US2630535A - Charger-reader - Google Patents

Description

March 3, 1953 o. G. LANDsvERK 2,630,535

CHARGER-READER Filed June l, 1950 2 SHEETS-SHEET 2 Ff@ z www Patented Mar. 3, 1953 UNITED STATES PATENT OFFICE 2 Claims.

This invention relates to improved apparatus for reading and charging ionization chambers of the condenser type used for gamma and X-radia tion dosimetry. Such ionization chambers consist of a cylindrical conducting shell with an insulated central electrode and a gas, usually air, surrounding the central electrode Within the cylinder. They constitute a tubular capacitor in which the air is the dielectric. When such chambers are provided with means for fastening to the clothing or wearing on the person, they are usually referred to as pocket chambers. Without such provision, they are usually called thimble chambers.

A known potential difference is established between the central electrode and the cylinder by means of a charging apparatus. When ionizing radiation penetrates the chamber, ions are formed in the gas, and a current flows resulting in a loss of charge on the central electrode. The amount of discharge can be measured using a reading apparatus and is a measure of the amount of radiation which has impinged on the chamber. The chambers must then be recharged before further use. The charging and reading is done by the same apparatus. Such an apparatus is here referred to as a charger-reader, and is the subject of this invention.

It is an object of this improvement to provide a convenient to use, pocket sized, portable, light weight, shock resistant charger-reader which requires no batteries for its operation, and is sealed against dirt and moisture for use with thimble and pocket chambers of a specific type in gamma and X-radiation dosimetry.

Other objects and advantages of the invention will become evident from the following description when read in connection with the accompanying drawing in which:

Figure 1 is an enlarged cross-sectional view of the charger-reader unit.

Figure 2 is an enlarged longitudinal cross-sectional view of the microscope and electrometer assembly.

Figure 3 is an enlarged longitudinal cross-sectional view of the electrostatic charger and switch y like reference characters indicate like parts.

Referring more particularly to Figure 1, the charger-reader consists of a chassis I a portion 2 of which is shaped to form a iingerhold, a quartz fibre electrometer and microscope assembly 3, an electrostatic charger assembly 4, an

ionization chamber socket assembly 5 and a window to admit light to the microscope 6. A pocket chamber l is shown in the socket of the chargerreader ready to be charged or read.

The ionization chambers that are used with this charger-reader are the subject of application for Letters Patent Serial No. 134,385 filed December 22, 1949 by the undersigned inventor and are referred to therein as pocket chambers. Such chambers are approximately lfg long by 1/2 in diameter. If they are of suchconstruction as to give a full scale reading after exposure to 0.2 to 2 roentgens, they are referred to as low range pocket chambers or low range thimble chambers. When they give a full scale reading after exposure to radiation amounts in the: range from 10 to 200 roentgens or more, they are referred to as high range pocket chambers or high range thimble chambers.

In Figure 2 is shown a section of the quartz bre electrometer and microscope assembly.. This consists of an elongated hollow cylinder of conductive material 8, having within it at one end a charge responsive unit consisting of a very ne charge sensitive platinum coated quartz bre 9 mounted on support wire I0. This system is supported by polystyrene insulator II. A microscope is located within the cylinder at the opposite end. This consists of chassis I2 with objective lens aperture I3 as an integral portion of it and O-ring I4 for holding objective lens I5 in place. O-ring I4 is pressed against objective lens I5 by conducting sleeve I6 which is shaped to form objective lens aperture Il and is itself cemented into the end of chassis I2.

Chassis I2 is molded of black polystyrene. It has a sleeve at its upper end which is solvent welded into a socket of eyepiece shell I8 so as to press against the edges of and hold securely eyepiece scale I9. Eyepiece shell I8 is also molded of black polystyrene. Shell I8 has eyepiece lens 20 molded into it near its upper end so lens 28 is in focused relation with scale I9.

