JPH0543871A - Manufacture of stimulable phosphor material - Google Patents

Abstract

(57) [Summary] [Purpose] The purpose is to improve the sensitivity of photostimulable fluorescent materials. [Constitution] In the manufacturing process of the photostimulable phosphor material obtained by mixing raw material powder consisting of barium halide, europium halide and ammonium halide, firing it, and then pulverizing and classifying it, it is previously melted as barium halide and compressed. A stimulable phosphor is characterized by using a material that has been subjected to a densification treatment such as powder firing or amorphization.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing a stimulable phosphor material having improved luminous sensitivity. An X-ray image conversion sheet using a stimulable phosphor is combined with a digital image processing device to form an X-ray photography system.

That is, X-rays are used in a wide range of fields such as diagnosis of human bodies and identification of materials, but the greatest use is for X-ray diagnosis. The diagnosis is made by taking X-ray photographs and fluoroscopy, but since X-rays are radiation and are harmful to the human body, it is necessary that the exposure dose be as small as possible. Improvements have been made in terms of improving sensitivity, and inspections are now performed with a small amount of X-rays that is incomparable compared with the past.

However, when the sensitivity of the film is increased, deterioration of image quality is inevitable. On the other hand, the recently developed X-ray photography system uses an X-ray image conversion sheet and a computer to perform image processing. Specifically, the X-ray image conversion sheet is used instead of the conventional film for photographing. , After converting the X-ray image projected on the sheet into an electrical signal using laser light, the signal is processed by a computer, and this information is converted into the intensity of the laser light for normal photography. An X-ray photograph is formed by transferring it to film.

According to such a method, a few tens of times compared with the conventional method.
A clear image can be obtained with a dose less than a fraction. Here, the X-ray image conversion sheet is a sheet using a photostimulable phosphor that once accumulates radiation energy and then emits fluorescence again by excitation of heat or light.

The present invention relates to a photostimulable phosphor constituting such an X-ray image conversion sheet and a method for producing the same.

[0006]

2. Description of the Related Art An X-ray image conversion sheet is a transparent resin film such as a polyethylene terephthalate film on which an alkaline earth metal halide and eurobium halide (E
a mixture with u) is fired in a reducing gas to form a divalent europium-activated alkaline earth metal halide phosphor,
Such a stimulable phosphor is mixed with a binder and applied on a base film, and a thin film of Mylar is adhered on the base film to be used as a sheet.

Here, the principle of photostimulable fluorescence emission is that when a phosphor crystal is irradiated with X-rays, electrons in the valence band are excited to the conduction electron band, but immediately in the forbidden band. Stabilize by falling to the impurity level.

This corresponds to the accumulated recording of X-ray energy. Next, when a laser beam is irradiated for reading, the electrons in the impurity level absorb the energy of the laser beam and are excited to the conduction electron band, and then fall back to the original valence band.
At this time, the phosphor emits fluorescence, and its brightness is proportional to the amount of trapped electrons in the impurity level.

From the above, the surface of the X-ray image conversion sheet is scanned with a laser beam of a minute spot (diameter 100 μm),
The fluorescence emission of each pixel is detected using an interference filter, converted into an electronic signal by a photomultiplier tube, and recorded.

In such a stimulable phosphor, Eu ²⁺ is an effective element in forming a luminescent center, and is formed by reduction of an Eu compound such as europium bromide (EuBr ₃ ). Specifically, a mixer such as barium bromide (BaBr ₂ ) and europium halide such as EuBr ₃ and ammonium halide such as ammonium bromide (NH ₄ Br) such as V-blender. The resulting powder is mixed in a heat-resistant container such as a quartz baking dish, and the mixture is mixed in a neutral atmosphere such as nitrogen (N ₂ ) or helium (He) or hydrogen (H ₂ ) in argon (Ar). 80 in a weak reducing atmosphere
0 to 900 ° C. of E into BaBr ₂ crystal by firing at a temperature
A stimulable phosphor composed of BaBr ₂ : Eu ²⁺ in which u atoms are dispersed is formed.

Next, after crushing the phosphor, this powder and a binder (for example, polymethylmethacrylate abbreviated as PMM) are used.
A) and a solvent (for example, toluene) are kneaded to form a coating solution, which is applied evenly on the resin film, and the solvent is dried, after which the resin film (for example, Mylar) is applied.
An X-ray image conversion sheet is made by sticking.

