o n e .
V a l u e s of a l p h a c a n be d e t e r m i n e d from t h i n - z o n e models d i r e c t l y o r f r o =
d i f f e r e n t i a t i n g t h e c o u n t r a t e s o b t a i n e d from l o g g i n g a n i n t e r f a c e between t w 1 3
t h i c k z o n e s of a model. The d i f f e r e n t i a t i o n p r o d u c e s a h y p o t h e t i c a l c o u n t
r a t e p r o f i l e t h a t would 5e o b s e r v e d from a n i n f i n i t e s m a l l y t h i n o r e zone
l o c a t e d a t t h e i n t e r f a c e b e t w e e n t h e two t h i c k z o n e s . m e n t h e p r o f i l e i s
p l o t t e d on s e m i l o g a r i t h m i c p a p e r , t h e s l o p e of t h e c u r v e g i v e s t h e v a l u e o f
a l p h a (Conaway, 1 9 8 0 ) .
I n t h e p r e s e n t e x p e r i m e n t s , t h e v a l u e s of a l p h a v e r e o b t a i n e d by f i r s t
p l o t t i n g t h e d i f f e r e n t i a l c o u n t r a t e s on s e m i l ~ g a r t h m i cg r a p h s and t h e n
s e l e c t i n g t h e d a t a which f e l l a l o n g s t r a i g h t l i n e s i 2 t h e b a r r e n zone f o r
e n t r y i n t o an e x p o n e n t i a l curve f i t t i n g r o u t i n e t o determine alpha. In this
way, t a i l s of t h e c u r v e s which d e p a r t e d from a n e x p o n e n t i a l r e l a t i o n s h i p were
a v o i d e d , and b e t t e r v a l u e s of a i p h a were o b t a i n e d t h a n c o u l d 3 s d e t e r n i n e d
from s t r i c t l y g r a p h i c a l mechods. The r e s u i t s f o r t h e f i l t e r e d EenCiv p r o b e
s i d e v a l l e d i n c h e g r o s s ~ a n i a - r a v w a t e r model a r e shown Ln Tab12 3 f o r ;ole
d i a m e t e r s f r o 3 L . 5 i n c h e s ;o 3 . 6 i n c h e s . For w a t e r - f i l l 2 d h o l e s , t3.s v z l u e o f
a l p h a d s c r e a s e d f r o a 0.31-inch-' t o c.27-inc5-' a s the hole dianecer
i n c r e a s e d from 4.5 i n c h e s t o 8.6 i n c h e s . T h i s c o r r e s p o n d s t o a 1 3 p e r c e n t
change i n a l p h a a s a f u n c t i o n of w a t e r - f i l l e d h o l e s i z e . The s m a l l e r v a l u e s
of a l p h a mean t h a t t h e gamma-rays a r e l e s s a t t e n u a t e d i n t h e l a r g e r d i a m e t e r
w a t e r f i l l e d h o l e s . T h i s i s r e a s o n a b l e b e c a u s e t h e gamma-rays w i l l t r a v e l
f a r t h e r t h r o u g h w a t e r t h a n t h r o u g h t h e c o n c r e t e of t h e c a l i b r a t i o n model.
Only t h e 4.5-inch h o l e was logged d r y , and a v a l u e of 0.29-inch-I was
o b t a i n e d f o r a l p h a . The d e c r e a s e i n a l p h a from 0.31-inch-I f o r t h e same
hole f i l l e d with water i s again c o n s i s t e n t with a t t e n u a t i o n d i f f e r e n c e s f o r
gamma r a y s i n a i r and i n w a t e r .
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References
John G. Conaway
McPhar Geophysics
I n t r o d u c t i o n and Background
I d e a l l y , w e would l i k e g a m a r a y l o g s t o g i v e e x a c t i n f o r m a t i o n
r e g a r d i n g t h e q u a n t i t y and d i s t r i b u t i o n of r a d i o a c t i v e m a t e r i a l ( s a y ,
uranium o r e ) w i t h d e p t h a l o n g a b o r e h o l e . I n t h i s i d e a l gamma r a y
f a c t o r s i n t e r f e r e w i t h t h i s i d e a l , and d i s t o r t t h e shape of t h e l o g .
d i s t o r t i o n , t h e r e b y c a u s i n g t h e p r o c e s s e d gamma r a y l o g t o approach t h e
deconvolution techniques.
a r e t h e e f f e c t of t h e a n a l o g r a t e m e t e r time c o n s t a n t ( f o r a n a l o g s y s t e m s ) ,
t h e e f f e c t of d e t e c t o r l e n g t h , and t h e e f f e c t of b o r e h o l e p a r a m e t e r s
i n c l u d i n g d i a m e t e r , c a s i n g , and f l u i d . I n g e n e r a l , t h e most s i g n i f i c a n t
zone o b v i o u s l y a r e n o t c o n s t r a i n e d t o t r a v e l i n t h a t zone, b u t , i n f a c t ,
p r o p a g a t e i n a l l d i r e c t i o n s ; s o l i d r o c k i s t r a n s l u c e n t t o gamma r a y s .
Thus, a t h i n r a d i o a c t i v e zone p e r p e n d i c u l a r t o t h e b o r e h o l e ( F i g u r e l a )
smeared anomaly s p r e a d o v e r p e r h a p s 1 - 2 m p e r p e n d i c u l a r t o t h e t h i n
zone (Figure lc). This smeared anomaly may be called the geologic
number
that date. Further work by Suppe and Khaykovich (1960) and Davydov (1970)
laid the foundation for the concept of the geologic impulse response,
some modification, has proven quite useful in dealing with the geologic
impulse response. Roesler (1965) applied gamma ray logging for making
between detector length and spatial resolution; Roesler did not suggest
shape of gamma ray anomalies (Czubek, 1961; 1962; 1969) and on the
however, Czubek and Zorski (1976) report that Jonas applied the
techniques incorrectly. Jonas has certainly not been alone in his
valid for unprocessed gamma ray logs, under ideal conditions the
average grade over a complete gamma log anomaly having area A (from
This was the well-known GAMLOG program, which represented the earliest
gamma ray logs. The response of the logging system to a thin zone of
Given that the equation G = KA/T is valid, then the anomaly resulting
determined thin zone response function is applied to the raw field log
and t h e r e s u l t f e d back i n t h e form of an e r r o r s i g n a l . This process
c o n t i n u e s i t e r a t i v e l y u n t i l t h e d e s i r e d d e g r e e of improvement o c c u r s ,
o r u n t i l t h e p r a c t i c a l l i m i t imposed by n o i s e i s reached.
e s t a b l i s h e d as a p o w e r f u l group of r e l a t e d t e c h n i q u e s f o r t h e a n a l y s i s
of d a t a g a t h e r e d s e q u e n t i a l l y i n t i m e o r s p a c e . I n geophysics t h e s e
t e c h n i q u e s a r e a s s o c i a t e d l a r g e l y w i t h seismology, a l t h o u g h t h e y a r e
c o n s i d e r e d s e p a r a t e l y t h e e f f e c t s of t h e g e o l o g i c impulse r e s p o n s e ,
computer-simulated gamma r a y l o g s i l l u s t r a t i n g t h e s e e f f e c t s b o t h i n
t h e i d e a l c a s e and i n t h e p r e s e n c e of s t a t i s t i c a l n o i s e ( u n a v o i d a b l e i n
n u c l e a r l o g g i n g ) , u s i n g a combined i n v e r s e f i l t e r ( s p a t i a l d e c o n v o l u t i o n )
and smoothing t e c h n i q u e .
T h e o r e t i c a l l y t h e two t e c h n i q u e s g i v e i d e n t i c a l r e s u l t s i n t h e i d e a l c a s e .
I n p r a c t i c e , s l i g h t d i f f e r e n c e s between t h e p r o c e s s e d l o g s r e s u l t from
u n a v o i d a b l e a p p r o x i m a t i o n s made i n a p p l y i n g b o t h t e c h n i q u e s . Inverse
f i l t e r i n g h a s t h e a d v a n t a g e t h a t i t r e q u i r e s o n l y on t h e o r d e r of 3% a s
b e a v a i l a b l e t o t h e computer b e f o r e p r o c e s s i n g can b e g i n , i n v e r s e
f i l t e r i n g i s a one-pass s e q u e n t i a l o p e r a t i o n and t h u s c a n be a p p l i e d
i n r e a l time d u r i n g t h e l o g g i n g o p e r a t i o n , g i v e n s u i t a b l e equipment.
p e r p e n d i c u l a r t o t h e b o r e h o l e i s c a l l e d t h e system impulse r e s p o n s e ,
o r t h e system r e s p o n s e f u n c t i o n . I n an i n f i n i t e s i m a l l y t h i n borehole
u s i n g a p o i n t d e t e c t o r t h e system r e s p o n s e f u n c t i o n $(z)would g e n e r a l l y
z i s d e p t h a l o n g t h e b o r e h o l e and a i s a p a r a m e t e r r e f e r r e d t o a s t h e
shape c o n s t a n t .
E q u a t i o n ( 1 ) d e s c r i b e s a double-sided e x p o n e n t i a l , which h a s a
b e a u t y of t h i s e q u a t i o n f o r t h i s a p p l i c a t i o n i s i n i t s s i m p l i c i t y . By
i n v e r s e f i l t e r i s a d a p t e d e a s i l y t o changing c o n d i t i o n s . Moreover,
may be removed from the data separately, and in any order (at least to
the limit that they may be removed at all). Thus, it is not necessary
in the log near the radioactive zone, the extent depending on borehole
diameter, detector size, ratemeter time constant, etc. These may also
be considered individually.
meters on the shape of the system response function. Such effects have
1971; 1972), Rhodes and Mott (1966), McDonald and Palmatier (1969),
Davydov (1970) , Conaway and Killeen (1978a), Conaway (1979, 1980a, 1980b,
1981), and Conaway et a1 (1979, 1980). Other work by BFEC and LASL
formation.
..
(e g the 1.76 Piev2l4gi window of uranium) .
For unscattered gamma rays, a decrease in the energy of the
Conclusions
obtained.
Figure I
(a) Geologic column showing an infinitesimally thin
radioactive ore zone sandwiched between two thick
barren zones, a 'geologic impulse' of radioactive ore.
(b) Plot of radioelement concentration with depth
corresponding to Figure 1a.
(c) Noise-free response of a pant-detector to the thin
ore zone, the 'geologic impulse response'.
REFERENCES
Conaway, J . G .
1979: Problems i n gamma-ray l o g g i n g : The e f f e c t of d i p p i n g
zones on t h e a c c u r a c y of o r e g r a d e d e t e r m i n a t i o n s ; i n
C u r r e n t Research, P a r t A, G e o l o g i c a l Survey of Canada,
Paper 79-lA, p.41-44.
Czubek, J . A .
1961: Some problems of t h e t h e o r y and q u a n t i t a t i v e i n t e r -
p r e a t i o n o f t h e gamma-ray l o g s ; Acta Geophysica P o l o n i c a ,
v . 9 , p.121-137.
1966: P h y s i c a l p o s s i b i l i t i e s of gamma-gamma 1 o g g i n g ; g
R a d i o i s o t o p e I n s t r u m e n t s i n I n d u s t r y and Geophysics,
volume 2 , I n t e r n a t i o n a l Atomic Energy Agency P r o c e e d i n g s
S e r i e s , IAEA, Vienna.
Czubek, J.A.
1969 : Influence of borehole construction on the results of
spectral gamma-logging: in Nuclear Techniques and
Mineral Resources, International Atomic Energy Agency
Proceedings Series, IAEA, Vienna.
1971: Differential interpretation of gamma-ray logs: I: Case
of the static gamma-ray curve; Report No. 76011, Nuclear
Energy Information Center, Polish Government Commissioner
for Use of Nuclear Energy, Warsaw, Poland.
1972: Differential interpreation of gamma-ray logs: 11: Case of
the dynamic gamma-ray curve: Nuclear Energy Information
Center, Polish Gov. Comm. for Use of Nuclear Energy,
Warsaw, rep. no. 793/1.
Davydov, Y.B.
1970: Odnomernaya obratnaya zadacha gamma-karotazha skvazhin
(One dimensional inversion problem of borehole gamma
logging); Izvestiya Vysshoya Uchebnoye Zavedeniya
Geologiya i Razvedka, No.2, p.105-109 (in Russian).
Jonas, J.T.
1975: Digital data processing techniques applied to the natural
gamma-ray log; M.S. thesis T-1778, Colorado School of
Mines.
Roesler, R.
1965: Ein neues Auswerteverfahren fur radiometrische
Bohrlochmessungen uter besonderer Berucksichtigung der
K2 0-Bestimmung aus Messungen der naturlichen Gammastrahlung
in Bohrlochern; Freiberger Forschungshefte, C180, Geophysik,
VEB Duetsch. Verlag Fur Grundstoffindustrie, Leipzig.
Scott, J.H.
1962: The GAMLOG computer program: U.S. Atomic Energy Commission
rep. RME-143, September, Grand Junction, CO.
Stromswold, D.C.
1979: Measurement of the deconvolution parameter "a" for
uranium; Spectral Gamma-Ray Borehole Logging Technical
Note, Bendix Field Eng. Corp., Grand Junction, Col.
Suppe, S.A.
1957: Gamma-ray borehole logging; Radiometric Methods in
the Prospecting of Uranium Ores, V.V. Alekseev,
A.G. Grammakov, A.I. Nikonov, and G.P. Tafeev, ed.,
Translation available as UC-tr-3738 (Book 2), U.S.
Atomic Energy Agency.
Wilson, R.D.
1979: Log deconvolution with the inverse digital filter;
Spectral Gamma-Ray Logging Technical Note 9, Bendix
Field Engineering Corp., Grand Junction, Colorado.
Gross Count Logging
Reduction and Analysis
of Field Logs
. -
K(R) -I
P I- 70
CALIPER
-I
INCHES
1.0 I- 7
U(A) PP#
-1 75. I- 100
T(R) 4
PP#
10.
, 40
F I E L D PROCESSING FOR LARGE N A I DETECTOR
IFSMALL N A I DETECTOR
THEN GO TO 2x2
THEN GO TO 3x3
WAS
,
'3x3 WAS 2x2
T(RFIW) CPS
1 3.5 I- 10
HOLE TRUCK DEMD LOG TRUCK 1980
AREA HOLIDFlY INN, G J COLD SER # 5
UPER R. PRICE DATE 02-17-81
CALIPER INCHES
r i 1.0 I- 7
THE EFFECTS OF BOREHOLE DIAMETER, BOREHOLE FLUID,
AND CASING THICKNESS ON GAMMA RAY LOGS IN
LARGE DIAMETER BOREHOLES
Project 740085
Conaway, J.G., Allen, K.V., Blanchard. Y . B . , Bristow. Q., Hyatt, W . C . , and Killeen. P.G.,The e f f e c t s
o f borehole diameter, borehole fluid, and casing thickness on gamma ray logs in large diameter
boreholes; & Current Research. Part C , Geological Survey o f Canada. Paper 79-lC, p . 37-40. 1979.
Abstract
The response o f a gamma ray logging system to a thin zone of radioactive material depends on a
number o f instrumental. borehole, and formation parameters. This paper considers the e f f e c t s of
borehole diameter, borehole fluid, and casing thickness on the shape o f the system response function
and the area beneath it in total-count gamma ray logging.
Introduction a n d C z u b e k (197 1) w h e r e i n t h e n o i s e - f r e e r e s p o n s e 6 ( 2 ) of a
p o i n t d e t e c t o r t o a t h i n z o n e of r a d i o a c t i v e m a t e r i a l a t
T h e n o l s e - f r e e r e s p o n s e of a g a m m a r a y logging s y s t e m
d e p t h z = 0 w a s a p p r o x i m a t e d by
t o a t h i n z o n e of radioactive m a t e r i a l p e r p e n d ~ c u l a r t o t h e
b o r e h o l e 1s c a l l e d t h e s y s t e m r e s p o n s e f u n c t i o n . T h e s h a p e @ ( z ) - -e
a2 - a / z I
a n d a m p l i t u d e s of t h e g a m m a ray log f r o m a b o r e h o l e a r e
d e t e r m i n e d by t h e o r e d i s t r i b u t i o n a n d t h e s y s t e m r e s p o n s e w h e r e a is a c o n s t a n t f o r a given s e t of I n s t r u m e n t . o o r e h o l e .
f u n c t i o n ; t h u s , s u c c e s s f u l q u a n t i t a t i v e i n t e r p r e t a t i o n of t h e a n d f o r m a t i o n p a r a m e t e r s . The I n v e r s e f i l t e r c o e f f i c i e n t s a r e
log d e p e n d s o n a k n o w l e d g e of t h e f o r m of t h e s y s t e m g i v e n by
response function. T h e s h a p e a n d a r e a of t h l s f u n c t i o n
depend on man\ instrumental. formarlon, and borehole
p a r a m e t e r s . In t h s p a p e r w e c o n s l d e r t h e e f f e c t s of t h r e e
borehole parameters: borehole dlameter (over t h e range from
w h e r e Az 1s t h e s a m p l i n g i n t e r v a l a l o n g t h e b o r e h o l e .
9 - 3 3 c m ) , b o r e h o l e fiuld ( a l r o r w a t e r ) , a n d c a s i n g t h l c k n e s s
( f r o m 1.6-12.7 m m s t e e l casing). T h e r e s u l t s p r e s e n t e d h e r e A s l m p i e m e t h o d f o r d e t e r m i n i n g a which I S valld i~
a r e b a s e d o n t e s t s in t h e b o r e h o l e c a l i b r a t i o n m o d e l s l o c a t e d e l t h e r m o d e l o r f i e l d b o r e h o l e s h a s b e e n d i s c u s s e d by
a t t h e U.S. D e p a r t m e n t of E n e r g y r a d i o m e t r i c c a l i b r a t i o n C o n a w a y (in press). All t h a t is r e q u i r e d is a d i g i t a l log a c r o s s
f a c ~ l i t i e sa t G r a n d J u n c t i o n C o l o r a d o ( M a t h e w s et al., 1975). a n interface between a barren z o n e and a n o r e zone, a h e r e
t h e b a r r e n z o n e is e s s e n t i a l l y h o m o g e n e o u s o v e r a d l s t a n c e of
p e r h a p s 1.5-2 m a w a y f r o m t h e I n t e r f a c e (Fig. 6.!a). It is n o t
Theoretical Background
n e c e s s a r y t h a t t h e o r e z o n e b e h o m o g e n e o u s o r infiniteiy
T h e t h e o r e t i c a l b a s i s f o r q u a n t ~ t a t l v ei n t e r p r e t a t i o n of t h i c k . T h e c o n s t a n t ( e x c e p t f o r s t a t i s t i c a l n o i s e ) 'backgrocrnd'
g a m m a r a y logs is g i v e n by t h e e q u a t i o n r a d i a t i o n i n t e n s i t y In t h e b a r r e n z o n e is s u b t r a c t e d f r o m e a c h
d i s c r e t e value. a n d r h e r e s u l t i n g d a r a a r e p l o t t e d a s t h e
n a t u r a l l o g a r ~ t h mo r t h e c o u n t r a t e s ( ' b a c k g r o u n d ' c o r r e c t e d )
a s a f u n c t i o n of d e p t h (Fig. - 6. :b). The desired ~ a l u e
1
o f a is t h e s l o p e o n this p l o t of t h e !inear anornal) f l a n k
( S c o t t e t al.. 1961). H e r e . A is t h e a r e a b e n e a t h a g i k e n
o u t s i d e of t h e o r e z o n e . T h i s t e c h n i q u e is m o r e difficult t o
a n o m a l k o n t h e g a m m a ray log, T is t h e t h i c k n e s s of t h e
a p p l y t o d a r a f r o m a n a n a l o g logging s b s t e m b e c a u s e of t h e
r a d l o a c t l v e z o n e c a u s l n g t h e a n o m a l y , G is t h e a v e r a g e
d i s t o r t i o n i n t r o d u c e d by t h e a n a l o g r a t e m e t e r ( C o n a w a ~ .in
r a d ~ o e l e m e n tc o n c e n t r a t i o n o r g r a d e o v e r t h a t t h l c k n e s s , a ~ d
press). This s e m i - i o g s l o p e t e c h n i q u e f o r d e t e r m i n i n g a 1s u s e -
K is t h e c o n s t a n t of p r o p o r t i o n a l i t y . E q u a t l o n ( 1 ) a s s u m e s
ful for studying t h e behavlor or t h e svstem response fbnction
t h a t t h e s y s t e m is l l n e a r (1.e. f o l l o w s t h e p r i n c i p l e of s u p e r -
a s a f u n c t ~ o nof b o r e h o l e d i a m e t e r , b o r e h o l e fluid, a n d c a s i n g
p o s i t ~ o n ) . T h e c o n s t a n t K IS g e n e r a l l y d e t e r m i n e d In m o d e l
t h l c k n e s s , a n d will b e u s e a In s u b s e q u e n t s e c t i o n s of t h i s
c a l i b r a t i o n b o r e h o l e s u n d e r s t a n d a r d conditions of c a s i n g
paper.
t h i c h n e s s , b o r e h o l e a l a m e t e r , a n d b o r e h o l e fluld. If t h e s e
conditions a r e d i f f e r e n t In t h e f i e l d t h a n in t h e model. t h e
sensitivity of t n e s v s t e m t o a g i v e n r a a ~ o e l e m e n tm a y c h a n g e . Steel Casing
requiring a c o m p e n s a t i n g c h a n g e in K ( u s u a l l ~ a p p l i e d in
F l g u r e 6.2a s h o w s a p l o t of g a m m a ray Intensltk a s a
t n e f o r m of s e p a r a t e c o r r e c t i o n f a c t o r s . e.g. Dodd a n d
f u n c t l o n of d e p t n m e a s u r e d In a m o d e l b o r e h o l e c o n t a i n i n g a
E s c h l l m a n , 1972).
