JP2583418B2 - Radiation image forming method - Google Patents

Description

Description: FIELD OF THE INVENTION The present invention relates to a radiation image forming method using a screen / film photographing system.

[Technical Background and Prior Art of the Invention] In radiographic photography in various fields such as medical radiography such as X-ray photography for medical diagnosis and industrial radiography for non-destructive inspection of substances. A radiographic intensifying screen (intensifying screen) is used so as to be in close contact with one side or both sides of a radiographic film (for example, an X-ray film).

The radiographic film has a basic structure comprising a support and a photographic emulsion layer provided on one or both sides thereof and comprising a binder containing and supporting silver halide in a dispersed state.

The radiographic intensifying screen has a basic structure including a support and a phosphor layer provided on one surface thereof. The phosphor layer is made of a binder that contains and supports the phosphor particles in a dispersed state, and the phosphor particles have a property of emitting high-luminance light when excited by radiation such as X-rays. is there. Therefore, the phosphor emits light of high brightness in accordance with the amount of radiation that has passed through the subject, and the radiographic film, which is placed in contact with the surface of the phosphor layer of the radiographic intensifying screen, is superposed on this phosphor. Since the body is also sensitized by light emission from the body, sufficient exposure of the radiation film can be achieved with a relatively small radiation dose.

Conventionally, a radiographic film having a structure in which a photographic emulsion layer is provided on both sides of a support to enhance the sensitivity and image quality of a radiographic film (double-sided film)
And a radiographic intensifying screen (a front screen located on the radiation incident side and a back screen located behind the radiation film on the opposite side) arranged on both sides of the film. Film-based).

In general, the sensitivity and image quality (sharpness, granularity) of the above-described imaging system largely depend on the characteristics of the radiation intensifying screen incorporated in the system. Therefore, the radiation intensifying screen must have a high sensitivity to minimize the exposure dose of the subject as much as possible (that is, the phosphor has a high absorption efficiency for radiation and a high radiation efficiency of the fluorescent light from the screen surface). Is desirable, and it is desired to provide an image having excellent image quality (sharpness, granularity, etc.).

Conventionally, with the aim of increasing the sharpness of the image,
A technique has been proposed in which phosphor particles are arranged so that the particle diameter of the phosphor constituting the phosphor layer of the radiation intensifying screen is large on the screen surface side (the side from which fluorescence is extracted) and small on the support side. No.55-33560, JP5
No. 8-71500). When such intensifying screens are respectively arranged on both sides of the radiographic film, it is possible to obtain high sensitivity because the particle diameter of the phosphor near the film is relatively large, in other words, the phosphor When the sensitivity is the same as that of a known intensifying screen having a uniform particle diameter in the thickness direction, sharpness can be increased. Also,
Since the phosphor particles having a small particle diameter on the support side serve as a reflective layer, the fluorescent light reflection and scattered light paths can be shortened and taken out from the screen surface, which also increases the sharpness (low frequency region). Enhanced.

In general, the larger the particle size of the phosphor, the higher the sensitivity of the radiographic intensifying screen, and conversely, the smaller the particle size, the better the sharpness and granularity of the image.

[Summary of the Invention] It is an object of the present invention to provide a radiation image forming method which provides an image with high sensitivity and improved sharpness and granularity.

An object of the present invention is to provide a radiographic image forming method using a screen / film photographing system in which radiographic intensifying screens are respectively disposed on the front and rear surfaces of a radiographic film. The phosphor particles constituting the phosphor layer of the radiation intensifying screen on the radiation incident side have a particle diameter from the screen surface side facing the film toward the support side. Are arranged so as to be smaller, and the phosphor particles constituting the phosphor layer of the radiation intensifying screen on the side opposite to the radiation incident side have a particle diameter from the screen surface side facing the film toward the support side. This can be achieved by the radiation image forming method of the present invention, which is arranged so as to be large.

In the present invention, the screen surface means the surface on the side opposite to the support, and means the surface of the phosphor layer or, if a protective film is provided thereon, the surface of the protective film.

The inventors of the present invention have conducted repeated studies to obtain images with improved image quality in a radiographic image forming method using a radiographic system in which secondary radiographic intensifying screens are arranged on both sides of a radiographic film. The effect of the particle size of the phosphor constituting the phosphor layer of the sensitive screen on the imaging system was found to be different between the front side and the back side. From this, the phosphor layers of both screens were moved in a specific direction. By adopting a configuration in which the particle diameter is changed, it is possible to obtain an image having high sharpness and excellent granularity without lowering the sensitivity.