It is seen that the microscope comprises an integral unit which slides into cylinder 8 and is centered and cushioned against shock therein by O-ring 58 and which can be adjusted so as to focus the image of fibre 9 on scale I9. Shell I8 is provided with a flange 2l for convenience in manipulating the microscope in obtaining an exact focus. i A

The entire microscope and electrometer assembly which is shown in Figure 2 is the same general construction as is fully described in an application for Letters Patent by the undersigned dated January l0, 1950, Serial No. 137,783. Fully described there are the structure, function and techniques of constructing and adjusting the voltmeter assembly'consisting of quartz bre 9, support wire I3 'and insulator II. Similarly described are the relative positions and functions of objective lens I5, eyepiece chassis I8, eyepiece reticle I9, eyepiece lens 20, microscope chassis I2, conducting sleeve I6 and aperture Il, Gering 50 for centering and shock-proofing the microscope and sealing it from dirt and moisture and O-ring I4 for applying continuous pressure vto the objective lens. Described also are the various suitable mixtures and modes of fabricating conducting tube 8.

The microscope which is shown in Figure 2 `differs from those in application No. 137,783 in the fact that both the eyepiece I8 and the chassis I2 are hollow shells instead of solid transparent cylinders. They are, therefore, preferably molded of opaque plasticmaterials such as black `polystyrene.

The novel features of this microscope are as follows:

l. The 'microscope 'is all plastic.

2. An integral 'microscope is slipped into the hollow cylinder 8 to focus on an object which is mounted at the other 'end of the 'cylinder said objectbeing the quartz fibre 9 of an electrometer. The microscope is then cemented in place. The lange by which the microscope unit was con- -trolled during these manipulations is trimmed `-A'that are now in use 'for 'this type of instrument. AFibre support wire Il) extends through the in- 'sulator II. The portion'abovetheinsulator be- 'come's the `charge-s'c-:nsitive Aelement which in LIthis instrument yservesV as 'avery sensitive volt- -meter. `extends about 1A; below the insulator an'ge.

The portion that is below the insulator From *that point a 'lg" long Asection is bent so the two parts form an upright but 'tilted V or crotch 23, Figure 2. The end of the charging 'electrode v24 is sprung into this crotch so as'to make a sliding contact with it, the apex of the crotch is somewhatoi the line which is the normal `position of electrode 24.

Referring to Figure 3, the charging unit 'consis'ts of a -mounting Iplate or disc 25, a rotator 2S with -a knob 21, Orings 23, insulating support tube 29, metallic support strips 30 and 3 I, charge 4pad `32 and charge 33, lcontact extension 34 vto support strip 3I,'washer 35 whose shape constitutes a portion-of a cylinder, contact arm 36,

drivescrew 3T. Numeral 24 denotes the cham- -ber socket Velectrode Aand 39 Vdenotes the negative" electrode which is va portion Vof Vthe chargervreader chassis.

The vcharger'consists 'of VAthree dissimilar substances, felt charge pad 33, chamois charge pad 32, and polystyrene rotator 26 which is 'cylinbarrel.

drical and is positioned between the other two and is in intimate contact with them and which when rotated by the use of knob 2T generates an electrostatic charge. This is in conformity with the well known principle that if two dissimilarv substances are rubbed together they become charged, one positively, the other negatively. In this case the polystyrene will remove electrons from the felt charger pad and supply electrons to the chamois thus giving the former a positive and the latter a negative charge.

Contact arm 36 is attached to the outer end of rotator 2B and rotates with it because a disc shaped part of it is squeezed between rotator 26 and cylindrical washer 35 by drive screw 31 thus forming a friction clutch. When the contact arm encounters electrode 24 or grounded member'39 the clutch slips thus maintaining contact as cylinder 25 rotates and charging continues in the first instance or the charger is grounded in the second instance.

Figure 4 shows a section along `line 4-"4 of Figure 3. insulating tube 29 has two slots'fcut parallel to its axis in which support strips 3l) and 3| are held. The slots are cut at such distance from the axis of rotator 26 that chargepadsl32 and 33 maintain suitable frictional contact with it. An extension 54S of strip 3'is so placedas to be in sprung contact with the chassis -I when the charger is mounted in its socket. O'ring 33 seals the charger into thechassi's.

