JPH0548276B2 - - 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 composite halide phosphor activated with divalent europium, and a radiation image conversion panel used in the method.

[Background of the Invention] Conventionally, as a method of obtaining a radiation image as an image,
A so-called radiographic method is used which uses a combination of a radiographic film having an emulsion layer made of a silver salt photosensitive material and a sensitizer (sensitizing screen). 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. This method involves absorbing radiation transmitted through the subject or radiation emitted from the subject into a stimulable phosphor.
Then, by exciting this phosphor in a time-series manner with electromagnetic waves (excitation light) such as visible light and infrared rays, the radiation energy accumulated in the phosphor is released as fluorescence (stimulated luminescence). 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.

As a stimulable phosphor used in the above radiation image conversion method, JP-A-55-12145 discloses a rare earth element-activated alkaline earth metal fluoride halide phosphor represented by the following composition formula: .

(Ba _1-x , M ²⁺ _x )FX: yA (where M ²⁺ is Mg, Ca, Sr, Zn, and Cd
X is at least one of Cl, Br, and I; A is Eu, Tb, Ce,
at least one of Tm, Dy, Pr, Ho, Nd, Yb, and Er, and x is 0≦x≦0.6,
(y is 0≦y≦0.2) After absorbing radiation from the X-direction, this phosphor emits light in the near-ultraviolet region (stimulated luminescence) when irradiated with electromagnetic waves in the visible light to infrared region. It is something.

As mentioned above, the above rare earth element-activated alkaline earth metal halide phosphors have been known as phosphors used in radiation image conversion methods that ideally use stimulable phosphors; however, they exhibit photostimulability. Not much is known about the phosphor itself other than this rare earth element-activated alkaline earth metal halide phosphor.

[Summary of the Invention] The present invention is based on the discovery of a novel stimulable phosphor, and provides a radiation image conversion method using the stimulable phosphor, and a radiation image conversion panel used in the method. It is something to do.

The present inventors have conducted various studies with the aim of searching for stimulable phosphors. As a result, the novel divalent europium-activated composite halide phosphor represented by the following compositional formula () exhibits stimulated luminescence.
After irradiating with radiation such as gamma rays, alpha rays, and beta rays,
The inventors discovered that stimulated luminescence occurs in the near-ultraviolet to blue region when excited by electromagnetic waves in the visible to infrared region of 450 to 900 nm, and based on this knowledge, they completed the present invention.

Composition formula (): M〓X ₂・aM〓X′:xEu ²⁺ () (However, M〓 is at least one alkaline earth metal selected from the group consisting of Ba, Sr, and Ca; M〓 At least one alkali metal selected from the group consisting of Li, Rb and Cs;
X′ are the same (i.e., X=X′), and
is a halogen of any one of Cl, Br, or I; and a is a numerical value in the range of 0.1≦a≦20.0, and x is a numerical value in the range of 0<x≦0.2) In other words, the radiographic image of the present invention The conversion method involves absorbing the radiation transmitted through the object or emitted from the object into a divalent europium-activated composite halide phosphor represented by the above composition formula (), and then absorbing the radiation into this phosphor with a wavelength of 450 to 900 nm. By irradiating electromagnetic waves in the wavelength range, the radiation energy stored in the phosphor is released as fluorescence,
It is characterized by detecting this fluorescence.

Further, the radiation image storage panel of the present invention substantially comprises a support and at least one phosphor layer formed on the support and comprising a binder containing and supporting the stimulable phosphor in a dispersed state. It is configured,
At least one of the phosphor layers is characterized in that it contains a divalent europium-activated composite halide phosphor represented by the above compositional formula ().

[Structure of the Invention] FIG. 1 illustrates the stimulated excitation spectrum of the divalent europium-activated composite halide phosphor used in the radiation image conversion method of the present invention.
In Figure 1, curve 1 and curve 2 are respectively
BaBr ₂・LiBr: 0.001Eu ²⁺ phosphor and BaBr ₂・
This is the photostimulation excitation spectrum of CsBr:0.001Eu ²⁺ phosphor.

As is clear from FIG. 1, the BaBr ₂ LiBr: 0.001Eu ²⁺ phosphor used in the present invention and
BaBr ₂ CsBr:0.001Eu ²⁺ phosphor exhibits stimulated luminescence when excited with electromagnetic waves in the wavelength range of 450 to 900 nm after irradiation with radiation. In particular, when excited with electromagnetic waves in the wavelength range of 500 to 800 nm, it is easy to separate the stimulated luminescence and excitation light, and the stimulated luminescence has high brightness. In the radiation image conversion method of the present invention, the wavelength of the electromagnetic wave used as excitation light is
It is based on this fact that the range is defined as 450 to 900 nm.