That is, in the radiation intensifying screen (front screen) on the radiation incident side, the particle diameter of the phosphor constituting the phosphor layer is on the screen surface side (on the side from which fluorescence is taken out and on the side facing the radiation film). ) From the support side to the support side, while the particle size of the phosphor decreases from the support side to the screen surface side in the radiation intensifying screen (back screen) on the opposite side. To

By placing an intensifying screen in which phosphor particles are arranged so that the particle diameter increases along the radiation incident direction on the back side of the imaging system, relatively small phosphor particles gather on the film side. Therefore, the sharpness and the graininess of the image can be significantly improved. In particular, an intensifying screen having such a configuration has not been known so far, and according to the screen, an image having uniformity in sharpness and graininess can be obtained.

Also, on the front side, an intensifying screen in which phosphor particles are arranged so that the particle diameter increases along the direction that is the direction of incidence of radiation and the direction that is also the direction of extraction of fluorescence is arranged, so that the film The sensitivity can be increased because phosphor particles with relatively large particle diameters are gathered nearby, and the sharpness of the image is maintained at the same level as a conventional intensifying screen in which the particle diameter distribution is uniform in the thickness direction. be able to.

And, by combining these characteristics of both front screen and back screen, sensitivity,
It is possible to obtain a photographing system which is excellent in all points of sharpness and granularity, that is, which is well-balanced in characteristics.

[Structure of the Invention] The radiographic intensifying screen (front screen and back screen) used in the present invention basically comprises a support and a phosphor layer provided thereon.

The radiographic intensifying screen can be manufactured, for example, by the following method.

The support can be appropriately selected from various materials used as supports for intensifying screens (or intensifying screens) in conventional radiography. Examples of such materials include films of plastic substances such as cellulose acetate and polyethylene terephthalate, metal sheets such as aluminum foil, ordinary paper, baryta paper, and resin-coated paper. A preferred support material in the present invention is a plastic film,
In this plastic film, a light-absorbing substance such as carbon black may be kneaded for the purpose of improving sharpness, or a light-reflecting substance such as titanium dioxide is kneaded for the purpose of increasing sensitivity. You may.

The surface of the support on the side where the phosphor layer is provided,
An adhesiveness-imparting layer, a light-reflecting layer, a light-absorbing layer, and the like may be provided, and fine irregularities may be uniformly formed as described in JP-A-58-182599. (The irregularities are formed on the surface of the support by an adhesion imparting layer, a light reflecting layer,
When a light absorbing layer or the like is provided, it is formed on the surface thereof).

 Next, a phosphor layer is formed on the support.

The phosphor layer of the radiation intensifying screen, which is a characteristic requirement of the present invention, is a layer made of a binder that contains and supports phosphor particles in a dispersed state.

Various kinds of phosphors are already known. Examples of the phosphor which preferably emits light in the near ultraviolet to visible region to be used in the present invention include the following compounds.

