JPH01191084A - Radiation detector - Google Patents

Abstract

PURPOSE:To effectively utilize the light emission of a scintillator which is sintered by using a hot hydrostatic pressing method effectively and to improve the sensitivity of the detector by reducing the thickness of the scintillator to 0.5-1.5mm and reducing the light loss. CONSTITUTION:When an X-ray photon 2 enters the polycrystalline scintillator 1, the scintillator is excited with the X-ray photon 2 to emit scintillation light 3 in a 4pi direction. This light 3 is scattered by interfaces of scintillator crystal particles and emitted out of the polycrystalline scintillator 1 as scattered light. The quantity of the scintillation light 3 is proportional to the quantity of the incident X-ray photon 2. The quantity of the emitted light is measured to measure a radiation dose secondarily. The density of this scintillator-sintered body is set to >=95% and the thickness of the scintillator-sintered body is 0.5-1.5mm.

Description

Detailed Description of the Invention [Field of Industrial Application] The present invention relates to a solid-state radiation detector comprising a scintillator and a semiconductor light-receiving element used in a computer-aided X-ray tomography apparatus (X-ray CT apparatus). The present invention relates to a detector structure suitable for effectively utilizing the light emitted from the light to improve the sensitivity of the detector.

[Conventional technology]

In conventional radiation detectors using polycrystalline scintillators, as described in JP-A-59-27283, the thickness of the scintillator must be increased to completely block incident radiation. No particular consideration was given to effectively utilizing the light emitted from the scintillator.

[The problem that the invention attempts to solve]

The above-mentioned conventional technology does not take into account the drawback of the translucent body of polycrystalline scintillators, which is the reduction in efficiency due to absorption and scattering of light within the scintillator, which lowers the effective rate of the scintillator and reduces the sensitivity of the detector. There was a layer between low and high dependence on the energy of incident radiation.

The present invention aims to solve the problem of realizing an efficient radiation detector by reducing light loss due to absorption and scattering inside a polycrystalline scintillator.

[Means to solve the problem]

The above problem is to use hot isostatic pressing (HIP) as a sintering method for polycrystalline scintillators, reduce the thickness of the sintered scintillator to 0.5 to 1.5 mm, and reduce optical loss. It is solved by

[Effect]

FIG. 1 is a cross-sectional view of a polycrystalline scintillator. When an X-ray photon 2 is incident on the polycrystalline scintillator 1, it is excited by the X-ray photon 2 and scintillation light 3 is emitted in the 4π direction. The light 3 is scattered at the interface of the scintillator crystal particles, becomes scattered light, and is emitted to the outside of the multi-crystalline scintillator 1. The amount of scintillation light 3 is proportional to the amount of incident X-ray photons 2. Therefore, the radiation dose can be measured secondarily by measuring the amount of emitted light.

Although polycrystalline scintillators have better sensitivity characteristics than single-crystal scintillators, as mentioned above, there is a lot of light scattering and absorption at the scintillator particle interface, so the scintillation light 3 is more concentrated than the polycrystalline scintillators 1. It has the disadvantage that it is difficult to extract into a single crystal, and because there are many grain boundaries, the effective density is lower than that of a single crystal. In the present invention, the following means are used to solve these interlayer points. First, the HIP method is used as a sintering method for polycrystalline scintillators. The raw material Gd2O2S:Pr, F, Ce phosphor is an advantageous material with high luminous efficiency and large X-ray blocking ability, but the S in the composition tends to be separated.

It is also a substance that is extremely difficult to crystallize. However) I
In the IP method, the raw material is sealed in a capsule and sintered isotropically under high pressure and high temperature, so stable and homogeneous sintering can be performed without scattering of S. Further, an effective density of 95 to 99% can be achieved, and a decrease in X-ray stopping ability due to a decrease in density can be prevented. Furthermore, since the spaces between the phosphor particles can be almost eliminated, translucency is improved and light loss can be reduced. By using the polycrystalline scintillator sintered in this way with a reduced thickness, it can be used without further deterioration in efficiency.

