Method for preparation of radiographic image conversion panel and radiographic image conversion panel thereby

A method for preparing a radiographic image conversion panel and the panel prepared thereby is disclosed. In the method a vapor flow of photostimulable phosphor or its raw material is applied to a support at a particular angle of incidence with respect to the normal direction of the support.

BACKGROUND OF THE INVENTION 
The present invention relates to a preparation method for a radiographic 
image conversion panel using a photostimulable phosphor and a radiographic 
image conversion panel prepared by the method. 
Radiographic images, such as X-ray images, are widely used for disease 
diagnosis and other purposes. 
Recently, U.S. Pat. No. 3,859,527 and Japanese Patent O.P.I. Publication 
No. 12144/1980 each disclose a method of radiographic image conversion 
using a photostimulable phosphor in the presence of visible light or 
infrared rays as stimulating excitation light. These methods use a 
radiographic image conversion panel comprising a support and a layer of 
photostimulable phosphor formed thereon. The layer of photostimulable 
phosphor of this radiographic image conversion panel is irradiated with 
radioactive rays that passed through the subject to accumulate radiation 
energy according to the radiation permeability of each portion of the 
subject for forming a latent image (cumulative image); the layer of 
photostimulable phosphor is then scanned with stimulating excitation light 
to cause it radiate the radiation energy accumulated in each portion and 
convert it to light; an image is obtained on the basis of the light signal 
corresponding to the intensity of this light. The eventual image thus 
obtained may be reproduced as a hard copy or on CRT. 
The radiographic image conversion panel having a layer of photostimulable 
phosphor, used for this method of radiographic image conversion, needs to 
produce images of good graininess and high sharpness, as well as to have 
high percent absorption of radiation and high photoconversion efficiency 
(hereinafter together referred to as "radiation sensitivity") similarly in 
the radiography using the conventions fluorescent screen. 
Recently a conversion panel containing no binding agent was developed. 
Thought this panel is advantageous because it has high packing density of 
phosphor and therefore has a satisfactory sensitivity with a thin phosphor 
layer, there is certain room to improve image sharpness. The sharpness 
depends on the directional characteristics of the stimulating excitation 
light introduced into the phosphor layer. 
In the light of this drawback, the following methods have recently been 
proposed one by one with the aim of improving image sharpness: 
(1) The method in which, as shown in FIG. 10, fine prismatic blocks 94 are 
prepared by depositing a photostimulable phosphor 93 on a support 92 
having a fine rugged pattern (tiles etc.) 91 to form gaps 95 among the 
prismatic blocks 94 (Japanese Patent O.P.I. Publication No. 142497/1986). 
(2) The method in which, as shown in FIG. 11, gaps 105 formed among blocks 
104 obtained by depositing a photostimulable phosphor 103 on a support 102 
having a fine rugged pattern 101 are grown by shock treatment (Japanese 
Patent O.P.I. Publication No. 142500/1986). Note that 106 is a protective 
layer. 
(3) The method in which, as shown in FIG. 12, gaps 113 are formed in a 
layer of photostimulable phosphor 112 deposited on the upper surface of a 
support 111 from the upper face of the layer of the phosphor (Japanese 
Patent O.P.I. Publication No. 39797/1987). Note that 114 is a protective 
layer. 
(4) The method in which, as shown in FIG. 13, a layer of photostimulable 
phosphor 123 having hollows 122 is formed on the upper surface of a 
support 121 by atmospheric vapor deposition, and this is followed by heat 
treatment etc. to grow the hollows 122 to form gaps (Japanese Patent 
O.P.I. Publication No. 110200/1987). Note that 124 is a protective layer. 
However, the method of (1) above is faulty in that the process of forming 
the fine rugged pattern 91 on the support 92 is complicated and there is a 
limitation on fining the pattern 91, which in turn limits image sharpness. 
The method of (2) requires a process of shock treatment, leading to an 
additional cost of production. 
The methods (3) and (4) are both faulty in that uniformization of gap 
density on panels of large area is difficult, and a process of shock 
treatment is necessary as in the method of (2). 