Tungstate phosphors (CaWO ₄ , MgWO ₄ , CaWO ₄ : Tb
Terbium-activated rare earth oxysulfide phosphor [Y ₂ O ₂ S:
Tb, Gd ₂ O ₂ S: Tb, La ₂ O ₂ S: Tb, (Y, Gd) ₂ O ₂ S: Tb, (Y, G
d) ₂ O ₂ S: Tb, Tm, etc.], terbium-activated rare earth phosphate-based phosphors (YPO ₄ : Tb, GdPO ₄ : Tb, LaPO ₄ : Tb, etc.), terbium-activated rare earth oxyhalide phosphors (LaOBr : Tb 、 La
OBr: Tb, Tm, LaOCl: Tb, LaOCl: Tb, Tm, GdOBr: Tb, GdOCl:
Tb etc.), thulium-activated rare earth oxyhalide-based phosphors (LaOBr: Tm, LaOCl: Tm, etc.), barium sulfate-based phosphors [BaSO ₄ : Pb, BaSO ₄ : Eu ²⁺ , (Ba, Sr) SO ₄ : Eu ²⁺ etc.], divalent europium activated alkaline earth metal phosphate phosphors [Ba ₃ (PO ₄ ) ₂ : Eu ²⁺ , (Ba, Sr) ₃ (PO ₄ ) ₂ : Eu ²⁺ etc.],
Divalent europium activated alkaline earth metal fluoride halide-based phosphor [BaFCl: Eu ²⁺ , BaFBr: Eu ²⁺ , BaFCl: Eu ²⁺ , T
b 、 BaFBr: Eu ²⁺ , Tb 、 BaF ₂・ BaCl ₂・ KCl: Eu ₂ ⁺ 、 BaF ₂・ BaC
l ₂ xBaSO ₄ KCl: Eu ²⁺ , (Ba, Mg) F ₂ BaCl ₂ KCl: E
u ²⁺ ] and other iodide-based phosphors (CsI: Na, CsI: Tl, NaI, KI: T
l), sulfide-based phosphors [ZnS: Ag, (Zn, Cd) S: Ag, (Z
n, Cd) S: Cu, (Zn, Cd) S: Cu, Al etc.], hafnium phosphate based phosphor (HfP ₂ O ₇ : Cu etc.), europium activated rare earth oxysulfide based phosphor [Y ₂ O ₂ S: Eu, Gd ₂ O ₂ S: Eu, La ₂ O ₂ S: Eu,
(Y, Gd) ₂ O ₂ S: Eu, etc.], europium-activated rare earth oxide-based phosphor (Y ₂ O ₃ : Eu, Gd ₂ O ₃ : Eu, La ₂ O ₃ : Eu, (Y, Gd)
₂ O ₃ : Eu], europium activated rare earth phosphate phosphor (YP
O ₄ : Eu, GdPO ₄ : Eu, LaPO ₄ : Eu, etc.) and europium-activated rare earth vanadate phosphors (YVO ₄ : Eu, GdVO ₄ : E
u, LaVO ₄ : Eu, (Y, Gd) VO ₄ : Eu].

The phosphor used in the present invention is not limited to these, and any phosphor may be used as long as it emits light in the near ultraviolet region or visible region upon irradiation with radiation.

However, it is necessary to prepare phosphor particles having different particle diameters. Specifically, two or more kinds of phosphors having different average particle diameters are prepared. For example, a phosphor having an average particle diameter in a range of 8 to 15 μm is prepared as a phosphor having a large particle diameter, and a phosphor having an average particle diameter in a range of 2 to 5 μm is prepared as a phosphor having a small particle diameter. I do. Preferably, three types of phosphors having an average particle diameter in the range of 8 to 15 μm, 5 to 8 μm, and 2 to 5 μm, respectively, are prepared.

In the formation of the phosphor layer, first, for each kind of the phosphor having a different average particle diameter, the phosphor particles and the binder are mixed with a suitable solvent (for example, lower alcohol, chlorine atom-containing hydrocarbon, ketone, ester, Ether, etc.) and thoroughly mixing to prepare a coating solution in which the phosphor is uniformly dispersed in the binder solution.

Examples of the binder include binders represented by proteins such as gelatin, and synthetic polymer substances such as polyvinyl acetate, nitrocellulose, polyurethane, polyvinyl alcohol, polyalkyl (meth) acrylate, and linear polyester. Can be mentioned. The mixing ratio between the binder and the phosphor in the coating solution is usually selected from the range of 1: 8 to 1:40 (weight ratio).

These coating solutions are evenly and simultaneously applied on the surface of the support in a multilayer manner to form a coating film of the coating solution and then dried to complete the formation of the phosphor layer on the support. At this time, in the case of manufacturing a front screen, a coating liquid containing the phosphor particles having the smallest average particle diameter is arranged on the support side, and the coating liquid containing the phosphor particles having the larger average particle diameter becomes farther away from the support. The liquid is arranged and simultaneous multilayer coating is performed. In the case of manufacturing a back screen, on the contrary, a coating solution containing the largest phosphor particles having an average particle diameter is arranged on the support side,
Simultaneous multi-layer coating is performed by arranging a coating solution containing phosphor particles having a smaller average particle diameter as the distance from the support increases.

Alternatively, a multilayer phosphor layer may be formed on the support by repeating the operation of coating and drying each coating solution one by one. The thickness of the phosphor layer is generally 50 to
500 μm.

Further, a transparent protective film for physically and chemically protecting the phosphor layer may be provided on the surface of the phosphor layer opposite to the side in contact with the support. Examples of the material used for the transparent protective film include cellulose acetate, polymethyl methacrylate, polyethylene terephthalate, and polyethylene. The thickness of the transparent protective film is usually about 3 to 20 μm.

In this way, the front screen in which the phosphor particles are arranged so that the particle size decreases from the screen surface side toward the support, and the phosphor such that the particle size increases from the screen surface side toward the support side A back screen in which the particles are arranged is obtained.