Further, FIG. 2 illustrates the photostimulated excitation spectrum of the divalent europium-activated composite halide phosphor used in the radiation image conversion method of the present invention. In FIG. 2, curve 1 and curve 2 are respectively BaBr ₂・LiBr: 0.001Eu ²⁺ phosphor and
This is the stimulated emission spectrum of BaBr ₂ CsBr:0.001Eu ²⁺ phosphor.

As is clear from FIG. 2, the BaBr ₂ LiBr: 0.001Eu ²⁺ phosphor used in the present invention and
BaBr ₂ / CsBr: 0.001Eu ²⁺ phosphor exhibits stimulated luminescence in the near-ultraviolet to blue region, and the peaks of its stimulated emission spectrum are approximately 405 nm and 410 nm, respectively.
It is in.

The stimulated luminescence properties of the divalent europium-activated composite halide phosphor used in the present invention have been explained using a specific phosphor as an example. However, other phosphors used in the present invention can also be After irradiating with radiation such as rays, 450 ~
When excited with electromagnetic waves in the wavelength range of 900 nm, stimulated luminescence occurs in the near-ultraviolet to blue region (peak wavelength of emission:
390 to 420 nm).

Figure 3 shows the a value and stimulated emission intensity of the BaBr ₂ aLiBr: 0.001Eu ²⁺ phosphor [stimulated emission intensity when excited with He-Ne laser light (632.8 nm) after irradiation with 80 KVp X-rays. FIG. As is clear from Figure 3, the a value is
_BaBr2・aLiBr in the range of 0.1≦a≦20.0:
0.001Eu ²⁺ phosphor exhibits stimulated luminescence. The a value in the divalent europium-activated composite halide phosphor used in the radiation image conversion method of the present invention is 0.1≦
It is based on this fact that the range of a≦20.0 is specified. Also, from Figure 3, the a value is 0.1
Used in the present invention in the range of ≦a≦20.0
BaBr ₂・aLiBr: Among the 0.001Eu ²⁺ phosphors,
It is clear that a phosphor having an a value in the range of 1.5≦a≦10.0 exhibits stimulated luminescence with higher brightness. Furthermore, for the divalent europium-activated composite halide phosphors used in the present invention other than the BaBr ₂ /aLiBr:0.001Eu ²⁺ phosphor, the relationship between the a value and the stimulated emission intensity is similar to that shown in Figure 3. It has been confirmed that there is a trend.

The divalent europium-activated composite halide phosphor used in the radiation image conversion method of the present invention has a stimulated excitation spectrum in a wide wavelength range of 450 to 900 nm, and therefore the radiation image conversion method of the present invention using this phosphor has a wide wavelength range of 450 to 900 nm. In this method, the wavelength of the excitation light can be changed appropriately, that is, the excitation light source can be appropriately selected depending on the purpose.
For example, the photostimulation excitation spectrum of the above phosphor is approximately
Since the wavelength extends to 900 nm, a compact semiconductor laser (having an emission wavelength in the infrared region) with a small size and low driving power can be used as an excitation light source, and therefore, it is possible to use a device for implementing the radiation image conversion method. It becomes possible to downsize the . In addition, from the point of view of stimulation of stimulated luminescence and wavelength separation from the emitted light, the excitation light in the radiation image conversion method of the present invention is
Preferably, it is an electromagnetic wave in the wavelength range of 500 to 800 nm.

In the radiation image conversion method of the present invention, the divalent europium-activated composite halide phosphor represented by the above compositional formula () is used in the form of a radiation image conversion panel (also referred to as a stimulable phosphor sheet) containing it. is preferred.

The basic structure of a radiation image storage panel is a support and at least one phosphor layer provided on one side of the support. The 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 is preferably carried out using a radiation image conversion panel having a phosphor layer made of a divalent europium-activated composite halide phosphor represented by the above compositional formula ().

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 can be emitted as stimulated luminescence (fluorescence) by exciting it with electromagnetic waves (excitation light) in the wavelength range of 450 to 900 nm, and this stimulated luminescence can be read photoelectrically and converted into an electrical signal. By doing so, it becomes possible to image the accumulated radiation energy.

The radiation image conversion method of the present invention will be specifically explained using the schematic diagram shown in FIG. 4, 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. 4, 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. 4 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. 4, 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.

