Method of radiphotography using light-stimulable radiation image storage panel

A radiation image storage panel having a stimulable phosphor layer provided on a substrate with a honeycomb structure constituted of a number of cells partitioned by wall members filled with the stimulable phosphor is prepared by forming the substrate for phosphor layer by casting in a mother mold or etching of the substrate and filling the cells on the substrate with the stimulable phosphor. This radiation image storage panel can give images of markedly improved sharpness.

BACKGROUND OF THE INVENTION 
This invention relates to a radiation image storage panel using a 
stimulable phosphor, and more particularly to a radiation image storage 
panel capable of providing an image of high sharpness and methods for 
preparing the same. 
In the prior art, the so called radiophotography employing a silver salt 
for obtaining radiation images has been utilized. In recent years, 
particularly on account of the problem of exhaustion of silver resources 
on a global scale, it would be more desirable to picturize radiation 
images without recourse to a silver salt. 
As the substitute method for the above radiophotography, there is proposed 
the method in which radiation transmitted through an object to be 
photographed is absorbed in a phosphor, and then exciting the phosphor 
with a certain kind of energy to permit the radiation energy stored in the 
phosphor to be radiated as luminescence, which luminescence is in turn 
detected to produce an image. More specifically, for example, U.S. Pat. 
No. 3,859,527 and Japanese Unexamined Patent Publication No. 12144/1980 
propose a radiation image storage method in which a stimulable phosphor is 
used as the phosphor and electromagnetic radiation selected from visible 
light and IR-rays is used as the excitation energy. This storage method 
employs a panel having a stimulable phosphor layer formed on a support and 
obtains an image corresponding to the intensity of light by storing 
radiation energy corresponding to the intensity of the radiation 
transmitted through an object to be photographed in the stimulable 
phosphor layer of the panel and then scanning the stimulable phosphor 
layer with a stimulable excitation ray (hereinafter called merely as 
"excitation ray") thereby to take out the stored radiation energy as 
signals of light. The final images may be reproduced as a hard copy or 
reproduced on a CRT. 
As is well known in the art, sharpness of the image in the radiophotography 
of the prior art is determined depending on spreading of momentary 
emission (emission on irradiation of radiation) of the phosphor in the 
screen. In contrast, sharpness of the image in the radiation image storage 
method utilizing a stimulable phosphor as described above is not 
determined by spreading of the stimulated emission of the phosphor in the 
radiation image storage panel, namely spreading of emission of the 
phosphor as in the case of radiophotography, but determined depending on 
spreading of the excitation ray within the panel. For, according to the 
radiation image storage method, the radiation image information stored in 
the radiation image storage panel is taken out sequentially, and therefore 
the stimulated emission by the excitation ray irradiated at a certain 
period of time (t.sub.i) is collected desirably wholly and recorded as the 
output from a certain image element (x.sub.i, y.sub.i) on the panel on 
which the excitation ray is irradiated; if the excitation ray is spread 
through scattering, etc. within the panel to excite the phosphor existing 
outside of the irradiated image element, an output from a wider region 
than the image element is recorded as the output of the above image 
element (x.sub.i, y.sub.i). Accordingly, provided that the stimulated 
emission by the excitation ray irradiated at a certain period of time 
(t.sub.i) is only the emission from the image element (x.sub.i, y.sub.i) 
on the panel on which the excitation ray is directly irradiated, sharpness 
of the image obtained will not be influenced by the emission regardless of 
the extent of spreading thereof. 
The radiation image storage panel to be used in the radiation image storage 
method as described above has at least a phosphor layer comprising a 
stimulable phosphor. The phosphor layer is generally provided on an 
appropriate substrate. Further, as a usual practice, a protective layer 
for protecting physically or chemically the phosphor layer is provided on 
the layer surface on the side opposite to the surface to be contacted with 
the substrate. In such a radiation image storage panel of the prior art, 
the mean free path of the excitation ray within the phosphor layer will be 
elongated by scattering, etc. of the excitation ray, whereby the 
excitation ray is spread relatively greatly within the phosphor layer to 
be disadvantageously deteriorated markedly in sharpness, and improvement 
of this drawback is strongly desired. 
As the methods for improvement of sharpness of the radiation image storage 
device, there have been known the method in which white powder is 
incorporated in the phosphor layer of the radiation image storage panel, 
as disclosed in Japanese Unexamined Patent Publication No. 146447/1980, 
and the method in which the radiation image storage panel is colored so 
that the mean reflectance in the exicited wavelength region of the 
stimulable phosphor is smaller than the mean reflectance in the 
stimulation emission wavelength region of the stimulable phosphor as 
disclosed in Japanese Unexamined Patent Publication No. 163500/1980. 