SUMMARY OF THE INVENTION 
A purpose of the present invention, intended for a solution to these 
problems, is to provide a radiographic image conversion panel with an 
improved sensitivity and graininess and a high sharpness (directional 
characteristics of the stimulating excitation light and photostimulated 
luminescence). Another purpose of the invention is to provide a 
radiographic image conversion panel that can be produced easily and 
stably. 
A further purpose is to provide a method for producing such panels. 
A radiographic image conversion panel of the present invention comprises a 
support and at least one layer of photostimulable phosphor formed thereon 
by vapor deposition, and said layer of photostimulable phosphor comprises 
separate, oblong, prismatic crystals at a inclination with respect to the 
normal of the support. 
The gaps among said oblique, oblong, prismatic crystals is preferably 
packed with a substance of high reflectance or high absorption of light. 
In producing the panel, a vapor flow of the photostimulable phosphor is 
applied to the support at a particular angle of incidence with the normal 
direction of the support.

DETAILED DESCRIPTION OF THE INVENTION 
The present invention is described in detail below. 
FIG. 1 shows a partial section of the radiographic image conversion panel 
(also simply referred to as conversion panel) of the present invention. 
In the figure, 11 is a support, and 12 is a layer of photostimulable 
phosphor formed on the support 11. The layer of photostimulable phosphor 
12 comprises separate, oblong, prismatic crystals 13 grown by vapor 
deposition (oblique vapor deposition) at a particular angle .theta..sub.2 
with the normal direction R of the support 11, and fine gaps 14 are 
provided at the above angle among the prismatic crystals 13. 
For producing the separate, oblong, prismatic crystals 13 (i.e. fine gaps 
14), a vapor flow of the photostimulable phosphor (indicated by arrows) is 
applied to the support 11 held by the support holder 15 at a particular 
angle of incidence .theta..sub.2 with the normal direction R of the 
support 11, as shown in FIG. 2. For example, when the vapor flow of 
photostimulable phosphor 16 is deposited at an angle of incidence of 
.theta..sub.2 =60.degree., the angle of growth of the crystals 13 
(.theta..sub.1) is about 30.degree., and the shaded portions produced in 
the back of the crystals during their growth become fine gaps 14. 
In this case, for improving MTF (image modulation transfer function), it is 
preferable that the width of prismatic crystal 13 be about 1 to 50 .mu.m, 
more preferably 1 to 30 .mu.m. That is, when the prismatic crystal 13 is 
slenderer than 1 .mu.m, the MTF decreases because the stimulating 
excitation light is scattered by the prismatic crystals; also when the 
prismatic crystal 13 is wider than 50 .mu.m, the directivity of the 
stimulating excitation light decreases, thus causing MTF reduction. 
Also, the width of gaps 14 should preferably be less than 30 .mu.m, more 
preferably less than 5 .mu.m. When the width of gaps 14 exceeds 30 .mu.m, 
the packing ratio of the phosphor in the layer of phosphor becomes low, 
leading to sensitivity reduction. 
Methods of growing crystals of photostimulable phosphor on the support 11 
by applying a vapor flow 16 of the photostimulable phosphor to the support 
11 at an angle of incidence .theta..sub.2 include the method in which the 
support is inclined with respect to the crucible 16' containing a source 
of evaporation as shown in FIG. 3(a), the method in which the support 11 
is placed horizontally and the evaporation surface of the crucible 16' 
containing a source of evaporation is inclined as shown in FIG. 3(b), and 
the method in which the support 11 and the evaporation surface of the 
crucible 16' are both placed horizontally and the oblique component alone 
of the vapor flow 16 is deposited while being regulated using a regulatory 
material 11'. In these cases, it is appropriate to separate the support 
11' and the crucible 16' at the shortest distance of about 10 to 60 cm 
according to the average flight distance of the photostimulable phosphor. 
Note that the width of the above-mentioned prismatic crystal 13 tends to 
decrease as the temperature of the support 11 decreases. 
Although there is no particular limitation on the choice of the angle of 
growth .theta..sub.1, as long as it is greater than 0.degree. and smaller 
than 90.degree., it is preferably between 10.degree. and 70.degree. more 
preferably between 20.degree. and 55.degree.. The angle of incidence 
.theta..sub.2 may be chosen between 20.degree. and 80.degree., or 
40.degree. and 70.degree. to ensure the angle of growth .theta..sub.1 
being between 10.degree. and 70.degree., or 20.degree. and 55.degree. 
respectively. When the angle of growth .theta..sub.1 it is too great, the 
layer becomes brittle. It is of course possible, even when the angle is 
too great, to strengthen the layer by packing gaps 14 formed among the 
prismatic crystals with a packing material 17, such as a substance of high 
reflectivity or high absorption of light. 
