CA1038682A - Radiographic combination - Google Patents

Abstract

ABSTRACT OF THE DISCLOSURE
A combination of photosensitive materials suited for radiography comprising :
(1) a silver halide photographic material comprising a support and silver halide having associated therewith at least one colour coupler being capable of producing in said material a negative silver and colour image, and (2) at least one X-ray fluorescent intensifying screen material comprising a phosphor layer, which contains a phosphor or a phosphor mixture consisting wholly or mainly of a rare earth metal-activated lanthanum oxychloride or lanthanum oxybromide, said phosphor or phosphor mixture having more than half its spectral emission above 410 nm, more than half its visible light spectral emission betwenn 400 and 500 nm and its maximum emission peak below 500 nm, and wherein said phosphor layer has a coverage of lanthanum oxyhalide phosphor of 100 to 800 g per sq.m, said screen material has an intensification factor of at least 20 at 40 kV and at least 25 at 80 kV; and the intensification factor of said phosphor layer is at least 2 times as high as that of a lead barium sulphate phosphor layer having substantial indentity with regard to layer thickness, binder composition phosphor particle size and phosphor content per sq.m.

Description

103~6~Z
The present invention relates to an improved combination of photosensitive elements suited for use in radiography and more particularly to a combination comprising an ~-ray intensifying screen of the fluorescent type and a silver halide recording element yielding a colour image.
From the United States Patent 3,734,735 of Jacques ~lie Bories issued May 22, 1973 a radiographic process for forming a monochromic image, optionally together with a silver image, is known. ~he monochromic image thus obtained offers an easy visual retrieval of more information than is contained in a corresponding black-and-white image.
Said process includes the following steps :
(1) directly or indirectly recording penetrating radiation as (a) developable latent silver image(s) in a photographic silver halide material, which at least at the moment of development,contains a substance or substances that with the aid of the exposed silver halide and possibly by reaction with (an) other substance(s) so-called oxidized colour developing agent(s) is tare) capable of forming in said material by means of one or more silver halide emulsion layers a monochromic image ma;nly absorbing in two primary colour spectral regions, preferably ~he red and green,

(2) developing the recorded latent image(s) by means of (a) reducing substance(s) that produce(s) (a) silver image(s) together with said monochromic image by oxidation in situ &V.800 PC~

-103~Z
or by oxidative couplin~ with (a) colour coupling agent(s), so-called colour coupler(s), and

(3) inspecting the obtained monochromic image, after optional removal of the silver image(s), with white light, and optionally inspecting it with coloured light whose spectral composition is such that it is modulated by the mono-chromic image, e.g. inspection with yellow or red light in case the dye image absorbs or modulates red and green light.
Preferably the spectral absorption of the monochromic image takes place in two primary colour spectral regions la~ing within the spectral wavelength range of 500 to 700 nm.
In the examples relating to said process the exposure of the photographic material proceeds with ~-rays that are con-verted in ultraviolet radiation and blue light by means of fluorescent calclum wolframate screens.
From the published German Patent Application (Dt-OS) 2,326,617 filed May 25, 1973 by Agfa-Gevaert A.G. an analogous process is known in which for the production of a radiographic colour image a radiographic silver halide material is used in combination with an ~-ray intensifying fluorescent screen containing terbium-activated gadolinium oxysulfide phosphors emitting for more than 50 % above 410 nm, more particularly in the green light spectral region.
Although having a particularly high intensification factor these screens are less suited for radiography since they need GV.800 PCT - 2 -103~6~Z
specially spectrally sensitized silver halide emulsions that have to be processed in non-practical dark-room conditions i.e. in red light. Moreover, they operate with a more pro-nounced "cross-over" effect which impairs the image sharpness and which will be explainèd below.
Barium lead sulphate screens, e.g. Eodak (trademark) ~ype 80 Intensifying Screens (see the advertising brochure of Eodak "X-Ray Intensifying Screens" for Medical Radiography (1958) p.6), and europium-activated barium strontium sulphate phosphor screens as described, e.g, in the published German Patent Application 2,051,262 filed October 19, 1970 by ~odak Ltd., absorb a large fraction of the incident ~-ray energy and emit violet light and ultraviolet radiation to which the X-ray silver halide film is highly sensitive. Therefore, they have been preferred up till now in high-speed screen/film systems over the calcium wolframate screens emitting mainly blue light.
~ or medical X-ray purposes the intensifying fluorescent screens used together with the radiographic silver halide materials in practice are almost exclusively screens that comprise calcium wolframate, lead barium sulphate or europium-activated barium strontium sulphate as phosphor, because the skilled art worker has never questioned the superiority of these screens over the large variety of screens comprising other types of phosphors emitting ultraviolet radiation or blue-light.