The operation of reading out the image information accumulated in a radiation image conversion panel as fluorescence is generally performed by scanning the panel in time series with a laser beam, and then transmitting the fluorescence emitted from the panel by this scanning through a suitable light condenser. This is done by detecting with a photodetector such as a photomultiplier tube and obtaining a time-series electrical signal. In order to obtain an image with better observation and interpretation performance, this readout may consist of pre-reading scanning by irradiating low-energy excitation light and main reading operation by irradiating high-energy excitation light. -Refer to Publication No. 67240). By performing this pre-read operation, there is an advantage that the read conditions for the main read operation can be suitably set.

Furthermore, for example, solid-state photoelectric conversion elements such as photoconductors and photodiodes can be used as photoelectric conversion devices (Japanese Patent Application No. 58-86226, Japanese Patent Application No. 58-86227, Japanese Patent Application No. 58-219313, and Specifications of Application No. 58-219314 and JP-A-58-
(See Publication No. 121874). In this case, a large number of solid-state photoelectric conversion elements may be configured to cover the entire surface of the panel, and may be integrated with the panel, or may be arranged in close proximity to the panel. Further, the photoelectric conversion device may be a line sensor in which a plurality of photoelectric conversion elements are connected in a line,
Alternatively, it may be composed of one solid-state photoelectric conversion element corresponding to one pixel.

In addition to a point light source such as a laser, the light source in the above case may be a line light source such as an array of light emitting diodes (LEDs), semiconductor lasers, etc. arranged in a row. By performing readout using such a device, it is possible to prevent loss of fluorescence emitted from the panel, and at the same time, increase the solid angle of light reception and increase the S/N ratio. Furthermore, since the obtained electrical signals are converted into time series not by time series irradiation of excitation light but by electrical processing of the photodetector, it is possible to increase the readout speed. .

The radiation image conversion panel from which the image information has been read is irradiated with light in the wavelength range of the excitation light of the phosphor or heated to erase any remaining radiation energy. It is possible and preferable to do so (Japanese Patent Laid-open No. 1983
-11392 and Japanese Unexamined Patent Publication No. 12599/1983).
By performing this erasing operation, it is possible to prevent nozzles from occurring due to afterimages when the panel is used next time. Furthermore, by performing the erasing operation twice, once after reading and immediately before the next use, it is possible to prevent the generation of noise due to natural radioactivity, etc., and to perform erasing more efficiently (Japanese Patent Laid-Open Publication No.
(Refer to Publication No. 57-116300).

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. Furthermore, when obtaining a radiation image of the subject, the radiation directly emitted from 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 900 nm, light sources for electromagnetic waves that excite the phosphor that has absorbed radiation from the subject or subject as described above include:
Light sources such as lasers such as Ar ion lasers, He-Ne lasers, ruby lasers, semiconductor lasers, glass lasers, YAG lasers, Kr ion 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, preferred laser beams are Ar ion laser, Kr ion laser, He-
Ne laser and semiconductor laser. Also,
Semiconductor lasers are preferable as excitation light sources because they are compact, require low driving power, and can be directly modulated, making it easy to stabilize laser output.

The light source used for erasing may be one that emits light in the excitation wavelength range of the stimulable phosphor; examples include tungsten lamps, fluorescent lamps, halogen lamps, and high-pressure sodium lamps. can.

The radiation image conversion method of the present invention includes: a storage section that absorbs and stores radiation energy in a stimulable phosphor; a photodetection (readout) section that irradiates the phosphor with excitation light and emits the radiation energy as fluorescence; It can also be applied to a built-in type radiation image conversion device in which an eraser for emitting the energy remaining in the phosphor is built into one device (Japanese Patent Application No. 57-84436 and Patent Application No. 66730-1989). (see specification). By using such a built-in device, the radiation image conversion panel (or the recording material containing the stimulable phosphor) can be reused and a stable and homogeneous image can be obtained. can. Further, by using a built-in type, the device can be made smaller and lighter, and its installation and movement become easier. Furthermore, by mounting this device on a mobile vehicle, it becomes possible to carry out circular radiography.

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 conversion panel consists of a support substantially including a support and a support provided on the support containing a divalent europium-activated composite halide phosphor represented by the composition formula () in a dispersed state. and at least one phosphor layer made of a binder.

The radiation image conversion panel having the above configuration can be manufactured, for example, by the method described below.

First, the divalent europium-activated composite halide phosphor represented by the above composition () used in a radiation image storage panel will be explained.

