JP2649530B2 - Radiation detector - Google Patents

Description

The present invention relates to a radiation detector for detecting X-rays, γ-rays, etc., and particularly to X-rays and CT (computerized tomography).
Alternatively, the present invention relates to a radiation detector suitable for use in a positron camera or the like.

[Prior Art] There are various types of X-ray CT, but usually 20 to 1000
A radiation detector with the same performance is required.

Conventionally, radiation detectors used for X-ray CT and the like include a xenon gas chamber or a combination of BGO single crystal (bismuth germanate) and a photomultiplier tube, Cs
A combination of a single crystal of I: Tl or a single crystal of CdWO ₄ and a photodiode has been used. The xenon gas chamber requires a thick window to enclose high-pressure xenon gas in the detector, and has two collimator plates per element, so the X-ray utilization efficiency is about 50%. Would. BGO has a low luminous efficiency (about 1%), so it is used in combination with a photomultiplier tube, but it requires a photomultiplier tube and a high-voltage power supply attached to it, making it difficult to use multiple elements. It is.

CsI: Tl is a highly efficient but deliquescent phenomena and is a phenomenon of afterglow (light emission after X-rays are turned off), and has practical problems.

CdWO ₄ has a problem in that it has low luminous efficiency, is easily cleaved when cut, and is toxic.

A drawback common to the single crystal scintillators described above is that there is variation in light emission characteristics within the single crystal. A single crystal is generally grown from a melt, but a lattice defect is likely to spread along the crystal during the growth process, so that an afterglow phenomenon may appear. Further, an activator is often added to the scintillator, but it is difficult to uniformly disperse the activator in the crystal. Therefore, uneven light emission occurs in the crystal. The above-mentioned problems mean that it is extremely difficult to match the characteristics of each detector.

To solve this problem, some of the present inventors have already proposed a radiation detector using phosphor particles as a scintillator as shown in Japanese Patent Publication No. 60-4856. Usually, in order to obtain a cross-sectional area in a radiation detector for X-ray CT, the width is about 1 to 3 mm and the length is about 20 mm.
Therefore, the number of phosphor particles in one radiation detector is, for example, about 300,000, depending on the particle size. The characteristics of individual phosphor particles may be slightly different, but by mixing well and using as one scintillator, the variation in characteristics as a scintillator,
One-square root of the number of particles, that is, about 0.01%, a satisfactory result can be obtained.

This radiation detector will be described with reference to FIG.
After the incident X-rays 1 pass through the lid 5 and the light scattering layer 4 made of an aluminum thin film, the scintillator particle layer 2 (a phosphor obtained by solidifying the phosphor with polystyrene) emits light. This light emission reaches the photodiode 3 after passing through the space layer 7 and the secondary radiation prevention layer 8 (lead glass), and is converted into a current. Further, in order to efficiently guide light emitted from the scintillator particle layer to the photodiode, the entire container 6 is covered with a reflective film. As described above, the detector can obtain approximately twice the output as compared with a detector combining a single crystal scintillator and a photodiode, and is extremely desirable as a detector for head X-ray CT. However, there are some problems in applying it to a detector for the whole body. This is because the image processing methods for the head and the whole body are different. In FIG. 1, the light emission characteristics of the scintillator layer 2 are uniform, but the light repeatedly hits the reflective film covering the space layer 7 until the light reaches the photodiode 3. Therefore, if there is unevenness in the reflectance of the reflective film, accurate information on the incident X-rays cannot be obtained. for that reason,
If such a detector is polymorphized, the characteristics will vary among the elements. As a result, artifacts occur in the reproduced image obtained using this detector.

In order to solve this problem, it is necessary to adopt a structure as shown in FIG. That is, the silicon photodiode 3 is arranged at the bottom of the container 6 made of brass, and the inner surface of the container 6 has a light reflecting surface made of aluminum. In the container 6, a lead glass 8 is arranged on a silicon photodiode 3, and a scintillator layer 2 is further formed thereon. Lead glass is provided to cut fluorescent X-rays emitted from the scintillator.

In the structure shown in FIG. 2, when a scintillator particle layer is used, it is difficult to efficiently guide light emission to the silicon photodiode because the particle layer itself is optically opaque. Gd ₂ O ₂ S: Pr, Ce, F
Even when a scintillator is used, there is a problem that a signal output is almost the same as that of a detector combining a single crystal scintillator CdWo ₄ and a silicon photodiode.

[Problems to be solved by the invention]

SUMMARY OF THE INVENTION An object of the present invention is to solve the above-mentioned problems of the prior art and to provide a radiation detector having a high optical output.