Accordingly the present invention provides a novel and GV.800 PC~

1038~i8Z
improved radiographic combination of a fluorescent screen and a silver halide photographic material containing a colour coupler, which combination is suited for low dose ~-ray photo-graphy and needs no special darkroom conditions in the pro-cessing of the silver halide material.
This invention also provides a radiographic screen-silver halide colour film system of higher speed with a same image sharpness quality as compared with prior art ultraviolet radiation or blue light fluorescent screen/silver halide colour film systems.
In accordance with the present invention these objects are attained with a combination of photosensitive materials suited for radiography and comprising :
(1) a silver halide photographic material comprising a support and silver halide having associated therewith at least one colour coupler being capable of producing in said material a negative silver and colour image, and (2) at least one X-ray fluorescent intensifying screen material comprising a phosphor layer, which contain~ a phosphor or a phosphor mixture consisting wholly or mainly of a rare earth metal-activated lanthanum oxychloride or lanthanum oxybromide, preferably a terbium- or terbium and ytterbium-activated lanthanum oxychloride or lanth~num oxybromide phosphor, said phosphors optionally also being activated with cerium and.having a terbium oxyhalide content preferably of not more than 0.006 mole per mole of the oxyhalide, said phosphor or phosphor mixture having more GV.800 PC~ - 4 -~ 03~6~2 than half its spectral emission above 410 nm, more than half its visible light spectral emission between 400 and 500 nm and its maximum emission peak below 500 nm, and wherein said phosphor ayer has a coverage of lanthanum oxyhalide phosphor of 100 to 800 g per sq.m, said screen material has an intensification factor of at least 20 at 40 kV and at least 25 at 80 kV, and the intensification factor of said phosphor layer is at least 2 times as high as that of a lead barium sulphate phosphor layer having substantial identity with regard to layer thickness, binder composition, phosphor particle size and phosphor content per sq.m.
By the term "radiography" we designate a recording technique that makes use of penetrating radiation, which includes highly energetic radiation such as X-rays, ~-rays, ~-rays and fast eiectrons, e.g. as ~btained in an ~lectron microsco~e.
By "intensification factor" is to be understood a factor measured at a pre-elected density D, indicating the exposure required to produce this density when the film is exposed to X-rays without intensifying screen, divided by the exposure required to produce the same density, e.g. density D=1.00, when the film is exposed with the screen, the wavelength distribution of the X-ray radiation and the conditions of development being maintained constant.
It has been experimentally stated that the usual colour couplers formi~g quinonimine dyes have an inherent GV.800 PC~ - 5 -" 103!~Z
absorption of ultraviolet radiation. Ultraviolet radiation absorbed by the coupler i9 lost for the formation of the latent silver image so that when screens emitting ultraviolet radiation are used, not all the emitted light is used effectively in the production of the visible image. A
screen emitting mainly blue light and containing terbium- or terbium and ytterbium-activated lanthanum ox~chloride or lanthanum oxybromide does not suffer from said disadvantage and therefore is particularly interesting for use in combination with silver halide materials that contain colourless indazolone and/or phenol and/or naphtol colour couplers.
Phosphors emitting blue light that are within the scope of the above definition and their use in X-ray intensifying screens have been described in the United Eingdom Patent 1,247,602 filed October 9, 1969 by General Electric Company and published Ge~man Patent Application (Dt-OS) 2,161,958 filed December 14, 1971 by General Electric Company.
Phosphors that are particularly suitable for use according to the present invention in the X-ray fluorescent intensifying screen film combination are represented by the following general formula :

(1_n) n wherein :
is chlorine or bromine, ~b+3 is trivalent terbium, and n is 0.0001 to 0.006.
GV.800 PC~ - 6 -6~Z
~ he halogen X is preferably present in an amount of about - the stoichiometric amount, but may be less, e.g. only about 2.5 percent thereof.
Phosphors emitting blue light particularly strongly are lanthanum oxybromide phosphors that are activated with small amounts of terbium, e.g. with n = 0.002, and in which the ratio of gram atoms of oxygen to gram atoms of bromine is 1:1.
The preparation of terbium-activated lanthanum oxychloride and lanthanum oxybromide phosphors is described in the United Eingdom Patent 1,247,602 as mentioned hereinbefore, French Patents 2,021,398 filed October 23, 1969 and 2,021,399 filed October 23, 1969 both by General Electric Company, and published German Patent Applications 1,952,812 filed October 21, 1969 by General Electric Company and 2,161,958 already mentioned before.
~ he emission spectrum ~r a la~tha~um ox~bromi~e conta ning stoichiometric amounts of oxygen and bromine and that has been activated with 0.002 gram atoms of terbium with respect to lanthanum is represented in the graph of the accompanying Figure 1, wherein the relative emission intensity expressed in percent v~es (% I) is plotted versus the wavelengths expressed in nm. ~he applied excitation radiation was 313 nm -ultraviolet radiation. The same fluorescent light emission is obtained with the screen I of Example 1. The ytterbium content has only an effect on the reduction of the after-glow.
Other particularly useful phosphors for application according to the present invention are described in the GV.800 PCT - 7 -lQ3~6~2 published German Patent Application 2,161,958 mentioned above corresponding with the Canadian Patent 927,089 filed April 11, 1972 by General Electric Company. These phosphors are terbium- and ytterbium-activated lanthanum oxychlorides or lanthanum oxybromides corresponding to the following general formula :
~a1 w yO~:lrbwYby wherein :
~ i9 chlorine or bromine, W i8 from 0.006 to 0.0005 mole per mole of the oxyhalide, and y is from 0.005 to 0.00005 mole per mole of the oxyhalide.
~he presence of the ytterbium strongly reduces the after-glow effect that follows the ~-ray irradiation so that the formation of ghost images is excluded and sharper images are obtained. ~he preparation of this class of phosphors has been described in the published German Patent Application 2,161,958 as mentioned above. Particularly interesting for the purpose of the present invention are said phosphors wherein w is 0.002.
he screen-colour film combination of the present invention among other things has the following advantages in comparison with commercial screen-black-and-white and 8creen-colour film systems :
(1) the possibility of operating with a lower silver halide content resulting in less expensive silver halide matsrials, which constit~es an advantage with regard to rapid processing and roller transport;
GV.800 PC~ - 8 -103~Z
(2) reduced X-ray dose.
As a consequence of a lower ~-ray dose for a same image density shorter exposure times can be applied, which is interesting for producing non-blurred images of moving objects.
The lower ~-ray dose is further particularly i~portant in medical X-ray applications in which harmful biological effects of the radiation are to be excluded or to be kept at a minimum;
(3) by the possibility of decreasing the exposure time an additional gain in image sharpness can be obtained because of the decrease of the well-known Schwarzschild-effect in the silver halide material;

(4) the possibility of reducing the voltage of the X_ray tube, which gives rise to an increase of contrast without need for a higher ~-ray dose;

(5) the possibility of obtaining improved sharpness at usual ~-ray dose by eliminating scattered radiation with a more selectively operating scatter grid. Since the scatter grid (Potter-Bucky diaphragm) attenuates the radiation intensity it is important to dispose of a phosphor with high conversion of ~-ray radiation energy into visible light;

(6) the possibility of increasing at usual ~-ray dose the object-film distance and to apply thereby image magni-fication. This is mainly efficient when an X-ray tube with a small focus is used. Eowever, such tubes having - GV.800 PCT - 9 -1~3~6~2 only a low X-ray emission capacity need a long exposure time when known screen-film combinatlons are used and so could only be used for radiography of non-moving objects (extremities) ~p till now;

(7) the possibility when operating with a usual X-ra~ dose of using in the silver halide materials filtering dyes that increase the image sharpness;

(8) the possibility of using single-side coated silver halide emulsion films, which substantially do not suffer from the cross-over effect that is characteristic for double-side coated silver halide materials;