However, these methods are not satisfactory, because improvement of 
sharpness will necessarily result in marked lowering in sensitivity. 
SUMMARY OF THE INVENTION 
This invention has been accomplished in view of the drawbacks as described 
above of the radiation image storage panel employing a stimulable 
phosphor, and an object of this invention is to provide a radiation image 
storage panel capable of providing images of high sharpness and methods 
for preparation thereof. 
We have made extensive studies on the radiation image storage panel 
employing a stimulable phosphor. As a consequence, in accordance with this 
invention, the radiation image storage panel which can accomplish the 
object as mentioned above is constituted of a radiation image storage 
panel having a stimulable phosphor layer wherein the stimulable phosphor 
is filled into respective cells in a honeycomb structure comprising a 
number of cells partitioned by partitioning wall members.

DESCRIPTION OF PREFERRED EMBODIMENTS 
FIG. 1 and FIG. 2 show an embodiment of the radiation image storage panel 
of this invention. 10 is a phosphor layer substrate. This substrate 10 is 
constituted of a bottom portion 11 and a partitioning member 12. The 
bottom portion 11 is not essentially required, but it is provided for the 
purpose of avoiding deformation of the partitioning member 12. Therefore, 
if the partitioning member 12 has a sufficiently great strength, no such 
bottom portion 11 is necessary. The partitioning wall has a structure as 
shown in FIG. 2, in which a large number of partitioning members are 
crossed over each other to form a large number of cells 13. The form of 
the cells 13 is not limited to that as shown in FIG. 2, but it may be 
circular as shown in FIG. 3 or any other shape such as hexagonal shape, 
rectangular shape and elliptical shape may be also employed. And it may be 
a groove as shown in FIG. 13. The arrangement of cells 13 is not also 
limited to that as shown in FIG. 2, but the arrangement as shown in FIG. 3 
may be also available. Any other desired arrangement may be available, 
provided that divided cells can be provided thereby. For prevention of 
moire, the shapes of the cells and/or arrangement of the cells should 
preferably be made random. Each of these cells is filled with a stimulable 
phosphor 14 to form a phosphor layer. The partitioning member 12 is 
preferably absorptive or reflective relative to the excitation ray and 
more preferably reflective for improvement of sensitivity. The bottom 
portion 11 may also be transmissive relative to the excitation ray. The 
partitioning member 12 may be preferably made of a material which can 
absorb or reflect the excitation ray or made by forming a layer absorbing 
or reflecting excitation ray thereon by means of coating or vapor 
deposition. 
The substrate 10 may be transmissive, absorptive or reflective of emission 
from the stimulable phosphor 14, but it is preferably reflective to 
emission for improvement of luminance. For making the substrate absorptive 
or reflective relative to emission, the substrate may be made of a 
material absorptive or reflective of emission, or made by forming a layer 
absorbing or reflecting emission by means of coating or vapor deposition. 
In the radiation image storage panel having such a constitution, the 
excitation ray for releasing the radiation energy stored in the stimulable 
phosphor 14 as the stimulated emission will proceed in all directions due 
to scattering, etc. and the excitation ray directed to the partitioning 
member 12 is absorbed (when the partitioning member is absorptive of the 
excitation ray) or reflected (when the partitioning member is reflective 
of the excitation ray). Also, the excitation ray directed to the bottom 
portion 1 will be absorbed (when the bottom portion material is absorptive 
of the excitation ray) in the bottom portion, reflected (when the bottom 
portion material is reflective of the excitation ray) by the bottom 
portion or transmitted (when the bottom portion material is transmissive 
of the excitation ray) through the bottom portion. 
Accordingly, in spreading of the excitation ray irradiated on one point on 
the radiation image storage panel as shown in FIG. 4, the skirts of spread 
are cut off by the partitioning member 12 to give a radiation image with 
good sharpness. 