This divalent europium-activated composite halide phosphor can be manufactured, for example, by the manufacturing method described below.

First, as phosphor raw materials, (1) BaCl ₂ , SrCl ₂ , CaCl ₂ , BaBr ₂ , SrBr ₂ ,
Alkaline earth metal halide selected from the group consisting of CaBr ₂ , BaI ₂ , SrI ₂ and Cal ₂ , (2) LiCl, RbCl, CsCl, LiBr, RbBr, CsBr,
An alkali metal halide selected from the group consisting of LiI, RbI, and CsI; and (3) a compound selected from the group consisting of europium compounds such as halides, oxides, nitrates, and sulfates.

In some cases, ammonium halide (NH ₄ X''; where X'' is Cl, Br or I) may also be used as a flux.

When producing a phosphor, the above (1) alkaline earth metal halide, (2) alkali metal halide, and (3) europium compound are used to stoichiometrically form the composition formula (): M 〓X ₂・aM〓X′:xEu () (where M〓 is at least one kind of alkaline earth metal selected from the group consisting of Ba, Sr, and Ca; at least one alkali metal selected from;
X′ are the same (i.e., X=X′), and
is a halogen of any one of Cl, Br, or I; and a is a numerical value in the range of 0.1≦a≦20.0, and x is a numerical value in the range of 0<x≦0.2). A mixture of phosphor raw materials is prepared by weighing and mixing as follows.

The phosphor raw material mixture may be prepared by (i) simply mixing the phosphor raw materials in (1), (2) and (3) above, or (ii) first by mixing the phosphor raw materials in (1), (2) and (3) above. By mixing the phosphor raw materials in 1) and (2), heating this mixture at a temperature of 100°C or higher for several hours, and then mixing the phosphor raw material in (3) above into the resulting heat-treated product. (iii) First, the phosphor raw materials in (1) and (2) above are mixed in a solution state, and this solution is heated (preferably
50 to 200° C.) by vacuum drying, vacuum drying, spray drying, etc., and then mixing the phosphor raw material of (3) above into the obtained dried product.

In addition, as a modification of method (ii) above, methods (1) and (2) above can be used.
A method of mixing the phosphor raw materials of (1), (2) and (3) above and subjecting the obtained mixture to the above heat treatment, and a modification of the above method (iii), A method may also be used in which the raw materials are mixed in a solution state and the solution is dried.

In any of the above methods (i), (ii), and (iii), mixing can be done using various mixers, V-type blenders,
Conventional mixers such as ball mills and rod mills are used.

Next, the phosphor raw material mixture obtained as described above is filled into a heat-resistant container such as a quartz board, an alumina crucible, or a quartz crucible, and fired in an electric furnace. The firing temperature is suitably in the range of 400 to 1300°C, preferably in the range of 700 to 1000°C. Although the firing time varies depending on the filling amount of the phosphor raw material mixture and the firing temperature, 0.5 to 6 hours is generally appropriate. As the firing atmosphere, 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. Generally, a trivalent europium compound is used as the phosphor raw material in (3) above, but in this case, during the firing process, the trivalent europium becomes divalent due to the weakly reducing atmosphere mentioned above. Returned to europium.

A powdered phosphor is obtained by the above firing.
Note that the obtained powdered phosphor may be further subjected to various general operations in the production of phosphors, such as washing, drying, and sieving, as necessary.

In the method for producing a phosphor of the present invention, X and X' in the alkaline earth metal halide (M〓X ₂ ) and the alkali metal halide (M〓X') are the same (that is, X=X'). shall be. From the viewpoint of stimulated luminescence brightness, X representing halogen is preferably Br or Cl. Also, in the composition formula ()
The a value representing the ratio of M〓X ₂ and M〓X′ is 1.5≦a≦
It is preferably in the range of 10.0, in which case M〓 representing the alkali metal is preferably Ba.
Furthermore, from the viewpoint of stimulated luminescence brightness, the x value representing the activation amount of europium in the composition formula () is 10 ^-5 ≦
It is preferable that x≦10 ⁻² .

Examples of binders for the phosphor layer formed by dispersing the divalent europium-activated composite halide phosphor include proteins such as gelatin, polysaccharides such as dextran, or gum arabic. natural polymeric substances such as; and
Synthesis of polyvinyl butyral, polyvinyl acetate, nitrocellulose, ethylcellulose, vinylidene chloride/vinyl chloride copolymer, polyalkyl (meth)acrylate, vinyl chloride/vinyl acetate copolymer, polyurethane, cellulose acetate butyrate, polyvinyl alcohol, linear polyester, etc. Examples include binders typified by polymeric substances. 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. be.