(9) the possibility of obtaining a photographic system with still high speed even when using a higher amount of phenol or naphthol colour coupler that inherently absorbs ultraviolet radiation and is capable of producing a quL~oni~ne dye with ~ oY.~:d~ ~eA p-phenylenediamine t~pe developer. The higher amount of colour coupler improves the colour development speed;

(10)with respect to black-and-white screen film combinations more information is visually retrievable by white light inspection of a developed film material containing a silver image together with a dye image. Moreover, when producing e.g. bue dye images a higher information content is retrievable from that image in the lower density portions by ~spection with red light. This is due to an observed increase in contrast in said portions.
GV.800 PCT - 10 -103~6~2 Particularly interesting is the economy on silver halide in the emulsion by ~uilding up the image density partly with dyes. Such may proceed b~ introducing (a) colour coupler(s) into the emulsion, which form(s) (a) dye(s) with the oxidation product of an aromatic primar~ amino developing agent, e.g.
of the p-phenylenediamine type, which dye(s) absorb(s) in the visible part of the spectrum.
Preferabl~ a monochromic radiographic dye image is formed which has its main absorption in the red region (600-700 nm) of the visible spectrum and absorbs in the greenregion (500-600 nm) of the visible spectrum for at least 30 % in respect of the red region. In other words cyan dye images with a fairly large side-absorption in the green region and blue dye images are favoured.
A preferred photographic material for use according to the present inve~tion comprises a support and at least one silver halide emulsion layer, each such emulsion layer con-taining at least one colour coupler producing on colour de-velopment with a p-phen~lenediamine developing agent a quinoneimine dye image that absorbs in the region of 700-600 nm and in the region of 600-500 nm to the extent of at least 30 % of its absorption in the region of 700-600 nm and has in the region of 400-500 nm at 450 nm a spectrum absorption not higher than the maximum of the absorption being situated in the region of 600-500 nm, the aggregate amount of silver ` halide i~ the material corresponding to 5 to 16 g of silver . GV.800 PC~ - 11 -nitrate per sq.m. ~ ~ ~ Z
For improving the infcrmation content retrieval those phenol or ~-naphthol t~pe colour couplers are particularly suitable that on colour development of the silver halide with an aromatic primary amino developing agent form a quinoneimine dye mainly absorbing in the red and also absorbing in the green and having an absorption maximum in the spectral wave-length range of 550 to 700 (ref. therefor is made e.g. to the published German Patent Application Dt-OS 1,946,652 filed September 15, 1969 by Agfa-Gevaert AG and the United States Patent 3,734,735 mentioned before).
Phenol couplers suited for that purpose correspond, e.g., to the following general formula :
OH