1.5 m t h i c k 'ore' z o n e b e t w e e n t w o b a r r e n z o n e s , for n o
T h e v a l i d i t y of e q u a t i o n ( 1 ) is i n d e p e n d e n t of t h e s h a p e c a s i n g a n d f o r six t h i c k n e s s e s of s t e e l c a s i n g (1.6. 3.2. 4.5.
of t h e s y s t e m r e s p o n s e f u n c t i o n . H o w e v e r , i f t h e g a m m a ray 6.4. 9.5. a n d 12.7 m m ) . T h e b o r e h o l e is w a t e r fille6 a n d
log is t o b e d e c o n v o l v e d t o p r o d u c e a r e c o r d of r a d l o e l e m e n : 11.4 c m in d i a m e t e r . All o f t h e c u r v e s h a b e been n o r m a l i z e d
c o n c e n t r a t i o n a s a f u n c t l o n of d e p t h (e.g. S c o t t , 1963; s o t h a t t h e l r a r e a s a r e e q u a l , f o r comparison; t h i s h a s n o
C o n a w a v a n d K i l l e e n , 1975) t h e n t h e s h a p e of t h e s y s t e m e f f e c t on t h e c o m p u t e d v a l u e of a. The digltal samoling
r e s p o n s e f u n c t i o n m u s t b e known a t l e a s t a p p r o x i m a t e l l s o l n t e r v a l Az = ? c m , logging v e i o c i t v v = 0.3 m / m i n . and t h e
t h a t a n appropriate deconvolution operator can be derived. d e t e c t o r 1s 2 5 \ 7 5 rnm NaI(T1) w ~ t h t h e l o w e r e n e r g )
t h r e s h o l d of t h e i n s t r u m e n t s e t a t 100 keV.
4 a ~ g l t a lI n v e r s e f l l t e r for d e c o n v o l u t i o n of g a m m a rab
logs h a s b e e n g l i e n bv C o n a w a y a n d K i l l e e n ( 1 9 7 8 ) based o n
e a r l l e r work b) S u p p e a n d Khaikovlch ( 1 9 6 0 ) . D a v ~ d o v(1979).
INTENSITY LOG, (INTENSITY)
-
- 80
~ -
0
DEPTH icml
,~ .
80
-
a
- ,
-- b
1. Killeen, P.G.
1975: Nuclear t e c h n i q u e s f o r b o r e h o l e l o g g i n g in mineral e x p l o r a -
t i o n ; i n Borehole Geophysics appl i e d t o Metal 1 i c Mineral
P r o s p e c t i n g - a r e v i e w . E d . by A . V . Dyck, Geol. S u r v .
Can. Paper 75-31 , p p . 39-52.
2. Killeen, P.G.
1976: P o r t a b l e b o r e h o l e gamma-ray s p e c t r o m e t e r t e s t s ; Geol. S u r v .
Can. Paper 76-1A, p p . 487-489.
3. K i l l e e n , P . G . and B r i s t o w , Q .
1976: Urani um e x p l o r a t i o n by b o r e h o l e gamma-ray s p e c t r o m e t r y
using off-the-she1 f instrumentation; Exploration f o r
Urani urn Ore. Depos i t s ( P r o c . Symp. Vienna, 1976) IAEA
Vienna, pp. 393-414.
4. K i l l e e n , P.G.
1976: Trends i n gamma-ray l o g g i n g o f mineral e x p l o r a t i o n bore-
h o l e s ; CIM B u l l e t i n Farch 1976 ( A b s t r a c t ) .
5. K i l l e e n , P . G . and B r i s t o w , Q .
1976: A backpack p o r t a b l e b o r e h o l e gamma-ray s p e c t r a l l o g g i n g
system w i t h d i g i t a l r e c o r d i n g ; i n Geophysics - A Key t o
Energy Independence: 46th Annual Meeting o f t h e S . E . G .
( A b s t r a c t ) , p . 105.
6. K i l l e e n , P . G . and Dyck, A . V .
1977: Geophysical l o g g i n g o f MacDougall Core Hole l A , P r i n c e
Edward I s l a n d ; Appendix 3 , p . 23 i n R . D . Howie, Geologi-
c a l S t u d i e s and E v a l u a t i o n o f MacDougall Core Hole lA,
Western P r i n c e Edward I s l a n d , Geol. S u r v . Can. Paper 77-20.
7. Killeen, P.G.
1977: Cal i b r a t i o n f a c i 1 i t i e s f o r downhole uranium a s s a y vri t h a
b o r e h o l e gamma-ray s p e c t r a l l o g g e r ; in Geophysics - Global
R e f l e c t i o n s : 47th Annual Meeting o f t h e S.E. G . ( A b s t r a c t )
p . 39.
8. K i l l e e n , P.G.
1977: Gamma-ray s p e c t r a l l o g g i n g f o r uranium a s s a y ; i n Canadian
E x p l o r a t i o n Geophysical S o c i e t y (KEGS) Monthly C i r c u l a r ,
November.
9. Bristow, Q .
1977: A system f o r t h e o f f l i n e p r o c e s s i n g o f b o r e h o l e gamma-ray
s p e c t r o m e t r y d a t a on a NOVA minicomputer; Geol. S u r v . Can
Paper 77-1A.
10. K i l l e e n , P.G., Conaway, J.G. and B r i s t o w , Q
1978: A gamna-ray s p e c t r a l l o g g i n g system i n c l uaing d i g i t a l pl ay-
back w i t h recommendations f o r a new g e n e r a t i o n s y s t e m ; in
Geol . S u r v . Can. Paper 78-l A, pp. 235-241 .
14. Conaway, J . G .
1978: Problems i n gamma-ray l o g g i n g : t h i n zone c o r r e c t i o n f a c t o r s ;
i n C u r r e n t Research, P a r t C , Geol. Surv. Can. Paper 78-1C,
-
p . 19-21.
15. B r i s t o w , Q . and K i l l e e n , P . G .
1978: A new computer-based gamma-ray s p e c t r a l l o g g i n g system; i n
Geophysics Golden Gateway t o Energy, 4 9 t h Annual Meeting of
t h e S.E.G. ( A b s t r a c t ) , pp. 117-118.
18. Conaway, J . G .
1979: Computer p r o c e s s i n g o f gamma-ray l o g s : a program f o r t h e
d e t e r m i n a t i o n o f r a d i o e l ement c o n c e n t r a t i o n s ; in C u r r e n t
Research, P a r t B . Geol . Surv. Can. Paper 79-18? p p . 27-32.
Conaway , J . G .
1979: Uranium o r e c o n c e n t r a t i o n s from gamma-ray l o g s ; Paper
p r e s e n t e d 8 1 s t . CIM Annual General Meeting. A b s t r a c t
i n CIM B u l l . , V . 72, pp. 96-98.
Killeen, P.G.
1979: Gamma-ray l o g g i n g problems i n high g r a d e uranium o r e
zones; CIM B u l l . ( A b s t r a c t ) Vol. 72, No. 803, p . 9 8 .
Killeen, P.G.
19'79: A p p l i c a t i o n o f gamma-ray s p e c t r a l l o g g i n g t o u r a n i urn
e x p l o r a t i o n ; i n T e c h n i c a l Program, A b s t r a c t s and Bio-
g r a p h i e s , 4 9 t h Annual I n t e r n a t i o n a l Meeting o f t h e S . E . G .
( A b s t r a c t ) , p. 99.
Conaway, J . G . , B r i s t o w , Q . and K i l l e e n , P . G .
1980: O p t i m i z a t i o n o f gamma-ray l o g g i n g t e c h n i q u e s f o r uranium;
G e o p h y s i c s , Vol. 4 5 , No. 2 , pp. 292-311.
Conaway, J . G .
1980: E x a c t i n v e r s e f i 1 t e r s f o r t h e deconvol u t i o n o f gamma-ray
l o g s ; G e o e x p l o r a t i o n , Vol. 1 8 , p . 1 - 1 4 .
Conaway , J . G .
1980: Urani um c o n c e n t r a t i o n s and t h e s,ystem r e s p o n s e f u n c t i o n
i n gamma ray l o g g i n g ; i n C u r r e n t Research, P a r t A, Geol .
S u r v . Can. , Paper 80-~,p~. 77-87.
Bristow, Q .
1979: A i r b o r n e and v e h i c l e mounted geophysi ca1 d a t a a c q u i s i t i o n
system c o n t r o l l e d by Nova mi ni computers ; i n Proceedi ngs
of t h e 6 t h Annual Data General U s e r ' s
O r l e a n s , Dec. 4-7, 1979.
roc
Meeting, New
Conaway, J . G.
1980: Problems a s s o c i a t e d w i t h gamma r a y l o g g i n g f o r t h e e v a l u a -
t i o n of high grade uranium d e p o s i t s ; T r a n s a c t i o n s , American
Geophysical Union ( A b s t r a c t ) , Vol. 6 1 , No. 1 7 , A p r i l 2 2 , 1980,
p. 415.
28. B r i s t o w , Q . , Conaway, J.G. and K i l l e e n , P.G.
1980: A m i c r o p r o c e s s o r - b a s e d s o f t w a r e - c o n t r o l l e d p o r t a b l e bore-
hole-1 oggi ng s y s tern; T r ? n s a c t i o n s , Ameri can Geophysi c a l
Union ( A b s t r a c t ) , Vol. 6 1 , No. 1 7 , April 2 2 , 1980, p. 415.
31. Conaway, J . G .
1980: D i r e c t d e t e r m i n a t i o n o f t h e gamma-ray l o g g i n g system
r e s p o n s e f u n c t i o n i n f i e 1 d b o r e h o l e s ; Geoexpl o r a t i o n ,
1 8 , p . 187-199.
34. Conaway, J . G.
1981: Deconvolution o f gamma-ray l o g s i n t h e c a s e o f d i p p i n g
r a d i o a c t i v e zones; Geophysics, \Jol . 4 6 , No. 2 , p . 198-203.
COMPUTER PROCESSING OF GAMMA-RAY LOGS: ITERATION AND INVERSE FILTERING
Project 740085
John G. Conaway and P.G. Killeen
Resource Geophysics and Geochemistry Division
Abstract
Conaway, John G., and Killeen, P.G., Computer processing of gamma-ray logs: Iteration and inverse
filtering; Current Research, Part B, Ceol. Surv. Can., Paper 78-18, p. 83-88, 1978.
For nearly two decades an iterative computer technique has been used for processing gamma-
ray logs to determine the distribution of uranium along a borehole. Recently an inverse filter
technique has been developed for the same application. Analysis of the iterative technique shows
that it approaches theoretical equivalence with the inverse filter technique as the number o f
iterations increases. In tests with gamma-ray borehole logs with a sampling interval of 10 cm there
was little difference in the results produced by the two methods. In practice a sampling interval
shorter than 10 cm should be used to improve resolution and reduce aliasing errors. In this case a
smoothing filter is required with both techniques to reduce the high-frequency noise.
The inverse filter technique generally requires less than 5 per cent as much computing time as
iteration, and may be accomplished using an 'open-ended' algorithm, thereby making possible on-line
processing of the data using a minicomputer or microprocessor, concurrent with the logging of the
borehole.
Figure 13.1
Inverse Filterinrr
u
rhen In the space domain (see e.g. Sokolnikoff and Sokolnikoff, 1941). As can be seen
g(z) = C(Z) * f(z) ............................. .(4)
from Figure 13.2b, t h e condition given by equation ( 6 ) will be
valid. Thus, a f t e r many iterations the value of Cn(w)approaches
where the inverse filter f(z) is the Fourier transform of F(w).
In the specla1 case of the infinitesimally thin ore zone
(Fig. 13.1)
C(w) = S(w) which is identical to equation (3). Thus it has been shown
that'the inverse filter technique and the iterative technique
Therefore, from equation (3) for processing gamma-ray logs a r e theoretically equivalent
operations.
Referring once again t o the flow chart for the iterative
algorithm (Fig. 13.3) consider the step shown in the dashed
In theory, then, the flat spectrum of the impulse has been box, that of setting negative ore grade values equal to zero.
recovered by inverse filtering, in the absence of noise. As will be shown more fully later, the iteration process
amplilies high frequencies while exerting relatively little
The Iterative Algorithm e f f e c t on low frequencies. Thus, t h e scatter in the iterated
o r e grade values is greater than the scatter in gamma-ray
The heart of the computer program given by Scott counts. This means that some of the processed w e grade
(19621, a s well a s of the modern counterpart of that program, values may be negative; however, the mean grade over a
is an iterative algorithm which, in its simplest form, is shown given zone will be correct. The a c t of setting negative grade
in the flow chart given in Figure 13.3. The step enclosed in values equal to zero introduces statistical bias, causing t h e
the dashed box, that of setting negative grade values equal to mean calculated grade over the zone to b e erroneously high.
zero will b e ignored for the present. Letting the contribution In general this is a small effect, but since this step in t h e
of the ith step in the iteration to the value of g(z) be given by processing of the log is unnecessary and invalid, it should b e
bi(z), from the flow chart we have: eliminated.
initial s t a t e bo(z) = C(Z)
input DCUT, N, OP
1
I
"T-1
.
input RAW LOG
K=K+l
e determine DMAX
YES
NO
GRADE= GRADE + DIF
----L ----7
r r e t negative GRADE values
tun)
L ----
to 0
-r - 1
Figure 13.5. Amplitude spectrum of the noise-free geologic
impulse response (shown in Fig. 13.2b) a f t e r
application of the theoretical inverse operator
E
(a), and approximate inverse operators cor-
responding t o sampling intervals of I cm(b), 3 c m
(c), 5 c m (d), and 10 c m (el.
output GRADE
Iteration and Inverse Filtering in Practice
The problem of developing an inverse filter operator for
processing gamma-ray logs may be approached from many
directions. Perhaps the simplest solution has been presented
by Conaway and Killeen (in press), based in part on earlier
Figure 13.3. Flow c h a r t for the iterative algorithm used for work by Czubek (1971) and Davydov (1970). Here t h e CIR is
determining ore grade values from a gamma-ray approximated by t h e function
log. The parameters used are:
N - t h e number of iterations t o be performed.
OP - t h e digitized system impulse response function
determined in a model borehole. where the constant a is most easily determined in a model
borehole. This function has been found to provide a
RAWLOG - the array containing t h e raw gamma-ray log. reasonable f i t to t h e experimentally determined response
GRADE - the array containing t h e approximate grade function with Geological Survey of Canada gamma-ray
values being iterated. logging equipment. The amplitude spectrum of the theoretical
inverse operator is shown a s curve a in Figure 13.4. This
DIF - defined in flow chart. theoretical inverse operator may be approximated by a simple
DMAX - maximum value of DIF. %point operator given by
DCUT - assigned cutoff value of DMAX t o stop pro-
cessing before N iterations have been reached.
Figure 13.7. (a) Amplitude spectrum of the noise-free
geologic impulse response. The other curves
show t h e amplitude spectrum of the GIR a f t e r
I iteration (b), 2 iterations (c), 5 iterations (dl,
10 iterations (e), 15 iterations (f), 20 iterations
(g), and 30 iterations (h).
- r GAMMA-RAY INTENSITY C c o u n t s / s ) ~
0 4000 0 4000 0 4000
- I I I I I
-
-
-
-
-
140- -
E" -
-
E
a -
Ei -
- (a) Raw gamma-ray log from a uranium
- o r e zone; logging velocity v =
3 mlmin, sampling interval Az = I0 cm.
- (b) The log shown in (a) processed
- - iteratively using 10 iterations.
- - (c) The log shown in (a) processed with
t h e approximate 3-point inverse
150- 8 - 8
I GAMMA-RAY INTENSITY tcounts/'Sl I
Figure 13.10
(a) Raw gamma-ray log from the same ore zone a s in Figure 13.9;
logging velocity v = 1 m/rnin, sampling interval Az = 3.3 cm.
(b) The log shown in (a) processed iteratively using 10 iterations.
(c) The log shown in (a) processed with the approximate 3-point
inverse operator.
Conaway, John C., and Killeen, P.C., Computer processing of gamma-ray logs: Iteration and inverse
filtering; 2 Current Research, Part B, Geol. Surv. Can., Paper 78-1 8, p. 83-88, 1978.
For nearly two decades an iterative computer technique has been used for processing gamrna-
ray logs to determine the distribution of uranium along a borehole. Recently an inverse filter
technique has been developed for the same application. Analysis of the iterative technique shows
that it approaches theoretical equivalence with the inverse filter technique as the number of
iterations increases. In tests with gamma-ray borehole logs with a sampling interval of 10 cm there
was little C i f f erence in the results produced by the two methods. In practice a sampling interval
shorter than 10 crn should be used to improve resolution and reduce aliasing errors. 1n this case a
smoothing filter is required with both techniques to reduce the high-frequency noise.
The inverse filter technique generally requires less than 5 per cent as much computing time as
iteration, and may be accomplished using an 'open-ended' algorithm, thereby making possible on-line
processing of the data using a minicomputer or microprocessor, concurrent with the logging of the
borehole.
Figure 13.1
Inverse Filtering
Representing the geologic impulse response function
(a) Geologic column showing an infinitesimally thin
radioactive ore zone sandwiched between two thick
(Fig. 13.1~)by the symbol s(z), the relationship between the
barren zones, a 'geologic impulse' of radioactive ore.
noise-free gamma-ray log c(z), and the distribution of
radioactive material along a borehole, g(z), is given by (b) Plot of radioelement concentration with depth
corresponding to Figure 13. la.
(c) Noise-free response of a point-detector to the thin
ore zone, the 'geologic impulse response'.
where C(w), G(w) and S(w) are the Fourier transforms of f(z), It can be shown that the series
g(z), and s(z), respectively. Thus i n the frequency domain the
distribution of radioactive material is given by
contribution of -
bl(z) = C(Z) c(z)*s(z)
first iteration
contribution of -
b2(z) = C(Z) ZC(Z)*S(Z)+ c(z)*s(z)*s(z)
second iteration
contribution of b 3 ( ~ =) C(Z)- ~c(z)*s(z)
third iteration
+ 3c(z)*s(z)*s(z) - c(z)*s(z)*s(z)*s(z)
Expressing this in the frequency domain, where the contribu-
tion of the i t h step in the iteration is Bi(w),
t , f (cm-'1
0 .I .2 .3 .4 .5
In general terms, then
Bi(w) .
C(U) [I - s(w)] ' .
where i 0,1,2
Thus, in the frequency domain the processed log after n
,..., n Figure 13.2
(a) Amplitude spectrum of a spike (Fig. 13.1 b).
iterations, Cn(w), is given by (b) Amplitude spectrum of the noise-free geologic
impulse response (Fig. 13.1~). Two horizontal axes
are shown for convenience. The lower one, spatial
frequency (f), is given by f = d 2 n . The upper scale is
calibrated i n sampling interval (Az), to make i t easy
to study the amplitude spectra i n relation to the
Nyquist frequency f for various sampling intervals,
lI2Pz. ?he amplitude spectrum is a plot
:t?izpf~t;de as a function of spatial frequency (f);
the upper horizontal axis, Az, is provided for
reference only. Note especially the signific
amount of energy at frequencies higher than
Nyquist frequency for Az = 10 cm (dashed line).