The radiation film used in the radiation image forming method of the present invention comprises, as a basic structure, a support and photographic emulsion layers provided on both sides thereof.

Examples of the material of the support include a film of a plastic substance such as polyethylene terephthalate. The plastic film may be colored with a suitable coloring agent such as a blue dye or a red dye in order to block the crossover light and further improve the image quality of the image.

The photographic emulsion layer comprises a binder such as gelatin which contains and supports silver halide in a dispersed state. For example, a photographic emulsion layer having sensitivity in the blue region, that is, having a regular sensitivity,
It can be formed by coating a gelatin solution in which silver iodobromide (AgBrI) grains are dispersed on a support and drying. In addition, a photographic emulsion layer having sensitivity in the green region (ie, ortho-sensitivity) and a photographic emulsion layer having sensitivity in the red region (ie, panchromatic type) have, for example, an increase in silver iodobromide grains such as a red dye. It can be obtained by using a substance to which a dye is adsorbed.

The silver halide may be spherical grains or tabular grains. The silver halide is contained in an amount in per unit area both surfaces of 2 to 10 g / m ² of the emulsion layer, preferably in the range of 3 to 5 g / m ^2. In addition, as the red dye, a cyanine dye, a merocyanine dye, or the like can be used. The thickness of the emulsion layer is usually in the range of 1 to 20 μm.

Further, a protective layer made of gelatin or the like is provided to physically and chemically protect the photographic emulsion layers on both sides.

Next, a radiation image forming method of the present invention using an imaging system in which a front screen and a back screen each having a different phosphor particle diameter in the thickness direction of the phosphor layer will be described with reference to the accompanying drawings.

FIG. 1 is a view schematically showing an example of the radiation image forming method of the present invention, and FIG. 2 is an enlarged sectional view of the photographing system shown in FIG.

In FIG. 1, the screen / film photographing system 3 comprises:
It comprises a radiographic film 5 arranged at the center and two radiographic intensifying screens 4 and 6 arranged on both sides thereof. The intensifying screen 4 is a front screen located on the X-ray incident side, and the intensifying screen 6 is a back screen located behind the radiation film 5. That is, the two screens 4 and 6 are arranged before and after the radiation film 5. The imaging system 3 is arranged so as to face the radiation generator 1 with the subject 2 interposed therebetween.

As shown in FIG. 2, the front screen 4 is composed of a support 4a, a phosphor layer 4b, and a protective film 4c in this order, and faces the radiation film 5 on the protective film side surface. Phosphor layer 4b
The phosphor particles in the inside are arranged such that the particle diameter gradually increases from the support side toward the screen surface side (in the X-ray incident direction and in the fluorescence extraction direction). The back screen 6 is composed of a support 6a, a phosphor layer 6b and a protective film 6c in this order, and faces the radiation film 5 on the protective film side surface. The phosphor particles in the phosphor layer 6b are arranged such that the particle diameter gradually increases from the screen surface side toward the support side (in the X-ray incident direction). The radiation film 5 comprises photographic emulsion layers 5b and 5b 'and protective layers 5c and 5c' provided on both sides of a support 5a.

After the radiation radiated from the radiation generator 1 passes through the subject 2, a part thereof is absorbed by the phosphor particles of the screen 4 and converted into fluorescent light, and the light exposes the adjacent film 5. On the other hand, the remaining radiation passes through the screen 4 and the film 5 and is then absorbed by the phosphor particles of the screen 6 and converted into fluorescence, and this light further exposes the adjacent film 5.

In this way, a radiation image of the subject is formed on the radiation film 5, and after photographing, the film is developed to obtain a visible image on the film.

Normally, the reflection and scattering of the fluorescent light on the back screen greatly affects the image quality. However, since the phosphor particles having a small particle diameter are present on the film side of the back screen 6, the granularity of the image is remarkably improved. At the same time, the sharpness of the image can be significantly enhanced by minimizing the reflection and scattered light paths of the fluorescent light.

Further, the front screen 4 can have high sensitivity because the phosphor particles having a large particle diameter exist on the film side that greatly contributes to image formation. In general, the smaller the particle size, the higher the sharpness. However, since it is on the X-ray incidence side, the sharpness is given by giving an image with sharpness equivalent to that of a conventional screen whose particle size distribution is constant in the thickness direction. It does not lower.

Next, examples and comparative examples of the present invention will be described. However, these examples do not limit the present invention.