~11--N~K2 R1~N- ~1 wherein :
each of R1 and R2 represents a carboxylic acid acyl or sulphonic acid acyl group including said groups in substituted state, e.g. an aliphatic carboxylic acid acyl group, an aromatic carboxylic acid acyl group, an heterocyclic carboxylic acid acyl group, e.g. a 2-furoyl group or a 2-thienoyl group, an aliphatic sulphonic acid acyl group, an aromatic sulphonic acid acyl group, a sulphonyl thienyl group, an aryloxy-sub-stituted aliphatic carboxylic acid acyl group, a phenyl carb-amyl aliphatic carboxylic acid acyl group, or a tol71 carb-G~.800 PCT - 12 -103~6~Z
oxylic acid acyl group.
For such types of phenol colour couplers and their pre-paration reference may be made to United States Patents 2,772,162 of Ilmari F.Salminen and Charles R.Barr issued ~ovember 27, 1956 and 3,222,176 of Jan ~aeken issued December 7, 1965 and to United ~ingdom Patent 975,773 filed September 4, 1961 by Gevaert Photo-Producten N.V.
In very low silver halide content materials preferably so-called 2-equivalent couplers are used to restrict the consumption of silver to a minimum. ~hese couplers need 2 instead of 4 molecules of exposed silver halide for the pro-duction of 1 dye molecule. Such couplers contain in the coupling position, e.g. a halogen atom such as iodine, bromine, or chlorine (see, e.g. United States Patent 3,006,759 of ~nthony Ioria, Warren A.Reckhow and Ilmari ~.Salm;nen issued October 31, 1961). The density of the image i~ thus re~lised by addition of the densities-of the silver image(s) to that tthose) Of the dye image(s).
Accordi~g to the Belgian Patent 777,581 filed December 30, 197~ by Agfa-Gevaert N.V. it has been found possible to obtain for radiographic colour elements of the type described above, upon exposure and rapid colour processing at elevated tem-perature (at least 30C) as compared with normal development at ambient temperature, improved speed values and the same or even improved va'ues for the gradation, by adding to the radiographic image-forming silver halide emulsion, before ~n~ a silver chloride-containing e~ulsion having such a low speed GV.800 PCT _ 13 -~ L0 3 ~ ~ ~ Z
that no visible image is produced therein under the conditions of exposure and development of the radiographic image-forming silver halide emulsion.
In a preferred embodiment of the present invention a radiographic colour silver halide emulsion material thus comprises a mixture of silver halide emulsions in which one silver halide emulsion is capable of producing a visible image upon blue light exposure and colour development, and a silver chloride-containing emulsion whose speed is insufficient to produce a visible image upon said exposure and development, and incorporates at least one colour coupler producing a monochromic dye image by coupling with an oxidized aromatic primary amino developing agent.
As can be learned from said Belgian Patent 777,581 the blue-light sensitivity of the image-forming silver halide emulsion is preferably at lea~t 100 times as large as the blue-light sensitivity of the silver chloride-containing emulsion. Though the amount of low speed silver chloride-containing emulsion to be added to the image-forming silver halide emulsion ma~ vary within very wide limits, the ratio of low speed silver chloride to image-forming silver halide, expressed in equivalent parts by weight of silver nitrate, is preferably comprised between 1:50 and 1~ he low-speed silver chloride-containing emulsion is preferably a fine-grain sil~er chloride-conta;n;ng emulsion having a particle size in the range from 50 to 500 nm. Though it is preferred to use a pure silver chloride emulsion as low-speed emulsion GV.800 PCT _ 14 _ 103E~ 2 it is also possible to use an emulsion of mixed silver halides comprising silver chloride, e.g. a silver chlorobromide emulsion.
~ he image-forming layer containing a mixed silver halide emulsion contains preferably in addition to the low-speed silver chloride emulsion a medium or high-speed image-forming silver halide emulsion in which the silver halide is pre-dominantly silver bromide, e.g. pure silver bromide emulsions and silver bromoiodide emulsions whose iodide content is less than 10 mole %. The average silver halide grain-size is preferably comprised between 500 nm and 1200 nm.
~ he total silver halide content in the mixed silver halide emulsion is generally such that after double-side coating on a suitable support the amount of silver halide expressed as equivalent silver nitrate is in the range of about 3 to about 7 g, preferably between 4 and 6 g, per sq.m and per side of the support.
A disadvantage of silver halide photographic materials having poor silver halide content lies in the increase of "cross-over", a phenomenon associated with silver halide emulsion materials carrying at both sides of a support that is transparent for fluorescent light a silver halide emulsion layer, which during the X-ray exposure stands in close con-tact with a fluorescent screen.
Indeed, the light emitted by one of these fluorescent screens gives rise not only to an image-wise blackening in GV.800 PC~ - 15 _ 103~6E~Z
the adjacent silver halide emulsion layer but also pene-trates in a considerable amount through the relatively thick support and produces an unsharp image in the oppositely situated silver halide emulsion layer. ~his phenomenon is called "cross-over". ~he degree of cross-over substantially determines the quality of the image obtained in the radio-graphic recording material.
~ he cross-over image is unsharp because of the diffusion of light in the different layers and support sheet of the recording material and also because of the diffuse re-fraction and reflection of light taking place at the boundaries of said layers and support sheet.
In order to diminish the cross-over at least one colloid layer and/or the base material of the light-sensitive mate-rial of the present invention may containg a dye called hereinafter "filtering dye" absorbing light in the wavelength range emitted by the fluorescent screen used in the combination.
~ he filtering dyes used in the silver halide emulsion re-cording material are preferably incorporated in the hydro-philic colloid layer between the silver halide emulsion layersor in the emulsion layers themselves. ~hey may, however, also be incorporated in one or more subbing layers and even in the support. ~he dyes may have such chemical and/or physical characteristics that they can be removed or decolourized in one of the processing baths.
According to a preferred embodiment of the present in-vention filtering dyes absorbing in the wavelength range GV.800 PC~ - 16 -1103~i82 of about 400 to 500 nm are used when fluorescent screens are applied that substantially emit light in the wavelength range of 400-500 nm.
The amount of filtering dye is preferably in the range of amounts that reduce the cross-over light to such an extent that its intensity becomes smaller than 30 % of the intensity of the light impinging on an adjacent emulsion layer. ~or example 2~ to 1000 mg per sq.m of filtering dye(s) are used but here likewise lower or higher amounts may be appropriate according to the result aimed at.
8uitable filtering dyes that can be removed from hydro-philic colloid layers are ~artrazina and the dyes described in the United States Patent ~,624,229 of Daniel Maurice ~immerman, August Jean Van Paesscken and Albert Emiel Van Hoof issued November 30, 1971.
Cro~s-over is excluded substantially when the silver halide is present in a single coating. ~ormally, however, a duplitized or dual coating is used i.e. a photographic material having a silver halide emulsion layer on each side of a transparent support.
In the radiographic combination of X-ray fluorescent screens and optionally spectrally sensitized silver halide radiographic materials of the present invention, the screens may be arranged separately from the radiation-sensitive silver halide material or they may form with the silver h~ide emul-sion layer an integral arr~ngement so that on one and the same GV.800 PCT - 17 -103~32 support both a silver halide emulsion layer and an X-ray fluorescent screen are provided.
The spectral sensitivity of the silver halide emulsions may be enlarged or improved by spectral sensitization in the wavelength range of 400 to 500 nm with common spectrally Rensitizing dyes used ~ silver halide emulsions, which in-clude cy~n;ne d~es and merocyanine dyes as well as other dyes as described by F.M.Hamer in "~he cyanine dyes and related compounds", Interscience Publishers (1964). These d~es are preferably used in an amount in the range of 20 mg to 250 mg per m~le of silver halide.
~ he silver halide in the emulsion layer(s) may comprise varyng amounts of silver chloride, silver iodide, silver bromide, silver chlorobromide, silver bromoiodide, and the li~e, but when coated must be capable, after exposure and processing, of producing a n~gative silver image remaining thereon, i.e. in situ. Particularly good results are ob-tained with silver bromoiodide emulsions in which the average grain size of the silver bromoiodide crystals is in the range of about 0.1 to about 3 pm.
In view of a particularly interesting economy on silver the silver halide photographic material comprises a support and silver halide being capable of producing in said material a combined negative silver and colour image having a covering power greater than about 50, the silver halidebeing present in an equivalent concentration of less than about 8 g of silver per sq.m.
By the term "covering power" is understood here the reci-GV.800 PCT - 18 -lQ3~6~Z
procal of the photographic equivalent of developed silver i. e .
the number of grams of developed silver per sq.dm divided by the visual maximum optical density of the combined negative silver and colour image, the development being carried out at 41C for 45 s with the colour developing bath described in Example 1.
When a duplit1zed silver halide coating is employed pre-ferably each such coating contains silver halide in an amount equivalent to less than about 4 g of silver per sq.m.

As these layers are applied by means well-known in the art it is desirable in the combin~tions of our inven-tion that the silver halide-contain;ng coating(s) be capable of transmitting less than about 40 % and pre-ferably less than about ~0 % of the incident radiation from the screen at wa~elength~ longer than 410 ~m when said silver halide coverage is within the above ranges.
~ he proper transmittance can be obtained in a variety of ways? such as e.g. by the incorporation of optically separating barriers, e.g. undercoats, which can be positioned between the silver halide-containing layers, by altering the . composition of.said layers, by including dyes or other materials, by adjusting the halide balance or by modifying the silver halide grain shape, grain size, size distribution and the like.
~ he image-forming silver halide emulsion may be chemically sensitized by any of the known procedures. ~hey may be digested with naturally active gelatin or with small GV.800 PCT - 19 -1~3~6~Z
amounts of sulphur-containing compounds such as allyl thio-cyanate, allylthiourea, sodium thiosulphate, etc. ~he~
may be sensitized likewise by means of reductors, e.g. tin compounds as described in the United Kingdom Patent 789,823 filed April 29, 1955 by Ge~aert Photo-Producten N.V., polyamines, e.g. diethyltriamine, and small amounts of noble metal compounds such as of gold, platinum, palladium, iridium, ruthenium, and rhodium as described by R.Eoslowsky, Z.Wiss.
Phot. 46, 67-72 (1951). Representative examples of noble metal compounds are ammonium chloropalladate, potassium chloroplatinate, potassium chloroaurate and potassium auri-thiocyanate.
Emulsion stabilizers and antifoggants may be added to the silver halide emulsion, e.g., the known sulphinic and selenic acids or salts thereof, aliphatic, aromatic or hetero-cyclic mercapto compounds or disulphides, e.g. those described and claimed in published German Patent Application 2,100,622 filed January 8, 1971 by Agfa-Gevaert A.G., preferably com-prising sulpho groups or carboxyl groups, mercury compounds, e.g. those described in Belgian Patents 524,121 filed November 7, 1953 by ~odak Ltd., 677,~37 filed March 4, 1966, 707, 386 filed December 1, 1967 and 709,195 filed January 11, 1968 all by Gevaert-Agfa N.V., and tetra-azaindenes as described by Birr in Z.Wiss.Phot. 47, 2-58 t1952), e.g. the hydroxy tetra-azaindene~ of the following general formula :