1-
-
d
e==l
m input DCUT, N, OP
input RAWLOG
Dl F = RAWLOG-OP* GRADE
Figure 13.4. Amplitude spectrum of the theoretical inverse
operator (curve a ) and of the 3-point approxi-
m a t e inverse operators for sampling intervals of
1 c m (b), 3 cm (c), 5 c m (dl, and 10 c m (el.
-
determine D M A X
4 YES
is D M A X less than DCUT?
1
I 1 GRADE= GRADE + DIF I
I
- - -L ----7
r s e t negative GRADE values to 0
L----
7-----'
+ Figure 13.5. Amplitude spectrum of the noise-free geologic
is K equal to N? impulse response (shown in Fig. 13.2b) a f t e r
1
application of the theoretical inverse operator
YES } I (a), and approximate inverse operators cor-
responding to sampling intervals of 1 cm(b), 3 c m
(c), 5 c m (dl, and 10 c m (el.
ourput GRADE
Iteratim and Inverse Filtering in Practice
The problem of developing an inverse filter operator for
processing gamma-ray logs may be approached from many
directions. Perhaps t h e simplest solution has been presented
by Conaway and Killeen (in press), based in part on earlier
Figure 13.3. Flow chart for the iterative algorithm used for work by Czubek (1971) and Davydov (1970). Here t h e GIR is
determining o r e grade values from a gamma-ray approximated by t h e function
log. The parameters used are:
N - t h e number of ,iterations to be performed.
OP - t h e digitized system impulse response function
where the constant a is most easily determined in a model
determined in a model borehole.
RAWLOG - t h e array containing the raw gamma-ray log.
borehole. This function has been found to provide a
reasonable fit to the experimentally determined response
GRADE - the array containing t h e approximate grade function wlth Geological Survey of Canada gamma-ray
logging equipment. The amplitude spectrum of the theoretical
values being iterated.
inverse operator is shown a s curve a in Figure 13.4. This
DIF - defined in flow chart. theoretical inverse operator may b e approximated by a simple
DMAX - maximum value of DIF. 3-point operator given by
DCUT - assigned cutoff value of DMAX t o stop pro-
cessing before N iterations have been reached.
Figure 13.7. (a) Amplitude spectrum of the noise-free
geologic impulse response. The other curves
show the amplitude spectrum of the GIR a f t e r
I iteration (b), 2 iterations (c), 5 iterations (dl,
10 iterations (e), 15 iterations (f), 20 iterations
(g), and 30 iterations (h).
I I I I j aztcm) '
10 5 3 2 1
Figure 13.10
(a) Raw gamma-ray log from the s a m e ore zone as in Figure 13.9;
logging velocity v = 1 mlmin, sampling interval Az = 3.3 cm.
(b) The log shown in (a) processed iteratively using 10 iterations.
(c) The log shown in (a) processed with the approximate 3-point
inverse operator.
Conaway, J.G., Killeen, P.G., and Hyatt, W.G., A comparison o f bismuth germanate, cesium iodide,
and sodium iodide scintillation detectors for gamma ray spectral logging in small diameter boreholes;
in Current Research, Part B, Geological Survey o f Canada, Paper 80-18, p. 173-177, 1980.
-
Abstract
Preliminary studies comparing a 19 x 76 mrn bismuth germanate scintillation detector
( BibGe 0 1*, commonly called BGO) to thallium activated sodium iodide (Nal(T1)) and sodium
activated cesium iodide (CsNNa)) detectors o f the same size have been completed. The potential
advantage of BGO in gamma ray spectrometry is due to its high density (7.13 g / c m 3 ) ,which is almost
twice that o f the most commonly used detector material, Nal(T1) (3.67 g/cm3). The increased
stopping power for high energy gamma rays o f the high density BGO is evident in both the gamma ray
logs and gamma ray spectra recorded in the model boreholes at the Geological Survey's calibration
facility at Bells Corners, Ontario. The calibration factors (stripping factors and proportionality
constants) for the three types o f detectors are tabulated and compared both for the standard set o f
energy windows commonly used in portable spectrometers and for a set o f wider energy windows
which offer improved accuracy under some circumstances. The relative performance o f the three
detectors for determining uranium concentrations (using both sets of windows) was computed and
tabulated for a range in U/Th concentration ratios from 10:l to 1:lO. A reduction of more than 50%
in statistical errors in uranium determinations was found in comparing the BGO detector to Nal(T1).
Csl o f f e r s a more modest improvement of about 10%. In hardrock mining applications where the
borehole diameter imposes a severe detector size restriction, the BGO detector appears to o f f e r
considerable advantages for uranium exploraton and evaluation.
B
= r a t i o of Th g a m m a rays in U window t o Th g a m m a rays
in Th window
= r a t i o of Th g a m m a rays in K window t o Th g a m m a rays
in Th window
a u t h o r s with a small l 3 'Cs source alongside t h e d e t e c t o r . y = r a t i o of U g a m m a rays in K window t o U g a m m a rays in
U window
All measurements w e r e made by interchanging a = r a t i o of U g a m m a rays in Th window t o U g a m m a rays
d e t e c t o r s in t h e s a m e borehole probe. In this way n o in U window
p a r a m e t e r s e x c e p t those d u e t o t h e d e t e c t o r and i t s integral- b = r a t i o of U g a m m a rays in Th window t o K g a m m a rays
mount photomultiplier t u b e changed during t h e comparison in K window
tests.
g = r a t i o of K g a m m a rays in U window t o K g a m m a rays in
Calibration checks w e r e m a d e b e f o r e and a f t e r e a c h K window
measurement t o minimize t h e potential problem of gain
shifts. Because of t h e versatility m a d e possible by full
s p e c t r a l recording i t is possible t o reproduce g a m m a ray T o t a l Count Window Proportionality Constants
s p e c t r a l logs using energy windows of any desired widths or ( C P S = counts/second)
positions in t h e g a m m a ray energy spectrum. Comparisons : % K/CPS in t o t a l c o u n t window
w e r e t h e r e f o r e made with t w o s e t s of energy windows a s KK
shown in Table 18.2. The 'standard' windows represent those = ppm U/CPS in t o t a l count window
KU
commonly used in portable and airborne g a m m a ray KTh : ppm Th/CPS in t o t a l count window
spectrometers. The 'wide' uranium window has t h e a d v a n t a g e
of including t h e 2.24 MeV g a m m a ray peak from t h e uranium
decay series, b u t t h e disadvantage of a n increased s c a t t e r e d K, U, and Th Window Proportionality Constants
thorium component in t h e uranium window. This requires a = % K/CPS in K window
larger stripping f a c t o r a ( s e e Conaway and Killeen, 1980; CK
..
950 ppm U
E (MeV)
a. 256 channel gamma ray spectrum (12 keV per channel)
recorded in 350 ppm thorium model ore zone using a
19 x 76 mm NaI(T1) detector.
b. Same as ( a ) but using a 19 x 76 mm CsKNa) detector.
Note that at the high energy end o f the spectrum the
count rate does not drop to zero as in the NaI(T1)
spectrum (a). This is due to the implanted " ' A m source,
as explained in t e x t .
c . Same as ( a ) but using a 19 x 76 mm BGO detector.
Figure 18.1
References
Bristow, Q.
1980: NOVA-based airborne and vehicle mounted
systems for real-time acquisition, display and
recording of geophysical d a t a ; Proceedings of
t h e 6 t h Annual Dara General Users Group
Meeting, New Orleans, Dec. 4-7, 1979.
Chase, G.D. and Rabinowitz, J.L.
1968: Principles of radioisotope methodology; Burgess
Pub. Co., Minneapolis, 6 3 3 p.
Conaway, J.G. and Killeen, P.G.
1980: Gamma-ray spectral logging for uranium;
Canadian Institute of Mlnlng and Metallurgy
Bulletin, v. 73, no. 813, p. 115-123.
BGO Killeen, P.G.
1978; Gamma-ray spectrometric calibration
facilities - a preliminary report; & C u r r e n t
Research, P a r t A, Geoiogical Survey of Canada,
Paper 78-IA, p. 243-247.
1979: G a m m a ray s p e c t r o m e t r i c methods in uranium
exploration - application and interpretation;
Geophysics and Geochemistry in t h e Search for
Metallic Ores; P e t e r J. Hood, Editor; Geological
Survey of Canada, Economic Geology Report 31,
p. 163-229.
Killeen, P.G. and Bristow, Q.
1976: Uranium exploration by borehole gamma-ray
s p e c t r o m e t r y using off-the-shelf instrumentation;
-
in Exploration for Uranium O r e Depos
Proceedings Series, International Atomic Enc:
Agency, Vienna, p. 393-414.
Killeen, P.G. and Conaway, J.G.
1978: New facilities f o r calibrating gamma-ray
s p e c t r o m e t r i c logging and s u r f a c e exploration
Figure 18.3. Plot of g a m m a r a y intensity a s a function of equipment; Canadian Institute of Mining and
d e p t h using t h e s t a n d a r d uranium s p e c t r a l window and t h r e e Metallurgy Bulletin, v. 71, no. 793, p. 84-87.
different d e t e c t o r materials, a s indicated. Killeen, P.G., Conaway, J.G., and Bristow, Q.
1978: A gamma-ray s p e c t r a l logging s y s t e m including
Several conclusions c a n b e drawn from Table 18.4 for digital playback, with recommendations for a new
t h e 19 x 76 mrn d e t e c t o r size. generation system; & C u r r e n t Research, P a r t A,
Geological Survey of Canada, P a p e r 78-lA,
1. The wide windows a r e b e t t e r than t h e standard windows p. 235-241.
for a l l 3 d e t e c t o r materials for U/Th ratios of 10:l and
1:I. For BGO t h e wide windows a r e also b e t t e r f o r t h e Nestor, O.H. and Huang, C.Y.
1:10 U/Th ratios, b u t this is n o t t r u e for NaI(T1) o r 1975: Bismuth germanate: a high-Z gamma-ray and
sI(Na). charged p a r t i c l e d e t e c t o r ; Institute of Electrical
and Electronics Engineers Transactions on
2. CsI(Na) exhibits a relative e r r o r improved by about 10% Nuclear Science, NS-22, p. 68-71.
compared t o NaI(T1) with t h e s a m e window widths.
Scott, J.H., Dodd, P.H., Droullard, R.F., and Xludra, P.J.
3. BGO produces a n improvement in r e l a t i v e e r r o r on t h e 1961: Q u a n t i t a t i v e interpretation of gamma-ray logs;
order of 5 0 per c e n t o r more under a l l conditions. Geophysics, v. 26, no. 2, p. 182-191.
Conclusion
It is c l e a r t h a t BGO is t h e b e s t of t h e t h r e e d e t e c t o r
materials t e s t e d for slim hole g a m m a ray s p e c t r a l logging.
BGO's improved ruggedness compared with NaI(T1) is also a n
advantage. A t present t h e price of BGO is on t h e o r d e r of
double t h e price of t h e o t h e r d e t e c t o r materials, however,
this price differential is still not high enough t o rule o u t t h e
use of BGO in s p e c t r a l logging, considering i t s g r e a t
advantages in slim probes.
MULTIPIT, A METHOD FOR
CALIBRATION OF LOGGING SYSTEMS
by
Merle E. C r e w
Page
Abstract ................................................................. 1
Introduction ............................................................ 1
Concept .................................................................. 1
Options ............................................................... 3
Discussion ................................................................ 4
Conclusions .............................................................. 5
Acknowledgements ........................................................ 5
References ............................................................... 6
Merle E. Crew
Abstract
Introduction
Concept
The l e a s t s q u a r e s method of f i t t i n g a s t r a i g h t l i n e t o a s e t of d a t a p o i n t s i s
a s t a n d a r d mathematical p r o c e d u r e and need n o t be d e s c r i b e d .
TABLE 1
Dead time
i n microseconds c(y-y1)2
The s i m p l e s t s t r a t e g y f o r s o l u t i o n would be t o s t a r t a t a s l i g h t l y n e g a t i v e
v a l u e of dead t i m e and t e s t f o r sum of t h e s q u a r e s of d i f f e r e n c e s a t 0.01
microsecond i n c r e m e n t s u n t i l a minimum v a l u e i s a t t a i n e d . The MULTIPIT
program i s a n i t e r a t i v e method of i n c r e m e n t a l l y i n c r e a s i n g t h e dead t i m e used
t o c o r r e c t t h e observed c o u n t r a t e s . For each v a l u e of dead t i m e used, t h e
observed c o u n t s , a t e q u a l i n c r e m e n t s (commonly 0.5 f o o t ) from background v a l u e
t o background v a l u e , a r e dead t i m e c o r r e c t e d and summed t o g i v e t o t a l a r e a
under t h e curve. When a r e a s have been o b t a i n e d f o r a l l model h o l e s b e i n g
c o n s i d e r e d , a l e a s t s q u a r e s f i t i s made t o a l i n e , and t h e sum of t h e s q u a r e s
of d i f f e r e n c e s c a l c u l a t e d . T h i s v a l u e i s t h e n compared t o t h e v a l u e o b t a i n e d
from t h e p r e v i o u s i t e r a t i o n . I f t h e new sum i s s m a l l e r t h a n t h e p r e v i o u s sum,
a n o t h e r increment of dead time i s made and a n o t h e r i t e r a t i o n c o n t i n u e s . If
t h e v a l u e of t h e sum of t h e s q u a r e s of t h e d i f f e r e n c e i s l a r g e r t h a n t h e
p r e v i o u s sum i t i n d i c a t e s t h a t a minimum was reached somewhere i n t h e i n t e r v a l
of t h e two p r e v i o u s increments. The program t h e n backs up two i n c r e m e n t s ,
r e d u c e s t h e dead time increment by one t e n t h and proceeds with i t e r a t i o n s a t
t h e s m a l l e r dead time increments.
Opt i o n s
Discussion
TABLE 2
MULTIPIT
dead t i m e = 0.25 microsecond
K f a c t o r = 0.00002577
c ( ~ - =~ 0.00335
~ ) ~
N3 U3 U2 U1
Area 40806 69182 169009 328332
GT 0.9976 1.7975 4.3691 8.4563
Calc. GT 1.0515 1.7826 4.3548 8.4601
diff. -0.0539 +0.0149 +0.0143 -0.0038
TABLE 3
C u r r e n t method
dead time = 1.696 microsecond
K f a c t o r = 0.00002495
1 (y-y1)2 = 0.00720
Area
GT
Calc. GT
diff.
From t h e above t a b l e s i t i s e v i d e n t t h a t n e i t h e r method e x a c t l y f i t s t h e
a s s i g n e d g r a d e of t h e model h o l e s , however, u s i n g t h e sum of t h e s q u a r e s of
t h e d i f f e r e n c e s between t h e a s s i g n e d g r a d e t h i c k n e s s and t h e c a l c u l a t e d g r a d e
t h i c k n e s s product a s a n i n d e x , t h e v a l u e f o r t h e MULTIPIT method i s l e s s t h a n
h a l f of t h a t f o r t h e c u r r e n t method.
Conclusions
Program MULTIPIT R e s u l t s
hrn
md)
mCI)CID
*I f
M W U
mmb
8-h
emu3
a * .
B<UN
Appendix B
Input Data
**$ INPUT DeTA FOR P I T U-1 S t *
DATA ENTRY CODES ARE AS FOLLOWS
ENTER 0 FOR LAST ENTRY
ENTER 2 TO DELETE LAST DATA POINT ENTERED
ENTER 3 TO RESTART ENTRY FOR THIS P I T
StS INPUT DATA FOR P I T U-2 tSS
DkTA ENTRY CODES ARE AS FOLLOWS
ENTER 0 FOR LAST ENTRY
ENTER 2 TO OELETE L6ST 06th POINT ENTERED
ENTER 3 TO RESTRRT ENTRY FOR THIS P I T
t X t INPUT DhTh FOR P I T U-3 tt*
DATA ENTRY CQDES fiRE AS FOLLOWS
ENTER 0 FOR LAST ENTRY
ENTER 2 TO DELETE LAST DATA POINT ENTERED
ENTER 3 10 RESTART ENTRY FOR THIS P I T
$$* INPUT DRTh FOR P I T N-3 S t *
DATR ENTRY CODES ARE AS FOLLOUS
ENTER FOR LAST ENTRY
ENTER TO DELETE LflST DATA POINT ENTERED
ENTER TO RESTRRT ENTRY F O R T H I S P I T
UNITED STATES ATOMIC ENERGY COMMISSION
GRAND JUNCTION OFFICE
MINING D M S I O N
by
.
M. E . C r e w and E W. Berkoff
April 1969
(Grand Junction, Colorado)
CONTENTS
Page
Abstract ........................ 1
Introduction . . . . . . . . . . . . . . . . . . . . . . 1
Two Pit Concept . . . . . . . . . . . . . . . . . . . . . 5
Application . . . . . . . . . . . . .
Effect of Dead Time . . . . . . . . . . . . . . . . 8
Evaluation . . . . . . . . . . . . . . . . . . . . . 11
Summary . . . . . . . . . . . . . . . . . . . . . . . . 16
References . . . . . . . . . . . . . . . . . . . . . . . 17
ILLUSTRATIONS
Figure 1 . .....
Loss of area due to dead time 4
2. .....
Dead time correction curves 9
3; .....
Effect of dead time on grade 10
4. TWOPIT output ............. 13
5. Comparison of TWOPIT and
conventional factors........... 14
TABLES
APPENDIX
ABSTRACT
INTROW CTION
The construction of the Casper test pits in the summer of 1967 pro-
vided the first uniform-high-grade, apparent - infinite -thickness ore zone in
a full scale model bore hole. Analysis of both AEC and company logs of these
pits, which were obtained using conventional geiger or scintillation probes
resulted in under-interpretation of the high grade pit to varying degrees.
Investigations into the reasons for this under estimation led to development
of the two-pit concept a s a means for correcting for the discrepancy.
To calibrate gamma-ray logging equipment for quantitative evaluation
of uranium ore, it is essential to know the dead time of the system. This
may be determined electronically o r by the two-source method wherein first
a background measurement is taken, then a first source is placed close enough
to the probe to give a medium counting rate for the system and the count rate
in cps taken. Next a second source is placed adjacent to the first and the
count rate for both sources combined is determined, then the first source
removed the count rate for the second source only is determined.
1/
Dead time can then be calculated by the following equation: -
Dead time
2 2 2 2
where C = M 4 MB - MI - M2
3
After dead time has been determined, the next step i s to determine the
proportionality constant o r K-factor which relates the response of the system,
commonly expressed in terms of area under the curve, to grade-thickness
product. This is done by logging a test pit of known grade-thickneis, applying
appropriate correction for dead time, using the equation N = n , to
1 - nt
each observed count rate, n, to obtain true count rate, N, and using the sum of
t h e true count rates X N , a s a value for the area, A , under the log curve then
substituting in the equation
AK = GT (2)
a s developed by Scott, et al, 2/.
Area, a s used in equation (2) consists of the observed counts area plus
the dead time correction a r e a and is normally obtained bysumming the dead
time corrected count rates a t half foot intervals and is thus in units of half
feet times counts p e r second. The value of K is commonly calculated to relate
the area so derived to the G T but can be computed for any interval of integration.
Figure 1, shows the relationship between observed count rate and dead
time corrected count rate on a log of the Casper high pit with a grade of 2.242%
eU308 made with a scintallation probe having 3/4 x 1 inch crystal and 5 micro
seconds dead time. The a r e a between the observed and corrected log curves
represents the loss in area, o r gamma-rays detected, because of system
dead time.
't-
o
TWO PIT CONCEPT
AK = GT
where A = sum of dead time corrected counts
K = proportionality constant of system
G = mean radiometric equivalent grade
T = thickness in feet
Now consider the case of two test pits with different grade-thickness
products in which
AIK = (GT)l
represents the low grade pit and
A2K = (GT)2
represents the high grade pit. Since the above relationships a r e true, it can
also be said that
. . .
l-m t
1 l-m2t 1-m3t 1-mzt
using the term m in the denominator to designate observed counts in the high
grade pit whereas the n in the numerator represents observed counts in the low
grade pit.
In equation (7) GT1 and GT2 a r e lcnown values and the various values
for the n and m terms a r e observed values, thus leaving t a s the only
unknown in the equation. A direct algebraic solution is difficult if not impossible
because of the indefinite lecgth of the series, but a computer solution by trial
and e r r o r is relatively simple. First the ratio of the two GT values is determined,
then by trial and e r r o r , the computer solves for the dead time that will make the
ratio on the left side of the equation equal to the ratio of the GT products.
