JPH0214395B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of the Invention] The present invention relates to a radiation image conversion method and a radiation image conversion panel used in the method. More specifically, the present invention relates to a radiation image conversion method using a divalent europium-activated alkali metal halide phosphor coactivated with stimulable boron, and a radiation image conversion panel used in the method. It is. [Background of the Invention] Conventionally, so-called radiography has been used as a method of obtaining radiation images as images, using a combination of a radiographic film having an emulsion layer made of a silver salt photosensitive material and an intensifying screen. law is being used. As an alternative to the conventional radiographic method, a radiation image conversion method using a stimulable phosphor is known, for example, as described in Japanese Patent Application Laid-Open No. 12145/1983. In this method, radiation transmitted through the subject or radiation emitted from the subject is absorbed into a stimulable phosphor, and then the phosphor is exposed to electromagnetic waves (excitation light) such as visible light or infrared rays in a time-series manner. By exciting the phosphor, the radiation energy stored in the phosphor is released as fluorescence (stimulated luminescence), this fluorescence is read photoelectrically to obtain an electrical signal, and this electrical signal is converted into an image. . The radiation image conversion method has the advantage that it is possible to obtain an X-ray image with a rich amount of information with a much lower exposure dose than when conventional radiography is used. Therefore, this radiation image conversion method has a very high utility value especially in direct medical radiography such as X-ray photography for the purpose of medical diagnosis. Conventionally, divalent europium-activated alkaline earth metal fluoride halide phosphors (M〓FX:
Eu ²⁺ , where M〓 is at least one kind of alkaline earth metal selected from the group consisting of Ba, Sr, and Ca, and X is a halogen other than fluorine) has been proposed. After absorbing radiation such as X-rays, this phosphor emits light in the near-ultraviolet region (stimulable luminescence) when irradiated with electromagnetic waves in the visible to infrared region.
This shows that. As mentioned above, the radiation image conversion method utilizes the photostimulability of phosphors, but little is known about the stimulable phosphors themselves other than this divalent europium-activated alkaline earth metal halide phosphor. Not yet. The present applicant has already filed a patent application for a radiation image conversion method and a radiation image conversion panel using a new divalent europium-activated alkaline earth metal halide phosphor represented by the following compositional formula (Japanese Patent Application No. No. 193162). ^{Compositional} formula: _{M 〓} is at least one kind of halogen selected from the group consisting of Cl, Br, and X≠X′; and a is 0.1≦
It is a numerical value in the range of a≦10.0, and x is 0<x≦0.2
) This divalent europium-activated alkaline earth metal halide phosphor can be determined from its X-ray diffraction pattern as described in the above specification.
FX: It has been found that Eu ²⁺ phosphor is a different type of phosphor with a different crystal structure, and after irradiation with radiation such as X-rays, ultraviolet rays, and electron beams,
When excited with electromagnetic waves in the 1000nm wavelength range, 405n
It exhibits near-ultraviolet to blue light emission (stimulated light emission) with an emission maximum near m. The radiation image conversion method using the radiation image conversion panel made of the above-mentioned stimulable phosphor is a very advantageous image forming method as described above, but it is important that the sensitivity of this method be as high as possible. desirable. Generally, the sensitivity of a radiation image storage panel to radiation increases as the stimulated luminance of the phosphor used therein increases. Therefore, it is desired that the stimulable phosphor used in the panel has as high a stimulable luminance as possible. [Summary of the Invention] An object of the present invention is to provide a radiation image conversion method with improved sensitivity and a radiation image conversion panel used in the method. In order to achieve the above object, the present inventors conducted various studies on the above-mentioned novel divalent europium-activated alkaline earth metal halide phosphor. As a