GV. 800 PCT - 20 -103~ 2 R q"C ~ ~ "C R
R -C C = N
2 ~N~

wherein :
each of R1 and R2 represents hydrogen, an alkyl, an aralkyl or an aryl group, and R3 represents hydrogen, an alkyl, a carboxyl, or an alkoxy-carbonyl group, such as 5-methy1-7-hydroxy-s-triazolo ~1,5-a}pyrimidine.
The radiation-sensitive emulsions for use in the present invention may be coated on a wide variety of supports, e.g.
films of cellulose nitrate, cellulose esters, polyvinylacetal, polystyrene, polyethylene terephthalate and other polyester materials as well as ~ ,~ -olefin-coated papers, e.g. paper coated with polyethylene or polypropylene.
Preferred supports comprise a linear condensation polymer, polyethylene terephthalate being an example thereof.
~ he supports used in the present recording materials may be coated with subbing layers for improving the adhesion of (a) gelatino-silver halide emulsion layer(s) thereto.
The mechanical strength of melt-extruded supports of the polyester t~pe can be improved by stretching. In some cases as described in the United Eingdom Patent 1,2~4,755 filed September 28, 1967 by Gevaert-Agfa N.V. the support may carry a subbing layer in the stretching stage.
GV~800 PC~ - 21 -103~6~Z
Suited subbing layers are known to those skilled in the art of silver halide photography. With regard to the use of hydrophobic film supports reference is made ~ the composition of subbing layers described in the United Eingdom Patent 1,234,755 mentioned hereinbefore.
According to said patent a hydrophobic film support has 1) a layer which is directly adherent to the said hydrophobic film support and comprises a copolymer formed from 45 to 99.5 % by weight of at least one of the chlorine-containing monomers vinylidene chloride and vinyl chloride,from 0.5 to 10 % by weight of at least an ethylenically un-. saturated hydrophilic monomer, and from O to 54.5 % by weig~tof at least one other copolymerisable eth~lenically un-saturated monomer; and 2) a layer comprising in a ratio of 1:3 to 1:0.5 by weight a mixture of gelatin and a copoly~er of 30 to 70 % by weight of butadiene with at least one copoly-merisable ethylenically unsaturated monomer.
Other additives may be present in one or more of the -hydrophilic colloid layers of the radiation-sensitive silver halide elements of the present invention, e.g. hardening Pgents such as $ormaldehyde, dialdehydes, hydroxyaldehydes mucochloric and mucobromic acid, acrolein, and glyoxal, morda~ng agents for anionic colour couplers or dyes formed therefrom, plasticizers-and coating aids e.g. saponin, e.g.
dialky~sulphosuccinic acid salts such as sodium diisooctyl sulphosuccinate, alkylar~l polyether sulphuric acids, alkyl-aryipolyethyi ether sulphonic acids, carboxyalkylated poly-G~.800 PCT - 22 _ ~ 03~ 2 ethylene glycol ethers or esters as described in French Patent 1,537,417 filed Sep'ember 18, 1967 by Agfa-Gevaert N.V.
8 17 6H4(0C~2C~2)80CH2COONa, fluorinated sur factants, e.g. those described in Belgian Patent 742,680 filed December 5, 1969 by Gevaert-Agfa N.V. and the published German Patent Applications 1,950,121 filed October 4, 1969 by Dupont de Nemours and 1,942,665 filed August 21, 1969 by Ciba A.G., inert particles such as silicon dioxide, glass, starch and pol~methyl methacrylate particles.
In the production of colour images together with silver images use is preferably made of aromatic primary amino colour developing agents, e.g. N,N-dialkyl-p-phenylenediamines and derivatives thereof, e.g. N,~-diethyl-p-phenylenediamine, N-butyl-N-sulphobutyl-p-phenylenediamine, ?-amino-5-di-ethylaminotoluene hydrochloride, 4-am;no-~-ethyl-~ -methane sulphonamidoethyl)-m-toluidine sesquisulphate monohydrate and N-hydroxy_ethyl-~-ethyl-p-phenylenediamine. The colour de-veloping agent can be used together with black-and-white developing agents, e.g. 1-phenyl-3_pyrazolidinone and p-mono-methylaminophenol, which are known to have a superadditive effect on colour development (see ~.~.A. Mason, J.Phot.Sci.