A description and lising of the computer program called TWOPIT which solves
the equation is attached a s Appendix A .
A cfnsi- approximation to the dead time evaluation by the above computer
metkiwi can be made manually o r with a desk calculator using ratios of peak
obscrvcd counts in the respective pits rather than area under the curve, pro-
vided that the "ore" zones in the models a r e of uniform grade and the thickness
is equal to o r greater than the diameter of the effective sample volume influenc-
ing the detector, generally 3 feet o r slightly less; o r provided that thickness
TI is equal to thickness T2 and the ore zones a r e homogeneous with respect
to grade.
It has been shown by Scott, -
3/, that under certain conditions
G = 2KN (8)
Then following the same reasoning a s described above with respect
to areas under the curve and grade thickness products it can be said that
Evaluation
To support the premise presented in this paper, the Casper test pits
were logged with Unit LP-1, probe 4. This is an AEC owned logging unit
developed, constructed, and operated by Lucius Pitkin, Inc ., an AEC service
contractor. The following table shows the conventional factors and the factors
arrived at by the TWOPIT program:
TABLE 1
Conventional TWOPIT
PROGRAM TWOPIT R E S U L T S
I LOW P I T D A T A H I P I T DATA
-
o OBSERVED
GT = 0.99300 GT a 6.72600
CORRECTED OBSERVED CORRECTED
I COUhTS COUNTS COUNTS COUNTS
100. 100. 200. 200.
300. 301. 700 704.
1150. 1162. 2850. 2922.
4900. 5117. 14500 16582.
7650. 8193. 34100. 48390.
8150. 8769. 39750. 606 1 6
8020. 8619. 40000 61200.
7950. 8538. 40250. 61787.
6700. 7113. 38350. 57420.
2800. 2870, 24500 31098.
550. 553. 6250. 6608.
170. 170. 1400 1417.
80. 80. 350. 351.
Figure 4
TABLE 2
INTERPRETATION O F TEST PIT LOGS, UNIT LP- 1, PROBE 4
-
2/ Scott, J . H., Dodd, P. H., Droullard, R. F . , and Mudra, P. J . , 1961,
Quantitative Interpretation of Gamma Ray Logs: Geophysics, Vol. X M ,
No. 2, p. 182-191.
-
3/ Scott, J . R., 1962, the GAMLOG Computer Program: RME-143, USAEC .
BPECf R A t GAMMA-RAY
LOGGlNG SfLlblE8
SPECTRAL GAMMA-RAY LOGGING STUDIES
Robert D. Wilson
and
David C. Stromswold
January 1981
The results presented are based mainly on experiments performed at the United
States Department of Energy (DOE), Grand Junction calibration facility. The
theoretical calculations of gamma-ray transport were performed at the Los
Alamos Scientific Laboratory (LASL) in work funded by DOE, Grand Junction.
ACKNOWLEDGMENTS
The authors acknowledge Bendix Field Engineering Corporation and the United
States Department of Energy staff members who offered support throughout
this project.
The authors also thank Michael L. Evans of the Los Alamos Scientific
Laboratory for his valuable contributions to this project. Radiation transport
calculations performed by Mr. Evans and his colleagues were supported
by the United States Department of Energy under Contract No. W-7405-Eng. 36.
Valuable technical discussions and exchanges have taken place with the
professional staff at the Geologic Survey of Canada, and with John G.
Conaway in particular. For these exchanges we are grateful.
CONTENTS
Page
Page
References. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 183
ILLUSTRATIONS
-
Page
Page
Page
Page
TABLES
Page
Page
Page
Page
Page
APPENDIX
CALIBRATION
INTRODUCTION
C a l i b r a t i o n of r a d i a t i o n p r o b e s f o r e x p l o r a t i o n p u r p o s e s r e l a t e s t h e c o u n t
r a t e i n t h e p r o b e s ' d e t e c t o r s t o t h e c o n c e n t r a t i o n s of r a d i o e l e m e n t s p r o d u c i n g
the counts. For s p e c t r a l gamma-ray p r o b e s , c a l i b r a t i o n r e l a t e s t h e number of
gamma r a y s i n s p e c i f i c e n e r g y windows t o c o n c e n t r a t i o n s o f p o t a s s i u m ( R ) ,
uranium ( U ) , and thorium (Th). The methods of c o l l e c t i n g and a n a l y z i n g c a l i -
bration data a r e discussed i n the following sections.
CALIBRATION THEORY
where A i s a p r o p o r t i o n a l i t y c o n s t a n t .
I d e a l l y , o n l y gamma r a y s from a s i n g l e r a d i o a c t i v e s o u r c e c o n t r i b u t e t o c o u n t s
i n a l i m i t e d e n e r g y r a n g e o r window; however, i t i s p o s s i b l e f o r gamma r a y s
w i t h e n e r g y i n i t i a l l y o u t s i d e a window t o s h i f t i n t o t h e window ( e . g . , by
Compton s c a t t e r i n g ) . Because of t h i s e n e r g y s h i f t , i t i s n e c e s s a r y t o c a l c u -
l a t e t h e c o n t r i b u t i o n s i n e a c h e n e r g y window from gamma r a y s of a l l t h e pos-
s i b l e sources. The r i g h t s i d e of e q u a t i o n ( 1 ) c a n be expanded a s f o l l o w s t o
show c o n t r i b u t i o n s t o t h e c o u n t s , R, from a l l gamma r a y s :
R = AC +x (A'C') (2)
For KUT a n a l y s i s t h e f o l l o w i n g i n d e x c o n v e n t i o n i s u s e d :
The d o u b l e i n d i c e s a r e i n t e r p r e t e d a s f o l l o w s :
A
The c a l i b r a t i o n m a t r i c e s and r e l a t e t h e r e s p o n s e of t h e r a d i a t i o n
d e t e c t o r i n c o u n t s p e r second t o t h e c o n c e n t r a t i o n of r a d i o e l e m e n t s producing
t h e counts. These c a l i b r a t i o n m a t r i c e s p r o v i d e a means f o r a n a l y z i n g c o u n t
r a t e d a t a c o l l e c t e d i n t h e f i e l d where c o n c e n t r a t i o n s a r e n o t a l r e a d y known.
The e q u a t i o n f o r c o n v e r t i n g c o u n t r a t e t o c o n c e n t r a t i o n i s
E q u a t i o n ( 9 ) c a n be w r i t t e n i n non-matrix n o t a t i o n a s f o l l o w s :
CALIBRATION METHODS
K + 0.18
6.76 - 2 . 7 +- 0.3 2.4 +
- 0.6
U + 0.24
0.84 - 498.3 - + 12.1 +
5.6 - 1.3
1 5 i n 3 t o 25 i n 3 (medium volume)
3
5 in t o 1 5 i n 3 ( s m a l l volume).
4
N
d
aJ
!-!
aJ
U
rl
.d
kl
N
Q 3
X X
4 u-l
3
T a b l e 1-3. C a l i b r a t i o n Counting Times
241-L
242-L
25 -< V < 35 1500 1000 1000 2000
23 1
232
<V
15 - < 25 3000 2000 2000 4000
252-L
253-L
241-S
242-S
5 -
< V < 1 5 4500 3000 3000 5000
2 52-S
253-S
The c l o s e n e s s of t h e a v e r a g e d c a l i b r a t i o n s t o t h e s i n g l e p o i n t c a l i b r a t i o n s
shows t h a t i t i s n e c e s s a r y o n l y t o c o l l e c t d a t a a t t h e c e n t e r of t h e o r e zone
f o r a c c e p t a b l e c a l i b r a t i o n s . The u n i f o r m i t y of t h e d a t a i n Table 1-4 a l s o
shows t h a t t h e r e i s no d i f f i c u l t y i n p o s i t i o n i n g t h e probe a t t h e c e n t e r of
t h e o r e zone. As a check on equipment o p e r a t i o n two s e p a r a t e d a t a c o l l e c t i o n s
a r e now made d u r i n g c a l i b r a t i o n w i t h o u t moving t h e probe. C o n s i s t e n c y between
two s e t s of d a t a p r o v i d e s c o n f i d e n c e t h a t t h e equipment d i d n o t m a l f u n c t i o n
(e.g., s t o p p r e m a t u r e l y ) d u r i n g d a t a c o l l e c t i o n .
SUMMARY
C a l i b r a t i o n d a t a f o r s p e c t r a l gamma-ray p r o b e s a r e c o l l e c t e d i n t h e Grand
J u n c t i o n models. The c o u n t i n g t i m e s f o r c o l l e c t i n g t h e s e d a t a v a r y w i t h
d e t e c t o r s i z e , and a p p r o p r i a t e t i m e s have been p r e s e n t e d i n Table 1-3 f o r a
r a n g e of d e t e c t o r volumes.
The c o l l e c t e d d a t a a r e a n a l y z e d u s i n g m a t r i x mathematics t o o b t a i n t h e
c o n v e r s i o n f a c t o r s between c o u n t r a t e s and c o n c e n t r a t i o n s and t o d e t e r m i n e t h e
gamma-ray s c a t t e r components t h a t produce i n t e r f e r e n c e s among t h e d i s c r e t e
e n e r g y windows. I n t h i s t e c h n i q u e of a n a l y s i s , a l i b r a t i o n c o n s i s t s of
determining t h e matrix A-' u s i n g e q u a t i o n 8. A-f can t h e n be used t o
c a l c u l a t e ( e q u a t i o n 9 o r 1 0 ) unknown c o n c e n t r a t i o n s i n t h e f i e l d based on
observed c o u n t r a t e s .
Table 1-4. Comparison of Calibration Data Taken at One Point and at
Five Points
K r:odel
-
I n I m v V 0 0
C
-
0
,& i & u L 0
"
0
: LY)Z
-
u
C W u Y L
L
0
P w =, 0 0
c .A
- \ r w ~ w
m+m s= 2o m C in
.- -. r ,
C , 0 1 .azc, C Ln
ww.
"7
w
L m
-
7 .
0L 0
u
1Z6 4s
0 Y)
I :::. a
Y)
1) .?m- mu.- 0
a Y)
.- ,
C OIW A
.,
m r .-
C
.
w
,, 1 e !: .z:
"
=S
c'
I
= ,
I c
.-T 0
v 3 aOk5
> O
k5aO
20
&s m s c
3 aO 0
L C
3
*I
L
w = ~a O
CIU a . u =, E I 2:- gS Y
I
"74- 1 UU"7 ;Q .-Z U0 I > "
"7UU
> O
4 u m
600 5ZP0 9.033t.12 8.983 ' 5390.2 ' 715 1.1961.G4 1.133 680.2 70 O.llG*.Cl 0.115 69.0
400 14552 36.380t.30 36.10214440.8 1779 1772.2 215 0.537*.03 0.503 201.2
17.268r.16 , 17.103 10262. 1749 1793.0 57 0.095?.01 0.116 69.8
53.2036 ' 53.93 21572.2 2523 6.307!.12 6.451 2580.6 260 0.650l.04 0.648 259.2
51.432?.35 1
51.295 20518.2 2847.8 284 0.710?.04 0.720 288.2
3129178i 252 400 6 0 6 2 15.155:.19 15.081 6032." 2295.07 2.330 932.0 107 0.267~02 0.303 121.4
3/29/78 231 400 10627' 265672.25 26.835'10734.2 1388 3.470i.09 3494 1397.8 228 0.570i.03 0.529 211.8
I
3/29/78 242-5 400 10.892z.16, 10.944l4377.6 654 1.635t06 1.664 665.8 66 0.165i.02 0.158 63.2
3297
2/21/78,
2/14/78'
242
252
242-5
4 0
400
400
22388
6059
4350
I
55970.37
15.!47!.19
10.875:.16 '
55.73222920
15.194 6077.8
10.749 4299.6
35661 8.915:.14
711
644
1.777*.06
1.6101.06
9.049
1.845
1.651
3619.6
738.0
660.4
425
80
69
1.062!.05
0.200*.02
0.172*.02
1.038
0.196
0.139
4154
78.6
55.6
2/13/78 242-L 400 22638 56.595..37 56.334 22533.0 3254 8.1352.14 7.9205 3168.2 277 0.692i.04 0.736 294.4
U Rodel
6/6/78
6/5/78 I 252-5
252-L
1
300
200
25167 1
83.890*.52 1 83.576 25073.0
1
69983 349915~132' 348.128 69625.6
'
8
23266 77 553i.50
7556 3 5 7 7 8 0 3 3
77.362
357.01
1
23208.6
!
714022
1
411
1999
1.370t.06
9.995-22
1.464
10.012
439.2
2002.4
6/5/78 ,
6/1/78
242-8
242-L
300
200
31732 105.773,.59 105906 31772.2
96290 481 45021 5 5 480.534 '36l06.8
26720 1 89.066. 5 4
1
97005 4P.025.1 5 5 1 89130
488.830
26739.2
1 17766.0
494
2589
1.646?.07
12.945.2 5
1.822
13033
5468
2606.6
5/25/78,
3/29/18
242-L
252
200
200
97554 1487.770.1.56 486.062 97212.4
29766 148.930 8 6 149.313 : 29862.6 /
102841 514.205'1.60
29686 148.430+.86
102869.0
29771."
3373
923
16.865..29
4.615. .15
16.684
4.606
3336.8
921.2
3/29/78
3/29/76
3/29/78
231
242-5
200
200
200
49l53/245765~l.lOi
19533 97.665.6 9
98845 494.225+l.57
246.105 49221.0
193160
98262.2
17736 1
50071 l250.355ll.11
88.680: .66
104254 521.27OI.61
500l7.6
17526.8
104257.4
1636
319
3212
8.180?.20
1.595?,08
16.060~28
8513
1.481
16.171,
1702.6
296.2
3234.2
2/21/78 L 29406.8 28546 '142.730s.84 142.213 28442.6 685 3.425-.I3 3.384 676.8
19364.6 16956 84.780..65 84.468 16893.6 292 1.460*.08 1.432 286.4
98313.4 102359 511.795.1.59 511.587 102317.4 3032 15.16P.27 15.521 3104.2
T h Mod., l
ABSTRACT
When 54Mn p i l e - u p c o u n t r a t e s a r e n o t a v a i l a b l e b e c a u s e of a n o n s t a n d a r d
d e t e c t o r c o n f i g u r a t i o n o r b e c a u s e of i n c o m p l e t e knowledge of t h e 5 4 ~ ns o u r c e
s t r e n g t h , d i r e c t measurements may be o b t a i n e d i n a low background model now
a v a i l a b l e a t t h e Grand J u n c t i o n c a l i b r a t i o n f a c i l i t y .
INTRODUCTION
C o n c e n t r a t i o n s a r e d e t e r m i n e d by s u b t r a c t i n g background c o u n t r a t e s b e f o r e
m u l t i p l y i n g by t h e c a l i b r a t i o n m a t r i x A-1 :
In equation (2), B
i s a 3 x 1 m a t r i x c o n t a i n i n g t h e background c o u n t r a t e s f o r
K, U , and Th, and CB i s t h e background c o r r e c t e d c o n c e n t r a t i o n m a t r i x .
Comparing e q u a t i o n s ( 1 ) and ( 2 ) i t i s c l e a r t h a t t h e c a l c u l a t e d c o n c e n t r a t i o n s
w i l l be t o o h i g h i f background i s n o t s u b t r a c t e d from t h e o b s e r v e d c o u n t i n g
data.
O R I G I N OF BACKGROUND COUNTS
I n t h i s d i s c u s s i o n , background c o u n t s a r e d e f i n e d a s c o u n t s i n a d e t e c t o r
which a r e n o t a t t r i b u t a b l e t o t h e p r e s e n c e o f K , U , o r Th. I n KUT p r o b e s
c o n t a i n i n g a r a d i o a c t i v e s o u r c e f o r e n e r g y s t a b i l i z a t i o n , t h i s s o u r c e c a n be a
major c o n t r i b u t o r t o background. I n KUT p r o b e s u s e d by Bendix, 54Mn s o u r c e s
o f a p p r o x i m a t e s t r e n g t h 0.7 and 4 m i c r o c u r i e s a r e used t o s t a b i l i z e t h e l a r g e
and s m a l l d e t e c t o r s , r e s p e c t i v e l y . T h i s s o u r c e produces a gamma r a y of e n e r g y
0.835 MeV, which i s w e l l below t h e KUT e n e r g y windows. However, t h e chance
a r r i v a l of two 0.835 MeV gamma r a y s a t t h e same t i m e i n a d e t e c t o r produces a
sum o r p i l e - u p spectrum t h a t l o o k s s i m i l a r t o t h e p u l s e h e i g h t spectrum from a
s i n g l e gamma r a y h a v i n g a p p r o x i m a t e l y t w i c e t h e e n e r g y o f t h e i n d i v i d u a l gamma
rays. T h i s p i l e - u p s p e c t r u m e x t e n d $ i n e n e r g y t o t w i c e 0.835 MeV o r 1.67 MeV
and g i v e s c o u n t s i n b o t h t h e K and U e n e r g y windows.
Background c o u n t s c a n be produced by t h e p r e s e n c e of r a d i o a c t i v e e l e m e n t s t h a t
e m i t gamma r a y s h a v i n g e n e r g i e s w i t h i n K, U, o r Th windows. This o r i g i n o f
background i s g e n e r a l l y minor compared t o o t h e r o r i g i n s of background c o u n t s ,
and i t seldom p r o d u c e s s e r i o u s problems f o r d a t a a n a l y s i s .
F i n a l l y , background c o u n t s c a n come from t h e p h o t o m u l t i p l i e r t u b e on t h e
detector. These c o u n t s a r e low i n e n e r g y , and t h e y do n o t produce any
s i g n i f i c a n t c o n t r i b u t i o n s t o t h e K , U, and Th windows i n a p r o p e r l y o p e r a t i n g
probe.
BACKGROUND MEASUREMENTS
I d e n t i f i c a t i o n o f Background S o u r c e s
Pile-up Spectrum
54
From 0.6 pCurie Mn
54
Mn Pilot
Window
1
0
CHANNEL NUMBER
Figure 2-1. KUT probe background spectra as acquired within the low
background water tank.
28
filled. R e s u l t s were v i r t u a l l y i d e n t i c a l t o t h e p r e v i o u s measurement w i t h o u t
the liner. R e s u l t s of a l l 4 measurements a r e summarized i n Table 2-1.
5 4 ~ nP i l e - u p Count R a t e s
5 4 ~ nSource Count
Strength K Window U Window Th Window Time
( PC> Counts Counts Counts (Seconds)
54 MII Source
Strength K Window U Window Th window
(u c> (CPS > (CP~) (cps)
5 4 ~ nSource Count
Strength K Window U Window Th Window Time
(LIc) Count Count Count (Seconds)
5%1n Source
Strength K Window U Window Th Window
(Fc C) (cps) (CPS) (cps)
where So i s t h e s o u r c e s t r e n g t h e x p r e s s e d a s a p i l o t window c o u n t r a t e
(KCPS) a t some i n i t i a l t i m e to ( i n d a y s ) , X i s t h e 5 4 ~ ndecay c o n s t a n t and
i s e q u a l t o 2.218 x days-1, and t 1s t h e c u r r e n t t i m e ( i n d a y s ) .
Once t h e c u r r e n t 54Mn s o u r c e s t r e n g t h h a s been d e t e r m i n e d , t h e K and u
window c o u n t r a t e s are computed from t h e a n a l y t i c polynomial f i t s t o t h e
measured i n s t r u m e n t a l background d a t a p r e s e n t e d i n F i g u r e s 2-2 and 2-3 and
reproduced below.
SUMMARY
INTRODUCTION
Water f a c t o r c o r r e c t i o n s t o gamma-ray l o g g i n g d a t a a r e d e s i g n e d t o c o r r e c t
probe r e s p o n s e f o r t h e v a r y i n g gamma-ray s i g n a l a t t e n u a t i o n r e s u l t i n g from
changes i n t h e w a t e r - f i l l e d b o r e h o l e d i a m e t e r . These c o r r e c t i o n s a r e c r u d e l y
a p p l i e d t o t o t a l gamma-ray l o g g i n g d a t a by i n t r o d u c i n g a s i n g l e f a c t o r f o r a
g i v e n p r o b e and b o r e h o l e , b a s e d on t h e s i z e of t h e b i t used t o d r i l l t h e h o l e .