The phosphor layer can be formed on the support, for example, by the following method.

First, a 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. I can do it. Examples of such materials include films of plastic materials such as cellulose acetate, polyester, polyethylene terephthalate, polyamide, polyimide, triacetate, polycarbonate, metal sheets such as aluminum foil, aluminum alloy foil, ordinary paper,
Examples include baryta paper, resin-coated paper, pigment paper containing pigments such as titanium dioxide, and paper sized with polyvinyl alcohol.

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 described in Japanese Patent Application Laid-Open 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 to each other 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 layer containing the divalent europium-activated composite halide phosphor of the composition formula () is sufficient, and the luminous efficiency against radiation increases gradually toward the surface of the panel. A structure in which a plurality of phosphor layers are stacked may be used. 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, A is Ca, 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 ), as described in JP-A-55-12144.
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 the present application M〓X ₂・aM〓X′ ₂ :xEu ²⁺ (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 at least one kind of halogen selected from the group consisting of Cl, Br, and I, and ≠
and a is a numerical value in the range of 0.1≦a≦10.0, and x is a numerical value in the range of 0<x≦0.2).

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.

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

Example 1 After weighing 297.15 g of barium bromide (BaBr ₂ ), 86.84 g of lithium bromide (LiBr), and 0.392 g of europium bromide (EuBr ₃ ), they were thoroughly mixed and pulverized in a ball mill to obtain a phosphor raw material mixture. Prepared.

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 850° C. for 2 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 powdered divalent europium-activated barium lithium bromide phosphor (BaBr ₂ .LiBr: 0.001Eu ²⁺ ) was obtained.

Example 2 Example 1 except that 212.90 g of cesium bromide (CsBr) was used instead of lithium bromide.
By performing the same operation as in Example 1, a powdered divalent europium-activated barium cesium bromide phosphor (BaBr ₂ .CsBr: 0.001Eu ²⁺ ) was obtained.

Example 3 Same method as in Example 1 except that 208.25 g of barium chloride (BaCl ₂ ) was used instead of barium bromide and 120.92 g of rubidium chloride (RbCl) was used instead of lithium bromide. By performing this operation, a powdered divalent europium-activated composite halide phosphor (BaBr ₂ / RbCl:
0.001Eu ²⁺ ) was obtained.

Next, each of the phosphors obtained in Example 1 and Example 2 was irradiated with X-rays at a tube voltage of 80 KVp, and then He
The stimulated emission spectrum when excited with -Ne laser light (wavelength 632.8 nm) and the stimulated excitation spectrum at the peak wavelength of the stimulated emission were measured. The results obtained are shown in FIGS. 2 and 1.

In Figure 2, curve 1 and curve 2 are Curve 1: Stimulated emission spectrum of BaBr ₂・LiBr: 0.001Eu ²⁺ phosphor, Curve 2: Stimulated emission spectrum of BaBr ₂・CsBr: 0.001Eu ²⁺ phosphor , indicates.

In addition, in Fig. 1, curve 1 and curve 2 are respectively curve 1: the stimulated excitation spectrum of BaBr ₂・LiBr: 0.001Eu ²⁺ phosphor, and curve 2: the brightness of BaBr ₂・CsBr: 0.001Eu ²⁺ phosphor. The exhaustion excitation spectrum is shown.

Example 4 The powdered divalent europium-activated odorous barium lithium phosphor (BaBr ₂ .
Methyl ethyl ketone was added to a mixture of LiBr (0.001Eu ²⁺ ) and a linear polyester resin, and nitrocellulose with a degree of nitrification of 11.5% was added to prepare a dispersion containing a phosphor in a dispersed state. Next, tricresyl phosphate, n-butanol,
After adding methyl ethyl ketone, the phosphor is sufficiently stirred and mixed using a propeller mixer to ensure that the phosphor is uniformly dispersed, the binder and phosphor are mixed in a ratio of 1:10, and the viscosity is 25 to 35 PS (at 25°C). ) was prepared. Next, the coating solution was uniformly applied using a doctor blade onto polyethylene terephthalate mixed with titanium dioxide (support, thickness: 250 μm) placed horizontally on a glass plate. After coating, the support on which the coating film was formed was placed in a dryer, and the temperature inside the 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 5 In Example 4, the
BaBr ₂ CsBr: 0.001Eu ²⁺ By performing the same operation as in Example 4 except for using the phosphor, a radiation image conversion panel composed of a support, a phosphor layer, and a transparent protective film was prepared. Manufactured.