11 (1963) 136-139), and other p-aminophenol derivatives, e.g.
those according to French Patent 1,283,420 filed February 16, 1961 by Ilford ~imited such as 3-methyl-4-hydroxy-N,N-diethylaniline, 3-methyl-4-hydroxy-~-ethyl-N-~ -hydroxy-ethylaniline, 1-methyl-6-hydroxy-1,2,3,4-tetrahydroquinoline, 1-~ -hydroxyethyl-6-hydroxy-1,2,3,4-tetrahydroquinoline, GV.800 PC~ - 23 _ 103~;8Z
N-(4-hydroxy-3'-methylphenyl)-pyrrolidine, etc. It is also possible to use combinations of aromatic primary amino -colour developing agents to obtain an increased rate of colour development (see e.g. German Patent 954,311 filed December 5, 1953 by Agfa A.G. and ~rench Patent 1,299,899 filed September 8, 196~ by Agfa A.G.); favourable effects are obtained, e.g., by the use of N-ethyl-N-2-hydroxyethyl_ p-phenylenediamine together with N-butyl-N-sulphobutyl_p-phenylendiamine, 2-amino-5-diethylamino-toluene hydrochloride or ~,N-diethyl-p-phenylenediamine hydrochloride.

lhe developing solutions may also comprise any of the usual additional ingredients~e.g. sodium sulphite and hydroxyl-amine or derivatives thereof, hardening agents, antifoggants~
e.g. benzotriazole, 5-nitro-benzimidazole, 5-nitro-indazole, halides such as potassium bromide, silver halide solvents, toning and intensifying compounds, solvents~e.g. dimethyl-formamide, dimethylacetamide and N-methylpyrrolidone for chemical ingredients that are difficult to dissolve in the preparation of the developing solutions or that tend to pre-cipitate upon standing, etc.
Development accelerators may be used either in the silver halide emulsion, in adjacent layer(s) or in the developing bath.
~hey include alkylene oxide compounds of various types,e.g.
alkylene oxide condensation products or polymers as described in GV.800 PC~ - 24 -103~36~Z
United States Patents 1,970,578 of Conrad Schoeller and Max Wittner issued August 21, 1934, 2,240,472 of Donald R.Swan issued April 29, 1941, 2,42~,549 of Ralph Eingsley ~lake, William Alexander Stanton and ~erdinand Schulze issued July 8, 1947, 2,441,389 Or Ralph ~ingsley Blake issued May 11, 1948, 2,531,8~2 of William Alexander Stanton issued ~ovember 28, 1950 and 2,5~3,990 Or Ralph Eingsley Blake issued December 12, 1950 and in United ~ingdom Patents 920,637 filed May 7, 1959, 940,051 filed ~ovember 1, 1961, 945,340 filed October 2~ 1961 all by Gevaert Photo-Producten N.V., 991,608 filed June 14, 1961 by Eodak Ltd. and 1,015,023 filed December 24, 1962 by Gevaert Photo-Producten N.V.
Other compounds accelerating the development are onium and polyonium compounds, preferably Or the ammonium, phosphonium~
and sulphonium, e.g. trialkyl sulphonium salts such as di-methyl-n-nonyl sulphonium p-toluene sulphonate, tetraalkyl ammonium salts such as dodecyl trimethyl ammonium o-toluene sulphonate, alkyl pyridinium and aIkyl quinolinium salts such as 1-m-nitrobenzyl quinolinium chloride and 1-dodecylpyri-dinium chloride, bis-alkylene pyridinium salts such as N,N'-tetramethylene bispyrid;n;um chloride, quaternary ammonium and phosphonium polyoxyalkylene salts especially polyoxyalkylene bispyridinium salts, examples Or which can be found in United States Patent 2,944,900 Or ~urt H.Carroll, ~ubert S.Elins, James ~.Graham and Charles V.Wilson issued July 12, 1960, etc.
GV.800 PCT - 25 _ 103~682 The exposed radiographic elements of the present inven-tion are preferably processed in an automatic processing apparatus for X-ray films in which the photographic material may be guided automatically and at a constant speed from one processing unit to the other, but it will be understood by those skilled in the art that the radiographic image recording elements disclosed herein can also be processed apart from the above mentioned automatic processing apparatus in a variety-of ways, such as by using the manual conventional multi-tank methods well known in the art.
For common emulsion preparation processes and the use of particular emulsion ingredients reference is made in general to the Product Licensing Index of December 1971 in which the following terms are dealt with in more details :
I/II Emulsion type and preparation of said element iII Chemicai sensitization I~ Development modifiers V Antifoggants and stabilizers VI Developing agents VII Hardeners VIII Binding agents or polymers for silver halide layers and other layers I~ Antistatic layers Supports ~I Plasticizers and lubricants XII Coating aids GV.800 PCT - 26 -.. .

103~ 2 2V Spectral sensitization agents for silver halides xxlII Colour material ingredients ~VI Absorbing and filter d~es ~1 Physical development systems, and gVII and ~VIII Additio~ agents and coating procedures.
~ he fluorescent screen materials for use according to the present invention include such materials wherein the lanthanum ox~halide phosphor is mixed with yttrium oxysulphide phosphor activated with terbium. The preparation of phosphors of the latter type has been described in the French Patent 11580,544 filed July 25, 1968 by N.V. Philips'Gloeilampen-fabrieken and in the United States Patents 3~418,246 of Martin R.Royce issued December 24, 1968 and ~,418,247 of Perry N.Yocom issued December 24, 1968 and in the United Eingdom Patent 1,247,602 as already mentioned hereinbefore.
In the radiographic combination of ~-ray fluorescent screens of the present invention the screens may be arranged separately from the radiation-sensitive silver halide material or they may form with the silver halide emulsion layer an integral arr~n~ement so that on one and the same support both the silver halide emulsion layer and the ~-ray fluorescent screen are provided. ~he radiographic material m~y be a single- or double-coated radiographic ma~erial, which means that the radiographic material comprises either at only one side or at both sides of the support a radiation-sensitive silver halide emulsion layer. The fiuorescent screens may be provided at both sides of a single- or double-W .800 PCT - 27 _ 103~
coated radiographic material. The radiographic combination of fluorescent screens and radiographic materials may ~urther comprise the common intermeaiate and/or protective and/or stripping l~yers, which may be arranged between or over the radiation-sensitive emulsion layers and the fluorescent screens.
The selected fluorescent substance(s) is (are) in the form of a la~er applied to a support or applied as a self-supporting layer or sheet. Suited layers or sheets have a thickness of preferably 0.05 to 0.5 mm and contain the fluorescent substance(s) or phosphors dispersed in a binder in an amount preferably of 80 to 95 % by weight. ~uch binder i8, e.g., an organic high-molecular weight polymer. Suitable binding agents are, e.g., cellulose nitrate, ethylcellulose, cellulose acetate, polyvinyl acetate, polystyrene, poly-vinylbutyral, polymethyl methacrylate and the like.
~ preferred grain size of the fluorescent substances is in the range of about 1-25 ~m.
- The surface of the fluorescent material layer ma~ be protected against moisture and mechanical damage by a coating of an organic high polymer applied to a thickness of 0.001 to 0.05 mm. Such protecting coating is, e.g., a thin film of cellulose nitrate, cellulose acetate, poly-methyl methacrylate and the like.
~ he following examples illustrate the present in~ention.
EXam~le 1 ~ radiographic colour material was prepared in the GV.800 PC~ - 28 -~0;~6~Z
following way.
~o 155 g of a high speed silver bromoiodide emulsion (9 mole % silver iodide), which comprises 15.5 g of gelatin and an amount of silver halide equivalent to 23.9 g of silver nitrate And which has an average silver halide grain-si~e of ~00 n~, 200 g of a low-speed silver chloride emulsion com~
prising 16.8. g of gelatin and an amount of silver chloride equivalent to 24 g of silver nitrate.
The low-speed silver chloride emulsion was prepared b~
admixing an aqueous solution of silver nitrate to an aqueous gelatin/sodium chloride solution, precipitating the gelatin emulsion with ammonium sulphate, washing and peptizing.
Gelatin was then added as well as 5-methyl-7-hydroxy-s-triazolo ~1,5-a~pyrimidine so that no chemical ripening occurred. ~he mean grain-size of the siiver chloride was 220 nm.
~hc mi~t-~re uas molten b~ heating for 1 h at 38C where-upon were added :
a) 14.5 g of the colour coupler having the formula :