result, it was discovered that a phosphor obtained by coactivating the phosphor with a specific amount of boron exhibits high-intensity stimulated luminescence, leading to the present invention. That is, the radiation image conversion method of the present invention converts radiation transmitted through a subject or emitted from a subject into a divalent europium-activated alkaline earth metal halide co-activated with boron represented by the following compositional formula (). After being absorbed by the phosphor, the phosphor is irradiated with electromagnetic waves in the wavelength range of 450 to 1000 nm, thereby emitting the radiation energy stored in the phosphor as fluorescence, and detecting this fluorescence. Features. Composition formula (): M〓X ₂・aM〓X′ ₂ :xEu ²⁺ , yB ... () (However, M〓 is at least one alkaline earth metal selected from the group consisting of Ba, Sr, and Ca. Yes; both X and X' are at least one kind of halogen selected from the group consisting of Cl, Br, and X≠X'; and a is 0.1≦
It is a numerical value in the range of a≦10.0, and x is 0<x≦0.2
is a numerical value in the range of 2×10 ^-4 ≦y≦2×
10 ^-1 ) Furthermore, the radiation image conversion panel of the present invention is a radiation image conversion panel substantially composed of a support and a stimulable phosphor layer provided on the support. The stimulable phosphor layer is characterized in that it contains a divalent europium-activated alkaline earth metal halide phosphor co-activated with boron and represented by the above compositional formula (). In the present invention, the novel divalent europium-activated alkaline earth metal halide phosphor is further co-activated with a specific amount of boron, and after irradiating the phosphor with radiation such as X-rays,
This was completed based on the new knowledge that stimulated luminescence brightness is significantly improved when excited by electromagnetic waves in the wavelength range of . Therefore, by using the boron-coactivated divalent europium-activated alkaline earth metal halide phosphor represented by the above compositional formula (),
The sensitivity of the radiation image conversion method can be improved. Furthermore, the radiation image conversion panel of the present invention made of the above-mentioned phosphor exhibits significantly improved sensitivity. [Structure of the Invention] The divalent europium-activated alkaline earth metal halide phosphor co-activated with boron used in the present invention has a compositional formula (): M〓X ₂・aM〓X′ ₂ :xEu ²⁺ , yB...() (However, M〓 is at least one kind of alkaline earth metal selected from the group consisting of Ba, Sr, and Ca; X and X' are both at least one kind selected from the group consisting of Cl, Br, and It is a kind of halogen, and X≠X′; and a is 0.1≦
It is a numerical value in the range of a≦10.0, and x is 0<x≦0.2
is a numerical value in the range of 2×10 ^-4 ≦y≦2×
It is a number in the range 10 ^-1 ). In the phosphor represented by the above compositional formula (), from the viewpoint of stimulated luminance, the y value representing the amount of boron is preferably in the range of 4×10 ⁻⁴ ≦y≦10 ⁻¹ . Also, M〓X ₂ and M〓X′ ₂ in the composition formula ()
It is preferable that the a value representing the ratio of
x, which represents the activation amount of europium
Preferably, the value is in the range 10 ^-5 ≦x≦10 ^-1 . In the BaCl ₂・BaBr ₂ :0.001Eu ²⁺ ,yB phosphor, which is an example of the phosphor represented by the above compositional formula (), the y value representing the amount of boron in the phosphor and the stimulated luminance are The relationship is as shown in the figure. Figure ₁ shows ^the y value and _stimulated luminescence luminance [80KVp
It is a graph showing the relationship between the stimulated luminescence brightness when excited with semiconductor laser light (780 nm) after irradiation with a laser beam. As is clear from Figure 1, the y value is 2
BaCl ₂ in the range ×10 ^-4 ≦y≦2×10 ^-1
The BaBr ₂ :0.001Eu ²⁺ ,yB phosphor exhibits stimulated luminescence with higher brightness than the phosphor without boron (y=0). The y value in the boron-coactivated divalent europium-activated alkaline earth metal halide phosphor used in the radiation image conversion method of the present invention was defined in the range of 2×10 ^-4 ≦y≦2×10 ^-1 . The thing is,