Figure 5 shows the position of a pocket chamber in the socket during the process of charging and reading. The socket consists of shell 4I, charging electrode insulator42 mounted in an aluminum sleeve and flange 52, contact pin l'43.'. compression spring S44 and chamber lsocket-electrode 2li. At the openingfto the soc-ketare-ball and spring-45 for preventing the chambers Ifrom falling out of the socket and tol securegood contact between the socket shell and the `chamber O-ring 4t seals the socket shell 'from dirt and moisture. The chamber barrel is numbered 5I.

Chamber 1 is shown with its cylindrical,

charged electrode, insulator '53, flexible "dia- `phragm 48 and diaphragm pin 49. When chamber I `is pushed with a force of 4 to fp'oun'ds, contact pin 43 presses against pin '43thus flexing diaphragm 48 land causing pin 49 to contact' electrode 47.

nDiaphragm 148 cannot be kdamaged Ybyexcess use of force because sprin'g 44 wil `compres when a force of 10 pounds is applied'to it until the chamber barrel stops against-the bottom flange of shell 4I. The charger is novel in several respects, particularly in the way the 'charge :pads are supported, in thegeneral designwhich'permitseasy mounting in a hole of lsuitabl'e diameter kwith automatic grounding of the-negative charge Lpad and also in the automatic switching arrangement. This maintains electrical connection 4between the contact armLand-'the positive 'charge pad while the contact arm operates asia switch which by clockwise turning of rotator 126 vcharges the electrode, then sets itexactly to zero with a Vernier like smoothness by a counterclookwis'e motion of the rotator and finally after counterclockwise rotation of about l; turn, discharges the charger so as to bring the-fibre back tothe 'scale if it is raccidentally overcharged.

When a chamber -and the electrometer is given tion on the "scalevjindicat pointrepresents a charge of about 200 Volts.

After the chamber' has been exposed to radiation.

the charge on the chamber has been reduced and when this charge is shared with that of the fully charged electrometer the resultant equilibrium position oi the nbre image indicates the drop of voltage of the charger-reader and the chamber as a unit. This in turn is directly proportional to the quantity of radiation in Roentgens that has penetrated the ionization chamber.

The volume, the electrostatic capacity and the material in the wall of the ionization chamber, the electrostatic capacity of the electrometer, the length and diameter of the quartz nbre and the magnication of the microscope are chosen to achieve the desired full scale dosage range. The chambers are initially calibrated by means of a known dosage. To take care of variations in the above mentioned factors a length of scale is then chosen for the microscope from a number of sizes that are available such that the :full scale dosage reading is accurate within about two yper cent. Scales are marked directly in Roentgen units or in milliroentgens depending on whether the chambers are the high or low range type.

In addition to the adjustments that are de scribed above, the electrometer and microscope assembly must be adjusted so that it will fulfill the following conditions:

l. The arc made by the portion of the libre that the microscope views as it crosses the axis of the microscope must lie as nearly as possible in a plane perpendicular to this axis.

2. The fibre image must be caused to reach the mid point of the scale at approximately some predetermined desirable voltage of, say 150 volts.

3. The ima-ge of the iibre must remain perpendicular to the longitudinal axis of the scale over the observed portion of its travel.

4. Equal voltage changes to within about must be required to move the bre over segments of equal length at various parts of the scale.

5. The fibre must remain sharply in focus over the entire length of scale.

These conditions are only independent in part, but those skilled in the art can so manipulate the portion of the bre support wire which is between the insulator and the bre so as to satisfy these conditions.

To operate the charger-reader, the index and two neighboring fingers of the left hand are inserted into the ngerhold. The instrument rests in the palm of the hand and the thumb is placed against the edge of the chassis above the socket opening. Insert a chamber in the charger-reader as far as it will go with the use of only a slight amount of force. Look into the microscope and point the microscope barrel at a source of light so the microscope scale is illuminated. Adjust the bre position to zero on the scale by rotating the charger knob with the fingers of the right hand. Move the nbre slightly past zero and then back it down to zero. This disconnects the charger. Now -press the chamber into the socket with the thumb until it stops against the flange in the shell of the socket. Contact is made with the chamber electrode by the diaphragm pin during this operation. The position that is now assumed by the fibre image on the scale is the reading of the chamber in roentgens or in milliroentgens as the case may be. Now operate the charger until the fibre is again at zero 0f the scale. When the pressure of the thumb against the chamber is removed, the diaphragm discond as' zero. Y "I'vhe zerof nects the charging pin from thesocket andthe-A chamber is charged.

