JP2871523B2 - Radiation detector - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a radiation detector used in a facility where γ-rays and β-rays and neutrons are mixed.

[0002]

2. Description of the Related Art Among radiation handling facilities, neutrons may be present in nuclear reactor facilities, accelerator facilities, fusion reactor experimental facilities, nuclear fuel reprocessing facilities, etc. in addition to gamma rays and beta rays. . In such a facility, it is important to control exposure by neutrons as well as γ-rays and β-rays, and a neutron detector is required for neutron exposure management.

However, neutrons are not charged particles and do not directly cause ionization. Therefore, neutrons cannot be detected by ordinary radiation detectors used for detecting γ-rays and β-rays. In order to detect neutrons, the reaction between neutrons and substances is used to detect neutrons, and to use neutrons as heavy charged particles such as protons and α-rays (hereinafter, charged particles such as protons, deuterium nuclei, and α-rays) In order to distinguish the particles from β-rays, they are collectively referred to as “heavy charged particles”. As a detector using such a method, a proportional counter using BF ₃ gas and the like have been conventionally known. In recent years, a neutron detector using a semiconductor detector has also been used. I have.

In this semiconductor neutron detector, a converter layer made of ⁶ LiF (lithium fluoride) is provided on the detection surface side of a semiconductor detector using Si or the like, and a nuclear reaction occurring when neutrons enter the converter layer. A neutron is detected indirectly by detecting an α ray generated by (n, α) with a semiconductor detector.

The use of a semiconductor detector makes it possible to reduce the size and sensitivity of a neutron detector. A small and highly sensitive neutron pocket dosimeter using such a semiconductor neutron detector has also been developed. It is used to monitor neutron exposure of individuals.

In a facility where neutrons and γ-rays and β-rays coexist as described above, such a neutron dosimeter and a γ-β-ray dosimeter are conventionally used for radiation management. By using them together, the neutron dose and γ-ray and β-ray dose were measured separately.

[0007]

However, there is a problem that it is bulky and inconvenient to mount the two types of dosimeters together as described above.
There is a demand for a small dosimeter capable of measuring both X-rays and β-rays. To meet this demand, dosimeters have been developed in which a semiconductor neutron detector and semiconductor detectors for γ-rays and β-rays are incorporated in one case.

However, in such a dosimeter, it is necessary to arrange a plurality of detectors corresponding to each line type on a substrate in parallel, and thus there is a limit to the miniaturization of the entire apparatus.

The present invention has been made to solve such a problem. One semiconductor detector detects both γ-rays and β-rays and neutrons, and the obtained detection signal is converted to γ-rays.・
Separation into those for β-rays and those for neutrons makes it possible to simultaneously obtain detection results for γ-rays and β-rays and for neutrons.
An object is to provide a lightweight radiation detection device.

[0010]

In order to achieve the above-mentioned object, a radiation detecting apparatus according to the present invention is a thin film layer which reacts with neutrons and emits heavy charged particles. Detects a converter layer set to a thickness such that the energy that charged particles lose before reaching the outside of the layer is equal to or less than a predetermined value, γ rays and β rays incident from the outside, and heavy charged particles incident from the converter layer. Semiconductor detector, wherein the thickness of the depletion layer is larger than the range of the incident heavy charged particles in the semiconductor material, and the β-ray of predetermined energy smaller than the energy of the incident heavy charged particles. A semiconductor detector set to be smaller than the range in the semiconductor material, and discrimination smaller than the energy of the incident heavy charged particle and larger than the predetermined energy for β-ray. A pulse discriminating circuit that discriminates the output pulse of the detector based on the value, based on the output of the pulse discriminating circuit, based on the output pulse of the detector, a detection pulse for neutrons, γ-ray or β-ray And counting separately.

Further, the radiation detecting apparatus according to the present invention is characterized in that a β-ray filter for blocking β-rays is provided on the radiation incident side of the converter layer.

[0012]

The energy of heavy charged particles generated by the reaction between the converter layer and neutrons is determined for each material of the converter layer. In the present invention, the converter layer is set to a thickness such that the loss energy until the generated heavy charged particles go out of the layer is equal to or less than a predetermined value. Will have more energy than the value.