Such a c o r r e c t i o n o b v i o u s l y c a n n o t a c c o u n t f o r l o c a l i z e d b o r e h o l e d i a m e t e r
v a r i a t i o n s , v i z , washout zones. For s p e c t r a l gamma-ray (KUT) l o g g i n g , t h e
b o r e h o l e w a t e r a t t e n u a t i o n problem i s much more c o m p l i c a t e d . A s of 1978 no
c o r r e c t i o n was made t o KUT f i e l d l o g s b e c a u s e t h e e x i s t i n g w a t e r f a c t o r d a t a
a r e considered inadequate. S i n c e BFEC KUT p r o b e s a r e c a l i b r a t e d under d r y
b o r e h o l e c o n d i t i o n s i n t h e Grand J u n c t i o n models, f i e l d l o g s i n w a t e r - f i l l e d
h o l e s w i l l y i e l d r e s u l t s t h a t a r e s y s t e m a t i c a l l y low. The c o r r e s p o n d i n g e r r o r
i n t h e KUT a s s a y f o r a 2.0-inch d i a m e t e r p r o b e and a 4.5-inch, w a t e r - f i l l e d
b o r e h o l e i s between 15 a n d 25 p e r c e n t and r i s e s t o a s much a s 100 p e r c e n t f o r
a 9-inch-diameter, w a t e r - f i l l e d b o r e h o l e .
T h e o r e t i c a l arguments p r e d i c t t h a t probe r e s p o n s e i n a d r y h o l e w i l l be
independent of h o l e s i z e s o l o n g a s t h e mixed o r e zone always p r e s e n t s a n
e f f e c t i v e l y i n f i n i t e medium t o t h e probe. R e s u l t s i n F i g u r e 3-1 seem t o be
i n d e p e n d e n t of h o l e s i z e f o r p o t a s s i u m and uranium w i t h i n t h e measurement
p r e c i s i o n s , w h i l e t h e r e i s a s y s t e m a t i c d e c r e a s e i n t h e thorium a s s a y
amounting t o a b o u t 1 p e r c e n t from t h e 3-inch t o t h e 12-inch h o l e s i z e . The
d e c r e a s e i s a t t r i b u t e d t o t h e f a c t t h a t f o r t h e thorium s i g n a l t h e model no
l o n g e r h a s t h e a p p e a r a n c e of a n i n f i n i t e medium i n t h e a x i a l d i r e c t i o n ( t h e
o r e zone t h i c k n e s s t o h o l e d i a m e t e r r a t i o h a s dropped t o 60/12 = 5.0). The
probe now " s e e s " t h e upper and l o w e r b a r r e n zones t o some d e g r e e . The a s s a y s
r e p o r t e d h e r e a r e based on e q u i v a l e n t d r y g r a d e s of t h e c a l i b r a t i o n models and
hence r e p r e s e n t - d r y b u l k g r a d e s f o r t h e KUT w a t e r f a c t o r model o r e zone.
These r e s u l t s a r e s y s t e m a t i c a l l y above t h e d e s i g n g r a d e s , e s p e c i a l l y f o r
p o t a s s i u m , where t h e a s s a y s a r e a b o u t 2 5 p e r c e n t high. P a r t of t h e d i f f e r e n c e
w i t h p o t a s s i u m may be due t o l a r g e a b s o l u t e u n c e r t a i n t i e s i n s t r i p p i n g r a t i o s
caused by t h e a s s a y e r r o r s f o r t h e U and Th c a l i b r a t i o n models.
D e ~ t hP r o f i l e s
-4 -2 0 +2 +4
Borehole C o n c e ~ l t r aito n
Diameter
(inches) % K PPm U PPm Th
Note: f v a l u e s r e p r e s e n t one s t a n d a r d d e v i a t i o n u n c e r t a i n t i e s
due t o w a t e r f a c t o r d a t a c o u n t i n g s t a t i s t i c s . They do n o t
i n c l u d e u n c e r t a i n t i e s i n t h e c a l i b r a t i o n matrix.
Thorium
Window
The 1.5-inch x 9-inch N~I(TL) detector of probe 253L has been calibrated
several times over the period from July to September 1978. These calibrations
are for both a wet and dry 4.5-inch-diameter borehole. The calibration of
August 22, 1978 was used in the analysis of the water factor model
measurements. Matrix elements for the A and A-1 matrices are given in Table
3-2. The values contained in Table 3-2 agree, within stated uncertainties,
with the calibration performed earlier for the same probe.
Table 3-3. Stripping Ratios Computed from the August 1978 Calibration
Results of Table 3-2
a ' A23/A33
6 ' A13/A33
Y A12/A22
A A32/A22.
I PRiNCETON GAMMA-TECH, INC. I!
U -235
Ro - 226
Figure 3-6. High resolution germanium spectr-~rnf o r t h e UUT wztzr factor model.
High r e s o l u t i o n gamma-ray t r a n s p o r t c a l c u l a t i o n s have been performed f o r t h e
b o r e h o l e geometry a t t h e Los Alamos S c i e n t i f i c L a b o r a t o r y . (See T e c h n i c a l h o t e
9 f o r a d i s c u s s i o n of t h e s e c a l c u l a t i o n s . ) R e s u l t s f o r a c e n t r a l i z e d probe with-
i n a w a t e r - f i l l e d b o r e h o l e i n d i c a t e d t h a t t h e "K window" t o 1765 keV gamma-ray
f l u x r a t i o i n c i d e n t on t h e d e t e c t o r s u r f a c e i n c r e a s e s by a b o u t 7 p e r c e n t when
t h e 4.5-inch b o r e h o l e i s f i l l e d w i t h w a t e r . A s t h e w a t e r - f i l l e d b o r e l l o l e
diameter i n c r e a s e s t o 9 inches, t h e r a t i o i n c r e a s e s by another 6 percent.
These c a l c u l a t i o n s do n o t i n c l u d e t h e e f f e c t of d e t e c t o r r e s p o n s e and hence
o v e r e s t i m a t e t h e changes i n s t r i p p i n g r a t i o w i t h w a t e r - f i l l e d h o l e s i z e .
In t h e a b s e n c e of d i r e c t measurements of a , 6, and y w i t h v a r y i n g h o l e s i z e
and c o n s i d e r i n g t h e i n d i r e c t e v i d e n c e from t h e work of PGT and LASL, i t w i l l
be assumed f o r now t h a t t h e s t r i p p i n g r a t i o s f o r w a t e r - f i l l e d b o r e h o l e s do n o t
change from t h o s e f o r t h e nominal 4.5-inch c a s e , a s g i v e n i n Table 3-3.
KUT Water F a c t o r s F o r S t r i p p e d R e s u l t s
f o r S i d e w a l l e d Probe
T a b l e 3-5. Water F a c t o r C o r r e c t i o n R a t i o s
f o r C e n t r a l i z e d Probe
D Potassium Window
o Uranium Window
x Thorium Window
-----<A
Probe I
O.D. I
'I 3lO
I
4.5
I
7.0
I
9.0
I
12.0 Inches
I
Probe O.D.
I
I I I I I I
3.0 4.5 7.0 9.0 12.0 Inches
P r i n c i p l e of t h e Technique
The d i f f i c u l t i e s w i t h p r e v i o u s a t t e m p t s a t KUT w a t e r f a c t o r c o r r e c t i o n s a r e
t h a t u n s t r i p p e d K, U , and Th window i n t e n s i t i e s are used i n forming t h e
KeV
Sidewalled Geometry
Solid Curves are from July 1978
PGT Intrinsic Germanium Probe Data
KeV
BFEC Results
O Potassium
0 Uranium
x Thorium
1 I I I I
3.0 4.5 7.0 9.0 12.0 Inches
1.6 -
---A
1.4.- Sidewalled
Probe
I 1
0 5 10 15 20 25 30 35
. 0-
1 .o
Probe
0.0.
<"I
I. 13 a ~ a e w a l l e d / A /
3.0 4.5
,
7.0
I
9.0
,
12.0 Inches
I m p l e m e n t a t i o n w i t h F i e l d Data
Dry Borehole
W a t e r - f i l l e d Borehole
C o r r e c t i o n c u r v e s f o r s t r i p p e d K, U, and Th window s e n s i t i v i t i e s a r e p r e s e n t e d
i n F i g u r e 3-8 f o r w a t e r - f i l l e d h o l e s . F i e l d d a t a s h o u l d be s t r i p p e d u s i n g
c a l i b r a t i o n r e s u l t s from t h e d r y 4.5-inch b o r e h o l e s of K, U, and Th models.
The s t r i p p e d f i e l d d a t a w i l l t h e n be m u l t i p l i e d by t h e a p p r o p r i a t e K, U, and
Th w a t e r f a c t o r s f o r t h e a v e r a g e h o l e s i z e measured o v e r e a c h l o g g i n g
interval.
F u t u r e Development
INTRODUCTION
When b o r e h o l e s a r e d r i l l e d i n s o f t m a t e r i a l , t h e h o l e s a r e o f t e n cased t o
p r e v e n t them from c o l l a p s i n g . R a d i a t i o n d a t a c o l l e c t e d i n b o r e h o l e s subse-
q u e n t t o t h e a d d i t i o n of c a s i n g i s a f f e c t e d by t h e p r e s e n c e of c a s i n g . The
c a s i n g a b s o r b s some of t h e gamma r a y s and s c a t t e r s o t h e r s t o lower e n e r g i e s .
It i s , t h e r e f o r e , n e c e s s a r y t o a p p l y c a s i n g c o r r e c t i o n f a c t o r s t o d a t a from
cased h o l e s i n o r d e r t o c a l c u l a t e c o r r e c t c o n c e n t r a t i o n s of r a d i o e l e m e n t s i n
formations. These c o r r e c t i o n f a c t o r s a r e f u n c t i o n s of t h e c a s i n g m a t e r i a l and
its thickness. C o r r e c t i o n f a c t o r s f o r s t e e l c a s i n g s w i t h t h i c k n e s s e s from
1 / 1 6 i n c h t o 112 i n c h a r e p r e s e n t e d below.
DATA COLLECTION
Length: 4.5 f e e t
I n s i d e Diameter: 3 inches
Wall T h i c k n e s s : 1116-inch, 118-inch, 3116-inch,
114-inch, 318-inch, 1 / 2-inch.
The c o u n t i n g t i m e s f o r d a t a c o l l e c t i o n were i n c r e a s e d a s t h e c a s i n g t h i c k n e s s
i n c r e a s e d i n o r d e r t o m a i n t a i n good c o u n t i n g s t a t i s t i c s . S e v e r a l r u n s with no
c a s i n g p r e s e n t were i n t e r s p e r s e d w i t h t h e c a s i n g r u n s t o check t h e s t a b i l i t y
of t h e d a t a c o l l e c t i o n system. The c o u n t s i n t h e potassium (K), uranium ( U ) ,
and thorium (Th) e n e r g y windows were r e c o r d e d from a m u l t i c h a n n e l a n a l y z e r .
The count r a t e s o b t a i n e d f o r t h e v a r i o u s c a s i n g t h i c k n e s s e s a r e g i v e n i n
T a b l e s 4-1, 4-2, a n d 4-3 f o r t h e K, U, and Th models, r e s p e c t i v e l y . The
u n c e r t a i n t i e s g i v e n i n t h e t a b l e s a r e t h e one s t a n d a r d d e v i a t i o n l i m i t s .
ANALY S I S
V a r i a t i o n of S t r i ~ ~ i nR ae t i o s w i t h Casing T h i c k n e s s
Casing K U Th
Thickness Energy Energy Energy
(inches) Window Window Window
+
0
1 / 16
118
318.8
294.9
270.8
+T+ 0.8
0.8
0.7
304.5
278.6
255.3
+
7
T
0.8
0.7
0.7
9.6
8.4
7.6
T
T
0.1
0.1
0.1
3/16 249.7 7 0.6 234.6 7 0.6 6.9 0.1
114
318
235.2
204.0
7
+
-
0.6
0.5
220.2
190.9 T
0.6
0.5
6.7
5.4 +7 0.1
0.1
112 175.4 T 0.4 164.0 -
T 0.4 4.8 - 0.1
T a b l e 4-3. Counts Per Second Obtained With S t e e l Casing i n t h e
Thorium (Th) Model
Casing K U Th
Thickness Energy Energy Energy
(inches) Window Window Window
Casing
Thickness a B Y
(inches)
3.00 + 0.01
0
1/16 3.02 7 0.02
3.02 T 0.02
1.38 +
1.40 T
1.42 +
0.004
0.01
0.01
1.04
1.05
1.05
+T+ 0.004
0.004
0.004
118
3/ 1 6 3.08 7 0.02 1.46 T 0.01 1.06 T 0.004
114 3.08 7 0.02 1.46 T 0.01 1.06 7 0.004
318 3.16 T 0.02 1.52 '7 0.01 1.06 T 0.004
112 T 0.02
3.24 - 1.56 - + 0.01 1.06 -
T 0.004
NOTES :
1. U n c e r t a i n t i e s a r e one s t a n d a r d d e v i a t i o n .
2. U n c e r t a i n t i e s i n t h e c o n c e n t r a t i o n s of t h e p i t s a r e n o t i n c l u d e d i n t h e
quoted s t a n d a r d d e v i a t i o n s because t h e y t e n d t o o b s c u r e t h e v a r i a t i o n of
the stripping ratios.
3. S t r i p p i n g r a t i o s a r e f o r probe 253L.
I I I I I I I I I
0,2 0.4 0.6 0.8 I .O 1.2 1.4 1.6
BOREHOLE CASING THICKNESS (centimeters)
V a r i a t i o n o f S t r i p p e d Window S e n s i t i v i t i e s w i t h C a s i n g T l l i c k n c s s
S t r i p p e d K, U, and Th window i n t e n s i t i e s , n o r m a l i z e d t o t h e z e r o c a s i n g t h i c k -
n e s s v a l u e s , a r e t a b u l a t e d i n T a b l e 4-5 and p l o t t e d i n F i g u r e 4-2. These
v a l u e s r e p r e s e n t t h e gamma-ray t r a n s m i s s i o n s of t h e s e e n e r g y windows f o r t h e
casing thicknesses considered. The p l o t s a r e i n s e m i l o g a r i t h m i c form, and
s t r a i g h t l i n e s were f i t t e d t o t h e t h o r i u m and p o t a s s i u m p l u s uranium r e s u l t s .
( P o t a s s i u m and uranium a r e combined b e c a u s e t h e y a r e done i n e n e r g y and t h e
e x p e r i m e n t a l d a t a f o r them o v e r l a p p e d . ) The s t r a i g h t l i n e f i t s y i e l d s l o p e s
o f 1.23 i n - 1 and 1.05 i n - l , f o r t h e t h o r i u m , and f o r t h e potassium p l u s
uranium windows, r e s p e c t i v e l y . The s e n s i t i v i t y f o r t h e thorium window t a k e s
i t s " h a l f - v a l u e " f o r a s t e e l c a s i n g 0.66 i n c h e s t h i c k . The c o r r e s p o n d i n g
t h i c k n e s s f o r p o t a s s i u m and uranium i s 0.56 i n c h e s .
T a b l e 4-5. S t r i p p e d Window I n t e n s i t y T r a n s m i s s i o n F a c t o r s f o r S t e e l
Borehole Casing
Casing K U Th
Thickness Energy Energy Energy
(inches) Window Window Window
It i s recommended t h a t c o r r e c t i o n s be made f o r t h e p r e s e n c e of s t e e l c a s i n g on
b o t h s t r i p p i n g r a t i o s and on s e n s i t i v i t i e s . T h i s i s accomplished by i n t i a l l y
performing s e p a r a t e probe c a l i b r a t i o n s f o r e a c h c a s i n g t h i c k n e s s . The d a t a
from t h e c a l i b r a t i o n s c a n be used t o d e t e r m i n e how t h e i n d i v i d u a l e l e m e n t s of
t h e A-1. c a l i b r a t i o n m a t r i x v a r y w i t h c a s i n g t h i c k n e s s . I n t h i s way
c o r r e c t i o n f a c t o r s a r e o b t a i n e d f o r t h e s t r i p p i n g r a t i o s and s e n s i t i v i t i e s :
( c a s i n g of t h i c k n e s s X )
correction factor for (x) = --
Lj (no c a s i n g )
Ai
The c o r r e c t i o n f a c t o r s t h u s o b t a i n e d a r e used t o modify (by m u l t i p l i c a t i o n )
t h e m a t r i x e l e m e n t s from s u b s e q u e n t c a l i b r a t i o n s o f t h e probe o b t a i n e d w i t h o u t
casing.
x Thorium .
Potassium/Uranium
T r a n s m i s s i o n = e ~ p [ - ~ /Zc o s 6 ] ,
SIGNAL DECONVOLUTION
INTRODUCTION
K Model
U Model
i APPARENT GRADE
0 DIFFERENTIAL GRADE
I I I I I I 1 I I
0.0
30 40 58 60 70 80 90 100 110 120
V E R T I C A L POSITION ABOVE ORE-ZONE CENTER
(centimeters)
Figure 5-2. Uranium model deptb -rofile and differential response for
1.5-inch x 9-inch ctor.
The d i f f e r e n t i a l r e s p o n s e i s c l e a r l y not s y m m e t r i c a l a b o u t i t s maximum v a l u e ,
a s expected f o r a p e r f e c t s t e p f u n c t i o n ore-barren i n t e r f a c e . Apparently
t h e r e a r e i n h o m o g e n e i t i e s o r i m p e r f e c t i o n s i n t h e i n t e r f a c e between t h e o r e
zone and upper barren-zone of t h e uranium model. The FWIIM of t h e d i f f e r e n t i a l
c u r v e i s 26.0 cm and FWTM i s 53.5 cm. IIowever, t h e s e d i f f e r e n t i a l r e s u l t s
c a n n o t be c o n s i d e r e d t h e t h i n uranium bed r e s p o n s e f u n c t i o n f o r t h i s probe.
Th Model
C o m ~ a r i s o nof D i f f e r e n t i a l R e s ~ o n s eF u n c t i o n s
P r e s e n t a t i o n of R e s u l t s
( E a s t ) 30 2.9 2.10
24 4.2 1.71
21 5.4 1. 6 1
18 7.9 1.39
15 14.4 1.21
12 27.1 1.091
10 45.6 1.068
8 78.0 1.021
7 105.3
6 142.6 1.01 6
5 195.7
4 255.3 0.987
3 307.0
2 341.1 0.990
(Red 1 359.9
Center) 0 365.8 0.990
1 350.1
2 327.9 1.00
3 283.8
4 228.6 1.04
5 177.3
6 135.1 1.07
7 98.1
8 73.4 1.10
10 42.9 1.12
13 20.1 1.16
16 10.7 1. 32
20 5.6 1.53
24 3.7 1.70
(West) 30 2.8 1.79
0.5-Foot Anomaly
.
1 0-Foo t Anomaly
The w e i g h t i n g c o e f f i c i e n t s d e t e r m i n e d f o r t h e uranium c h a n n e l i n s p e c t r a l
gamma-ray (KUT) p r o b e s have been i n s e r t e d i n t o t h e computer program GAMLOG
( S c o t t , 1962). T h i s program was o r i g i n a l l y w r i t t e n t o d e c o n v o l v e g r o s s c o u n t
gamma-ray l o g g i n g d a t a , b u t i t h a s been m o d i f i e d r e c e n t l y t o p r o c e s s uranium-
c h a n n e l KUT d a t a a l s o . GAMLOG i s now p a r t of a n e x t e n s i v e l o g a n a l y s i s s y s t e m
p l a c e d i n o p e r a t i o n a t t h e Oak Ridge DEC-10 computer f a c i l i t y by R. P r i c e and
K. Hayer.
FWHM = 36cm
*These w e i g h t i n g f a c t o r s a r e f o r a s m a l l t o t a l gamma c r y s t a l a s r e p o r t e d by
S c o t t i n h i s GAMLOG r e p o r t .