Now, the stimulable phosphor forming the X-ray image conversion sheet is thus a divalent Eu-activated barium bromide (B
Although it is made of aBr ₂ : Eu ²⁺ ), there is a great demand to improve the emission sensitivity and further reduce the irradiation X-ray dose, and further improvement of the stimulable phosphor is required.

[0013]

As the demand for X-ray image sheets increases in medical diagnosis and material inspection, there is a great demand to further reduce the irradiation X-ray dose.

Therefore, it is an object to put the sensitizing phosphor with higher sensitivity into practical use.

[0015]

[Means for Solving the Problems] The above problems are caused by BaBr ₂ and Eu.
In the manufacturing process of the stimulable phosphor powder obtained by mixing and firing raw material powder consisting of Br ₃ and NH ₄ Br, and pulverizing and classifying it, high density such as pre-melting as BaBr ₂ , compaction firing or amorphization The problem can be solved by producing a stimulable phosphor by using a material that has been subjected to a chemical treatment.

[0016]

[Function] As described above, the stimulable phosphor is composed of Eu ²⁺ activated barium halide obtained by mixing barium halide with europium halide and ammonium halide and firing the mixture. Barium bromide (BaBr ₂ ), barium fluorobromide (BaFBr), barium chlorobromide (BaBrCl) and the like are used as barium.

Incidentally, ammonium halide such as ammonium bromide (NH ₄ Br) which is added upon firing is a kind of reaction accelerator for creating a rich atmosphere of halogen.

The present inventors have selected BaBr ₂ as a barium halide.
We have been studying stimulable phosphor materials by using, and found that it is necessary to increase the density of Ba halides in order to increase the sensitivity of stimulable phosphors.

That is, a large amount of halogenated Ba is available.
Kumono is wet. For example, BaBr₂ Is BaBr₂ ・ 2H
₂O state is stable and BaCl₂Is BaCl₂・ 2H ₂State of O
The condition is stable.

Therefore, prior to the formation of the stimulable phosphor material, the halogenated Ba is heated to about 500 ° C. in the atmosphere for dehydration treatment, pulverized and then pulverized, and then a small amount of halogenated Eu and halogenated NH ₄ is added. And are mixed and fired, and Eu ²⁺ activated halogenated Ba
Is formed.

However, as a result of research conducted by the present inventors, the crystals of halogenated Ba that have been subjected to heat dehydration treatment contain voids due to dehydration, and even in the firing for the formation of Eu ²⁺ activated halogenated Ba, It was found that the voids are preserved, which hinders the luminescence sensitivity during X-ray irradiation.

Therefore, the present invention provides a method for densifying the halogenated Ba by eliminating voids: it is melted without being decomposed and then pulverized. It is conventionally heated to an anhydride, then pressed and fired. Makes it easy to melt in an amorphous state. One of the above methods is used.

The present invention will be described below by taking BaBr ₂ as the barium halide.

[0024]

Examples Example 1: (when melted) First, BaBr ₂ was charged into a baking container made of a quartz crucible, and then baked in a weak reducing atmosphere containing a small amount of hydrogen (H ₂ ) in helium (He). Temperature 850
Firing was performed by setting four kinds of temperatures, ℃, 900 ℃, 950 ℃ and 1000 ℃.

The firing conditions were that the temperature rising rate was 100 ° C./H, the temperature was maintained at the set temperature for 3 hours, and the material was gradually cooled at 15 ° C./H. Here, the melting point of BaBr ₂ is 847 ° C, and it is visually unmelted by firing at 850 ° C.

BaBr ₂ dehydrated in this way is crushed and classified, and this is used as a raw material. BaBr ₂ ... 150 g EuBr ₃ ... 0.4 g NH ₄ Br ... 4.5 g was sampled and mixed by a mixer, and the obtained powder was charged into a calcining vessel consisting of a quartz crucible in the same manner as above, and then the heating rate was set to 100 in a weak reducing atmosphere containing a trace amount of H _{2 in} He. C./H, slow cooling rate was 20.degree. C./H, and baking was performed at 850.degree. C. for 1 hour.

This was crushed and classified to obtain particles having a central particle size of 10 μm, and an X-ray image conversion sheet having a thickness of 300 μm was prepared in the same manner as in the conventional method, and its sensitivity was measured. In addition, BaBr ₂
The relative sensitivity was calculated by setting the sensitivity to 100 according to the conventional method in which the raw material was dehydrated at 500 ° C in air and used.