Semiconductor detector (hereinafter abbreviated as "detector")
The thickness of the depletion layer is set larger than the range of the incident heavy charged particles in the detector, so that the heavy charged particles emitted from the converter layer and incident on the detector are depleted in the detector. Stop losing its energy completely within. As a result, a pulse corresponding to the total energy of the incident heavy charged particles is output from the detector. Therefore, the detection pulse of the heavy charged particle has a wave height corresponding to the energy equal to or higher than a certain value.

On the other hand, the detection pulse of the detector for the incident γ-ray or β-ray is smaller than the detection pulse of the heavy charged particles. Because, in the present invention, since the thickness of the depletion layer of the detector is set to be smaller than the range of the β-ray having the predetermined energy smaller than the energy of the incident heavy charged particles, the energy of the incident heavy charged particles or more is set. When γ-rays and β-rays are incident, the γ-rays and β-rays pass through the depletion layer, and the energy consumed in the detector does not exceed the energy of the incident heavy charged particles. is there.

Accordingly, by performing pulse discrimination by a pulse discrimination circuit using an energy value smaller than the energy of the incident heavy charged particles and larger than the predetermined energy for the β-rays as a discrimination threshold, a detection pulse of γ-rays or β-rays can be obtained. And detection pulses of heavy charged particles (ie, neutrons) can be distinguished from each other. This makes it possible to separately count the neutron detection pulse and the γ-ray or β-ray detection pulse.

[0016]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Preferred embodiments of the radiation detecting apparatus according to the present invention will be described below with reference to the drawings.

FIG. 1 is a block diagram showing a first embodiment of the radiation detecting apparatus according to the present invention.

In FIG. 1, a converter layer 1 made of ⁶ LiF is provided on a detection surface side of a semiconductor detector 10 made of Si.
2 are provided. After the output of the semiconductor detector 10 is linearly amplified by the amplifier 14, it is input to a neutron wave height discriminating circuit 16 and a γ / β wave height discriminating circuit 18. Then, the neutron wave height discrimination circuit 16 performs wave height discrimination only of pulses having energy equal to or more than a predetermined neutron discrimination threshold among the output pulses of the amplifier 14 and outputs the pulse. The γ / β wave height discrimination circuit 18 outputs the
Only pulses having energy equal to or higher than a predetermined noise discrimination threshold are discriminated and output. Note that at least the detector 10 and the converter layer 12 are covered with a protective film 20 of aluminized mylar having a thickness of about 10 μm for shading, electrostatic shielding, blocking of heavy charged particles from the outside, and the like. .

In this embodiment, in the above-described configuration, the thickness of the depletion layer of the detector 10 is set to 300 μm or less, and the thickness of the converter layer 12 is set to 1 μm or less.

Next, the operation of this embodiment will be described.

When neutrons enter the radiation detecting apparatus of this embodiment, the incident neutrons
Reacts with Li atoms in the semiconductor to release heavy charged particles. This reaction is represented as follows:

[0022]

⁶ Li + n = t + α + 4.78 MeV In the above formula, “α” indicates an α particle, and “t” indicates a tritium nucleus ( ³ H). Further, of the energy of 4.78 MeV generated during this reaction, 2.05 MeV is α
The kinetic energy of the particles is obtained, and the remaining 2.73 MeV is the kinetic energy of the tritium nucleus.

The α-rays and tritium nuclei thus generated are detected by the detector 10 after exiting from the converter layer 12. At this time, the kinetic energy of the α-ray and the tritium nucleus is absorbed by the converter layer 12 itself before going out of the converter layer 12.
However, in this embodiment, the thickness of the converter layer 12 is 1
Since the value is as small as μm or less, the energy loss of α rays and tritium nuclei can be suppressed to 300 keV or less. Therefore, in the present embodiment, the α-rays and tritium nuclei emitted from the converter layer 12 and incident on the detector 10 have a kinetic energy of 1.75 MeV or more in theory.

In this embodiment, the thickness of the depletion layer of the detector 10 is 300 μm, and the thickness of the depletion layer is within the range (several tens μm) of α-rays and tritium nuclei in the Si semiconductor.
m), the α-rays and tritium nuclei incident on the detector 10 from the converter layer 12
The kinetic energy is completely lost in the zero depletion layer. As a result, the detector 10 outputs a detection pulse having a wave height corresponding to almost the entire kinetic energy of the heavy charged particles that have entered.