This is based on these facts. Furthermore, from FIG. 1, it is clear that phosphors having particularly y values in the range of 4×10 ⁻⁴ ≦y≦10 ⁻¹ exhibit stimulated luminescence with extremely high brightness. In addition, the y value and the stimulated luminescence brightness also apply to divalent europium-activated alkaline earth metal halide phosphors in which M〓, X, X′, a, and x are coactivated with boron other than those mentioned above. It has been confirmed that the relationship between In addition, various additives may be added to the divalent europium-activated alkaline earth metal halide phosphor co-activated with boron as long as the effect of adding boron (improvement in stimulated luminescence brightness) is not lost. Components may be added. The photostimulated excitation spectrum of the divalent europium-activated alkaline earth metal halide phosphor co-activated with boron expressed by the above compositional formula () is as follows:
This is almost the same as the stimulated excitation spectrum of the divalent europium-activated alkaline earth metal halide phosphor described in the specification of Japanese Patent Application No. 58-193162. The wavelength range of the stimulated excitation spectrum is as wide as 450 to 1000 nm, and therefore, in the radiation image conversion method of the present invention using this phosphor, the wavelength of the excitation light can be changed appropriately. It becomes possible to appropriately select a light source depending on the purpose. For example, since the photostimulation excitation spectrum of the above-mentioned phosphor extends to about 1000 nm, a compact semiconductor laser (having an emission wavelength in the infrared region) with low driving power can be used as a photostimulation light source. Therefore, it is possible to downsize the apparatus for carrying out the radiation image conversion method. Furthermore, from the viewpoint of the brightness of stimulated luminescence and the wavelength separation from the emitted light, the excitation light in the radiation image conversion method of the present invention is preferably electromagnetic waves in the wavelength range of 500 to 850 nm. The boron-coactivated divalent europium-activated alkaline earth metal halide phosphor represented by the above compositional formula () can be produced, for example, by the production method described below. First, as raw materials for the phosphor, (1) at least two types of alkaline earth metal halides selected from the group consisting of barium halides, calcium halides, and strontium halides; (2) boron halides such as halides and oxides; (3) At least one europium compound selected from the group consisting of europium compounds such as halides, oxides, nitrates, and sulfates. In some cases, ammonium halide or the like may also be used as a flux. When manufacturing a phosphor, first, using the above alkaline earth metal halide (1), boron compound (2), and europium compound (3), the composition formula (): M〓 X ₂・aM〓X′ ₂ :xEu, yB ……() (However, the definitions of M〓, Weigh and mix. The above mixture operation is carried out, for example, in the state of an aqueous solution. Then, by removing water from the aqueous solution of this phosphor raw material mixture, a solid dry mixture is obtained. This moisture removal operation is carried out at room temperature or at a moderate temperature (e.g. 200°C).
(below), drying under reduced pressure, vacuum drying, or both are preferably carried out. Of course, the mixing operation is not limited to the above method. Note that the boron compound (2) above may be added to this dry mixture without being added at the time of weighing and mixing the phosphor raw materials. The resulting dry mixture is then finely ground and
The pulverized material is filled into a heat-resistant container such as a quartz board or an aluminum crucible, and fired in an electric furnace. The appropriate firing temperature is in the range of 500 to 1300°C, and the firing time varies depending on the amount of phosphor raw material mixture and the firing temperature, but in general
0.5 to 6 hours is appropriate. The firing atmosphere is
A weakly reducing atmosphere such as a nitrogen gas atmosphere containing a small amount of hydrogen gas or a carbon dioxide atmosphere containing carbon monoxide is used. When the europium compound used contains trivalent europium, the weakly reducing atmosphere reduces the trivalent europium to divalent europium during the firing process. Note that a method may be used in which the phosphor raw material mixture is once fired under the above firing conditions, and then the fired product is left to cool, then pulverized, and further fired (secondary firing). Re-firing is performed at a firing temperature of 500-800°C in the weakly reducing atmosphere mentioned above or in a neutral atmosphere such as a nitrogen gas atmosphere or an argon gas atmosphere.