First, three types of radiographic intensifying screens were prepared by the following method.

(1) Production of radiographic intensifying screen I Terbium-activated gadolinium oxysulfide phosphor particles (Gd ₂ O ₂ S: Tb, average particle size: 4.4 μm), and linear polyester (Vylon # 500, manufactured by Toyobo Co., Ltd.) And nitrification degree 1
Mixture with 1.5% nitrocellulose (weight mixing ratio, 8:
2) was added to methyl ethyl ketone to prepare a dispersion containing the phosphor particles in a dispersed state. Further, tricresyl phosphate, n-butanol and methyl ethyl ketone are added to the dispersion, and the mixture is sufficiently stirred and mixed using a propeller mixer to uniformly disperse the phosphor particles, and the mixing ratio between the phosphor and the binder is 10%. : 1 (weight ratio) and viscosity 25-35
A coating solution A of PS (25 ° C.) was prepared.

A coating solution B was prepared by performing the same operation as described above except that terbium-activated gadolinium oxysulfide phosphor particles (average particle diameter: 6.0 μm) were used. Further, a coating solution C was prepared by performing the same operation as described above except that terbium-activated gadolinium oxysulfide phosphor particles (average particle diameter: 9.6 μm) were used.

Next, a titanium dioxide kneaded polyethylene terephthalate sheet (support, thickness: 2) placed horizontally on a glass plate
Coating solutions A, B, and C are arranged in this order on the surface of the support in the order of distance from the support, and the layers are uniformly and simultaneously coated using a doctor blade. The coating was dried by gradually increasing the temperature in the vessel from 25 ° C. to 100 ° C. In this manner, a phosphor layer composed of coating films C, B, and A was formed on the support in order, and each dried coating film had a thickness of about 60 μm and a total thickness of about 180 μm.

Then, a transparent film of polyethylene terephthalate (thickness: 12 μm, to which a polyester-based adhesive is applied) is placed on the phosphor layer with the adhesive layer side facing down, and adhered to the transparent protective film. To manufacture a radiographic intensifying screen I comprising a support, a phosphor layer having a phosphor particle diameter increasing from the screen surface side toward the support side, and a transparent protective film [FIG. (I), a: support, b: phosphor layer, c: protective film].

(2) Production of Radiation Intensifying Screen II In the production of the above-mentioned screen I, the same operation is performed except that the coating liquids A, B and C are arranged in the order from the support, so that the support and the screen are obtained. A radiographic intensifying screen II composed of a phosphor layer having a phosphor particle diameter decreasing from the surface side toward the support side and a transparent protective film was produced [FIG. 3 (II)].

(3) Production of Radiation Intensifying Screen III The above coating solutions A, B and C were mixed in equal amounts, respectively.
Coating solutions containing phosphor particles of various particle sizes dispersed therein were prepared.

In the production of the screen I, by performing the same operation except that this coating solution is used alone, the support, a phosphor layer having a uniform particle size distribution of the phosphor from the screen surface side to the support side, And a radiographic intensifying screen III composed of a transparent protective film.
(Fig. (III)).

[Example 1] The obtained radiographic intensifying screens I and II were pressed against a radiographic film (direct medical micro-particle ortho film, trade name: HR-A, manufactured by Fuji Photo Film Co., Ltd.) in a pressed state. Housed inside. The screen II was arranged so that the screen II was located on the radiation incident side (front side) and the screen I was located behind the film (back side).

In this way, a screen / film photographing system composed of a front screen, a back screen and a radiation film as shown in FIG. 2 was constructed.

[Comparative Examples 1 to 4] By performing the same operation as in Example 1 except that the radiation intensifying screens I, II, and III were used and the arrangement shown in Table 1 below was used. The screen and film photography system was configured.

Next, each screen / film photographing system was evaluated by a sensitivity test, an image sharpness test and an image graininess test described below.

(1) Sensitivity test An X-ray photograph was taken by irradiating a screen / film photographing system with X-rays having a tube voltage of 80 KVp. The sensitivity was measured from the image density of the obtained X-ray photograph.

(2) Image sharpness test X-ray photography is performed by irradiating a screen / film photographing system with X-rays having a tube voltage of 80 KVp through a resolving power chart and performing a contrast transfer function (CTF) of the obtained X-ray photograph.
Was measured and expressed as a value of a spatial frequency of 2 cycles / mm.