E3C-(CH2)12-CH=CE-CH2_CH_CON~_ ~ -OH O
- ~ CH2COOH ~ -NHCO-from an aqueous alkaline solution, b) sufficient aqueous acetic acid solution to neutralize the emulsion (pH 7), c) 5-methyl-7-hydrox~-s-triazolo~1,5-a~ yrimidine as emulsion stabilizer, d) saponin as coating aid, and e) mucochloric acid as hardening agent.
GV.800 PCT - 29 -103~6~Z
~ he emulsion was diluted to make 920 ml and then coated on both sides of a subbed polyethylene terephthalate support at a coverage at each side of an amount of silver halide corresponding with ~ g of silver per sq.m.
On both sides a gela~in anti-abrasion layer of 0.0015 mm was provided whereupon the radiogr~phic colour material formed was dried.~he covering power obtainable with said colour ma-terial under the described conditions was 175.
- Composition of the fluorescent screen material I
~he fluorescent screen used according to the invention was prepared as follows :
92.2 g of ~aOBr : 0.002 Tb : 0.0005 Yb phosphor particles pre-pared according to the method described in the published German Patent Application 2,161,958 as mentioned above were dispersed in a solution of 7.8 g of ~LVACIT~ 2044 (trade name of du Pont de ~emollrsS WilmIngton, Del., U~A, for a h~gh-molecular weight poly-n-butyl methacrylate) in 21.7 g of toluene.
~he obtained dispersion was filtered through a filter having passages with a mean diameter of 75 pm and was de-aerated by subjecting it to reduced pressure of 100 mbar (100 cm of water).
~ he content of solids of the obtained dispersion was 82.1 % by weight.
~ he dispersion was coated onto a subbed polyethylene terephthalate resin support of 250 pm. The subbing layer was GV.800 PCT - 30 -103~g2 proluced from a latex on the basis of a copolymer of vinyl chloride, vinylidene chlori~e, n-butyl acrylate and itaconic acid (weight ratio : 63/30/5/2).
The coating of the dispersion was effected in such a way that 35 mg of phosphor were applied per sq.cm.
Combined with the above described silver halide material and in the circumstances of the development (41C_45 s) of the present Example 1 the intensification factor of screen I was 7Q.
- Composition of the fluorescent screen material II
Europium-activated barium strontium sulphate phosphor particles (emitting mainly ultraviolet) prepared according to Example 7 of the United ~ingdom Patent 1,322,748 filed October 20, 1970 by Eodak ~td. were incorporated in an intensifying screen ;binder layer as described for fluorescent screen material I.
- Composition of the fluore~cent screen material III
A calcium wo~fr~m~te phosphor screen particles of the commercial type (manufactured by Riedel-de Haën, Seelze (Hannover), W.Germany) used in CaW04 screens were incorporated in an intensifying screen binder layer as described for fluorescent screen material I.
- Exposure The above light-se~sitive material was exposed with a 80 kV X-ray radiation filtered through a 6 mm aluminium sheet and modulated with a test object being a line screen made of lead wherein the width of the bars of the screen gradually diminishes, and their spatial frequency (number per mm) gradually increases from one side of the test object to the GV.800 PCT - 31 -~Q3g6~Z
other.
Each of three strips of the light-sensitive material - called materia~s A, ~ and C were exposed between two fluorescent screen material~ I, II and III respectively, arranged in contact with the opposite side~ of the light-sensitive material.
By applying the above test obaect in the exposure it is possible to obtain an objective value for the sharpness independently of subject contrast by determining the "sguare wave response function" (SWRF) (ref. Amer.J.Roentgenol. 106 (1969), pages 650-654).
After removal of the intensifying screens the radiographic colour materials were automatically colour-processed, which includes colour development (24 ~ at 41C), fixing (20 s at 41C), rinsing (25 9 at 41C) and drying (20 s at 55C).
~ he developing bath used had a p~ Or 10.6 and comprised per litre :
8 g of N-hydroxyethyl-~-ethyl-p-phenylenediamine, 1.5 g of hydroxylamine, 4 g of anhydrous sodium sulphite, 1 g of potassium bromide, and 65 g of anh~drous potassium carbonate.
~ ixing occurred by means of a sodium thiosulphate fixing solution.
~ he ~quare wave response function Or the test materials was derived from the measurements obtained by scanning the line pattern obtained in these materials with a microdensitometer.
GV.800 PCT - 32 -1~3~&~2 It was est~blis~ed that the combined use according to the invention of the above fluorescent screen I with said radio-graphic colour material yielded a more favourable relationship of square wave response value (at 1 line pair per mm) to speed than with the combinations of the same silver halide material with the screens II and III respectively.
With respect to the screen III film combination the screen I film combination yielded a speed four times as high for the same SWR-value.
With respect to the ~creen II film combination the screen I
film combination yielded a speed two times as high for the same SWR-value.
Example 2 Example 1 was repeated with the difference, however, that the 155 g of the high-speed silver bromiodide emulsion cnmprisea ~0.0 g nf gelatin ~nd An amount of silver halide equivalent to 48.0 g of silver nitrate.
The coating of this modified emulsion, which was diluted to 1300 ml instead of to 920 ml, was effected at such a coverage that to each side of the support an amount of silver halide equivalent to 7.0 g of silver was applied.
The relationship of SWR-value to speed and the speed relationship o~ the screen I film, screen II film and screen III film combinations were the same as described in Example 1.