The dimensions of the portion filled with a stimulable phosphor may be 
determined approximately with an aim to improve the image quality required 
for the radiation image storage panel employing a stimulable phosphor 
better than that of the prior art. A ratio of cell area in the top surface 
of the partitioning wall members is preferably 50% or more. It is 
preferable that cells have not more than 600 .mu.m across in the top 
surface of the partitioning wall. More specifically, as a measure, 
d.sub.1, d.sub.2, d.sub.3 and d.sub.4 may be made 10 .mu.m to 600 .mu.m, 
and the depth h.sub.1 about 30 .mu.m to 1000 .mu.m, whereby improved 
performance as compared with the radiation image storage panel of the 
prior art employing a stimulable phosphor can be obtained. The thickness 
of the partitioning wall W.sub.1 is preferably as thin as possible but in 
general may be made 10 to 300 .mu.m in view of preparation. 
In the radiation image storage panel of this invention, even when the 
stimulable phosphor may be deposited higher than the partitioning wall 
member 12 to give an appearance of the phosphor uniformly formed as shown 
in FIG. 5, provided that the height h.sub.2 from the top of the 
partitioning wall 12 is small (for example, in case h.sub.2 is not more 
than 0.4.times.h'.sub.2 wherein h'.sub.2 represents the height from the 
bottom portion), an effect of improved image quality similar to the case 
as shown in FIG. 1 can be obtained, although the image quality is slightly 
inferior as compared with the case of FIG. 1 wherein the surface of the 
upper face of the partitioning wall and the surface of stimulable phosphor 
are on the same level. Also, even in the case when the surface of the 
stimulable phosphor 14 is lower than the upper face of the partitioning 
wall 12 as shown in FIG. 6, an effect of improved image quality can be 
obtained similarly as in the case of FIG. 1. 
Further, in the case of a panel having a structure as shown in FIG. 7, 
wherein a partitioning wall member 12 is provided on a stimulable phosphor 
layer with a uniform height of h.sub.3 and the respective cells are filled 
with the stimulable phosphor, an effect of improved image quality can be 
obtained similarly as in the case of FIG. 1 (for example, in case h.sub.3 
is not more than 0.9.times.h'.sub.3 wherein h'.sub.3 represents the height 
of the partitioning wall member 12). In this case the partitioning wall 
member 12 is separate from the bottom portion 11 different from the case 
of the panel shown in FIG. 1. 
As the material to be used for the substrate for the phosphor layer of the 
radiation image storage panel in this invention, there may be employed 
various materials, such as various polymeric materials, glass, wool, 
cotton, paper, metals, etc., but they are not limitative of this 
invention. The substrate 10 for the phohsphor layer need not be made of 
one kind of material, but it may also be made of two or more kinds of 
materials. These substrates 10 for the phosphor layer may also have a 
subbing layer with adhesiveness to the phosphor on the face contacted with 
the phosphor within the cells, in order to hold more firmly the phosphor 
layer. When the substrate, in particular the bottom portion, for the 
phosphor layer employed is transmissive of the excitation ray, it is 
rendered possible to irradiate the radiation image storage panel with the 
excitation ray from the face on the opposite side to the face on which the 
phosphor layer is provided. 
The material to be used for the partitioning wall member may include 
various polymeric materials, glass, ceramic and metals, etc. Further, when 
the material itself is transparent, pigments or dyes in amount to make 
these materials opaque to the excitation ray or emitted light, may be 
contained in the material or opaque coated films may be provided on the 
inner walls of cells by vapor deposition or other means. The inner walls 
may further be subjected to mirror finishing by vapor deposition or 
chemical means to form reflective surfaces. Thus, there is no particular 
restriction with respect to the material for the partitioning wall member, 
only if the strength of the partitioning wall member during filling of the 
cells with the stimulable phosphor is taken into consideration. The 
stimulable phosphor to be used for the radiation image storage panel of 
this invention is a phosphor which exhibits stimulated emission by 
irradiation of excitation ray after irradiation of radiation as previously 
mentioned. From substantial aspect, it is preferably a phosphor exhibiting 
stimulated emission by the excitation ray with wavelengths of 500 to 800 
.mu.m. As the stimulable phosphor to be used in the radiation image 
storage panel of this invention, there may be included, for example, a 
phosphor represented by BaSO.sub.4 :Ax (wherein A is at least one kind of 
Dy, Tb and Tm, and x is 0.001.ltoreq.x&lt;1 mole %) as disclosed in Japanese 
Unexamined Patent Publication No. 80487/1973; a phosphor represented by 
MgSO.sub.4 :Ax (wherein A is at least one kind of Ho and Dy, and x is 
0.001.ltoreq.x&lt;1 mole %) as disclosed in Japanese Unexamined Patent 
Publication No. 80488/1973; a phosphor represented by SrSO.sub.4 :Ax 
(wherein A is at least one kind of Tm, Tb and Dy, and x is 
0.001.ltoreq.x&lt;1 mole %) as disclosed in Japanese Unexamined Patent 
Publication No. 80489/1973; a phosphor in which at least one kind of Mn, 
Dy and Tb is added to Na.sub.2 SO.sub.4, CaSO.sub.4, BaSO.sub.4 and the 
like as disclosed in Japanese Unexamined Patent Publication No. 