CALIBRATION MODELS
CALCULATED CONCENTRATIONS
where C = c a l c u l a t e d c o n c e n t r a t i o n m a t r i x (3x1)
A-'= c a l i b r a t i o n m a t r i x (3x3)
The c a l i b r a t i o n m a t r i x A-'was d e t e r m i n e d by u s i n g s t a t i c d a t a t a k e n i n t h e
models 3 days p r i o r t o t h e dynamic t e s t s . These s t a t i c c a l i b r a t i o n d a t a a r e
g i v e n i n T a b l e 6-5. The c o n c e n t r a t i o n s c a l c u l a t e d u s i n g e q u a t i o n ( 1 ) w i t h t h e
dynamic d a t a a r e g i v e n i n T a b l e s 6-6, 6-7, and 6-8 f o r t h e potassium ( K )
Table 6-3. Data Obtained from Dynamic Logging of t h e Uranium ( U ) Model
T a b l e 6-4. Data Obtained from Dynamic Logging of the Thorium (Th) Model
T a b l e 6-6. C o n c e n t r a t i o n s C a l c u l a t e d from Dynamic Logging Data f o r t h e
Potassium ( K ) Model
10 5 5.74
6.01 T
+ 0.53
0.54
2.9
0.5
+
T
1.6
2.2
0.9
4. 6 +T+ 1.8
2.8
6.77 T
- 0.56 -0.9 T
- 2.1 4.9 - 2.8
Note: S t a t i s t i c a l u n c e r t a i n t i e s a r e one s t a n d a r d d e v i a t i o n .
T a b l e 6-7. C o n c e n t r a t i o n s C a l c u l a t e d from Dynamic Logging Data f o r t h e Uranium ( U ) Model
1 5 4.38 +
4.03 476.8 + 21.2 11. 6 +13.4
6.40 7 4.01 464.1 T 21.0 19.0 7 13.7
2.63 7
- 4.05 488.3 7
- 21.4 7. 7 T
- 13. 3
5 2 2.76 + 4.97 502.6+26.5 - 1 . 5 + 16.6
5.06 7 4.78 446.0726.3 35.7719.3
-1.27 T
- 4.88 510.8 T
- 26.1 -14.7 7 - 15.3
5 5 5.39 + 3.96 462.8 + 20.7 13.2 + 13.2
4.37 7 4.06 485.6 7 21.2 5.1 7 13.2
2.99 T
- 4.01 478.9 - 21.2 11.0 -
7 13.4
10 5 7.43
2.64 +7-+ 3.95
3.91 440.0+20.5
470.0721.0
450.7 T
29.6+13.9
14.0T13.4
9.08 3.97 - 20.4 16.6 T
- 13.3
15 1 6.41 + 5.82 456.3 + 30.6 -7.2 + 19.0.'
3.81 7 6.02 483.3 7 32.4 0.6 7 21.1
-3.22 T
- 6.22 5 5 2 . 4 7-3 3 . 2 - 3 0 . 7 7- 17.5
Note: S t a t i s t i c a l u n c e r t a i n t i e s a r e one s t a n d a r d d e v i a t i o n .
T a b l e 6-8. C o n c e n t r a t i o n s C a l c u l a t e d from Dynamic Logging Data f o r t h e Thorium (Th) Model
15 2 -3.65 +
4.07 18.3 + 36.5 515.1 +
45.3
1.46 7 4.29 16.9 T 37.8 547.6 7 46.8
0.89 -T 4.22 21.0 - 37.1 530.1 - 4 6 . 0
Note: S t a t i s t i c a l u n c e r t a i n t i e s a r e one s t a n d a r d d e v i a t i o n .
model, uranium (U) model, and thorium (Th) model, r e s p e c t i v e l y . The
s t a t i s t i c a l u n c e r t a i n t i e s i n t h e t a b l e s a r e one s t a n d a r d d e v i a t i o n ; t h e y
r e p r e s e n t t h e t o t a l u n c e r t a i n t y due t o b o t h t h e c o u n t i n g s t a t i s t i c s i n t h e
dynamic d a t a and t h e u n c e r t a i n t y i n t h e probe c a l i b r a t i o n , A-1.
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T a b l e 6-10, and and t h e y a r e v e r y s i m i l a r t o t h e c o n c e n t r a t i o n s i n T a b l e 6-9.
The c o n c e n t r a t i o n s c a l c u l a t e d from t h e two c a l i b r a t i o n s a g r e e w i t h i n t h e
s t a t i s t i c a l u n c e r t a i n t i e s . T h i s agreement s u g g e s t s t h a t probe c a l i b r a t i o n
p a r a m e t e r s do n o t v a r y r a p i d l y and t h a t monthly c a l i b r a t i o n s s h o u l d be
adequate f o r o p e r a t i o n a l logging.
The u n c e r t a i n i t e s i n t h e c a l c u l a t e d p o t a s s i u m c o n c e n t r a t i o n s i n t h e U and Th
models a r e l a r g e ; t h e y have t h e same magnitude a s t h e c o n c e n t r a t i o n s
themselves. The r e s u l t i n g p e r c e n t u n c e r t a i n t i e s ( u n c e r t a i n t y : c o n c e n t r a t i o n
X 100 p e r c e n t ) a r e t y p i c a l l y 100 p e r c e n t t o 3 0 0 p e r c e n t f o r t h e p o t a s s i u m
concentrations. These l a r g e u n c e r t a i n t i e s a r e due t o t h e s t r i p p i n g of t h e
uranium and t h o r i u m c o u n t s from t h e potassium. The l a r g e u n c e r t a i n t i e s a r e
n o t caused by improper c a l i b : . a t i o n o r s t r i p p i n g ; r a t h e r , t h e y a r e i n e v i t a b l e
whenever t h e r e i s a h i g h c o n c e n t r a t i o n of uranium o r thorium. Stripping
removes t h e Compton-scattered uranium and thorium gamma r a y s from t h e
p o t a s s i u m e n e r g y window. The n e t p o t a s s i u m c o u n t s a r e :
where
From n u c l e a r s t a t i s t i c s , t h e r e s u l t i n g u n c e r t a i n t y i n t h e p o t a s s i u m i s
Potassium u n c e r t a i n t y = d~ota+
l U + Th
O r i g i n of
Model Uncertainty Percent K PPm u PPm Th
2. Data t a k e n a t 5 f t l m i n u t e a n d 10-second c o u n t i n g p e r i o d .
4. U n c e r t a i n t i e s a r e one s t a n d a r d d e v i a t i o n .
SUMMARY
INTRODUCTION
The u s e of 5 4 ~ nt o p r o v i d e t h e r e f e r e n c e s i g n a l c r e a t e s some p r o b l e m s ,
however, b e c a u s e t h e gamma r a y s from 54~.lni n t e r f e r e w i t h t h e n a t u r a l
gamma-ray s p e c t r u m i n t h e b o r e h o l e . A l t e r n a t e methods of p r o v i d i n g r e f e r e n c e
s i g n a l s which do n o t u s e gamma r a y s have been i n v e s t i g a t e d . Specifically,
a l p h a - p a r t i c l e s o u r c e s and l i g h t - e m i t t i n g d i o d e s have been t e s t e d f o r u s e i n
b o r e h o l e probes. A t t e n t i o n h a s been f o c u s e d i n t h e s e t e s t s on t h e t e m p e r a t u r e
dependence of t h e r e f e r e n c e s i g n a l s b e c a u s e t h i s i s t h e main c a u s e of
i n s t a b i l i t y when o p e r a t i n g i n b o r e h o l e e n v i r o n m e n t s .
THEORETICAL CONSIDERATIONS
Gamma-Ray R e f e r e n c e
Gamma-ray s o u r c e s p r o v i d e t h e s i m p l e s t means of o b t a i n i n g a r e f e r e n c e p u l s e o f
c o n s t a n t energy. Compton s c a t t e r i n g of t h e gamma r a y s makes i t e s s e n t i a l t o
s e l e c t a s t a b i l i z a t i o n s o u r c e w i t h gamma r a y s of l o w e r e n e r g y t h a n t h o s e i n
t h e n a t u r a l spectrum. For s p e c t r a l gamma-ray l o g g i n g , t h e 1460 keV gamma r a y
from 4 0 i~s t h e l o w e s t e n e r g y gamma r a y which i s t y p i c a l l y used i n t h e
n a t u r a l spectrum. There a r e o t h e r , l o w e r e n e r g y gamma r a y s i n b o t h t h e
uranium and t h o r i u m decay s e r i e s ( e . g . , 609 keV a n d 1120 keV from 2 1 4 ~ i ) ,
b u t t h e y a r e n o t g e n e r a l l y used. The gamma r a y from t h e s t a b i l i z a t i o n s o u r c e
must have a n e n e r g y low enough ( = I 2 0 0 keV) t o a v o i d i n t e r f e r e n c e w i t h t h e
p o t a s s i u m gamma r a y . The r a d i o a c t i v e s o u r c e used f o r s t a b i l i z a t i o n must a l s o
have a h a l f - l i f e s u f f i c i e n t l y l o n g t o make i t s u s e p r a c t i c a l i n probes. The
f o l l o w i n g gamma-ray s o u r c e s a r e s u i t a b l e f o r u s e :
The n e c e s s i t y f o r h a v i n g t h e s t a b i l i z a t i o n gamma r a y l o w e r i n e n e r g y t h a n t h e
n a t u r a l gamma r a y s p r e s e n t s two problems: (1) s l i g h t d r i f t s i n energy
s t a b i l i z a t i o n based on t h e low e n e r g y r e f e r e n c e a r e m a g n i f i e d a t t h e h i g h e r
e n e r g i e s , and ( 2 ) t h e p r e s e n c e of t h e s t a b i l i z a t i o n s o u r c e p r e v e n t s c o u n t i n g
of low e n e r g y gamma r a y s from t h e f o r m a t i o n (e.g., i t i s n o t p o s s i b l e t o
c o l l e c t s i m u l t a n e o u s l y b o t h s p e c t r a l d a t a and t o t a l c o u n t d a t a w i t h a low
threshold). S t a b i l i z a t i o n u s i n g a gamma-ray s o u r c e w i t h h i g h e n e r g y i s n o t
p r a c t i c a l because of Compton s c a t t e r i n g i n t o t h e lower e n e r g i e s of i n t e r e s t .
Alpha-Particle Reference
Light-Emitting Diode R e f e r e n c e
TEST RESULTS
LED
N a I (TI)
F i g u r e 7-2. D e t e c t o r assembly f o r s i m u l t a n e o u s s t a b i l i z a t i o n t e s t s
o f a l p h a s o u r c e s i n C S I ( T ~ )and N ~ I ( T ~and ) of l i g h t
e m i t t i n g d i o d e (LED).
Linear
Amplifier
ORTEC 4 5 0
1
Probe Multichannel
Analyzer
Amplifier
- Linear Gain Control
Amplifier Tracor Northern 1710
Amplifier
- L I
The d a t a c o l l e c t e d i n t h e s i m u l t a n e o u s t e m p e r a t u r e t e s t s of C S I ( T ~ ) ,N ~ I ( T ~ ) ,
and L E D a r e g i v e n i n T a b l e 7-1 f o r t h e s t a b i l i z e d node o f o p e r a t i o n and i n
T a b l e 7-2 f o r t h e u n s t a b i l i z e d mode. Approximately 3 h o u r s were a l l o w e d f o r
e a c h t e m p e r a t u r e change b e f o r e t h e d a t a were r e c o r d e d . From T a b l e 7-1, i t c a n
be s e e n t h a t none of t h e gamma-ray p e a k s moved s i g n i f i c a n t l y when t h e s y s t e m
was s t a b i l i z e d on t h e 662 keV peak from 13'cs. F u r t h e r m o r e , t h e a l p h a peak
from C s I ( T 1 ) moved much l e s s t h a n d i d t h e a l p h a peak from NaI(T1). The LED
peak p o s i t i o n d e c r e a s e d a s t h e t e m p e r a t u r e i n c r e a s e d . T h i s was d u e t o
i n c o m p l e t e t e m p e r a t u r e c o m p e n s a t i o n i n t h e e l e c t r o n i c d r i v i n g network of t h e
LED. S i g n i f i c a n t m o d i f i c a t i o n s were made t o t h e e l e c t r o n i c c i r c u i t a f t e r t h e
c o m p e n s a t i o n had been d e t e r m i n e d , and a f u t h e r r e v i s i o n f o r t e m p e r a t u r e
c o m p e n s a t i o n i s needed For a c r i t i c a l e v a l u a t i o n of t h e LED. The p r e s e n t
r e s u l t s f o r t h e L E D s h o u l d n o t be t a k e n a s a l i m i t on t h e a c c u r a c y of t h i s
technique f o r s t a b i l i z a t i o n .
Temp 662 keV CsI(Tt) 1173 keV 1332 keV NaI(T1) 2505 keV
(OF) Gamma Ray Alpha Gamma Ray Gamma Ray Alpha Gamma Ray LED
Temp 662keV CsI(p) 1173 keV 1332 keV NaI(T1) 2505 keV
(OF) Gamma Ray Alpha Gamma Ray Gamma Ray Alpha Gamma Ray LED
C
118 732 993 1274 1443 1819 2719 1 3337
Cs I (TI)
I I
I I I I
30 53 75 97 118
Temperature ( O F )
107
T a b l e 7-3. Temperature dependence of t h e e q u i v a l e n t gamma-ray e n e r g i e s
of t h e a l p h a p e a k s from 241Am i n C s I ( W ) and i n N a I ( ' E ) and o f
t h e LED peak. The e n e r g i e s were d e t e r m i n e d from d a t a i n T a b l e 7-2.
u n l e s s t h e t e m p e r a t u r e i s m o n i t o r e d and a c o r r e c t i o n i s made d u r i n g d a t a
c o l l e c t i o n f o r t h e d r i f t of t h e r e f e r e n c e peak. The a l p h a peak from 2 4 1 ~ m
i n & I ( @ ) p r o v i d e s a r e f e r e n c e peak s t a b l e enough f o r u s e i n s p e c t r a l
gamma-ray l o g g i n g , b u t i t i s n o t known i f a n a l p h a peak c a n be o b t a i n e d i n
C s I ( z ) above a n e q u i v a l e n t gamma-ray e n e r g y of 3 !lev. The l i g h t o u t p u t from
C s I ( E ) i s l e s s t h a n from N a I ( T l ) , and i t may be i m p o s s i b l e t o produce
s u f f i c i e n t l i g h t f o r t h e needed h i g h - e n e r g y r e f e r e n c e peak.
CONCLUSION
Three methods of o b t a i n i n g a r e f e r e n c e s i g n a l f o r e n e r g y s t a b i l i z a t i o n h a v e
been i n v e s t i g a t e d : gamma r a y , a l p h a p a r t i c l e and l i g h t - e m i t t i n g d i o d e .
S t a b i l i z a t i o n on t h e 8 3 5 keV gamma r a y from 94Mn i s c u r r e n t l y u s e d by BFEC
b e c a u s e of i t s s i m p l i c i t y , b u t t h e r e a r e s i g n i f i c a n t problems w i t h t h i s method
c a u s e d by i n t e r f e r e n c e of t h e s t a b i l i z i n g gamma r a y w i t h t h e n a t u r a l gamma
r a y s from t h e f o r m a t i o n b e i n g l o g g e d .
Alpha p a r t i c l e s o u r c e s and l i g h t - e m i t t i n g d i o d e s p r o v i d e p o t e n t i a l e n e r g y
r e f e r e n c e s i g n a l s which do n o t i n t e r f e r e w i t h t h e n a t u r a l spectrum. The
2 4 1 ~ ma l p h a s o u r c e i m p l a n t e d i n N a I ( T l ) was found t o be t o o t e m p e r a t u r e
dependent f o r p r a c t i c a l l o g g i n g u s e b e c a u s e i t s peak s h i f t e d by 1 2 p e r c e n t
from t h a t of gamma-ray i n t e r a c t i o n s o v e r t h e t e m p e r a t u r e r a n g e of 30" t o
118F. 241Am i n C s I ( v ) , however, p r o v i d e d a v a r i a t i o n of o n l y 1.3 p e r c e n t
when compared t o gamma-ray l i g h t o u t p u t o v e r t h e same t e m p e r a t u r e range. The
sample of C s I ( V ) w i t h 241Am used f o r t h e s e t e s t s , had i t s a l p h a peak a t a n
a p p a r e n t gamma-ray e n e r g y of l e s s t h a n 1 MeV, and i t i s n o t known i f a peak
above 3 MeV c a n be o b t a i n e d . I f t h i s i s n o t p o s s i b l e , t h e n 241Am i n CsI(TL)
c a n n o t be used f o r a s t a b i l i z a t i o n r e f e r e n c e i n b o r e h o l e l o g g i n g . CsI(Na)
w i t h 241Am may p r o v i d e h i g h e r l i g h t o u t p u t t h a n C s I ( T l ) , b u t a sample of
t h i s c r y s t a l has n o t y e t been o b t a i n e d f o r e v a l u a t i o n .
INTRODUCTION
P r e v i o u s e f f o r t s a t KUT l o g d e c o n v o l u t i o n have u t i l i z e d t h e i t e r a t i v e
procedure c o n t a i n e d i n t h e program GAMLOG. These e f f o r t s a r e d e s c r i b e d i n
T e c h n i c a l Note 5. R e c e n t l y , a new a p p r o a c h t o gamma-ray l o g d e c o n v o l u t i o n h a s
been d e s c r i b e d by J. G. Conaway (Conaway and K i l l e e n , 1978). Conaway's
t e c h n i q u e employs t h e i n v e r s e d i g i t a l f i l t e r method t o o b t a i n uranium g r a d e
v e r s u s d e p t h from t h e gamma-ray l o g r e s p o n s e .
where I ( z ) i s t h e u n i t y n o r m a l i z e d p r o b e r e s p o n s e a t p o s i t i o n z a l o n g t h e
b o r e h o l e a x i s from t h e t h i n zone, and a i s a p a r a m e t e r dependent on gamma-ray
e n e r g y , b o r e h o l e c o n d i t i o n s , f o r m a t i o n c o m p o s i t i o n , and f o r m a t i o n d e n s i t y .
I ( z ) i s c a l l e d " t h e Geologic Impulse F u n c t i o n " by Conaway. The f u n c t i o n i s
r e a l i s t i c o n l y f o r p o i n t d e t e c t o r s o r f o r d e t e c t o r s whose l e n g t h i s much l e s s
than l / a . When t h e e f f e c t of t h e d e t e c t o r l e n g t h i s i n c l u d e d , t h e f u n c t i o n
becomes more c o m p l i c a t e d (George, 1 9 7 9 a ) :
The s u c c e s s f u l d e c o n v o l u t i o n of gamma-ray l o g g i n g d a t a w i t h t h i s i n v e r s e
f i l t e r t e c h n i q u e depends on t h e c o r r e c t c h o i c e f o r t h e p a r a m e t e r a . In
a d d i t i o n , t h e d a t a must i d e a l l y be f r e e of n o i s e . The i n t r o d u c t i o n of n o i s e
( e . g . , u n c e r t a i n t i e s from c o u n t i n g s t a t i s t i c s ) d e g r a d e s t h e performance of t h e
deconvolution f i l t e r .
The p a r a m e t e r a i n t h e g e o l o g i c i m p u l s e f u n c t i o n i s b e s t d e t e r m i n e d by d i r e c t
e x p e r i m e n t a l measurement. The most p r e c i s e d a t a a r e o b t a i n e d i f p r o b e
r e s p o n s e i s measured t h r o u g h a t h i n zone of t h e r a d i o a c t i v e s p e c i e s of
i n t e r e s t ( p o t a s s i u m , e q u i l i b r i u m uranium, o r t h o r i u m ) . A " t h i n zone" i s one
whose t h i c k n e s s i s l e s s t h a n a b o u t h a l f t h e d e t e c t o r l e n g t h . The 2-inch zones
of t h e Grand J u n c t i o n models a r e a d e q u a t e f o r most d e t e c t o r s i n u s e f o r
s p e c t r a l gamma-ray l o g g i n g . I f t h i n zones a r e n o t a v a i l a b l e , t h e p a r a m e t e r a
clay be d e t e r m i n e d by m e a s u r i n g t h e p r o b e r e s p o n s e a c r o s s a p l a n e i n t e r f a c e
between a homogeneous o r e zone and a p e r f e c t l y b a r r e n zone. Both zones must
have t h e same b u l k d e n s i t y and be a t l e a s t 2 f e e t t h i c k t o a p p r o x i m a t e
s e m i - i n f i n i t e media.
Ore ~ o n e / B a r r e nZone R e s u l t s
K Model
DEPTH (centimeters)
6 - -6
5 - -5
4 - -4
3- -3
0
DEPTH (centimeters)
Figure 8-2. Potassium model profile for a 1.5-inch x 9-inch detector.