[Means for solving the problem]

The above object is a scintillator powder that emits light by radiation, and has a general formula (Ln _1-xy Pr _x Ce _y ) ₂ O ₂ S: (X) (where Ln is selected from the group consisting of Gd, La, and Y) X represents at least one element selected from the group consisting of F and Cl, and x represents 3 × 10 ⁻⁶ x
0.2, y is a value in the range of 10 ⁻⁶ y5 × 10 ⁻³ , and the amount of X is 2 to 1000 ppm). As a sintering aid, R ₂ GeF ₆ (R: Li, NH ₄ , Na, K), R′PF ₆ (R ′: Na, K, NH ₄ ), R ″ ₂ SiF ₆ (R ″: Li, Na, K), ZHF ₂ (Z: Na, K, NH ₄ ), Z ′ ₂ TiF ₆ (Z ′: Na, K), Z ″ ₂ ZuF ₆ (Z ″: K, NH ₆ ), ESiF ₆ (E: Mg, Sr), E′BF ₄ (E ′: Li, Na, K ), At least one compound selected from the group consisting of LiF and Na ₃ AlF ₆ is added in an amount of 0.001 to 10% by weight, the resultant is packed in a metal container, vacuum-sealed, and hot isostatically pressed. It is further achieved by a radiation detector in which a light-transmitting sintered body scintillator annealed in an atmosphere containing a trace amount of oxygen and a photodetector for detecting light emission of the scintillator are combined.

[Action]

The translucent sintered body can be obtained by HIPing at 0.001 to 10% by weight, a pressure of 500 to 2000 atm, and a temperature of 800 to 1700 ° C. However, under these conditions, when the pressure is low, it is necessary to perform HIP at a high temperature. Preferred HIP conditions are the addition amount of the sintering aid of 0.01 to 4% by weight, the temperature of 1100 to 1500 ° C., and the pressure of 800 to 1800 atm. As the material of the metal container used for the HIP, a metal which is easily deformed (softened) at a high temperature, such as pure iron, stainless steel, an alloy of nickel nickel and iron, and platinum are preferable.

A translucent sintered body can be obtained by adding a sintering agent and performing HIP. The production method is as follows, for example. Li ₂ GeF ₆ sintering aid was added 87 g was packed in a container made of pure iron with a size of 52φ × 37 (effective volume 21.9 cm ³ ), vacuum-sealed, and placed in a HIP device.
HIP is performed at 300 ° C., 1500 atm for 3 hours, the sintered body is taken out of the container, processed into a thin plate having a thickness of 1 mm, and then annealed at 1200 ° C. for 30 minutes in an Ar gas containing 1 ppm of oxygen. The amount of Li ₂ GeF ₆ added differs depending on the method described above. Were produced, and a detector as shown in FIG. 2 was prototyped using these sintered bodies, and the light emission output was examined. As a result, that the luminous output of the addition amount when Li ₂ GeF ₆ which was 100 to light output LiGeF ₆ no addition sintered body within a range from 0.001 to 10 percent of 130 or more. The optimum amount of addition At around 0.1%, the light output is 1
It turned out to be 92.

In the above, when annealing was performed in Ar gas containing no oxygen, the amount of Li ₂ GeF ₆ added was 0.001 to 10%.
The luminous output within the range is 110 or more, and the optimal addition amount is 0.1%
It is 160 near. This indicates that it is more desirable to anneal in an atmosphere containing oxygen.
The reason can be considered as follows. The increase in light output when annealing in pure argon is due to the promotion of crystallization, and the increase in light output in argon gas containing a small amount of oxygen is due to the former effect and Gd ₂ O ₂ S: Pr, It is presumed that the effect of eliminating oxygen or sulfur lattice defects in Ce and F by oxygen was combined.

As the gas used with the enzyme, in addition to Ar, He, N
e, Kr and Xe may be used.

The enzyme content is desirably greater than 0 and less than 1000 ppm, preferably 0.05 to 100 ppm. Since Gd ₂ O ₂ S than acting collapsing lattice defects is Gd ₂ 3 becomes more than 1000 ppm, the light emitting output decreases.

Further, it is considered that the oxygen content depends on the annealing time, and a preferable result was obtained by increasing the annealing time even if the oxygen content was relatively small.

In the above-mentioned sintering aid other than Li ₂ GeF ₆ , Li ₂
There are substantially the same effect as GeF _6.

The annealing temperature is preferably in the range of 800 to 150 ° C., preferably
It is good to carry out at 1000-1300 ° C.

The reason for limiting each symbol in the scintillator powder (Ln _1-xy Pr _x Ce _y ) ₂ O ₂ S: (X) is omitted because it is described in the above-mentioned JP-B-60-48561.

〔Example〕

Example 1 Scintillator powder To 87g, add 0.087g of Li ₂ GeF ₆ (addition amount: 0.1%), and add it to a pure iron container with a diameter of 52mm, a length of 37mm, and a thickness of 1mm (volume 21.9c
m ³ ) and vacuum sealed while heating to 250 ° C. Next, the container was placed in a HIP device, at 1300 ° C., 1500 atm.
After HIPing under the conditions of time, after cooling, the sintered body is taken out of the container, processed into a thin plate having a thickness of 1 mm, and then annealed at 1200 ° C. for 30 minutes in an argon gas containing 1 ppm of oxygen.
Using the sintered body thus obtained, a detector as shown in FIG. 2 was prepared, and the luminescence output by X-ray irradiation (tube voltage 120 kV, 100 mA) was measured. As a result, the luminous output of the detector using this sintered body was 192 when the luminous output of a detector similarly prepared without adding a sintering aid was 100. The light emission output was 160 when annealing was performed in pure argon gas and the rest was performed in the same manner as described above.