On the other hand, when γ-rays or β-rays enter the radiation detector of the present embodiment, the γ-rays and β-rays enter the detector 10 without being attenuated by the thin converter layer 12. As described above, the thickness of the depletion layer of the detector 10 is 3
The energy loss of β rays when passing through the depletion layer of this thickness is 300 keV or less. That is, even if a β-ray having an energy greater than 300 keV is incident, such a β-ray passes through the depletion layer, and only a maximum of about 300 keV energy is lost in the depletion layer. Therefore, in the configuration of the present embodiment, the detection pulse output from the detector 10 when the β-ray is incident has only a wave height corresponding to at most 300 keV. Further, γ-rays have a higher penetrating power than β-rays, and the energy loss of the γ-rays in the depletion layer is less than β-rays. Therefore, the pulse height of the detection pulse of the detector 10 for γ-rays is at most 300 keV.

FIG. 2 shows an energy spectrum of an output pulse of the detector 10 in this embodiment. As shown in FIG. 2, the detection pulse of heavy charged particles generated by the reaction becomes about 1.75 MeV or more, and the detection pulse of γ-ray and β-ray becomes 300 keV or less, so that these can be easily separated.

That is, the energy value between the minimum energy of the detection pulse of heavy charged particles and the maximum energy of the detection pulse of γ-ray or β-ray is set as the neutron discrimination threshold, and the output pulse of the detector 10 is determined based on the neutron discrimination threshold. , It is possible to completely discriminate the detection pulse of heavy charged particles from the detection pulse of γ-ray or β-ray.

In the present embodiment, this pulse discrimination is performed by the neutron wave height discrimination circuit 16. Neutron wave height discrimination circuit 16
, The neutron discrimination threshold is set to, for example, 1.5 MeV to perform the peak discrimination, so that the neutron pulse height discrimination circuit 16
, Only the detection pulse of heavy charged particles generated by the incidence of neutrons is discriminated and output. Therefore, by counting the output pulses of the neutron wave height discrimination circuit 16, a count value of incident neutrons can be obtained, and further, a neutron dose can be obtained from the count value.

In the present embodiment, the measured value of the γ-ray or the β-ray is obtained based on the output signals of both the neutron wave height discriminating circuit 16 and the γ / β wave height discriminating circuit 18. The γ / β wave height discrimination circuit 18 is a circuit for removing noise from the output pulse of the detector 10 and discriminates and outputs only pulses having energy equal to or higher than a predetermined noise discrimination threshold. Therefore, the γ / β wave height discrimination circuit 18 outputs both the γ-ray and β-ray detection pulses and the neutron detection pulse. Therefore, by subtracting the counting result of the output pulse of the neutron wave height discriminating circuit 16 from the counting result of the output pulse of the γ / β wave height discriminating circuit 18,
A count for the line can be obtained. Then, the doses of γ-rays and β-rays can be obtained from the counted values.

As described above, according to the present embodiment, the detection pulse of heavy charged particles caused by neutrons and the detection pulse of γ-rays or β-rays can be surely discriminated by their respective wave heights. With one detector, it is possible to simultaneously obtain a detection result for neutrons and a detection result for γ-rays and β-rays. Therefore, according to the present embodiment, neutrons and γ
Further miniaturization of the radiation detector for both X-ray and β-ray can be achieved.

FIG. 3 is a block diagram showing a modification of this embodiment. This modification is obtained by adding a β-ray filter 22 to the radiation incident direction side of the converter layer 12 in the configuration of FIG. The β-ray filter 22 is, for example, a filter having a thickness of about 5 to 10 mm made of light metal, resin, or the like, and is provided to prevent incidence of β-rays from outside to the detector 10. Other configurations of the β-ray filter 22 are the same as those of the apparatus shown in FIG.

Therefore, according to this modification, since the β-rays are cut by the β-ray filter 22, the detection pulse for only neutrons and γ-rays is output from the γ / β wave height discrimination circuit 18. Therefore, according to this modification, γ ·
By subtracting the result of counting the output pulses of the neutron wave height discriminating circuit 16 from the result of counting the output pulses of the wave height discriminating circuit 18 for β, a count value for only γ-rays can be obtained. The dose of gamma rays can be determined. Therefore, this modified example can be used as an apparatus for simultaneously measuring γ-rays and neutrons.

When the configuration shown in FIG. 1 and the configuration shown in FIG. 3 are used in parallel, the respective neutron, γ-ray, and β-ray count values and dose can be obtained simultaneously.