Example 6 In Example 4, the
BaCl ₂・RbCl: 0.001Eu ²⁺ By performing the same operation as in Example 4 except for using the phosphor, a radiation image conversion panel composed of a support, a phosphor layer, and a transparent protective film was prepared. Manufactured.

Next, after irradiating each radiation image conversion panel obtained in Examples 4 to 6 with X-rays at a tube voltage of 80 KVp,
The sensitivity (stimulated luminance) of each panel was measured by exciting 632.8 nm light. The results are shown in Table 1.

Table 1 Relative sensitivity Example 4 100 Example 5 80 Example 6 30

[Brief explanation of drawings]

FIG. 1 shows BaBr ₂ .
LiBr: 0.001Eu ²⁺ phosphor and BaBr ₂ /CsBr:
Figure 2 is the photostimulation excitation spectrum of the 0.001Eu ²⁺ phosphor (curves 1 and 2, respectively). Figure 2 shows the stimulated excitation spectra of BaBr ₂ .LiBr: 0.001Eu ²⁺ phosphor and BaBr ₂ .CsBr: 0.001Eu ²⁺ phosphor, which are specific examples of the divalent europium-activated composite halide phosphor of the present invention. (curves 1 and 2, respectively).
FIG. 3 shows BaBr ₂ .
It is a graph showing the relationship between the a value and stimulated luminescence intensity in aLiBr:0.001Eu ²⁺ phosphor. Figure 4 shows
FIG. 1 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: line-electric conversion device, 16: image reproduction device, 17: image display device, 18: filter.

Claims (1)

[Claims] 1. After the radiation transmitted through the subject or emitted from the subject is absorbed by a divalent europium-activated composite halide phosphor represented by the following compositional formula (), this phosphor is A radiation image conversion method characterized by emitting radiation energy stored in the phosphor as fluorescence by irradiating electromagnetic waves in a wavelength range of ~900 nm, and detecting this fluorescence. Composition formula (): M〓X ₂・aM〓X′:xEu ²⁺ () (However, M〓 is at least one alkaline earth metal selected from the group consisting of Ba, Sr, and Ca; M〓 At least one alkali metal selected from the group consisting of Li, Rb and Cs;
X' is X=X' and is any one of halogens such as Cl, Br, or I; and a is 0.1≦a
(a is a numerical value in the range of ≦20.0, and x is a numerical value in the range of 0<x≦0.2) 2 a in the composition formula () is 1.5≦a≦10.0
The radiation image conversion method according to claim 1, wherein the numerical value is in the range of . 3. The radiation image conversion method according to claim 1, wherein X in the compositional formula () is either Br or Cl. 4. The radiation image conversion method according to claim 1, wherein M in the compositional formula () is Ba. 5 x in the composition formula () is 10 ^-5 ≦x≦10 ^-2
The radiation image conversion method according to claim 1, wherein the numerical value is in the range of . 6. The radiation image conversion method according to claim 1, wherein the electromagnetic wave is an electromagnetic wave in a wavelength range of 500 to 800 nm. 7. The radiation image conversion method according to claim 1, wherein the electromagnetic wave is a laser beam. 8 Substantially composed of a support and at least one phosphor layer made of a binder containing and supporting the stimulable phosphor in a dispersed state provided on the support, A radiation image conversion panel characterized in that at least one layer thereof contains a divalent europium-activated composite halide phosphor represented by the following compositional formula (). Composition formula (): M〓X ₂・aM〓X′:xEu ²⁺ () (However, M〓 is at least one alkaline earth metal selected from the group consisting of Ba, Sr, and Ca; M〓 At least one alkali metal selected from the group consisting of Li, Rb and Cs;
X' is X=X' and is any one of halogens such as Cl, Br, or I; and a is 0.1≦a
(a is a numerical value in the range of ≦20.0, and x is a numerical value in the range of 0<x≦0.2) 9 a in the composition formula () is 1.5≦a≦10.0
9. The radiation image conversion panel according to claim 8, wherein the radiation image conversion panel has a numerical value in the range of . 10. The radiation image storage panel according to claim 8, wherein X in the compositional formula () is either Br or Cl. 11. The radiation image conversion panel according to claim 8, wherein M in the compositional formula () is Ba. 12 x in the composition formula () is 10 ^-5 ≦x≦
The radiation image conversion panel according to claim 8, which has a numerical value in the range of 10 ^-2 .