G~.800 PCT - 33 -

Claims (24)

The embodiments of the invention in which an exclusive property or privilege is claimed, are defined as follows :

1. A combination of photosensitive materials suited for radiography comprising :
(1) a silver halide photographic material comprising a support and silver halide having associated therewith at least one colour coupler being capable of producing in said material a negative silver and colour image, and (2) at least one X-ray fluorescent intensifying screen material comprising a phosphor layer, which contains a phosphor or a phosphor mixture consisting wholly or mainly of a rare earth metal-activated lanthanum oxychloride or lanthanum oxybromide, said phosphor or phosphor mixture having more than half its spectral emission above 410 nm, more than half its visible light spectral emission between 400 and 500 nm and its maximum emission peak below 500 nm, and wherein said phosphor layer has a coverage of lanthanum oxyhalide phosphor of 100 to 800 g per sq.m, said screen material has an intensification factor of at least 20 at 40 kV and at least 25 at 80 kV, and the intensification factor of said phosphor layer is at least 2 times as high as that of a lead barium sulphate phosphor layer having substantial identity with regard to layer thickness, binder composition phosphor particle size and phosphor content per sq.m.

2. The combination of claim 1, wherein said screen contains as fluorescent substance or substances one or more lanthanum oxyhalides activated with terbium or with terbium and ytterbium, the terbium oxyhalide content being not more than 0.006 mole per mole of the oxyhalide.

3. The combination of claim 2, wherein said phosphor corresponds to the following general formula :

wherein :
X is chlorine or bromine, Tb+3 is trivalent terbium, and n is 0.0001 to 0.006.

4. The combination of claim 3, wherein the halogen X is present in the range of an amount of about the stoichiometric amount and of about 2.5 percent thereof.

5. The combination of claim 3, wherein in the general formula n is equal to 0.002.

6. The combination of claim 2, wherein said phosphor corresponds to the following general formula :

wherein :
X is chlorine or bromine, w is from 0.006 to 0.0005 mole per mole of the oxyhalide, and y is from 0.005 to 0.00005 mole per mole of the oxyhalide.

7. The combination of claim 6, wherein w is 0.002 mole and y is 0.0005 mole.

8. The combination of claim 1, wherein the phosphor mixture contains said lanthanum oxyhalide and an yttrium oxysulphide phosphor activated with terbium.

9. The combination of materials according to claim 1, wherein the intensifying screen contains the fluorescent particles dispersed in a binder within the range of 80-95 % by weight.

10. A combination according to claim 1, wherein the intensifying screen contains fluorescent particles having a grain size within the range of about 1-25 µm.

11. The combination according to claim 1, wherein the silver halide is a silver bromoiodide having an average grain size in the range of about 0.1 to 5 µm.

12. The combination according to claim 1, wherein the silver halide material contains (a) colour coupler(s), which form(s) (a) dye(s) with the oxidation product of an aromatic primary amino developing agent.

13. The combination according to claim 1, wherein the silver halide material contains (a) colour coupler(s) capable of forming a monochromic radio-graphic dye image, which has its main absorption in the red region (600-700 nm) of the visible spectrum and absorbs in the green region (500-600 nm) of the visible spectrum for at least 30 % in respect of the red region.

14. The combination according to claim 13, wherein the silver halide material contains a support and at least one silver halide emulsion layer, each such emulsion layer containing at least one colour coupler producing on colour development with a p-phenylendiamine developing agent a quinoneimine dye image that absorbs in the region of 700-600 nm and in the region of 600-500 nm to the extent of at least 30 % of its absorption in the region of 700-600 nm and has in the region of 400-500 nm at 450 nm a spectral ab-sorption not higher than the maximum of the absorption being situated in the region of 600-500 nm, the aggregate amount of silver halide in the material corresponding to 5 to 16 g of silver nitrate per sq.m.

15. The combination according to claim 14, wherein the colour coupler corresponds to the following general formula :

wherein :
each of R1 and R2 represents a carboxylic acid acyl or sulphonic acid acyl group including said groups in sub-stituted form.

16. The combination according to claim 1, wherein said silver halide is coated on both sides of the support.

17. The combination according to claim 1, wherein the silver halide material contains a silver halide emulsion layer comprising a mixture of silver halide emulsions in which one silver halide emulsion is capable of producing a visible image upon exposure to blue light and colour development and a silver chloride-containing emulsion whose speed is insufficient to produce a visible image upon said exposure and development.

18. The combination of claim 17, wherein the total silver halide content expressed as silver nitrate in the mixed silver halide emulsion of a material with double-side coated support is in the range of about 3 to about 7 g per side of the support.

19. The combination according to claim 1, wherein the silver halide photographic material comprises a support and silver halide being capable of producing in said material a combined negative silver and colour image having a covering power greater than about 50, the silver halide being present in an equivalent concentration of less than about 8 g of silver per sq.m, and the covering power being defined as the reciprocal of the number of grams of developed silver per sq.dm divided by the visual maximum optical density of the combined negative silver and colour image, for a development carried out at 41°C for 45 s with a colour developing bath having a pH 10.6 and comprising per litre:
8 g of N-hydroxyethyl-N-ethyl-p-phenylenediamine, 1.5 g of hydroxylamine, 4 g of anhydrous sodium sulphite, 1 g of potassium bromide, and 65 g of anhydrous potassium carbonate.

20. The combination according to claim 19, wherein the photographic material contains a double side coated support and the silver halide present in each coating is equivalent to an amount of less than about 4 g of silver per sq.m.

21. The combination according to claim 1, wherein the silver halide material contains a filtering dye absorbing light in the wavelength range emitted by the fluorescent screen used in the combination.

22. The combination according to claim 1, wherein the fluorescent screen is in the form of a layer applied to a support or applied as a self-supporting layer or sheet.

23. The combination according to claim 1, wherein the fluorescent screen is arranged separately from the photosensitive material containing the silver halide.

24. The combination according to claim 1, wherein the fluorescent screen forms an integral arrangement with the photosensitive material containing the silver halide.