29889/1976; a phosphor such as of BeO, LiF, Mg.sub.2 SO.sub.4 and 
CAF.sub.2 as disclosed in Japanese Unexamined Patent Publication No. 
30487/1977; a phosphor of Li.sub.2 B.sub.4 O.sub.7 :Cu,Ag, etc. as 
disclosed in Japanese Unexamined Patent Publication No. 39277/1978; a 
phosphor such as Li.sub.2 O.(B.sub.2 O.sub.2)x:Cu (where x is 
2&lt;x.ltoreq.3) and Li.sub.2 O.(B.sub.2 O.sub.2)x:Cu,Ag (where x is 
2&lt;x.ltoreq.3) as disclosed in Japanese Unexamined Patent Publication No. 
47883/1979; a phosphor represented by SrS:Ce,Sm, SrS:Eu,Sm, La.sub.2 
O.sub.2 S:Eu, Sm and (Zn,Cd)S:Mn,X (where X is a halogen) as disclosed in 
U.S. Pat. No. 3,859,527; ZnS:Cu,Pb phosphor, a barium aluminate phosphor 
of the formula BaO.xAl.sub.2 O.sub.3 :Eu (where x is 
0.8.ltoreq.x.ltoreq.10 ) and an alkaline earth metal silicate type 
phosphor of the formula M.sup.II O.xSiO.sub.2 :A (where M.sup.II is Mg, 
Ca, Sr, Zm, Cd or Ba, A is at least one kind of Ce, Tb, Eu, Tm, Pb, Tl, Bi 
and Mn, and x is 0.5.ltoreq.x.ltoreq.2.5), as disclosed in Japanese 
Unexamined Patent Publication No. 12142/1980; an alkaline earth 
fluorohalide phosphor of the formula: (Ba.sub.1-x-y Mg.sub.x 
Ca.sub.y)FX:eEu.sup.2+ (where X is at least one of Br and Cl, x, y and e 
are numbers satisfying the conditions of 0&lt;x+y.ltoreq.0.6, xy.noteq.0 and 
10.sup.-6 .ltoreq.e.ltoreq.5.times.10.sup.-2, respectively) as disclosed 
in Japanese Unexamined Patent Publication No. 12143/1980; a phosphor of 
the formula:LnOX:xA (where Ln represents at least one of La, Y, Gd and Lu, 
X represents Cl and/or Br, A represents Ce and/or Tb, and x represents a 
number staifying 0&lt;x&lt;0.1) as disclosed in Japanese Unexamined Patent 
Publication No. 12144/1980; a phosphor of the formula: (Ba.sub.1-x 
M.sup.II x)FX:yA (where M.sup.II represents at least one of Ma, Ca, Sr, Zn 
and Cd, X represents at least one of Cl, Br and I, A represents at least 
one of Eu, Tb, Ce, Tm, Dy, Pr, Ho, Nd, Yb and Er, x and y are numbers 
satisfying the conditions of 0.ltoreq.x.ltoreq.0.6 and 
0.ltoreq.y.ltoreq.0.6) as disclosed in Japanese Unexamined Patent 
Publication No. 12145/1980; a phosphor of the formula: BaFX,xCe,yA (where 
X is at least one of Cl, Br and I, A is at least one of In, Tl, Gd, Sm and 
Zr, x and y are 0&lt;x.ltoreq.2x 10.sup.-1 and 0&lt;y.ltoreq.5.times.10.sup.-2, 
respectively) as disclosed in Japanese unexamined Patent Publication No. 