The angle of growth .theta..sub.1 of the respective primatic crystal is 
preferably within the range of +5.degree. with respect to an average angle 
.theta..sub.1 of the crystals in a panel. 
The object of packing fine gaps 14 with packing material 17 is to 
strengthen the layer of photostimulable phosphor and almost completely 
prevent the transversal diffusion of the stimulating excitation light that 
goes into the layer of photostimulable phosphor. Accordingly, since the 
stimulating excitation light goes through the above-mentioned separate, 
oblong, prismatic crystals 13 and reaches the surface of the support while 
repeating reflection in the interface of gaps 14, it noticeably upgrades 
the sharpness of images produced by photostimulated luminescence. 
The substance of high reflectivity of light reflects light emitted from the 
photostimulable phosphor, whose wavelength is 500-900 nm, specifically 
600-800 nm, more than 70% regarding a standard white plate of magnesium 
oxide as 100%. The substance of high absorption of light absorbs the light 
emitted from the stimulable phosphor, and its transmittance is preferably 
less than 70% measured by means of a cell having a thickness of 10 mm 
regarding air as 100%. Both the reflectivity and the transmittance are 
measured by an optical densitometer model 557, made by Hitachi. 
Referring to the above-mentioned packing material 17, examples of 
substances of high reflectance include aluminum, magnesium, silver, 
indium, and other metals, a white pigment, a green or red coloring agent. 
The white pigment respects emitted light. Examples thereof is shown below. 
Examples of substances of high absorption include carbon, chromium oxide, 
nickel oxide, and iron oxide; and a blue coloring agent. 
Of these substances carbon absorbs light emitted from the photostimulable 
phosphor. 
The pigment should preferably be of a high reflectance for photostimulated 
luminescence; white pigment is especially preferable from this viewpoint. 
Examples of white pigments include TiO.sub.2 (anatase type, rutile type), 
MgO, 2PbCO.sub.3.Pb(OH).sub.2, BaSO.sub.4, Al.sub.2 O.sub.3, M.sup.II FX 
(at least one of M.sup.II Ba, Sr and Ca; X represents at least one of C'l 
and Br), CaCO.sub.3, ZnO, Sb.sub.2 O.sub.3, SiO.sub.2, ZrO.sub.2, Nb.sub.2 
O.sub.5, lithopone (BaSO.sub.4 +ZnS), magnesium silicate, basic lead 
siliconsulfate, basic lead phosphate, and aluminum silicate. Since these 
white pigments have a strong hiding power and great refractive index, they 
easily scatter photostimulated luminescence by reflection or refraction, 
thus permitting noticeable improvement of the sensitivity of the obtained 
radiographic image conversion panel. 
Any organic or inorganic coloring material can be used. Examples of organic 
coloring materials include Zapon Fast Blue 3G (produced by Hoechst), 
Estrol Brill Blue N-3RL (produced by Sumitomo Chemical), D & C Blue No. 1 
(produced by National Aniline), Spirit Blue (produced by Hodogaya 
Chemical), Oil Blue No. 603 (produced by Orient), Kiton Blue A (produced 
by Chiba-Geigy), Aizen Catiron Blue GLH (produced by Hodogaya Chemical), 
Lake Blue AFH (produced by Kyowa Sangyo), Primocyanine 6GX (produced by 
Inabata & Co.), Brill Acid Green 6BH (produced by Hodogaya Chemical), Cyan 
Blue BNRCS (produced by Toyo Ink), and Lionoil Blue (produced by Toyo 
Ink). Mention may also be made of organic metal complex salt coloring 
materials such as Color Index Nos. 24411, 23160, 74180, 74200, 22800, 
23150, 23155, 24401, 14830, 15050, 15760, 15707, 17941, 74220, 13425, 
13361, 13420, 11836, 74140, 74380, 74350, and 74460. Examples of inorganic 
coloring materials include ultramarine, cobalt blue, cerulean blue, 
chromium oxide, and TiO.sub.2 -ZnO-CoC-NiO pigments. 