It takes place over 12 hours. The phosphor used in the present invention is obtained by the above baking. Note that the obtained phosphor may be further subjected to various general operations in the production of phosphors, such as washing, drying, and sieving, as necessary. By utilizing the manufacturing method described above, a boron-coactivated divalent europium-activated alkaline earth metal halide phosphor represented by the above compositional formula () can be obtained. In the radiation image conversion method of the present invention, the boron-coactivated divalent europium-activated alkaline earth metal halide phosphor represented by the above compositional formula () is used in a radiation image conversion panel containing it (a stimulable phosphor It is preferable to use it in the form of a sheet (also referred to as a sheet). The basic structure of a radiation image storage panel is a support and at least one stimulable phosphor layer provided on one side of the support. The stimulable phosphor layer consists of a stimulable phosphor and a binder that contains and supports the stimulable phosphor in a dispersed state. Note that a transparent protective film is generally provided on the surface of the phosphor layer opposite to the support (the surface not facing the support) to protect the phosphor layer from chemical deterioration or Protects from physical impact. That is, the radiation image conversion method of the present invention uses a radiation image conversion panel having a phosphor layer made of a divalent europium-activated alkaline earth metal halide phosphor co-activated with boron and represented by the above compositional formula (). It is desirable to implement using In the radiation image conversion method of the present invention using a stimulable phosphor represented by the composition formula () in the form of a radiation image conversion panel, the radiation transmitted through the subject or emitted from the subject is It is proportionally absorbed by the phosphor layer of the radiation image conversion panel, and a radiation image of the subject or subject is formed on the radiation image conversion panel as an image of accumulated radiation energy. This accumulated image is 450 to 1000 nm
By excitation with electromagnetic waves (excitation light) in the wavelength range of It becomes possible to convert the image into an image. The radiation image conversion method of the present invention will be specifically explained using the schematic diagram shown in FIG. 2, taking as an example an embodiment in which a stimulable phosphor represented by the composition formula () is used in the form of a radiation image conversion panel. . In FIG. 2, 11 is a radiation generating device such as an X-ray, 12 is a subject, 13 is a radiation image conversion panel containing a stimulable phosphor represented by the above composition formula (), and 14 is a radiation image conversion panel 13. 15 is a photoelectric conversion device that detects the fluorescence emitted from the radiation image conversion panel 13; 16 is a photoelectric conversion device detected by the photoelectric conversion device 15; A device for reproducing the signal as an image, 17 a device for displaying the reproduced image, and 18 a filter for transmitting only the fluorescence emitted from the radiation image conversion panel 13 without transmitting the reflected light from the light source 14. It is. Note that FIG. 2 shows an example of obtaining a radiographic image of a subject, but if the subject 12 itself emits radiation (herein referred to as the subject), the above method may be used. It is not necessary to particularly install the radiation generating device 11. Further, the photoelectric conversion device 15 to the image display device 17 can be replaced with other suitable devices that can reproduce information emitted as fluorescence from the radiation image conversion panel 13 as an image in some form. As shown in FIG. 2, when a subject 12 is irradiated with radiation such as X-rays from the radiation generating device 11, the radiation passes through the subject 12 in proportion to the radiation transmittance of each part of the subject 12. The radiation that has passed through the subject 12 then enters the radiation image conversion panel 13 and is absorbed by the phosphor layer of the radiation image conversion panel 13 in proportion to the intensity of the radiation. That is, a radiation energy accumulation image (a kind of latent image) corresponding to a radiation transmission image is formed on the radiation image conversion panel 13. Next, when the radiation image conversion panel 13 is irradiated with electromagnetic waves in the wavelength range of 450 to 1000 nm using the light source 14, the accumulated radiation energy image formed on the radiation image conversion panel 13 is emitted as fluorescence. The emitted fluorescence is proportional to the intensity of the radiation energy absorbed by the phosphor layer of the radiation image conversion panel 13. This optical signal composed of the intensity of fluorescence is converted into an electrical signal by a photoelectric conversion device 15 such as a photomultiplier tube, and is reproduced as an image by an image reproduction device 16, and the image display device 1
7 displays this image. For example, a radiation image accumulated on the radiation image conversion panel 13 is read by scanning the panel 13 with electromagnetic waves emitted from a light source 14, and by this scanning, fluorescence emitted from the panel 13 is transferred to the photoelectric conversion device 13.