84389/1980; a phosphor of divalent metal fluorohalide activated with a 
rare earth element of the formula: M.sup.II FX: xA:yLn (where M.sup.II is 
at least one kind of Ba, Ca, Sr, Mg, Zn and Cd, A is at least one kind of 
BeO, MgO, CaO, SrO, BaO, ZnO, Al.sub.2 O.sub.3, Y.sub.2 O.sub.3, La.sub.2 
O.sub.3, In.sub.2 O.sub.3, SiO.sub.2, TiO.sub.2, ZrO.sub.2, GeO.sub.2 , 
SnO.sub.2, Nb.sub.2 O.sub.5, Ta.sub.2 O.sub.5 and ThO.sub.2, Ln is at 
least one of Eu, Tb, Ce, Tm, Dy, Pr, Ho, Nd, Yb, Er, Sm and Gd, X is at 
least one of Cl, Br and I, x and y are numbers satisfying the conditions 
of 5.times.10.sup.-5 .ltoreq.x.ltoreq.0.5 and 0&lt;y.ltoreq.0.2) as disclosed 
in Japanese Unexamined Patent Publication No. 160078/1980; a phosphor of 
the formula ZnS:A, CdS:A, (Zn, Cd)S:A, ZnS:A,X and CdS:A,X (where A is Cu, 
Ag, Au or Mn and X is a halogen); a phosphor of the formula [I] or [II] as 
disclosed in Japanese Patent Application No. 148285/1982: 
EQU xM.sub.3 (PO.sub.4).sub.2.NX.sub.2 :yA Formula [I] 
EQU M.sub.3 (PO.sub.4).sub.2 :yA Formula [II] 
(wherein M and N each represents at least one kind of Mg, Ca, Sr, Ba, Zn 
and Cd, X represents at least one kind of F, Cl, Br and I, A represents at 
least one kind of Eu, Tb, Ce, Tm, Dy, Pr, He, Nd, Yb, Er, Sb, Tl, Mn and 
Sn, and x and y are numbers satisfying 0&lt;x.ltoreq.6 and 
0.ltoreq.y.ltoreq.1, respectively); and a phosphor of the formula [III] or 
[IV]: 
EQU nReX.sub.3.mAX.sub.2 ':xEu Formula [III] 
EQU nReX.sub.3. mAX.sub.2 ':xEu.ySm Formula [IV] 
(wherein Re represents at least one kind of La, Gd, Y and Lu, A represents 
at least one kind of alkaline earth metals, Ba, Sr and Ca, X and X' 
represent at least one kind of F, Cl and Br, x and y are numbers 
satisfying the conditions of 1.times.10.sup.-4 &lt;x&lt;3.times.10.sup.-1, 
1.times.10.sup.-4 &lt;y&lt;1.times.10.sup.-1, and n/m satisfies the condition of 
1.times.10.sup.-3 &lt;n/m&lt;7.times.10.sup.-1). 
However, the phosphor to be used in the radiation image storage method 
according to this invention is not limited to the phosphors as mentioned 
above, but any phosphor may of course be available, provided that it can 
exhibit stimulated emission when irradiated with excitation ray after it 
is irradiated with a radiation. 
The stimulable phosphor to be employed may have a mean grain size which may 
be chosen suitably within the range of from 0.1 to 100 .mu.m in view of 
the sensitivity of the radiation image storage panel and graininess of the 
phosphor. More preferably, a phosphor with a mean grain size of 1 to 30 
.mu.m may be used. However, it is not preferred to use a grain size 
greater than the cells. 
In the radiation image storage panel of this invention, the stimulable 
phosphor as described above is generally dispersed in a suitable binder 
and filled into the cells. As the binder, there may be employed binders 
conventionally used for layer formation, including, for example, proteins 
such as gelatin, polysaccharides such as dextran, gum arabic, polyvinyl 
butyral, polyvinyl acetate, nitrocellulose, ethyl cellulose, vinylidene 
chloride-vinyl chloride copolymer, polymethyl methacrylate, vinyl 
chloride-vinyl acetate copolymer, polyurethane, cellulose acetate 
butyrate, polyvinyl alcohol and others. More preferably, a polyvinyl 
acetal resin shown by the following formula may be employed. 
##STR1## 
where R represents a lower alkyl group; and X, Y and Z are integral 
numbers which satisfy the following formulas. 
EQU 0.40&lt;X/(X+Y+Z)&lt;0.79 
EQU 0.20&lt;Y/(X+Y+Z)&lt;0.54 
EQU 0&lt;Z/(X+Y+Z)&lt;0.20 
EQU 100&lt;X+Y+Z&lt;3000 
The polyvinyl acetal resin is a copolymer composed of vinyl acetal, vinyl 
alcohol and vinyl acetate which can be prepared by the reaction between 
polyvinyl alcohol and aldehyde and the characteristic changes according to 
variation of these compositions. So in view of some properties such as 
solubility, adhesion and the like, it is preferable that the composition 
of the polyvinyl acetal resin is within the range as mentioned above. 