The packing substance is introduced into the fine gaps whose width is 
preferably 1-30 .mu.m. The substance of fine particles having a diameter 
of several hundred micrometers may be introduced physically without 
previous processing. In case that the substance has lower melting point, 
it may be heated and introduced. The substance may be permeated into the 
gap when dissolved or dispersed in a liquid having suitable viscosity and 
is deposited by evaporation or modification by heating. The substance may 
be introduced into the gap by a gas phase deposition method. 
The photostimulable phosphor to be used as the above-mentioned source of 
evaporation is fed into a crucible after being uniformly dissolved or 
being shaped using a press or hot press. At that time, it is preferable to 
conduct degassing. The photostimulable phosphor is evaporated from the 
source of evaporation by scanning with an electron beam emitted from an 
electron gun, but other methods may be used to evaporate the phosphor. 
The source of evaporation should not necessarily be a photostimulable 
phosphor, and may be a mixture of starting materials for a photostimulable 
phosphor. 
An activator may be doped on the basic substance later. For example, Tl as 
an activator may be doped after vapor deposition of the basic substance 
RbBr alone. This is because satisfactory doping is possible even when the 
layer is thick, since the crystals are separate from each other, and MTF 
does not decrease since crystal growth is unlikely to occur. 
The activator may be doped into the prepared basic substance by a 
heat-diffusion or ion plating method. 
For improving the adhesion between the support 11 and the layer of 
photostimulable phosphor 12 to be adhered to the surface of the support, 
an adhesive layer or a reflection layer or absorption layer for 
stimulating excitation light and/or photostimulated luminescence may be 
previously prepared on the surface of support 11 as needed. 
Gas phase growth of the layer of photostimulable phosphor 12 can be 
achieved by the vapor deposition method, the sputtering method and the CVD 
method. 
In the vapor deposition method, the support is placed in a vapor deposition 
apparatus; the apparatus is then degassed to a degree of vacuum of about 
10.sup.-6 Torr; at least one layer of photostimulable phosphor as 
described above is heated and evaporated by the resistance heating method, 
the electron beam method, or other method to obliquely deposit the 
photostimulable phosphor on the surface of the support to the desired 
thickness. As a result, a layer of photostimulable phosphor containing no 
binder is formed; it is also possible to form a layer of photostimulable 
phosphor in two or more repetitions of the vapor deposition procedure. It 
is also possible to achieve vapor deposition using more than one 
resistance heaters or electron beams. In the vapor deposition method, it 
is also possible to vapor deposit material for photostimulable phosphor 
using more than one resistance heaters or electron beams to synthesize the 
desired photostimulable phosphor on the support and form a layer of 
photostimulable phosphor at a time. In the vapor deposition method, the 
subject of deposition may be cooled or heated during vapor deposition as 
needed. Heat treatment may be conducted on the layer of photostimulable 
phosphor after completion of vapor deposition. 
In the sputtering method, the support is placed in a sputtering apparatus; 
the apparatus is then degassed to a degree of vacuum of about 10 .sup.-6 
Torr as in the above vapor deposition method; an inert gas such as Ar or 
Ne, as the sputtering gas, is introduced into the apparatus to a gas 
pressure of 10.sup.-3 Torr. Oblique sputtering is then conducted on the 
photostimulable phosphor as the target to obliquely deposit the 
photostimulable phosphor on the surface of the support to the desired 
thickness. In this sputtering process, it is possible to form a layer of 
photostimulable phosphor in two or more repetitions as in the vapor 
deposition method, and also possible to form it by simultaneous or 
sequential sputtering of more than one targets of different 
photostimulable phosphors. Furthermore, in the sputtering method, it is 
possible to simultaneously or sequentially sputter more than one materials 
for photostimulable phosphor as the targets to synthesize the desired 
photostimulable phosphor on the support and form a layer of 
photostimulable phosphor at a time. Reactive sputtering may also be 
conducted in the presence of a gas such as 0.sub.2 or H.sub.2 as 
introduced as needed. In addition, the subject of deposition in the 
sputtering method may be cooled or heated as needed during sputtering. The 
photostimulable layer may also be subjected by heat treatment after 
sputtering. 