All units now.

1. It weighs only rlve ounces. available weigh from 4 to 10 pounds.

2. It is truly portable and pocket sized. chassis measures only 31A x 2%" x 1". By way of contrast the smallest unit of which we know is 1%" x 4% X 6%" and weighs eight to ten times` as much.

3. It requires no batteries `nor external source of power.

4. Its design is so simple that it has not one single connecting wire nor a soldered joint. All other units of which we know have many of each.

5. It is hermetically sealed as are certain other units but in this unit there is no cover` which is difficult to seal since the component parts are mounted in a solid chassis in sockets that are provided therein. The seals are simple reliable O-rings and these need never be opened for replacement of batteries.

6. The unit fits the hand and is under perfect control. All operations of charging and reading feel natural. There is no feeling of a need for a third hand or a table support as is true of all charge readers that have been available up to da e.

7. In summary this is the only design up to this time which is truly pocket sized, completely independent and fully portable.

From the above description of my invention it is apparent that I have provided an improved charger-reader for use with condenser ionization chambers in determining gamma and X-ray dosage.

What is claimed is:

1. In apparatus for charging an ionization chamber of the condenser type and for measuring the charge of such condenser, the ionization chamber being provided with an electrical contact for charging purposes, the combination which comprises a chassis provided with a socket projecting into the chassis from the outside and into which a portion of the ionization chamber carrying the contact fits slidably and also provided with a cavity extending from the bottom of the socket in the same direction as the socket, an elongated rst conductor disposed in the cavity and extending in the same direction as cavity and socket and insulated from the chassis, one end of this rst conductor being adapted to contact the contact of the ionization chamber when it is disposed in the socket, a static charger mounted in the chassis with an end adjacent to the cavity and extending transverse thereto, an electrometer of the quartz nbre type mounted in the chassis with an end adjacent to the cavity and extending transverse thereto, to the outside, in the same direction as the charger, the electrometer being farther away from the socket than the charger, rotatable means for operating the charger projecting outside the chassis and carrying switching means for contacting the elongated conductor, and another conductor connecting the electrometer to the elongated conductor.

2. In apparatus for charging an ionization chamber of the condenser type and for measuring the charge of such condenser, the ionization chamber being provided with an electrical contact for charging purposes, the combination its whichvzcomprses fachassis Aprovidedmwthi aisocket projecting into the chassis from z,theoutside and into lWhich amortion `of fthe ionization .chamber carrying `ythe contact .-ts slidably and also provided with a cavity extending from the bottom of the-socket in the samedirectonas `the socket, an elongated rstconductor disposedin the wcavity-and extending in the same direction as cavity and socket andinsulated fronrthe chassis. one end of l this rstconductor being adapted'to 'contact '.th'e contact Lof` the 'ionization chamber 'when it Vis disposed in the socket, a 'static `charger mounted in the chassis With an end adjacent to the cavity and'extending transverse thereto, an electrometer of the quartz fibre type mounted in the-chassiswith an end ladjacent Lto 'the cavity and extending "transverse thereto vtothefoutside andfprovidedfWithfviewingfmeans on'the outside, rotatable .means for fop'erating the `vchargerzprojectingioutside Lthe chassis .'and: carrying switching :means 'forcontacting "the, elongated :conductor, 1 and Lanother-conductoriconnecting fthe electrometerito the Yelongated conductor, .the chassis being provided vwitlrmaJ tniger .aperturen the'portion :thereof opposite thesocket.

OLE G. LANDSVERK.

REFERENCES 'CITED The :following references are of Arecord inthe le :of .this patent:

UNITED STATES :PATENTS GTI-IER REFERENCES MDDC.1396,"A Survey Meter'for the Measurementof Alpha, Beta, and Gamma Rays,'-Fas't1and 20 Slow Neutrons, Landsverk, Oct. 28, 1946 lMDDC, 562, The Ryerson Electrorneter,"Dec. 15, 1946.

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