5 to obtain time-series electrical signals. In the radiation image conversion method of the present invention, the radiation used to obtain a radiation transmission image of the subject is:
Any radiation may be used as long as it can exhibit stimulated luminescence when the phosphor is further excited by the electromagnetic waves after being irradiated with this radiation,
For example, commonly known radiation such as X-rays, electron beams, and ultraviolet rays can be used. Also,
The radiation directly emitted from the subject when obtaining a radiation image of the subject may be any radiation that is similarly absorbed by the phosphor and serves as an energy source for stimulated luminescence. Examples include radiation such as gamma rays, alpha rays, and beta rays. In addition to light sources that emit light with a band spectrum distribution in the wavelength range of 450 to 1000 nm, light sources for electromagnetic waves that excite the phosphor that has absorbed radiation from the subject or subject as described above include
Ar ion laser, Kr ion laser, He−
Light sources such as lasers such as Ne lasers, ruby lasers, semiconductor lasers, glass lasers, YAG lasers, dye lasers, and light emitting diodes can be used. Among these, laser light is preferable as the excitation light source used in the present invention because it can irradiate the radiation image conversion panel with a laser beam having a high energy density per unit area. Among them, preferable laser beams are He-Ne laser, Ar ion laser and
It is a Kr ion laser. In addition, semiconductor lasers are small, require low driving power,
It is preferable as an excitation light source because direct modulation is possible and the laser output can be easily stabilized. Next, a radiation image conversion panel used in the radiation image conversion method of the present invention will be explained. As described above, this radiation image storage panel consists essentially of a support and a boron-coactivated divalent europium-activated alkaline earth metal halogen provided on the support. and a stimulable phosphor layer made of a binder containing and supporting a compound phosphor in a dispersed state. The stimulable phosphor layer can be formed on the support, for example, by the following method. Examples of binders for the phosphor layer include proteins such as gelatin, polysaccharides such as dextran, or natural polymeric substances such as gum arabic; and polyvinyl butyral, polyvinyl acetate, nitrocellulose, ethylcellulose, and vinylidene chloride. Binders represented by synthetic polymeric substances such as vinyl chloride copolymers, polyalkyl (meth)acrylates, vinyl chloride/vinyl acetate copolymers, polyurethanes, cellulose acetate butyrate, polyvinyl alcohol, linear polyesters, etc. can. Particularly preferred among such binders are nitrocellulose, linear polyesters, polyalkyl(meth)
acrylates, mixtures of nitrocellulose and linear polyesters, and mixtures of nitrocellulose and polyalkyl (meth)acrylates. First, the above-mentioned particulate stimulable phosphor and a binder are added to a suitable solvent and thoroughly mixed to prepare a coating solution in which the stimulable phosphor is uniformly dispersed in the binder solution. Examples of solvents for preparing coating solutions include lower alcohols such as methanol, ethanol, n-propanol, and n-butanol; chlorine-containing hydrocarbons such as methylene chloride and ethylene chloride; and ketones such as acetone, methyl ethyl ketone, and methyl isobutyl ketone. ; esters of lower fatty acids and lower alcohols such as methyl acetate, ethyl acetate, and butyl acetate; ethers such as dioxane, ethylene glycol monoethyl ether, and ethylene glycol monomethyl ether; and mixtures thereof. The mixing ratio of the binder and the stimulable phosphor in the coating solution varies depending on the characteristics of the intended radiation image conversion panel, the type of phosphor, etc., but in general, the mixing ratio of the binder and the stimulable phosphor is , 1:1 to 1:100 (weight ratio), and particularly preferably 1:8 to 1:40 (weight ratio). The coating liquid also contains a dispersant to improve the dispersibility of the phosphor in the coating liquid, and a dispersant to improve the bonding force between the binder and the phosphor in the phosphor layer after formation. Various additives such as plasticizers may be mixed. Examples of dispersants used for such purposes include phthalic acid, stearic acid, caproic acid, lipophilic surfactants, and the like. Examples of plasticizers include phosphoric acid esters such as triphenyl phosphate, tricresyl phosphate, and diphenyl phosphate; phthalic acid esters such as diethyl phthalate and dimethoxyethyl phthalate; and ethyl phthalyl ethyl glycolate and butyl phthalyl butyl glycolate. Glycolic acid esters; and polyesters of polyethylene glycol and aliphatic dibasic acids, such as polyesters of triethylene glycol and adipic acid and polyesters of diethylene glycol and succinic acid. The coating solution containing the phosphor and binder prepared as described above is then uniformly applied to the surface of the support to form a coating film of the coating solution.