In the CVD method, a layer of photostimulable phosphor containing no binder 
is obtained on the support by decomposing an organic metal compound 
containing the desired photostimulable phosphor or a material therefor 
with heat, high frequency electric power, or other energy source. The 
method permits gas phase growth of a layer of photostimulable phosphor to 
separate, oblong, prismatic crystals at a particular inclination with 
respect to the normal direction of the support. 
Although the thickness of the layer of photostimulable phosphor of the 
radiographic image conversion panel of the present invention varies with 
the radiation sensitivity of the desired radiographic image conversion 
panel, the type of the photostimulable phosphor, and other factors, it is 
preferable to choose it in the range of 10 .mu.m to 1000 .mu.m, more 
preferably in the range of 20 .mu.m to 800 .mu.m. 
FIG. 5 shows the relationship between the thickness of the layer of 
photostimulable phosphor of the radiographic image conversion panel of the 
present invention, as well as the amount of adhered photostimulable 
phosphor corresponding to the layer thickness, and radiation sensitivity. 
As is evident in comparison with FIG. 9, which shows characteristics of a 
conventional panel, the layer of photostimulable phosphor of the 
radiographic image conversion panel of the present invention gives an 
adhesion amount (packing ratio) of photostimulable phosphor two times that 
of the conventional radiographic image conversion panel having binder, 
since the layer contains no binder; in the radiographic image conversion 
panel of the present invention, an improved radioabsorption ratio per unit 
thickness of the layer of photostimulable phosphor is obtained, leading to 
improvement of image graininess as well as higher radiation sensitivity, 
in comparison with the conventional radiographic conversion panel. 
In addition, containing no binder, the layer of photostimulable phosphor of 
the radiographic image conversion panel of the present invention has an 
excellent directional characteristics and is thus highly permeable for 
stimulating excitation light and photostimulated luminescence; therefore, 
it permits increasing the layer thickness over that of conventional 
radiographic image conversion panels. 
Furthermore, as stated above, the layer of photostimulable phosphor of the 
radiographic image conversion panel of the present invention has excellent 
directivity, thus mitigating scattering of stimulating excitation light in 
the layer of photostimulable phosphor and noticeably improving image 
sharpness. 
Various macromolecular materials, glass, metals, and other materials are 
used for the support for the present invention. Examples of preferable 
supports include plastic films such as cellulose acetate films, polyester 
films, polyethylene terephthalate films, polyamide films, polyimide films, 
triacetate films and polycarbonate films; metal sheets such as aluminum 
sheets, iron sheets and copper sheets; and metal sheets having a coating 
layer of any one of oxides of these metals. The surface of these supports 
may be smooth, or may be matted to improve adhesion with the layer of 
photostimulable phosphor. 
FIG. 6 shows a partial oblique view of the surface of a support and a 
section showing the state of deposition of a layer of photostimulable 
phosphor on the surface. As seen in FIG. 6(a), the support 11 has a 
surface structure in which separate, tile-like plates 11' are arranged. If 
oblique vapor deposition is conducted on the surface of the support 11, 
the layer of photostimulable phosphor 12 will be formed so that prismatic 
crystals 13 are isolated from each other at short intervals by gaps 14 and 
obliquely deposited while the outline of tile-like plates 11' is 
maintained by gaps 14', as seen in FIG. 7(b), and image sharpness will 
further improve. 
Although the thickness of the support varies with the material used and 
other factors, it is normally 80 .mu.m to 3 mm, and from the viewpoint of 
easy handling, it is preferably 200 .mu.m to 2 mm. 
In the radiographic image conversion panel of the present invention, a 
protective layer (not illustrated) for physical or chemical protection of 
the layer of photostimulable phosphor on the face opposite the face on 
which the support is laid. This protective layer may be formed by applying 
and drying a solution of a film-forming macromolecular substance in an 
appropriate solvent, as disclosed in Japanese Patent O.P.I. Publication 
No. 42500/1984, or may be adhered by applying an appropriate binder on one 
face of a film of a macromolecular substance. 