As a result, as the relationship between the firing temperature and (relative sensitivity), 850 ° C. (100), 900 ° C. (125), 950 ° C. (130),
A relationship of 1000 ° C (95) was obtained. From now on, if you use the one that is heated to 900 ℃ or more and melted, the sensitivity will increase.
It can be seen that when heated up to 1000 ° C, partial decomposition occurs and the sensitivity is lowered. Example 2: (When powder compacting) BaBr ₂ raw material in air
And fired for 3 hours at 500 ° C. dehydrated, filled in a firing container made of the quartz crucible after the anhydride, in a weakly reducing atmosphere containing H ₂ traces heating rate to He at 40 ° C. / H 845 After heating to ℃, it was gradually cooled to room temperature at 50 ℃ / H.

In this state, BaBr ₂ is sintered and not melted. After crushing and classifying such BaBr ₂ , use this as a raw material, and collect and mix BaBr ₂ ... 150 g EuBr ₃ ... 0.4 g NH ₄ Br ... 4.5 g After mixing by a machine, the obtained powder is filled in a firing container made of a quartz crucible in the same manner as above, and then 840 in advance.
It was placed in a tubular furnace maintained at ℃, baked for 30 minutes in a weak reducing atmosphere containing a trace amount of H _{2 in} He, and cooled to room temperature at a slow cooling rate of 50 ℃ / H.

This was crushed and classified to obtain particles having a central particle size of 10 μm, and an X-ray image conversion sheet having a thickness of 300 μm was prepared by the same method as in the conventional method, and its sensitivity was measured. In addition, BaBr ₂
The relative sensitivity was calculated by setting the sensitivity to 100 according to the conventional method in which the raw material was dehydrated at 500 ° C in air and used.

As a result, it was found that the sensitivity of the stimulable phosphor using BaBr ₂ which was compacted and baked was 125, which was highly sensitive. Example 3: (when amorphized) BaBr ₂ .2 H ₂ O
Is a deliquescent colorless crystal, H ₂ O 100g at 20 ℃
To 104.1 g is dissolved.

This aqueous solution was sprayed using a spray dryer and dried to obtain an amorphous powder. This powder was sintered by hot pressing at a temperature of 800 ° C and a pressure of 1000 kg / cm ² , and then ground and classified as a raw material. BaBr ₂ ··· 100 g EuBr ₃ ··· 0.27 g NH ₄ Br ... 3.0 g was sampled and mixed by a mixer, and the obtained powder was filled in a baking container made of a quartz crucible in the same manner as above, and then 840
It was placed in a tubular furnace maintained at ℃, baked for 30 minutes in a weak reducing atmosphere containing a trace amount of H _{2 in} He, and cooled to room temperature at a slow cooling rate of 50 ℃ / H.

This was crushed and classified to obtain particles having a central particle diameter of 10 μm, and an X-ray image conversion sheet having a thickness of 300 μm was prepared in the same manner as in the conventional method, and its sensitivity was measured. In addition, BaBr ₂
The relative sensitivity was calculated by setting the sensitivity to 100 according to the conventional method in which the raw material was dehydrated at 500 ° C in air and used.

As a result, it was found that the sensitivity of the stimulable phosphor using BaBr ₂ improved in the amorphous state and having a high reactivity was 145, which showed high sensitivity.

[0035]

The X-ray sensitivity can be improved by implementing the present invention in which a stimulable phosphor is formed by using BaBr ₂ having a high density, and the X-ray irradiation dose can be reduced accordingly. .

 ─────────────────────────────────────────────────── ─── Continuation of front page (72) Masami Hasegawa 1015 Kamiodanaka, Nakahara-ku, Kawasaki City, Kanagawa Prefecture, Fujitsu Limited (72) Inventor Soichiro Hidaka 1015, Kamedotachu, Nakahara-ku, Kawasaki City, Kanagawa Prefecture, Fujitsu Limited

Claims (4)

[Claims] 1. A method for producing a stimulable phosphor powder obtained by mixing raw material powders of barium halide, europium halide and ammonium halide, firing the mixture, and then pulverizing and classifying the powder, and the barium halide is previously prepared as the barium halide. A method for producing a stimulable phosphor material, characterized in that a densified material is used. 2. The method for producing a stimulable phosphor material according to claim 1, wherein the barium halide densification treatment is melting of the barium halide. 3. The method for producing a stimulable phosphor material according to claim 1, wherein the densification treatment of the barium halide is powder firing of the barium halide. 4. The method for producing a stimulable phosphor material according to claim 1, wherein the barium halide densification treatment is an amorphousization of the barium halide.