113
T l ~ e s ed a t a were t h e n f i t w i t h smooth c u r v e s and d i f f e r e n t i a l g r a d e s were
~ o m [ x i t c d . T a b l e 8-3 c o n t a i n s d i f f e r e n t i a l potassium g r a d e s f o r t h e 1.5-inch x
3.0-inch and 1.5-inch x 9.0-inch c r y s t a l s . Semilogarithmic p l o t s appear i n
F i g u r e s 8-3 and 8-4. These c u r v e s r e p r e s e n t t h e g e o l o g i c impulse f u n c t i o n s
f o r a potassium s o u r c e i n a c o n c r e t e medium w i t h a d r y 4.5-inch d i a m e t e r
borehole and f o r t h e 3.0-inch and 9.0-inch d e t e c t o r l e n g t h s .
47 0.003 45 0.002
53 0.005 50 0.003
59 0.01 1 55 0.004
65 0.018 60 0.008
71 0.032 65 0.013
74 0.045 70 0.024
77 0.058 74 0.042
80 0.078 78 0.075
83 0.118 82 0.123
86 0.158 86 0.148
89 0.178 88 0.150
92 0.205 90 0.155
95 0.183 92 0.155
98 0.130 94 0.160
101 0.085 96 0.170
104 0.050 98 0.162
107 0.032 100 0.140
110 0.025 105 0.081
116 0.015 110 0.033
122 0.009 115 0.015
120 0.008
125 0.007
130 0.007
The i n v e r s e f i l t e r p a r a m e t e r a c a n be o b t a i n e d from t h e d i f f e r e n t i a l c u r v e s i n
F i g u r e s 8-3 and 8-4. E q u a t i o n ( 2 ) shows t h a t t h e p r e d i c t e d g e o l o g i c impulse
f u n c t i o n f o r a d e t e c t o r of l e n g t h L f a l l s o f f e x p o n e n t i a l l y w i t h s l o p e a f o r
I z l -_> ~ / 2 . The d e r i v a t i o n o f e q u a t i o n (2) by D. George was a p p a r e n t l y stimu-
l a t e d by d i s c u s s i o n s w i t h J o h n Conaway i n which Conaway s u g g e s t e d a c o u l d be
o b t a i n e d from a s e m i l o g a r i t h m i c p l o t of t h e g e o l o g i c i m p u l s e r e s p o n s e , i n d e p e n d e n t
of d e t e c t o r l e n g t h and zone t h i c k n e s s (Conaway, 1 9 7 9 a ) . T h i s approach
DEPTH (centimeters)
Figure 8-3. Potassium model differential response for a
1.5-inch x 3-inch detector.
115
10
K MODEL DIFFERENTIAL PROBE RESPONSE
2 0 l n c h Probe D~arnefer
1 5 x 9.0 lnch Crystal
4 5 l n c h Diameter Borehole
DEPTH (centimeters)
T a b l e 8-4. a P a r a m e t e r f o r P o t a s s i u m Model
DEPTH (centimeters)
F i g u r e 8-5. Uranium model p r o f i l e f o r a 1.5-inch x 3-inch d e t e c t o r .
The p r e v i o u s l y measured uranium p r o f i l e f o r t h e 1.5-inch x 9 - i n c h d e t e c t o r
( s e e T e c h n i c a l Note 5 ) h a s b e e n r e p l o t t e d i n s e m i l o g a r i t h m i c f a s h i o n i n F i g u r e
8-6. T a b l e 8-7 c o n t a i n s t h e uranium model d e p t h p r o f i l e r e s u l t s from
T e c h n i c a l Note 5. The v a l u e o f a o b t a i n e d from t h e p r o f i l e i n F i g u r e 8-6 f o r
t h e 1.5-inch x 9-inch d e t e c t o r s i s 0.112 cm-l. T a b l e 8-8 c o n t a i n s n u m e r i c a l
v a l u e s f o r t h e d i f f e r e n t i a l g r a d e f u n c t i o n o b t a i n e d from F i g u r e 8-6. The
d i f f e r e n t i a l r e s p o n s e i s p l o t t e d i n F i g u r e 8-7. The a v e r a g e a v a l u e i s 0.123
crn-l. Again, t h e v a l u e o f a from t h e d i f f e r e n t i a l g r a d e f u n c t i o n i s h i g h e r
t h a n t h a t o b t a i n e d from t h e i n t e r f a c e p r o f i l e . The p r o f i l e v a l u e s of a a r e
low b e c a u s e t h e " b a r r e n zone" i s n o t t r u l y b a r r e n o f uranium. The
d i f f e r e n t i a l g r a d e f u n c t i o n y i e l d s more r e l i a b l e a v a l u e s .
62 12.0 92 226
64 13.5 94 257
66 15.9 96 290
68 18.6 98 330
70 23.7 100 35 1
72 28.2 102 380
74 34.3 104 406
76 42.3 106 424
78 52.6 108 443
80 65.5 110.5 453
82 84.2 113 475
83 93.4 118 492
84 106 123 495
86 132 128 496
88 159 133 506
90 191 138 506
64 0.9 96 17.5
68 1.7 100 13. 3
72 2.9 104 11.2
76 4.8 108 8.3
80 7.4 112 5.0
84 12.4 116 3.0
88 14.5 120 2.0
92 17 130 0.7
DEPTH (centimeters)
Figure 8-6. Uranium model profile for a 1.5-inch x 9-inch detector.
121
100 100
W)- -80
U MODEL DIFFERENTIAL PROBE RESPONSE
6 0- -60
20- -20
E
\O
E
a lo- - 10
a
8-
V F W H M = 2 7 cm -8
A
4
- 6- -6
I-
Z
W
m 4- -4
W
LL
-
LL
n
2- -2
4 F W T M = 5 3 . 3 cm
m
C3
z
-
3 1.0- - 1.0
z
4 .8 - - .8
K
3
.6 - - .6
4 - - 4
UPPER BARREN
.2 -
ZONE
ORE ZONE - .2
I I I I t 1
50 70 90 110 130
DEPTH (centimeters)
Figure 8-7. Uranium model differential response for a
1.5-inch x 9-inch detector.
122
A summary of a v a l u e s f o r t h e U model i s g i v e n i n T a b l e 8-9. A s with the K
model r e s u l t s of T a b l e 8-4, n i s l a r g e r f o r t h e l a r g e r d e t e c t o r . a for the
3-inc h l o n g d c t c t . t o r i s e s s e n t i a l 1 y i l ~ csame f o r K and For 11. For L I I ( \ 0 - i I N 11
d e t e c t o r , a i s s m a l l e r f o r U t h a n f o r K. Perhaps t h e s e l f - s h i e l d i n g c l - t e c t i s
l a r g e r f o r t h e lower e n e r g y p o t a s s i u m gamma r a y t h a n f o r uranirim, c a u s i n g '1
l a r g e r s l o p e a f o r t h e K model d i f f e r e n t i a l r e s p o n s e f u n c t i o n .
Th Model
I n t e r f a c e p r o f i l e measurements o f t h e t y p e p r e s e n t e d i n t h e l a s t s e c t i o n a r e
d i f f i c u l t t o perform b e c a u s e t h e y a r e time-consuming, e s p e c i a l l y f o r s m a l l e r
detectors. Furthermore, t h e c a l c u l a t i o n r e q u i r e d t o determine t h e
d i f f e r e n t i a l shape i n t r o d u c e s c o n s i d e r a b l e n o i s e t o t h e r e s u l t .
B e t t e r r e s u l t s a r e o b t a i n e d when t h i n beds of t h e r a a i o a c t i v e m a t e r i a l a r e
available. The 2-inch t h i c k h o r i z o n t a l uranium bed of t h e Grand J u n c t i o n
models was used t o measure t h e g e o l o g i c i m p u l s e f u n c t i o n f o r a v a r i e t y of
d e t e c t o r s i z e s and b o r e h o l e c o n d i t i o n s . Thin beds of p o t a s s i u m o r t h o r i u m a r e
n o t a v a i l a b l e s o t h e d i f f e r e n t i a l p r o f i l e r e s p o n s e s i n t h e K and Th models
r e p r e s e n t t h e o n l y measure of p o t a s s i u m and t h o r i u m g e o l o g i c i m p u l s e
functions.
T a b l e 8-10. Ore Zone/Upper B a r r e n Zone D e p t h P r o f i l e Thorium Model
P r o b e 253L 1 . 5 - i n c h x 3.0-inch C r y s t a l
4
63 23.4 96 354
68 30.3 98 390
74 51.0 100 412
76 68.4 102 439
78 85.0 104 453
80 103 106 471
82 127 108 464
84 151 113 502
86 184 118 510
88 21 1 123 505
90 248 128 512
92 283 133 513
93 292 136 527
94 328 138 522
DEPTH (centimeters)
400- - 400
-E
n
200- - 200
P
V
W
a
a
LT
(3
I00 - - 100
2
3
-
K 80- - 80
0
I
I-
60- -60
I-
Z
W
K
2
a
40- - 40
a
20. . a 20
UPPER BARREN
ORE ZONE
ZONE
l I I I i
- -
h
E
0
\
E
P
P
Y
g lo- - 10
Q FWHM-25 cm
E
C3 - -
I-
z -
W -
OZ
a
n
a
a
- -
A
-
a
t-
z
W
OZ
W
LL
-
LL
-
L3 -
F W T M = 4 9 cm
1
s b 70
I
90
I
110
I
I30 * I
DE PTH (centimeters)
Figure 8-10. Thorium model differential response for a
1.5-inch x 9-inch detector.
127
T a b l e 8-12. Ore Zone/Upper Barren Zone Depth P r o f i l e Thorium Model
25 0.06 65 1.16
30 0.09 68 1.93
35 0.11 70 2.88
40 0.17 72 4.25
45 0.26 74 6.35
50 0.52 76 8.47
55 0.70 80 10.4
60 0.96 84 14.0
65 1.6 88 17.3
70 3.0 92 18.3
72.5 3.9 96 15.7
75 5.2 100 12.2
77.5 7.2 104 8.3
80 9.6 108 4.5
82.5 12.5 112 2.9
85 16.2 116 2.1
87.5 20.6 120 1.3
90 23.0 130 0- 9
92.5 19.6
95 16.0
97.5 13.4
100 10.0
102.5 6.8
105 4.8
107.5 3.6
110 2.8
115 1.2
120 0.9
1.5-inch x 3-inch D e t e c t o r
2-inch x 5-inch D e t e c t o r
1 . 5 " ~3.0" F i l t e r e d
BED RESPONSE
Detector
_ 2 " Bed Thickness
F W H M = 2 1 crn
3-
-
-
F W T M = 55.6 cm
1-
-
-
Thin
Bed
122 ( e a s t ) 2.5
107 5.1
91.4 7. 6
76.2 10.2
61.0 12.7
50.8 15.2
40.6 17.8
30.5 20.3
25.4 25.4
20.3 30.5
17.8 40.6
15.2 50.8
12.7 61.0
10.2 76.2
7.6 91.4
5.1 107
2.5 122 (west)
0 (thin
bed)
If t h e a r e a under e a c h c u r v e i s measured f o r t h e d i s t a n c e r a n g e of + 4 0
c e n t i m e t e r s , t h e r a t i o of d r y l w a t e r - f i l l e d a r e a s i s 1.14. T h i s compares
f a v o r a b l y w i t h t h e w a t e r f a c t o r c o r r e c t i o n of 1.17 o b t a i n e d f o r t h i s probe and
b o r e h o l e d i a m e t e r from t h e t h i c k bed measurements p r e s e n t e d i n T e c h n i c a l Note
3. The agreement of t h e s e r e s u l t s i n d i c a t e s t h a t t h e t h i c k bed w a t e r f a c t o r
c o r r e c t i o n s measured i n t h e K!JT w a t e r f a c t o r model c a n be a p p l i e d t o t h i n bed
r e s u l t s a s well.
Barren
Zone
POSITION (centimeters)
F i g u r e 8-15. Thin uranium bed r e s p o n s e f o r a 2-inch x 5-inch d e t e c t o r and
a w a t e r - f i l l e d borehole.
136
Table 8-17. KUT Probe Response t o a Thin Uranium Bed P e r p e n d i c u l a r
t o t h e Borehole 2.0-inch Probe Diameter 1-inch x 2-inch C r y s t a l
2-inch Bed T h i c k n e s s 4.5-inch Diameter Dry Borehole
FWHM=I6 cm
100 - 100
-
-
FWTM=4? cm
10 - 10
-
.. .. -
Thin Bed
\
\
BARREN
+
\
\
ZONE $
+
\
t i Borehole
I
I 1
- 120
I
- 80 - 40 0
I
40
I
80
1
120
-I
POSITION (centimeters)
F i g u r e 8-16. Thin uranium bed r e s p o n s e f o r a 1-inch x 2-inch d e t e c t o r .
138
T a b l e 8-18. G e o l o g i c Impulse P a r a m e t e r a
West East
Thin 1 x 2 Dry 16 47 0.107 0.110
Horizontal 2 x 5 Dry 19 47 0.112 0.111
U Bed 2 x 5 Water-Filled 19 44 0.120 0.124 0.104
1.5 x 3 Dry 21 54 0.095 0.099
1.5 x 3 Dry 21 56 0.098 0.089
(Filtered)
1.5 x 9 Dry 25 53 0.118 0.114
P r e s e n t a t i o n of R e s u l t s
U Channel Concentration
1A f t e r Deconvolution
,r--
, Assigned Grade
Probe 253
1.5x3 Inch Detector
I
DEPTH ( f e e t )
F i g u r e 8-17. P r e s e n t a t i o n o f a KUT l o g f o r model N-5 b e f o r e and a f t e r
s p a t i a l deconvolution with t h e i n v e r s e d i g i t a l f i l t e r .
Average t h i n bed a w i t h f i l t e r
Filter factor =
Average t h i n bed a w i t h o u t f i l t e r
= (0.96) (0.112)
= 0.108 cm-I
O r , i n u n i t s of f e e t - l ,
a E s t i m a t e f o r N 5 = 3.29 f e e t - l ,
U n c e r t a i n t y e x i s t s i n t h e o f f i c i a l (tlathews, e t a l . , 1978) a s s i g n e d t h i c k n e s s
f o r t h e bottom two o r e zones and i n t h e o r d e r of a p p e a r a n c e of t h e b a r r e n zone
a t 9.0 f e e t and t h e o r e zone immediately above. There i s e v i d e n c e from d a t a
c o l l e c t e d by t h e G e o l o g i c Survey of Canada (Conaway, 1979b) and by BFEC
(George, 1979b) t o s u p p o r t t h e a s s i g n m e n t shown i n F i g u r e 8-17. This
a s s i g n m e n t r e p r e s e n t s a n i n t e r c h a n g e of t h i c k n e s s f o r t h e bottom two zones and
a n exchange of o r d e r f o r t h e b a r r e n zone and o r e zone above t h e b a r r e n zone.
Measurements a r e i n p r o g r e s s t o r e s o l v e t h i s u n c e r t a i n t y . The g r a d e
a s s i g n m e n t s o f F i g u r e 8-17 a r e t h e a u t h o r ' s b e s t e s t i m a t e a s o f .Tune 1979.
T;I h l c 8-20. E q ~ i i v a l e n tUranium G r a d e f o r Elodel N-5 A f t e r D e c o n v o l u t i o n
with Inverse F i l t e r
1 1 -
(a~z)' '
-
6.1 25
6.4 44
6.7 66
7.0 67
7.3 180
7.6 -1 15
7.9 -244
8.2 10,583
8.5 16,436
8.8 3,113
9.1 -312
9.4 1,463
9.7 3,614
10.0 9,271
10.3 9,124
10. 6 9,089
10.9 5,593
11.2 186
11.5 1,976
11.8 2,002
12.1 544
12.4 28
12.7 31
13.0 16
13.3 26
The s h a p e of t h e s t a t i c l o g between 7.5 and 8 f e e t p r o v i d e s s u p p o r t f o r t h e
c h o i c e of 3 . 6 f e e t - l f o r a . Since t h i s region i s near the i n t e r f a c e
between a h i g h g r a d e o r e zone and a n e a r l y b a r r e n zone, t h e s e m i l o g a r i t h m i c
p l o t s h o u l d c o n t a i n a l i n e a r p o r t i o n whose s l o p e i s t h e p a r a m e t e r a . The
computed s l o p e i s v e r y c l o s e t o 3.6 f e e t - l , i n agreement w i t h t h e v a l u e
o b t a i n e d by v a r y i n g a u n t i l t h e b e s t agreement w i t h a s s i g n e d g r a d e was
obtained. S i n c e probe and b o r e h o l e c o n d i t i o n s a r e t h e same a s f o r t h e U model
p r o f i l e measurements, t h e 10 p e r c e n t d i f f e r e n c e i n a must be due t o a b u l k
d e n s i t y o r c o m p o s i t i o n d i f f e r e n c e between models U and N5. Also shown on
F i g u r e 8-17 a r e a v a l u e s computed from o t h e r p o r t i o n s of t h e s t a t i c l o g where
the semilogarithmic p l o t is l i n e a r . The v a l u e o f 1.8. f e e t - l o b t a i n e d
between 9.5 and 1 0 f e e t i s c l e a r l y t o o low. T h i s v a l u e was i n c l u d e d t o
i l l u s t r a t e t h e f a c t t h a t o n l y n e a r t h e i n t e r f a c e between two zones of h i g h l y
d i f f e r e n t g r a d e c a n o n e hope t o o b t a i n a l i n e a r s l o p e t h a t i s c l o s e t o t h e
c o r r e c t v a l u e of a
b a r r e n of uranium.
. I d e a l l y , one of t h e two zones s h o u l d be c o m p l e t e l y
Any o t h e r s i t u a t i o n w i l l g i v e a e s t i m a t e s t h a t a r e t o o
small. The v a l u e of a o b t a i n e d from t h e l i n e a r r e g i o n between 1 2 and 1 3 f e e t
i s 3.1 f e e t - l . A p p a r e n t l y , t h e g r a d e d i f f e r e n t i a l between o r e and b a r r e n
zones a t 12.1 f e e t i s n o t s u f f i c i e n t l y l a r g e t o a p p r o a c h t h e i d e a l , and hence
t h e a v a l u e i s a b o u t 15 p e r c e n t low.
SUMMARY
INTRODUCTION
This t e c h n i c a l n o t e d i s c u s s e s t h e r e s u l t s of t h i s p r o j e c t a s of F e b r u a r y ,
1979, and how t h e s e r e s u l t s impact t h e i n t e r p r e t a t i o n of KUT l o g g i n g d a t a .
Element Z E (MeV)
A 13 0.046
Ca 20 0.079
Fe 26 0.11
Pb 82 0.50
U 92 0.62
- cm2 n atoms ) Z ,( e l e c t r o n s
(cm = o CQ ( e l e c t r o n ) 2: Ni(cmj L atom ) ,
i=1
atoms rams
No(=) pi(+)
N. =
rams
~i (k)
where N, i s Avogadro' s number, i s t h e p a r t i a l d e n s i t y of e l e m e n t i , and
A j i s i t s a t o m i c weight. Substituting equation (2) into equation (1):
If one d e f i n e s a p a r t i a l d e n s i t y weighted a v e r a g e Z / A f o r t h e f o r m a t i o n a s
follows:
0
-
$
c
X
0.9-
............**.*.......
3
J
LL
2.
0.8- -
cr
l
a
2
z
a
(3
0.7 - -
##
PC
I I I I
Oo 500 1000 1500 2000 2500
ENERGY ( k e V )
Figure 9-3. Gamma-ray flux ratio versus energy for sandstone media
with water saturated porosities of 0.1 and 0.3.
The s c a l i n g f a c t o r f o r b u l k d e n s i t y i s computed as f o l l o w s :
I11vc-rsc*I)II 1 k - ( 0 . 7 ) ( S a n d s t o n e M a t r i x ~ e n s i t y )+ (0.3) ( 1 . 0 ~ / c m ? ) (6
densicy r a t i o (0.9)(Sandstone Matrix Density) + (~.l)(l.~~/cm')
The s c a l i n g f a c t o r f o r a v e r a g e Z / A i s computed a s f o l l o w s :
- -
-
z (Z/AJ, (0.7) (2.6263) + (Z/A)ff 0 (0.3)
Inverse (-) ratio = [ 2.4637 I.
A
(a~,
( 0 . 9 ) (2.6263) + (z/A)
Hz0
(0.1)
'"'2.1384 (8)
so that,
z
I n v e r s e (-) Ratio =
(0.499)(1.8384) + (0.551)(0.3) 2.4637
A (0.499) (2.3637) + (0.551)(0.1) 2.1384
-
Z
I n v e r s e (-) R a t i o = 1.0827 . 2.4637 = 1,0104.