Examples of materials for the protective layer include cellulose 
derivatives such as cellulose acetate, nitrocellulose and methylcellulose, 
polymethyl methacrylate, polyvinyl butyral, polyvinyl formal, 
polycarbonate, polyester, polyethylene terephthalate, polyethylene, 
polyvinylidene chloride and nylon. It is normally preferable that the film 
thickness of these protective layers be about 1 .mu.m to 2000 .mu.m. 
The radiographic image conversion panel of the present invention, when used 
for the method of radiographic image conversion schematized in FIG. 7, 
provides excellent image sharpness, graininess and sensitivity. 
In FIG. 7, 61 is a radiation generator; 62 is a subject; 63 is a panel of 
the present application; 64 is a source of stimulating excitation light; 
65 is a photoelectric converter that detects the photostimulated 
luminescence radiated by the panel 63; 66 is an apparatus that reproduces 
the signals detected by the photoelectric converter 65 as images; 67 is a 
display apparatus for the reproduced images; 68 is a filter that separates 
stimulating excitation light and photostimulated luminescence and allow 
the photostimulated luminescence alone to pass through it. Note that the 
photoelectric converter 65 and other apparatuses represented by a greater 
number are not limited to the above descriptions, as long as they are 
capable of reproducing the optical information from the panel of the 
present applications 63 as images in any way. 
The radiation from the radiation generator 61 passes through the subject 62 
and goes into the panel of the present applications 63. The incident 
radiation is absorbed in the layer of photostimulable phosphor of the 
panel of the present application 63; its energy is accumulated therein and 
a cumulative image of the radiation transmission image is formed. This 
cumulative image is then excited by the stimulating excitation light from 
the source of stimulating excitation light 64 to emit photostimulated 
luminescence. Since the layer of photostimulable phosphor of the panel of 
the present application 63 contains no binder and thus shows high 
directivity, diffusion of stimulating excitation light in the layer of 
photostimulable phosphor is suppressed during scans with the above 
stimulating excitation light. 
Since the intensity of the radiated photostimulated luminescence is in 
proportion to the amount of accumulated radiation energy, it is possible 
to observe the radiation transmission image of the subject 62 by 
photoelectrically converting this optical signal using the photoelectric 
converter 65, e.g. a photomultiplier, reproducing it as an image using the 
image reproducer 66, and displaying it on the image display 67. 
The above-mentioned "photostimulable phosphor" means a phosphor which emits 
photostimulated luminescence corresponding to the amount of the irradiated 
starting light or high energy radiation in response to the optical, 
thermal, mechanical, chemical electric, or other stimulation (stimulating 
excitation) following the irradiation of the starting light or high energy 
radiation. However, from the viewpoint of practical application, it should 
be a phosphor which emits photostimulated luminescence in response to 
stimulating excitation light whose wavelength is preferably more than 500 
nm. Examples of the photostimulable phosphor for the radiographic image 
conversion panel of the present invention include the phosphor represented 
by BaSO.sub.4 : Ax, disclosed in Japanese Patent O.P.I. Publication No. 
80487/1973, the phosphor represented by MgSO.sub.4 : Ax, disclosed in 
Japanese Patent O.P.I. Publication No. 80488/1973, the phosphor 
represented by SrSO.sub.4 : Ax, disclosed in Japanese Patent O.P.I. 
Publication No. 80489/1973, the phosphor obtained by adding at least one 
of Mn, Dy, and Tb to Na.sub.2 SO.sub.4, CaSO.sub.4, BaSO.sub.4 etc., 
disclosed in Japanese Patent O.P.I. Publication No. 29889/1976, the 
phosphor such as BeO, LiF, MgSO.sub.4 and CaF.sub.2, disclosed in Japanese 
Patent O.P.I. Publication No. 30487/1977, the phosphors represented by 
Li.sub.2 B.sub.4 O.sub.7 : Cu, Ag, disclosed in Japanese Patent O.P.I. 