This coating operation can be carried out using conventional coating means such as a doctor blade, roll coater, knife coater, etc. The support may be arbitrarily selected from various materials used as supports for intensifying screens (or intensifying screens) in conventional radiography or materials known as supports for radiation image conversion panels. can. Examples of such materials include:
Cellulose acetate, polyester, polyethylene terephthalate, polyamide, polyimide,
Films of plastic materials such as triacetate and polycarbonate, metal sheets such as aluminum foil and aluminum alloy foil, ordinary paper, baryta paper, resin coated paper, pigment paper containing pigments such as titanium dioxide, paper sized with polyvinyl alcohol, etc. etc. can be mentioned. However, in consideration of the characteristics and handling of the radiation image storage panel as an information recording material, a particularly preferred material for the support in the present invention is plastic film. This plastic film may be kneaded with a light-absorbing substance such as carbon black, or may be kneaded with a light-reflecting substance such as titanium dioxide. The former is a support suitable for a high sharpness type radiation image conversion panel, and the latter is a support suitable for a high sensitivity type radiation image conversion panel. In known radiation image conversion panels, a phosphor layer is provided in order to strengthen the bond between the support and the phosphor layer, or to improve the sensitivity or image quality (sharpness, granularity) of the radiation image conversion panel. A polymeric substance such as gelatin is coated on the surface of the side support to form an adhesion-imparting layer, or a light-reflecting layer made of a light-reflecting substance such as titanium dioxide, or a light-reflecting layer made of a light-absorbing substance such as carbon black. It is known to provide an absorbent layer or the like. The support used in the present invention can also be provided with these various layers, and their configurations can be arbitrarily selected depending on the purpose, use, etc. of the desired radiation image storage panel. Furthermore, as disclosed in JP-A No. 58-200200, in order to improve the sharpness of the obtained image, the surface of the support on the phosphor layer side (the surface of the support on the phosphor layer side) When an adhesion-imparting layer, a light-reflecting layer, a light-absorbing layer, etc. are provided, minute irregularities may be formed on the surface (meaning the surface thereof). After forming the coating film on the support as described above, the coating film is dried to complete the formation of the stimulable phosphor layer on the support. The thickness of the phosphor layer varies depending on the characteristics of the intended radiation image conversion panel, the type of phosphor, the mixing ratio of the binder and the phosphor, etc.
Usually it is 20 μm to 1 mm. However, the thickness of this layer is preferably 50 to 500 μm. Furthermore, the stimulable phosphor layer does not necessarily need to be formed by directly applying a coating solution onto the support as described above, but can be formed by separately applying it onto a sheet such as a glass plate, metal plate, or plastic sheet. After forming a phosphor layer by applying a liquid and drying it,
The support and the phosphor layer may be bonded together by pressing this onto the support or using an adhesive. Although only one stimulable phosphor layer may be used, two or more layers may be stacked. In the case of multiple layers, at least one of the layers may contain a divalent europium-activated alkaline earth metal halide phosphor co-activated with boron of the composition formula (),
A structure may be adopted in which a plurality of phosphor layers are stacked so that the luminous efficiency with respect to radiation increases sequentially toward the surface of the panel. Furthermore, in both the single-layer and multilayer cases, a known stimulable phosphor can be used in combination with the above-mentioned phosphor. Examples of such known stimulable phosphors include:
In addition to the above-mentioned phosphors, ZnS:Cu, Pb, BaO and
xAl ₂ O ₃ :Eu (however, 0.8≦x≦10), and
M〓O・xSiO ₂ :A (However, M〓 is Mg, Ca, Sr,
Zn, Cd, or Ba, and A is Ce, Tb, Eu,
Tm, Pb, Tl, Bi, or Mn, and x is 0.5
≦x≦2.5), (Ba _1-xy , Mg _x , Ca _y )FX: aEu ²⁺ (However, X
is at least one of Cl and Br,
x and y are 0<x+y≦0.6 and xy≠0, and a is ^10-6 ≦a≦5× ^10-2 ), and There is
LnOX:xA (Ln is La, Y, Gd, and
At least one of Lu, X is at least one of Cl and Br, A is at least one of Ce and Tb, and x is 0<x<0.1