A 1.2346 2.1384
-
Tlie product of t h e ( Z / A ) and b u l k d e n s i t y i n v e r s e s c a l i n g f a c t o r s from
e q u a t i o n s ( 7 ) and ( 1 0 ) p r e d i c t s t h e gamma-ray f l u x r a t i o based on t h e change i n
t h e Compton l i n e a r a t t e n u a t i o n c o e f f i c i e n t :
The e f f e c t of a l a r g e c o n c e n t r a t i o n of h i g h Z e l e m e n t s , s u c h a s uranium
(2=92), h a s been c o n s i d e r e d e x p l i c i t y by LASL. Energy dependent f l u x r a t i o s
have been computed f o r uranium c o n c e n t r a t i o n s of 0.06, 0.2, 0.6, 2.0 a n d 6.0
p e r c e n t uranium, by weight. The r e s u l t s a r e shown i n F i g u r e s 9-4 and 9-5.
The f l u x r a t i o s a r e formed by computing t h e f l u x s p e c t r u m a t t h e s t a t e d
uranium g r a d e and d i v i d i n g by t h e r e s u l t f o r t h e same gamma-ray s o u r c e
strength (Figure 9-1) but f o r a t r a n s p o r t formation f r e e of t h e element
uranium. Formation b u l k d e n s i t y was h e l d c o n s t a n t t h r o u g h o u t . For uranium
g r a d e s l e s s t h a n o r e q u a l t o 0.6 p e r c e n t , t h e f l u x r a t i o i s n e a r u n i t y from
1.0 t o 2.6 MeV a n d b e g i n s t o d r o p a t l o w e r e n e r g i e s , t o a b o u t 0.98 a t 0.5 M e V
and t o 0.95 a t 0.3 MeV. T h i s s o - c a l l e d " Z - e f f e c t " t h e n amounts t o a 5 p e r c e n t
r e d u c t i o n i n gamma-ray f l u x a t 0.3 MeV f o r a 0.6 p e r c e n t uranium c o n c e n t r a -
tion. For uranium g r a d e s below 0.6 p e r c e n t and f o r e n e r g i e s g r e a t e r t h a n 0.5
MeV, t h e uranium "Z e f f e c t " may be n e g l e c t e d . For uranium g r a d e s above 0.6
p e r c e n t t h e Z e f f e c t i s i n c r e a s i n g l y i m p o r t a n t a t low e n e r g i e s . For t h e
+ p e r c e n t c a s e , t h e f l u x r a t i o a t 0.3 MeV h a s d e c r e a s e d t o a b o u t 0.7, a 30
p e r c e n t d r o p i n t h e gamma-ray f l u x . From 0.3 MeV t o a b o u t 1.5 MeV, t h e f l u x
r a t i o r i s e s t o a v a l u e of 0.975 and r e m a i n s c o n s t a n t a t h i g h e r e n e r g i e s ( s e e
Figure 9-4). T h i s means t h a t t h e p h o t o e l e c t r i c e f f e c t i s i m p o r t a n t t o
e n e r g i e s of a b o u t 1.5 MeV when t h e uranium c o n c e n t r a t i o n i s i n t h e p e r c e n t
range. The c o n s t a n t f l u x r a t i o o f 0.975 a t e n e r g i e s above 1.5 MeV i s
e x p l a i n e d by t h e i n v e r s e (Z/A) s c a l i n g of t h e Compton c r o s s s e c t i o n t h a t
r e s u l t s from t h e c o m p o s i t i o n change.
Conclusions
2. The gamma-ray f l u x a t a n y e n e r g y w i t h i n t h i s r a n g e w i l l s c a l e
i n v e r s e l y w i t h t h e f o r m a t i o n b u l k d e n s i t y p and w i t h t h e f o r m a t i o n
(Z/A). B
1 .o
A
A
D
- - A *
mte=A A
.
rn
. .. e . . ....
z
0
e
X
2 0.9 - FORMATION URANIUM -
A
LL CONCENTRATION RATIO
ZCKi b
6.0% U/O.OO/oU
I
0.6% U /O.OO/oU
a
z 0.8- A 0.06% U / O.OO/oU -
a
(3
ENERGY (KeV)
Figure 9-4. Gamma-ray flux ratio versus energy for sandstone media
containing differing uranium concentrations with the
gamma-ray source strength held constant.
a I I I
8
In
(\1
a
rl
a
4
0
r 52
- K 3 3
a Z 0
a z $! 8 0
r1
a
50 s s -8
a I-,":
41 3 3
a 0 I-
9a I-z 8 8
" w 4 q
41 nJ 0
a rz 2
0
88 4
4-
4
a -8 h
41
a >
a
Y
w
4I
41
a
>
a
4
L, -8Q 6
a
4
a
41 a
a
8 a
a a 0
1
4
a
a
-8
4 a
4
4 a
4
4
4
4
I 'I 4 0
9
- a, 00 be0
-
d 0 0
o~lwtlxmj AVU - vruwvg
3. The f o r m a t i o n ( Z / A ) v a r i e s l i t t l e from t h e nominal v a l u e of 0.500.
U s u a l l y t h e l a r g e s t changes i n (Z/A) a r e c a u s e d by v a r i a t i o n s i n
formation moisture content. But even t h e l a r g e s t p r a c t i c a l
v a r i a t i o n s i n m o i s t u r e c o n t e n t y i e l d l e s s t h a n a 2-percent change i n
(Z/A) f o r t h e f o r m a t i o n .
4. For t h e e n e r g y r a n g e of i n t e r e s t i n s p e c t r a l gamma-ray l o g g i n g , t h e
e f f e c t of f o r m a t i o n changes on gamma-ray f l u x i s w e l l d e s c r i b e d by a
simple i n v e r s e bulk d e n s i t y scaling. This is t r u e , within a percent
o r two, even when t h e f o r m a t i o n change i s c a u s e d by a l a r g e v a r i a t i o n
i n moisture content.
6. S p e c t r a l gamma-ray f i e l d l o g s c a n be c a l i b r a t e d f o r c o n c e n t r a t i o n i n
p e r c e n t o r ppm by w e i g h t w i t h o u t knowledge o f t h e f o r m a t i o n m o i s t u r e
c o n t e n t , i f t h e same m o i s t u r e c o n t e n t i s assumed t o e x i s t i n b o t h t h e
c a l i b r a t i o n model and t h e f i e l d f o r m a t i o n s . If i n - s i t u concentra-
t i o n s were s p e c i f i e d f o r t h e c a l i b r a t i o n model, t h e e r r o r i n t r o d u c e d
by making t h i s a s s u m p t i o n i s r e l a t e d t o (ZfA), and i t g e n e r a l l y
amounts t o o n l y a b o u t 1 p e r c e n t .
C o n c e n t r a t i o n s of e l e m e n t s w i t h l a r g e a t o m i c numbers ( i n c l u d i n g
uranium) do n o t a f f e c t gamma-ray t r a n s p o r t f o r t h e e n e r g y r a n g e from
0.5 MeV t o 2.6 MeV p r o v i d e d t h e i r c o n c e n t r a t i o n s a r e l e s s t h a n 0.6
percent. For h i g h e r c o n c e n t r a t i o n s , t h e gamma-ray f l u x a t t h e l o w e r
e n e r g i e s become i n c r e a s i n g l y a t t e n t u a t e d , and a t 6-percent uranium
c o n c e n t r a t i o n s t h e f l u x i s a t t e n u a t e d by a p p r o x i m a t e l y 30 p e r c e n t a t
0.3 MeV. However, f o r t h e e n e r g y r a n g e from 1 t o 2.6 MeV, which i s
of p a r t i c u l a r i n t e r e s t t o s p e c t r a l gamma-ray l o g g i n g , t h e f l u x a t
6-percent uranium i s a t t e n u a t e d by o n l y 3-percent.
Borehole Diameter E f f e c t s
PROBE I I I I I
O.D. I o; 4.5 7.0 9.0 12.0 INCHES
I
I
I I I I I I 1
5 10 15 20 25 30 35
BOREHOLE DIAMETER ( centimeters)
J
12.0 INCHES
I I I
5 10 15 20 25 30 35
BOREHOLE DIAMETER (centimeters)
Figure 9-13. Comparison of measured and calculated borehole water correction
for uranium.
X
2.0 - - 2.0
- L A S L TRANSPORT CALCULATION
FOR THORIUM WINDOW
1.6 - - 1.6
1.4 - - 1.4
1.2 - - 1.2
1 .o -------- --.
I 3.0 4.5 7.0 9.0
1 - 1.0
PROBE I 12.0 INCHES
O.D. I
I I I I 1 I I
5 10 15 20 25 30 35
BOREHOLE DIAMETER (centimeters)
Borehole Casing E f f e c t s
LASL BFEC
Energy Window Calculation Measurement
K 1.148 1. 1 7
U 1.128 1.17
Th 1.120 1.14
SUMMARY
ABSTRACT
F i n a l l y , f o r g r o s s c o u n t a p p l i c a t i o n s , Bi4Ge3012 produced a c o u n t r a t e
50 p e r c e n t g r e a t e r t h a n d i d t h e same s i z e NaI(T1) d e t e c t o r i n an u n f i l t e r e d
gamma-ray probe. When a g r a d e d f i l t e r was p l a c e d around t h e d e t e c t o r s t o
r e d u c e t h e number of low e n e r g y gamma r a y s d e t e c t e d , t h e c o u n t r a t e o b t a i n e d
from Bi4Ge3012 w a s 9 0 p e r c e n t g r e a t e r t h a n from NaI(Tl).
INTRODUCTION
A t t h e p r e s e n t t i m e , Bendix u s e s o n l y NaI(Tfl s c i n t i l l a t i o n d e t e c t o r s i n i t s
gamma-ray l o g g i n g p r o b e s f o r t h e U.S. Department of Energy. Different types
of s c i n t i l l a t o r s a r e c o m m e r c i a l l y a v a i l a b l e , b u t t h e y have n o t been w i d e l y
used i n t h e l o g g i n g i n d u s t r y . Tho of t h e s e s c i n t i l l a t o r s , CsI(Na) and
Bi4Ge3012, have been o b t a i n e d f o r e v a l u a t i o n a s gamma-ray d e t e c t o r s i n
l o g g i n g probes.
Bi4Ge3012
NaI(T1) CsI(Na)
Density (g/cm3) 3.67 4.51 7.13
Wave Length of Maximum 413 420 480
Emission (nm)
Decay Constant ( n s ) 230 650 300*
Nominal Energy R e s o l u t i o n 8 11 20
a t 662 keV ( p e r c e n t )
Nominal Pulse Height ( l i g h t 100 65-83 8 *
o u t p u t ) r e l a t i v e t o NaI(T1)
(percent)
Hygroscopic Yes Yes No
--
SPECTRAL TESTS
- I
Gain
(PROBE)---- Amplifier ,
Stabilizer
ADC MCA
F *
Or tec - 572 Tracor Tracor Tracor
Northern Northern Northern
NS-454 TN-1213 TN-1710
Energy
Model Window N ~ I ( T ~ ) ~ CSI(N~)~ CSI(N~)~
a ~ windows:
a ~ K(1320-1575 keV), U(1650-2390 keV), Th(2475-2765 keV).
b ~ I s windows : K( 1334-1 604 keV) , U( 163 1-2368 keV) , Th( 2440-2862 keV) .
T a b l e 10-4. Comparison of S t r i p p i n g R a t i o s f o r
2-inch x 5-inch NaI(T1) and CsI(Na) D e t e c t o r s .
Stripping
Ratio NaI ( ~ 1 ) ~ CSI(N~)~ CSI(N~)~
a ~ windows
a ~ : K( 1320-1 575 keV) , U(1650-2390 keV) , Th(2475-2765 keV).
bCsI windows: ~ ( 1 3 3 4 - 1 6 0 4 keV), U(1631-2368 keV), Th(2440-2862 keV).
173
1024
CHANNEL NUMBER
Energy
Model LJindow N ~ I ( T ~ ) ~ .BGO~ BGO~
a ~ a windows
I : K(1320-1575 k e ~ ) ,U(1650-2390 keV), Th(2475-2765 keV)
b~~~ windows: ~ ( 1 2 7 6 - 1 6 1 4 keV), U(1616-2395 keV), Th(2397-2855 keV)
T a b l e 10-7. Comparison of S t r i p p i n g R a t i o s f o r
1.5-inch x 3-inch N a I ( T a and BGO D e t e c t o r s .
Stripping
Ratio ~ a l ( T l ) ~ BGO~ BGO~
, . * ~ . , .
8 8
' ,
, . + . , , . . ,
rn
I-
Z
3
0
U
CHANNEL NUMBER
Na I Na I RGO BGO
Model Filtered Unfiltered Filtered Unfiltered
CONCLUSION
Enhanced c o u n t i n g e f f i c i e n c y i s i m p o r t a n t f o r s p e c t r a l gamma-ray l o g g i n g
bec:lusc of t h e low r a d i a t i o n l e v e l s e n c o u n t e r e d i n many l o g g i n g o p e r a t i o n s .
1f a more e f f i c i e n t d e t e c t o r i s u s e d , t h e n s e v e r a l b e n e f i t s become a v a i l a b l e :
I. b'aster l o g g i n g s p e e d s ;
2. I k t t c r precision in the data;
3. Improved t h i n bed r e s o l u t i o n ;
4. Slirnn~er prohc c o n s t r u c t i o n .
T h e d e c r e a s e i n t h e ~ n n g n i t u d c sof t h e primary s t r i p p i n g r a t i o s f o r c c s i t i n ~
i o d i d e and bismuth germanatc i s a d v a n t a g e o u s t o l o g g i n g d a t a r e d t ~ tc i o ~ ~ .
Because of t h e s m a l l e r s t r i p p i n g r a t i o s l e s s c o r r e c t i o n h a s t o be made t o t h e
raw d a t a t o remove i n t e r f e r e n c e s between t h e e n e r g y windows of i n t e r e s t .
E r r o r s caused by n e g l e c t i n g v a r i a t i o n s i n s t r i p p i n g r a t i o s due t o changing
b o r e h o l e c o n d i t i o n s s h o u l d be l e s s s i g n i f i c a n t f o r d e t e c t o r s wit11 s n l n l l e r
stripping ratios.
Czubek, J.A., 1961, Some problems of the theory and quantitative interpretation
of the gamma-ray logs: Acta Geophysica Polonica A, no. 112, p. 121-
137.
Evans M.L., 1977, NDA technology for uranium resource evaluation: Los Alamos
Scientific Laboratory Report LA-6996-PR, p. 2-12.
Evans R.D., 1955, The atomic nucleus: New York, McGraw-Hill Book Company,
p. 684, 698-699, 706.
George, D.C., Evans, H.B., Allen, J.W., Key, B.N., Ward, D.L., and
Mathews, M.A., 1979, A borehole gamma-ray spectrometer for uranium
exploration: Twentieth Annual Logging Symposium Transactions, v. 1,
paper X.
Hill, T.R., 1975, ONETRAN: A discrete ordinates finite element code for
the solution of the one-dimensional multi-group transport equation:
Los Alamos Scientific Laboratory Report LA-5990-MS.
Mathews, Mark A., Koizumi, Carl J., and Evans, Hilton R., 1978, DOE-GJ
logging model data synopsis: Bendix Field Engineering Corporation
Open-File Report GJBX-76(78), p. 11.
Scott, James H., 1962, The GAMLOG computer program: U.S. Atomic Energy
Commission Report RME-143, p. 11.
Stromswold, D.C., and Kosanke, K.L., 1978, Calibration and error analysis
for spectral radiation detectors: IEEE Transactions on Nuclear
Science, v. N5-25, no. 1, p. 782-786.
EQUIPMENT
U ~ h o l eE l e c t r o n i c s
F i g u r e A-1. Uphole e l e c t r o n i c s u s e d i n e a r l y e x p e r i m e n t s .
-a ..
- AMP STAB . n
ADC - MCA
i
F i g u r e A-2. Uphole e l e c t r o n i c s f i n a l c o n f i g u r a t i o n .
Probes
Q. Bristow
-
In: Proceedings o f t h e 1979 Annual Meeting o f Data General Users Group,
December 4-7, 1979, New O r l e a n s , p . 613-634.
AIRBORNE AND VEHICLE MOUNTED GEOPHYSICAL DATA ACQUISITION
SYSTEMS CONTROLLED BY NOVA MINICOMPUTERS
BACKGROUND
X-RAYS
COSMtC-RAYS
Charge sensttive
preamplifier
Photomultlpiiertube
(P.M.T.)
Figure 2: The scintillation detector is used for sensing and resolving gamma
radiation into an energy spectrum. I t is analagous to devices which
resolve visible Ii.ght into a spectrum of colours.
equivalent t o saying t h a t i t would b e desirable t o have a detection device capable
of distinguishing between radiation of different colours. This analogy is a c c u r a t e
and worth bearing in mind for t h e discussion which follows.
.--
Figure 6: The main components of the Geological Swvey of Canada airborne
gamma-ray spectrometer. A NOVA minicomputer controls the system.
CRT DISPLAY
GEOLOGIC&. SURVEY OF W M
"OIGI-PROBE" w-RAY
SPECTRAL LaffiInG SYSTEM
E=Ttl
6 PEN W A R T RECORDER
--= --- -- -
NOVA
GSC
Figure 8: The intensities of three peaks in each spectrum are processed by the
NOVA in real-time to generate profiles marked lfKff,"Uff and "Th"
which can be related to the concentrations of potassium, uranium and
thorium s c m e d by the gamma-ray detector.
signal giving direction (up or down). These signals a r e acquired by t h e NOVA via
an 1 / 0 interrupt interface for probe depth and velocity calculations and a r e also
used via s e p a r a t e hardware t o maintain t h e winch speed at a constant level which
can be preset. The NOVA i n t e r f a c e also has a line t o t h e winch controller which
a l l o w s ~ a u t o m a t i cstops under software control at predetermined depths entered
via t h e keyboard. Figure 11 shows some of t h e equipment in t h e vehicle and a
view of a typical set-up f o r logging a borehole.
NOVA INTERFACES
-"'
NQVA GENERAL. PURPOSE BOARD
DIGITIZED PULSE H E ~ G H T S
a
DATA X ~ A L ..
CHANNEL
'
" . ..
0 0
LOGIC CLOCK "d *
0 1 1 0 1
" M E M O R Y INCREMENT"
I D' R w? ':-
V " 4 " J " g
16 BIT G.P OUXPUT R E G E . *,E '
BIT ANALOG ' e B ~ ? " D A T CFOR s
CONV C H A N N E L ! 0. A A
/ PJ"
PULSE HEIGHTS
s3t:BT[ .
S *
C
oC
X - R A Y ENERGIES
1 GSC
Figure 13: The pulse-height ADC interface,^ special real-time clock and six D / A
converters for operating the six pen strip chart recorder, are all
contained in one NOVA general-purpose board.
This is accomplished by preloading both t h e WORD and ADDRESS counters
already on t h e general purpose board with t h e twos complement of t h e required
spectrum accumulation time, and interrupting t h e clock frequency t o one of them
whenever t h e ADC is busy. When t h e uninterrupted one reaches zero, marking t h e
end of t h e preset t i m e interval, t h e o t h e r one will contain a residual which is t h e
ADC dead time. The contents of this a r e brought.back into memory by software
and used t o c o r r e c t measured gamma-ray countrates.;
-
4029 A4137
.-./I
'5sC
Figure 14: The CRT display circuitry on a NOVA general purpose board scans the
text and gamma-ray spectra stored in the NOVA memory via the data
channel t o provide visual data on the X-Y monitor CRT unit.
a block diagram of t h e arrangement. An interrupt is generated a t t h e end of e a c h
page scan a t which t i m e t h e 'software r e s t a r t s t h e scan t o maintainha continuous
refresh rate. This approach- has a number of. a d ~ a ~ t a g e no s ; e x t e h a l rhemory is
required, no massive high speed -data t r a n s f e r s are r e q ~ i r e d ~ f r o tmh e 'NOVA to hn -
external memory in order.:to c h a n g e a page, and when apdates a r e made 15
memory locations in a page via t h e software (e.& postirig hew c o u h t r a t e d a t a orice
"
Figure IS: Typical display pages scanned from NOVA memory. Updating numbers
in memory automatically updates displayed data.
The i n t e r f a c e f o r t h e acquisition of depth pulses for t h e borehole logging
system and navigatibnal d a t a f o r t h e airborne system a r e virtually identical. One
general purpose NOVA board is used in each case with t h e interrupt logic being
arranged t o s e t t h e !'DONEtf flag when new d a t a a r e received in t h e general
purpose input register.
OPERATIONAL SOFTWARE