(3) Image graininess test X-rays with a tube voltage of 80 KVp are irradiated on a screen / film photographing system through a water phantom (thickness: 10 cm) and an aluminum plate (thickness: 10 mm) at a concentration of 1.2. X-ray photography was performed. This X-ray photographic film was developed at 35 ° C. using a developing solution (RD III, manufactured by Fuji Photo Film Co., Ltd.) by an automatic developing machine (New RN, manufactured by Fuji Photo Film Co., Ltd.). The obtained film was measured with a microphotometer (aperture: 300 μm × 300 μm), and R
The MS value was determined.

 The results obtained are summarized in Table 2.

As is clear from Table 2, the radiation image forming method (Example 1) of the present invention using the screen / film photographing system shown in FIG. Gave significantly improved images.

That is, the radiation image forming method of the present invention (Example 1)
Has the same sensitivity as the conventional method (Comparative Example 4) using a conventional radiation intensifying screen (III) in which the particle size distribution of the phosphor is uniform in the thickness direction of the phosphor layer, and They also have improved sharpness and graininess. Further, the sensitivity of the method of the present invention is lower than that of a known method using only a known radiation intensifying screen (II) in which phosphor particles having a large particle diameter are arranged on the film side (Comparative Example 3). Although slightly lower, sharpness and graininess were significantly improved, and were excellent and balanced through these three properties. Furthermore, it was found that the method of the present invention was superior to the method using another combination of screens (Comparative Examples 1 and 2) in all respects in sensitivity, sharpness and granularity.

[Brief description of the drawings]

FIG. 1 is a schematic diagram for explaining the radiation image forming method of the present invention. FIG. 2 is a sectional view showing an example of a screen / film photographing system according to the present invention. FIG. 3 is a sectional view showing an example of a radiographic intensifying screen, wherein (I) and (II) are a back screen and a front screen used in the present invention, respectively.
(III) is a conventional screen. 1: radiation generator, 2: subject, 3: screen / film photography system, 4,6: radiation intensifying screen, 4a, 6a, a: support, 4b, 6b, b: phosphor layer, 4c, 6c, c: protective film 5: radiographic film 5a: support, 5b, 5b ': photographic emulsion layer, 5c, 5c': protective layer

Claims (7)

(57) [Claims] 1. A method of forming a radiographic image using a screen / film photographing system in which radiographic intensifying screens are respectively disposed on the front and rear surfaces of a radiographic film. The phosphor particles constituting the phosphor layer of the radiation intensifying screen on the radiation incident side have a particle diameter from the screen surface side facing the film toward the support side. Are arranged so as to be smaller, and the phosphor particles constituting the phosphor layer of the radiation intensifying screen on the side opposite to the radiation incident side have a particle diameter from the screen surface side facing the film toward the support side. A radiation image forming method characterized by being arranged so as to be large. 2. The phosphor layer of the radiation intensifying screen on the radiation incident side, wherein the average particle diameter of the phosphor particles near the screen surface is in the range of 8 to 15 μm, and the average particle of the phosphor particles near the support is 2. The radiation image forming method according to claim 1, wherein the diameter is in a range of 2 to 5 [mu] m. 3. The phosphor layer of the radiation intensifying screen on the radiation incident side, wherein the average particle diameter of the phosphor particles in the vicinity of the screen surface is in the range of 8 to 15 μm, and the average particle diameter of the phosphor particles at the center is 3. The method according to claim 2, wherein the average particle diameter of the phosphor particles in the vicinity of the support is in the range of 2 to 5 [mu] m. 4. In the phosphor layer of the radiation intensifying screen on the side opposite to the radiation incident side, the average particle diameter of the phosphor particles near the screen surface is in the range of 2 to 5 μm, and the phosphor near the support is used. 2. The method according to claim 1, wherein the average particle diameter of the particles is in the range of 8 to 15 [mu] m. 5. The phosphor layer of the radiation intensifying screen on the side opposite to the radiation incident side, wherein the average particle diameter of the phosphor particles near the screen surface is in the range of 2 to 5 μm, Is in the range of 5 to 8 μm, and the average particle size of the phosphor particles near the support is 8 to 8 μm.
5. The radiation image forming method according to claim 4, wherein the radiation image is in a range of 15 [mu] m. 6. The radiation image forming apparatus according to claim 1, wherein the phosphor particles constituting the phosphor layer of each radiation intensifying screen are terbium-activated rare earth oxysulfide phosphors. Method. 7. The radiation according to claim 1, wherein said radiographic film is substantially composed of a support and photographic emulsion layers provided on both sides of said support. Image forming method.