), and so on. In a normal radiation image storage panel, as mentioned above, a transparent protective film is provided on the surface of the phosphor layer on the side opposite to the side that contacts the support to physically and chemically protect the phosphor layer. It is being Such a transparent protective film is preferably provided also in the radiation image conversion panel of the present invention. The transparent protective film may be made of a transparent material such as a cellulose derivative such as cellulose acetate or nitrocellulose; or a synthetic polymer material such as polymethyl methacrylate, polyvinyl butyral, polyvinyl formal, polycarbonate, polyvinyl acetate, or vinyl chloride/vinyl acetate copolymer. It can be formed by coating the surface of the phosphor layer with a solution prepared by dissolving a polymeric substance in an appropriate solvent. Alternatively, it can also be formed by a method such as adhering a transparent thin film separately formed from polyethylene terephthalate, polyethylene, polyvinylidene chloride, polyamide, etc. to the surface of the phosphor layer using a suitable adhesive. The thickness of the transparent protective film formed in this way is approximately 0.1 to
It is desirable that the thickness be 20 μm. Examples and comparative examples of the present invention are described below. However, these examples do not limit the invention. Example 1 Barium bromide (BaBr ₂ 2H ₂ O) 333.2 g, barium chloride (BaCl ₂ 2H ₂ O) 244.3 g, boron oxide (B ₂ O ₃ ) 0.0696 g, and europium bromide (EuBr ₃ ) 0.783 g was added to 800 ml of distilled water (H ₂ O) and mixed to form an aqueous solution. This aqueous solution was dried under reduced pressure at 60°C for 3 hours, and then further vacuum dried at 150°C for 3 hours. Next, the obtained phosphor raw material mixture was filled into an alumina crucible, which was then placed in a high-temperature electric furnace and fired. Firing was performed at a temperature of 900° C. for 1.5 hours in a carbon dioxide atmosphere containing carbon monoxide. After the firing was completed, the fired product was taken out of the furnace and cooled. In this way, a divalent europium-activated barium chloride bromide phosphor co-activated with boron (BaCl ₂ .BaBr ₂ : 0.001Eu ²⁺ , 0.002B) was obtained. Furthermore, by changing the amount of boron oxide in the range of 0 to 2.0 mol per 1 mol of BaCl ₂ /BaBr ₂ , various types of divalent europium-activated chlorobromide co-activated with boron with different amounts of boron were prepared. A barium phosphor (BaCl ₂ .BaBr ₂ :0.001Eu ²⁺ , yB) was obtained. Next, tube voltage was applied to each phosphor obtained in Example 1.
After irradiating with 80 KVp X-rays, the brightness of stimulated luminescence when excited with semiconductor laser light (780 nm) was measured. The results are shown in FIG. FIG. 1 is a graph showing the relationship between the amount of boron (y value) and stimulated luminance in a BaCl ₂ .BaBr ₂ :0.001Eu ²⁺ yB phosphor. As is clear from FIG. 1, the BaCl ₂・
BaBr ₂ : 0.001Eu ²⁺ , yB phosphor has a y value of 2×
In the range of 10 ^-4 ≦y≦2×10 ^-1 , the brightness of the stimulated luminescence is improved. In particular, the y value is 4×10 ^-4 ≦
A phosphor in the range of y≦10 ⁻¹ exhibits high-intensity stimulated luminescence. Example 2 The particles of the divalent europium-activated barium chloride bromide phosphor (BaCl ₂・BaBr ₂ : 0.001Eu ²⁺ , 0.002B) co-activated with boron obtained in Example 1 were thoroughly loosened, and a wire was formed between them. Methyl ethyl ketone was added to the mixture with the polyester resin, and nitrocellulose with a degree of nitrification of 11.5% was further added to prepare a dispersion containing the phosphor in a dispersed state. next,
After adding tricresyl phosphate, n-butanol, and methyl ethyl ketone to this dispersion, they were sufficiently stirred and mixed using a propeller mixer to ensure that the phosphor was uniformly dispersed and that the mixing ratio of the binder and the phosphor was 1:1. 10. A coating solution with a viscosity of 25 to 35 PS (25°C) was prepared. Next, the coating solution was uniformly applied using a doctor blade onto a titanium dioxide-mixed polyethylene terephthalate sheet (support, thickness: 250 μm) placed horizontally on a glass plate. After coating, the support on which the coating film has been formed is placed in a dryer,
The temperature inside this dryer was gradually raised from 25°C to 100°C to dry the coating film. In this way, a phosphor layer with a layer thickness of 250 μm was formed on the support. Then, a transparent film of polyethylene terephthalate (thickness: 12 μm, coated with a polyester adhesive) is placed on top of this phosphor layer with the adhesive layer side facing down, and bonded.
A transparent protective film was formed to produce a radiation image storage panel composed of a support, a phosphor layer, and a transparent protective film. Example 3 A sample co-activated with boron was prepared by carrying out the same procedure as in Example 1, except that 0.210 g of ammonium borofluoride (NH ₄ BF ₄ ) was used instead of boron oxide. divalent europium-activated barium chloride bromide phosphor ( _BaCl2 .