Publication No. 39277/1978, the phosphors such as Li.sub.2 O.(B.sub.2 
O.sub.2)x: Cu and Li.sub.2 O.(B.sub.2 O.sub.2)x: Cu, Ag, disclosed in 
Japanese Patent O.P.I. Publication No. 47883/1979, the phosphors 
represented by SrS: Ce, Sm, SrS: Eu, Sm, La.sub.2 O.sub.2 S: Eu, Sm, or 
(Zn, Cd)S: Mn.sub.x, disclosed in U.S. Pat. No. 3,859,527. Mention may 
also be made of the ZnS: Cu, Pb phosphor disclosed in Japanese Patent 
O.P.I. Publication No. 12142/1980, the barium aluminate phosphor 
represented by the formula BaO.Al.sub.2 O.sub.3 : Eu, and the alkaline 
earth metal silicate phosphor represented by the formula M.sup.II 
O.xSiO.sub.2 : A. 
Examples further include the alkaline earth fluoride halide phosphor 
represented by the formula (Ba.sub.1 -x-yMg x Cay)FX: Eu.sup.2+, disclosed 
in Japanese Patent O.P.I. Publication No. 12143/1980, the phosphor 
represented by the formula LnOX: xA.sub.1 disclosed in Japanese Patent 
O.P.I. Publication No. 12144/1980 the phosphor represented by a formula 
(Ba.sub.1 -xM.sup.II x)FX: yA, disclosed in Japanese Patent O.P.I. 
Publication No. 121451/1980, the phosphor represented by a formula BaFX: 
xCe, yA, disclosed in Japanese Patent O.P.I. Publication No. 84389/1980, 
the rare earth element activated divalent metal fluorohalide phosphor 
represented by the formula M.sup.II FX.xA: yLn, disclosed in Japanese 
Patent O.P.I. Publication No. 160078/1980 the phosphors represented by the 
formula ZnS: A, CdS: A, (Zn, Cd)S: A, X or Cds: A, X, the phosphor 
represented by any one of the formulas 
EQU xM.sub.3 (PO.sub.4).sub.2.NX.sub.2 : yA and M.sub.3 (PO.sub.4).sub.2 : yA, 
disclosed in Japanese Patent O.P.I. Publication No. 38278/1984, the 
phosphors represented by any one of the formulas nReX.sub.3.mAX'.sub.2 : 
xEu and nReX.sub.3.mAX'.sub.2 : xEu, ySm, disclosed in Japanese Patent 
O.P.I. Publication No. 155487/1984, the alkali halide phosphor represented 
by the formula M.sup.I X.aM.sup.II X'.sub.2.bM.sup.III X".sub.3 : cA, 
disclosed in Japanese Patent O.P.I. Publication No. 72087/1986, and the 
bismuth-activated alkali halide phosphor represented by the formula 
M.sup.I X: xBi, disclosed in Japanese Patent O.P.I. Publication No. 
228400/1986. 
Particularly, alkali halide phosphors are preferable, since they can easily 
be prepared as a layer of photostimulable phosphor by vapor deposition, 
sputtering, or other method. 
However, the photostimulable phosphor for the radiographic image conversion 
panel of the present invention is not limited to the above-mentioned 
phosphors; any phosphor can be used, as long as it emits photostimulated 
luminescence in response to irradiation of stimulating excitation light 
following irradiation of a radioactive ray. 
EXAMPLE 
The present invention is described in more detail by means of the following 
working example. 
On the surface of the heated a crystallized glass support of a thickness of 
1 m was vapor deposited an alkali halide phosphor (RbBr: 0.0006 Tl) at a 
condition shown in the Table with a vapor depositing apparatus shown in 
FIG. 14. In the FIG. 14, 11' is an aluminum slit which is placed at a 
distance of 60 cm from the source. The sample panels comprise a layer of 
photostimulable phosphor of a thickness of 300 .mu.m having gap width of 1 
.mu.m. 
Panel L is a comparative sample. Stimulating excitation light was applied 
to each panel in the directions a and b (45.degree.) and c as shown in 
FIG. 15 (1), and the direction of collecting emission of light was 
provided as shown in FIG. 15 (2); Relative sensitivity and sharpness were 
evaluated. 
1. Relative sensitivity 
Each test panel was irradiated with an X-ray of 80 KVp in an amount of 10 
mR from 1.5 m, and then it was stimulated with a semiconductor laser 
(Wavelength: 780 nm, Power at the surface of panel: 40 mW, irradiating 
spot diameter: 100 .mu.m). Intensity of emitted light was detected to give 
a relative sensitivity regarding the test number 3 as 100. 