〔Example〕

An embodiment of the present invention will be described below with reference to FIG. The polycrystalline scintillator 1 is coated with a light reflecting material 7 (for example, MgO, Ti
Apply powder such as O2, Al2O3, etc., or apply powder such as AQ, Ag
The scintillation light 3 excited and emitted by the incident X-ray photons 2 is efficiently applied to the light-receiving surface 5 of the semiconductor light-receiving element 4 provided on the reinforcing substrate 6. Create a guiding structure. The light 3 reaching the light receiving surface 5 is extracted as a current signal due to the photoelectric effect. X
Scintillation light 3 excited and emitted by line photon 2
is proportional to the amount of incident X-ray photons 2, and since the semiconductor photodetector 4 emits a photocurrent proportional to the amount of incident light, by measuring the photocurrent, the amount of incident X-ray photons (
or other radiation) is constructed. Polycrystalline scintillator 1 is Gd2O2S
: Pr, F, Cef & HIP method sintered material is used within the thickness range of 0.5 mm to 1.5 mm.

According to this embodiment, uniformity is improved by using the polycrystalline scintillator 1 as the scintillator.

That is, even if the efficiency of the phosphor powder varies, it is dispersed, so that in the sintered body as an aggregate, the efficiency is averaged and the uniformity is improved.

By using the HIP method as a sintering method, it is possible to sinter a phosphor with high luminous efficiency that is difficult to single crystallize at an effective density of about 95 to 99%, and it has excellent translucency (
It becomes possible to realize a multi-connection &'R scintillator (with a transmittance of approximately 55% at IIQm thickness).

Figure 3 shows the thickness and X of the polycrystalline scintillator according to the present invention.
This is a diagram showing the relationship between the light emission output due to linear (120 kV) excitation, the plate thickness, and the total light transmittance by light source A. The light emission output is relatively high when the scintillator plate thickness is in the range of 0.5 to 1.5 mm. , and also has high light transmittance. Figure 4 shows XICTIC.
This figure shows the relationship between the thickness of a polycrystalline scintillator and detector quantum noise when applied to a commercial detector in comparison with an ionization chamber detector. Quantum noise is 20% stronger than detection and shows a smaller value, making it possible to improve the performance of the detector.

〔Effect of the invention〕

According to the present invention, the sensitivity of the detector can be improved, and the sensitivity is 1.3 to 1.5 times that of an ionization chamber detector.

2.5 times more than a detector using CdW○4 single crystal,
Quantum noise can be reduced by over 20% compared to an ionization chamber detector, and the cost is about 1/2 compared to a single crystal scintillator.
This makes it possible to achieve higher image quality and lower radiation dose in X-ray CT equipment.

[Brief explanation of the drawing]

FIG. 1 is a cross-sectional view of a polycrystalline scintillator according to the present invention;
FIG. 2 is a partially cutaway perspective view of a solid-state radiation detector according to an embodiment of the present invention, FIG. 3 is an actual measurement value showing the relationship between the plate thickness, light emission output, and light transmittance of the scintillator of the present invention, and FIG. The figure shows actual open values showing the quantum noise amount of a radiation detector according to an embodiment of the present invention in comparison with an ionization chamber detector. 1... Polycrystalline scintillator, 2... X-ray photon, 3
... Scintillation light, 4... Semiconductor light receiving element. 5... Light receiving surface, 6... Reinforcement substrate, 7... Light reflecting film.

Claims (1)

[Claims] 1. In a radiation detector combining a scintillator sintered body made of phosphor powder to make it translucent and a semiconductor light-receiving element, the scintillator sintered body has a density of 95% or more, and the scintillator A radiation detector characterized in that the thickness of the sintered body is within the range of 0.5 mm to 1.5 mm. 2. Gd_2O_2S:Pr as the phosphor powder;
Claim 1 characterized in that F and Ce are used.
Radiation detector described in section. 3. The radiation detector according to claims 1 and 2, characterized in that a hot isostatic pressing (HIP) method is used as a means for sintering the phosphor powder.