Further, R represents a lower alkyl group, especially an alkyl group 
having 1 to 8 carbon atoms, most preferably 1 to 4 carbon atoms. 
Preferred degree of polymerization of the polyvinyl acetal resin is in the 
range from 100 to 3000, more preferably from 150 to 2000 in view of 
softening point and others. Still further, a mixture of the polyvinyl 
acetal resins and one or more resins which have good compatibility with 
the polyvinyl acetal resin may be employed. These resins include, for 
example, a phenol resin, a melamine resin, an epoxy resin, a maleic resin, 
an alkyd resin, a sulfurylamide resin, a nitrocellulose, and the like. In 
that case, it is preferable that the amount of the polyvinyl acetal resin 
is more than 40% by weight, more preferably, more than 60% by weight. The 
polyvinyl acetal resin as the binder can be used for not only a radiation 
image storage panel which has a honeycomb structure but also general 
radiation storage panel which does not have any honeycomb structure. 
Generally, such a binder may be employed in an amount of 0.01 to 1 part by 
weight based on 1 part by weight of the stimulable phosphor. However, in 
view of the sensitivity and sharpness of the radiation image storage panel 
obtained, the binder should preferably be employed in an amount as small 
as possible, more preferably within the range from 0.03 to 0.2 part by 
weight when taking also easiness in coating into account. 
Further, in the radiation image storage panel of this invention, a 
protective film is generally provided on the surface exposed outside of 
the phosphor layer (the surface not shielded by the bottom portion of the 
phosphor layer substrate) for protecting physically and chemically the 
phosphor layer. The protective film may be formed by coating on the 
phosphor layer directly with a coating solution for protective film, or 
alternatively a protective film separately formed may be adhered onto the 
phosphor layer. The material for the protective film may be a conventional 
material for protective film such as nitrocellulose, ethyl cellulose, 
cellulose acetate, polyester such as polyethyleneterephthalate, etc. 
When the protective film transmits the stimulated emission and irradiation 
of excitation ray is practiced from the protective film side, those which 
can transmit excitation ray may be selected from the materials as 
mentioned above. 
The radiation image storage panel of this invention can give images having 
sharpness when employed in the radiation image storage process as 
schematically illustrated in FIG. 8. 
To describe in detail, in FIG. 8, 16 is a radiation generating device, 17 
is an object to be photographed, 18 is the radiation image storage panel 
of this invention, 19 is an excitation ray source for permitting the 
latent radiation image on the radiation image storage panel to be radiated 
as luminescence, 20 is a photoelectric transducer for detection of the 
photoelectricity radiated from the radiation image storage panel, 21 is an 
image reproducing device for reproducing the photoelectric transducing 
signals detected at the photoelectric transducer 20, 22 is an image 
display device for displaying images reproduced, 23 is a filter which cuts 
the reflected light from the light source 19 and permits only the light 
radiated from the radiation image storage panel 18 to transmit 
therethrough. The photoelectric transducer 20 through the image display 
device 22 may be any desired system which can reproduce the optical 
information from the radiation image storage panel 18 as an image in some 
form, and they are not limited to those as described above. 
For cutting of the reflected light from the light source, in place of using 
a filter, it is also possible to use the method as disclosed in Japanese 
Patent Application No. 124744/1982, wherein delay in emission is utilized 
for separation of the lights. 
As shown in FIG. 8, when a radiation is irradiated with an object to be 
photographed disposed between the radiation generating device 16 and the 
radiation image storage panel 18, the radiation will transmit through the 
object to be photographed 17 corresponding to the transmissivity at the 
respective portions, and the transmitted image (namely the image with 
strong and weak radiations) will be incident on the radiation image 
storage panel 18. The incident transmitted image is absorbed by the 
phosphor layer in the radiation image storage panel 18, whereby electrons 
and/or positive holes in numbers in proportion to the dosage of radiation 
absorbed within the phosphor layer will be generated and stored at the 
trap level of the phosphor. In other words, stimulable image (latent 
image) of the transmitted radiation image is formed. 