_BaBr2 : 0.001Eu2 ⁺ , 0.002B) was obtained. Next, by performing the same process as in Example 2 except for using this stimulable phosphor,
A radiation image storage panel consisting of a support, a phosphor layer and a transparent protective film was manufactured. Comparative Example 1 A divalent europium-activated barium chloride bromide phosphor (BaCl ₂・BaBr ₂ : 0.001Eu) was prepared by performing the same operation as in Example 1 except that boron oxide was not added. ²⁺ ). Next, by performing the same process as in Example 2 except for using this stimulable phosphor,
A radiation image storage panel consisting of a support, a phosphor layer and a transparent protective film was manufactured. Each radiation image conversion panel obtained in Examples 2 and 3 and Comparative Example 1 was irradiated with X-rays with a tube voltage of 80 KVp and then excited with semiconductor laser light (780 nm). ) was measured. The results are shown in Table 1. 【table】

[Brief explanation of drawings]

FIG. 1 is a graph showing the relationship between the y value and the stimulated luminance in BaCl ₂ .BaBr ₂ :0.001Eu ²⁺ yB phosphor, which is a specific example of the phosphor used in the present invention. FIG. 2 is a schematic diagram illustrating the radiation image conversion method of the present invention. 11: Radiation generator, 12: Subject, 13:
Radiation image conversion panel, 14: light source, 15: photoelectric conversion device, 16: image reproduction device, 17: image display device, 18: filter.

Claims (1)

[Claims] 1. Radiation transmitted through the subject or emitted from the subject is absorbed by a divalent europium-activated alkaline earth metal halide phosphor co-activated with boron and expressed by the following compositional formula (). After that, the phosphor is irradiated with electromagnetic waves in the wavelength range of 450 to 1000 nm to release the radiation energy stored in the phosphor as fluorescence,
And a radiation image conversion method characterized by detecting this fluorescence. Composition formula (): M〓X ₂・aM〓X′ ₂ :xEu ²⁺ , yB ... () (However, M〓 is at least one alkaline earth metal selected from the group consisting of Ba, Sr, and Ca. Yes; both X and X' are at least one kind of halogen selected from the group consisting of Cl, Br, and X≠X'; and a is 0.1≦
It is a numerical value in the range of a≦10.0, and x is 0<x≦0.2
is a numerical value in the range of 2×10 ^-4 ≦y≦2×
10 ^-1 ) 2. The radiation image conversion method according to claim 1, wherein a in the compositional formula () is a numerical value in the range of 0.3≦a≦3.3. 3 y in the composition formula () is 4×10 ^-4 ≦y≦
10. The radiation image conversion method according to claim 1, wherein the value is in the range of 10 ^-1 . 4. The radiation image conversion method according to claim 1, wherein M in the compositional formula () is Ba. 5. The radiation image conversion method according to claim 1, wherein X and X' in the compositional formula () are each Cl or Br. 6. The radiation image conversion method according to claim 1, wherein x in the compositional formula () is a numerical value in the range of 10 ^-5 ≦x≦10 ^-1 . 7. The radiation image conversion method according to claim 1, wherein the electromagnetic wave is an electromagnetic wave in a wavelength range of 500 to 850 nm. 8. The radiation image conversion method according to claim 1, wherein the electromagnetic wave is a laser beam. 9. A radiation image conversion panel substantially composed of a support and a stimulable phosphor layer provided on the support, in which the stimulable phosphor layer contains boron represented by the following compositional formula (). A radiation image conversion panel comprising a divalent europium-activated alkaline earth metal halide phosphor co-activated with a divalent europium-activated alkaline earth metal halide phosphor. Composition formula (): M〓X ₂・aM〓X′ ₂ :xEu ²⁺ , yB ... () (However, M〓 is at least one alkaline earth metal selected from the group consisting of Ba, Sr, and Ca. Yes; both X and X' are at least one kind of halogen selected from the group consisting of Cl, Br, and X≠X'; and a is 0.1≦
It is a numerical value in the range of a≦10.0, and x is 0<x≦0.2
is a numerical value in the range of 2×10 ^-4 ≦y≦2×
10 ⁻¹ ) 10 The radiation image conversion panel according to claim 9, wherein a in the compositional formula () is a numerical value in the range of 0.3≦a≦3.3. 11 y in compositional formula () is 4×10 ^-4 ≦y≦
10. The radiation image conversion panel according to claim 9, wherein the value is in the range of 10 ^-1 . 12. The radiation image conversion panel according to claim 9, wherein M in the compositional formula () is Ba. 13. The radiation image storage panel according to claim 9, wherein X and X' in the compositional formula () are each Cl or Br. 14 x in composition formula () is 10 ^-5 ≦x≦10 ^-1
10. The radiation image conversion panel according to claim 9, wherein the radiation image conversion panel has a numerical value in the range of .