2. Sharpness 
A CTF chart was attached to each panel for the evaluation of MTF. The panel 
was irradiated in the same way as mentioned above and emitted light was 
read out by stimulating laser light scanned along the CTF chart. Values T3 
which is a summation of MTF values at 0.5, 1.0 and 2.0 lp/mm is shown in 
Table. 
TABLE 
__________________________________________________________________________ 
Direction 
of Width 
Sam- 
excitation 
Direction of 
Angle of 
Angle of 
Temperature of 
Packing MTF Relative 
of 
No. 
ple 
laser 
reading 
incident .crclbar..sub.2 
growth .crclbar..sub.2 
heated support 
substance (T3) 
sensitivity 
crystal 
__________________________________________________________________________ 
1 A a Q 25.degree. 
15.degree. 
100.degree. C. 
-- 190 91 5.mu. 
2 B a Q 45.degree. 
23.degree. 
100.degree. C. 
-- 195 99 5.mu. 
3 C a Q 60.degree. 
30.degree. 
100.degree. C. 
-- 200 100 5.mu. 
4 b P 60.degree. 
30.degree. 
100.degree. C. 
-- 208 94 
5 c P 60.degree. 
30.degree. 
100.degree. C. 
-- 197 102 
6 D a Q 70.degree. 
46.degree. 
100.degree. C. 
-- 199 97 5.mu. 
7 E a Q 75.degree. 
58.degree. 
100.degree. C. 
-- 194 95 5.mu. 
8 F a Q 80.degree. 
69.degree. 
100.degree. C. 
-- 189 90 5.mu. 
9 G a Q 65.degree. 
32.degree. 
250.degree. C. 
-- 194 104 10.mu. 
10 H a Q 65.degree. 
33.degree. 
350.degree. C. 
-- 186 101 16.mu. 
11 I a Q 60.degree. 
30.degree. 
100.degree. C. 
Lionol Blue SL *1 
215 88 5.mu. 
12 J a Q 60.degree. 
30.degree. 
100.degree. C. 
Cyan Blue BNRCS *1 
217 89 5.mu. 
13 K a Q 60.degree. 
30.degree. 
100.degree. C. 
Titan white *2 
211 96 5.mu. 
14 L a Q 0 0 100.degree. C. 
-- 185 84 5.mu. 
15 b P 0 0 100.degree. C. 
-- 182 88 5.mu. 
__________________________________________________________________________ 
*1: Solved in toluen/ethanol mixture, deposited at 200.degree. C. 
*2: Anatase type T: O.sub.2, average particle size 0.05 .mu.m. 
Panels of the present invention showed a sensitivity almost equal to that 
of comparison panel Lm, but gave improved sharpness. That is, panels 
having separate, oblong, prismatic crystals grown in an angle between 
20.degree. and 55.degree. showed an advantage both in the sensitivity and 
the sharpness when the direction of collecting emitting light was provided 
in a direction closer to the angle of growth of the crystal. An advantage 
is obtained when the direction of incidence of stimulating excitation 
light is oblique. It is also evident that panels I, J and K of the present 
invention which contain a packing substance enhanced the effect of panel A 
of the present. 
As stated above, since the radiographic image conversion panel of the 
present invention, comprising a support and a layer of photostimulable 
phosphor formed thereon by gas phase deposition, is characterized by 
growing, by gas phase deposition, said layer of photostimulable phosphor 
to separate, oblong, prismatic crystals at a particular angle with the 
normal of the support, scattering of the stimulating excitation light in 
the layer of photostimulable phosphor is mitigated and image sharpness 
increases. 
In addition, since image sharpness does not decrease due to the increase in 
the thickness of the layer of photostimulable phosphor, sensitivity and 
graininess can be improved by increasing the layer thickness. 
Moreover, a radiographic image conversion panel having excellent 
characteristics as described above can be produced cheaply and stably the 
simple means oblique vapor deposition. 
Furthermore, since the present invention is also characterized by packing a 
substance of high reflectivity or high percent absorption of light or a 
coloring agent in the gaps among the prismatic crystals, the transversal 
diffusion of the stimulating excitation light which came into the layer of 
photostimulable phosphor can be almost completely prevented, and thus the 
sharpness of images formed by photostimulated luminescence can be 
noticeably increased.