Example 2 Scintillator powder To 87 g, 0.0087 g of Li ₂ GeF ₆ (addition amount: 0.01%) was added, and the HIP process was performed in the same manner as in Example 1. The sintered body is taken out of the container, processed into a thin plate having a thickness of 1 mm, and then annealed at 1200 ° C. for 30 minutes in an argon gas containing 1 ppm of oxygen.
The light emission output of the thus obtained sintered body was measured by the method described in Example 1. As a result, the luminous output of the detector using this sintered body was 130 when the luminous output of the detector similarly prepared without adding a sintering aid was 100. The luminescence output was 110 when annealing was performed in pure argon gas and the rest was performed in the same manner as described above.

Example 3 A HIP sintered body obtained in the same manner as in Example 1 was taken out of the container, processed to a thickness of 1 mm, and then annealed at 1200 ° C. for 30 minutes in an argon gas containing 1000 ppm of oxygen.
The light emission output of the thus obtained sintered body was measured by the method described in Example 1. As a result, the luminous output of the detector using this sintered body was 165 when the luminous output of a detector similarly prepared without adding a sintering aid was 100. The light emission output was 160 when annealing was performed in pure argon gas and the rest was performed in the same manner as described above.

Example 4 A HIP sintered body obtained in the same manner as in Example 1 was taken out of the container, processed into a thickness of 1 mm, and then annealed at 1200 ° C. for 30 minutes in an argon gas containing 0.05 ppm of oxygen.
The light emission output of the thus obtained sintered body was measured by the method described in Example 1. As a result, the light emission output of the detector using this sintered body was 176 when the light emission output of a detector similarly prepared without adding a sintering aid was 100. The light emission output was 160 when annealing was performed in pure argon gas and the rest was performed in the same manner as described above.

Examples 5 to 27 Scintillator powder 0.087 g (addition amount: 0.1%) of various sintering aids were added to 87 g, respectively, and thereafter, a HIP sintered body was produced in the same manner as in Example 1.
Remove the sintered body from the container, process it to a thickness of 1 mm,
Anneal at 1200 ° C. for 30 minutes in an argon gas containing 1 pm of oxygen. The light emission output of each of the sintered bodies thus obtained was measured by the method described in Example 1. The luminescence output of a detector fabricated in the same manner as described above without the addition of a sintering aid is shown in the table below as 100.

[Effects of the Invention] According to the present invention, it is possible to obtain a sintered body having a high translucency having a composition of (Ln _1-xy Pr _x Ce _y ) ₂ O ₂ S: (X). The emission line detector combined with the photodiode has the effect of greatly increasing the light output as compared with the conventional one.

[Brief description of the drawings]

1 and 2 are cross-sectional views of a radiation detector for explaining the present invention. DESCRIPTION OF SYMBOLS 1 ... X-ray incident light 2 ... Scintillator layer 3 ... Silicon photodiode 4 ... Light scattering layer 5 ... Aluminum thin film 6 ... Container 7 ... Space layer 8 ... Lead glass 9 ...... Silicon grease

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Shuji Fujii 1-280 Higashi Koikekubo, Kokubunji-shi, Tokyo Inside the Hitachi, Ltd. Central Research Laboratory (72) Inventor Hiroyuki Takeuchi 1-280 Higashi Koikekubo, Kokubunji-shi, Tokyo Hitachi, Ltd. Central Research Laboratory (72) Inventor Kozo Toda 1-280 Higashi Koikekubo, Kokubunji-shi, Tokyo Hitachi Central Research Laboratory Co., Ltd. (56) References JP-A-63-113388 (JP, A) JP, A) JP-A-1-190108 (JP, A)

Claims (1)

(57) [Claims] 1. A scintillator which emits light by radiation and has a general formula (Ln _1-xy Pr _x Ce _y ) ₂ O ₂ S: (X) (where Ln is
X represents at least one element selected from the group consisting of Gd, La, Y, X represents at least one element selected from the group consisting of F and Cl, x is 3 × 10 ⁻⁶ x0.2, y Is a value in the range of 10 ⁻⁶ y5 × 10 ⁻³ , and the amount of X is 2 to 10
R ₂ GeF ₆ (R: Li, NH ₄ , Na, K), R′PF ₆ (R ′: Na, K, NH ₄ ), R ″ ₂ SiF ₆ (R ″: Li, Na, K), ZHF ₂ (Z: Na, K, NH ₄ ), Z ′ ₂ TiF ₆ (Z ′: Na, K), Z ″ ₂ ZuF ₆ (Z ″: K, _{NH 6), ESiF 6 (E} : Mg, Sr), E'BF 4 (E ': Li, Na, K), at least one compound selected from the group consisting of LiF and Na ₃ AlF ₆ 0.001 to 10 % By weight, packed in a metal container, vacuum sealed,
What is claimed is: 1. A radiation detector comprising: a scintillator obtained by hot isostatic pressing and annealing in an atmosphere containing a small amount of oxygen; and a photodetector for detecting light emission of the scintillator.