Next, this latent image is excited with an excitation ray to be radiated as 
the stimulated emission, thus effecting visualization. Since the phosphor 
layer in the radiation image storage panel 18 is divided into a number of 
cells with a partitioning wall member, spreading of the excitation ray 
within the phosphor layer is suppressed during excitation of the above 
phosphor layer. Intensity of the luminescence radiated is in proportion to 
the number of electrons and/or positive holes stored, namely in proportion 
to the intensity of the radiation energy absorbed in the phosphor layer in 
the radiation image storage panel 18, and this optical signal is 
transduced into an electrical signal by a photoelectric transducer 20 such 
as a photomultiplier tube, which electrical signal is reproduced as an 
image by means of the image reproducing device 21 and the image is 
displayed by the image display device 22. 
The method for preparation of the substrate constituted of the bottom 
portion and the partitioning member may be constituted either of the 
preparation method in which the above honeycomb structure is formed with 
the use of a mother mold (mold casting method) or of the preparation 
method in which the honeycomb structure is formed by etching of a 
substrate (etching method). 
In the aforesaid mold casting method, a large amount of substrates having 
the honeycomb structure can be prepared repeatedly at low cost and rapidly 
from one mother mold. On the other hand, according to the etching method, 
by utilization of photographic processes and others, honeycomb structures 
of precise and free shapes can be prepared, and there is no great 
limitation to the substrate materials. 
According to the mold casting method as described above, first a mother 
mold 24 is prepared as shown in FIG. 9 in a form conjugated with the 
phosphor layer substrate as shown in FIG. 1. This mother mold is prepared 
by forming grooves having a width W.sub.2 and depth h.sub.4 slightly 
greater than those of W.sub.1 and h.sub.1 shown in FIG. 1 with a diamond 
blade on the surface of a flat plate comprising a silicon crystal 
material. Then, a molding material is casted into the mother mold. This 
molding material may preferably a material, such as a white silicone 
rubber mixed with titanium oxide as the pigment, which transmits 
substantially no excitation ray through the partitioning wall after 
finishing, and can be molded with good flowability, excellent mold release 
property and small shrinkage. After the molding material is solidified, it 
is released from the mother mold to obtain a phosphor layer substrate as 
shown in FIG. 1. By filling the respective cells on this substrate with a 
phosphor, the radiation image storage panel of this invention can be 
prepared. 
Next, according to the etching method, when, for example, a photosensitive 
plate is used, a mask of which opaque portions to light have an 
island-like pattern is closely contacted on the surface of a nylon 
photosensitive resin (e.g. Printite, produced by Toyo Boseki Co., Ltd.) 
and UV-ray including the wavelengths within a photosensitive wavelength 
region of 250 to 400 nm is irradiated thereon. After light exposure, the 
photosensitive resin is developed. By this development, the non-exposed 
portions in the case of the above photosensitive resin are flown away, 
whereby the phosphor layer substrate 25 is formed as shown in FIG. 10. By 
filling the cells framed by this substrate 25 with a phosphor, the 
radiation image storage panel can be prepared. Also, in this case, since 
the photosensitive resins are generally transparent, a light-absorbing 
material or a light-reflective material 26 is provided on the inner 
surface of the partitioning walls of the cells by coating or vapor 
deposition as shown in FIG. 11. 
Further, the preparation method employing etching of a metal plate is now 
explained. First, on both surfaces of, for example, a nickel plate, a 
photosensitive resin AZ-1350 commercially available from Sippley Co. is 
evenly coated. Then, masks having an island-like pattern of the light 
transmitting portion is closely contacted on both surfaces of the above 
nickel plate so that the patterns on both surfaces may correspond to each 
other, and subjected to exposure with UV-ray. After exposure, the 
photosensitive resin is developed, whereby the exposed portions of the 
above photosensitive resin are flown away. Subsequently, after the nickel 
plate is baked at 120.degree. C. for 30 minutes, the nickel plate is 
etched with an acid to form a partitioning wall member 27 as shown in FIG. 
12. The partitioning wall member 27 is adhered to the bottom portion of, 
for example, polyethylene terephthalate 28, to form a phosphor layer 
substrate. By filling the cells (on the substrate) with a phosphor, the 
radiation image storage panel can be prepared. 
As described above, the radiation image storage panel, wherein the phosphor 
layer are divided into a number of parts by partitioning wall members and 
the excitation ray can be suppressed from spreading within the phosphor 
layers, can give images of markedly improved sharpness, and therefore it 
is of very high commercial value. 
This invention is further illustrated by referring to the following 
Examples. 
EXAMPLE 1 
On the surface of a nylon photosensitive resin (Printite, produced by Toyo 
Boseki Co., Ltd.) was closely contacted a mask having an island-like 
pattern of the non-transmissive portion, followed by exposure to UV-ray 
for one minute. After exposure, the photosensitive resin was devloped with 
water to prepare a phosphor layer substrate as shown in FIG. 10. The cells 
on this substrate had dimensions of d.sub.1 =d.sub.2 =100 .mu.m, and 
h.sub.1 =200 .mu.m and a thickness of the partitioning wall of W.sub.1 =40 
.mu.m and W.sub.3 =70 .mu.m. An aluminum layer with a reflectance of 80% 
was also deposited on the inner walls of the cells by vapor deposition 
(under vacuum of 2.times.10.sup.-5 Torr under heating). 
As the next step, 8 parts by weight of BaFBr:Eu phosphor with a mean grain 
size of 2 .mu.m and 1 part by weight of a polyvinyl butyral (binder) were 
mixed and dispersed with the use of a solvent (cyclohexanone) to prepare a 
coating solution. This coating solution was applied evenly on the above 
phosphor layer substrate horizontally placed to fill the respective cells 
with the phosphor, and the coated substrate was left to stand overnight to 
prepare a radiation image storage panel A. 
Separately, the above procedure was repeated except that the above coating 
solution was applied to a dry film thickness of 200 .mu.m on a 
polyethylene terephthalate film horizontally placed without using the 
above phosphor layer substrate to obtain a radiation image storage panel B 
for Control. 
Separately, a panel B' for control was obtained by the same procedure as 
the panel B except that as a substrate Printite having the same aluminum 
layer as the panel A thereon is used instead of the polyethylene 
terephthalate film. 
Then, the above radiation image storage panels A, B and B' were each 
irradiated with an X-ray of a tube voltage of 80 KVp, scanned with a He-Ne 
laser beam of 150 .mu.m .phi. to excite the phosphor, the emission from 
the phosphor was received by means of a light receiving means 
(photomultiplier tube) to be converted into electrical signals, followed 
by reproduction thereof into images by means of an image reproducing 
device, which were then displayed on a display device. The modulation 
transmission functions (MTF) for the respective images were examined. The 
results are shown in Table 1. 
TABLE 1 
______________________________________ 
Spatial frequency (LP/mm) 
Panel 0 0.5 1 1.5 2 2.5 3 4 
______________________________________ 
A 100(%) 95 90 81 72 66 58 26 
B 100 90 61 43 30 24 17 6 
B' 100 86 56 38 25 20 12 3 
______________________________________ 
As apparently seen from the above Table 1, the radiation image storage 
panel A having the phosphor layer divided gives images of extremely high 
sharpness as compared with the radiation image storage panel B or B' of 
the prior art. 
EXAMPLE 2 
By etching a nickel plate and contacting the etched nickel plate to a 
polyethylene terephthalate film, a phosphor layer substrate as shown in 
FIG. 12 was prepared. The cells on this substrate had dimensions of 
d.sub.1 =d.sub.2 =120 .mu.m, h.sub.1 =190 .mu.m and a thickness of the 
partitioning wall at its minimum of 35 .mu.m. Subsequently, a coating 
solution was prepared in the same manner as in Example 1 by use of a 
0.1YF.sub.3.0.9BaFBr:Eu phosphor in place of the BaFBr:Eu phosphor of 
Example 1, followed by coating and drying similarly as in Example 1, to 
prepare a radiation image storage panel C. 
On the other hand, separately, the above procedure was repeated except that 
the above coating solution was applied to a dry film thickness of 190 
.mu.m on a polyethylene terephthalate film horizontally placed without 
using the above phosphor layer substrate to obtain a radiation image 
storage panel D for Control. MTF values of the images obtained by storage 
the radiation images similarly as in Example 1 are shown in Table 2 below. 
TABLE 2 
______________________________________ 
Spatial frequency (LP/mm) 
Panel 0 0.5 1 1.5 2 2.5 3 4 
______________________________________ 
C 100(%) 96 92 84 75 67 60 30 
D 100 92 63 41 30 26 18 7 
______________________________________ 
As apparently seen from the above Table 2, the radiation image storage 
panel C having the phosphor layer divided gives images of extremely high 
sharpness as compared with the radiation image storage panel D of the 
prior art. 
As the effect of the present invention, simultaneously with accomplishment 
of the object of this invention, a general method for improvement of 
sharpness in the radiation image storage method employing a stimulable 
phosphor could be provided, thus contributing to the progress of this 
technical field.