In the above example, the crest discrimination circuit 18 for γ and β uses a crest discrimination circuit of a type that discriminates and outputs only pulses having a discrimination threshold value or more. A single channel analyzer that discriminates and outputs pulses in the energy range up to the discrimination threshold can also be used. In this case, the result of directly counting the output pulses of the single channel analyzer is
It becomes the total count value of γ rays and β rays (or the count value of γ rays).

In the above description, the converter layer 12
And the thickness of the depletion layer of the detector 10 is 30 μm or less.
Although an example in which the neutron discrimination threshold is 0 Mem or less and the neutron discrimination threshold is 1.5 MeV is shown, these values are merely examples. The point of the configuration of the present embodiment is that a detection pulse of heavy charged particles (ie, neutrons) and a detection pulse of γ-ray or β-ray are
It is completely separated by the wave height. Therefore,
In order to obtain the effect of the present embodiment, the combination of the thickness of the converter layer 12 and the thickness of the depletion layer of the detector 10 depends on the energy spectrum of the detection pulse of heavy charged particles and the energy of the detection pulse of γ-ray and β-ray. In principle, any combination may be used so long as the spectrum and the spectrum do not overlap each other. The neutron discrimination threshold may be any value in principle as long as it is a value between the minimum energy of the energy spectrum for heavy charged particles and the maximum energy of the energy spectrum for γ-rays and β-rays.

Further, in the above example, ⁶ LiF was used as the converter layer 12, but as the converter layer 12,
If it reacts with neutrons and emits heavy charged particles,
In principle, any material may be used. Detector 1
Regarding 0, other detectors (for example, a TeCd compound semiconductor detector) can be used instead of the Si semiconductor detector. However, when the materials of the converter layer 12 and the detector 10 are changed in this way, it is necessary to appropriately change the thickness of the converter layer, the thickness of the depletion layer, and the value of the neutron discrimination threshold.

[0037]

As described above, according to the present invention, by setting the thickness of the converter layer and the thickness of the depletion layer of the semiconductor detector so as to satisfy predetermined conditions, the neutron detection pulse and γ It is possible to completely separate the detection pulse of the line or the β-ray by the wave height. Therefore, according to the present invention, it is possible to simultaneously obtain a detection result for neutrons and a detection result for γ-rays and β-rays with one semiconductor detector, and measure neutrons and γ-rays and β-rays simultaneously. Thus, a compact radiation detection device can be obtained.

[Brief description of the drawings]

FIG. 1 is a block diagram showing a configuration of an embodiment of a radiation detection apparatus according to the present invention.

FIG. 2 is a diagram showing an energy spectrum of an output pulse of a semiconductor detector in an example.

FIG. 3 is a block diagram showing a configuration of a modification of the embodiment of the present invention.

[Explanation of symbols]

Reference Signs List 10 semiconductor detector, 12 converter layer, 14 amplifier, 16 neutron wave height discrimination circuit, 18 γ / β wave height discrimination circuit, 20 protective film, 22 β ray filter.

──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-2-54192 (JP, A) JP-A-4-130293 (JP, A) JP-A-56-129380 (JP, A) JP-A-5-129 3337 (JP, A) JP-A-6-66947 (JP, A) (58) Fields investigated (Int. Cl. ⁶ , DB name) G01T 1/00-7/12 H01L 31/00

Claims (2)

(57) [Claims] 1. A thin film layer which emits heavy charged particles by reacting with neutrons, wherein the thin film layer is set to a thickness such that the energy lost by the heavy charged particles generated by the reaction before it goes out of the layer becomes a predetermined value or less. A converter layer, and a semiconductor detector for detecting γ-rays and β-rays incident from outside and heavy charged particles incident from the converter layer, wherein the thickness of the depletion layer is the same as that in the semiconductor material. Β of a predetermined energy larger than the range of the incident heavy charged particle and smaller than the energy of the incident heavy charged particle
A semiconductor detector set to be smaller than the range of the line in the semiconductor material; and an output of the detector based on a discrimination threshold smaller than the energy of the incident heavy charged particle and larger than the predetermined energy for the β-ray. A pulse discriminating circuit for discriminating a pulse, and based on an output of the pulse discriminating circuit, an output pulse of the detector is changed to a detection pulse for a neutron, and γ
A radiation detection apparatus characterized in that the radiation detection apparatus separates and counts a detection pulse for a ray or a β ray. 2. The radiation detection apparatus according to claim 1, wherein a β-ray filter for blocking β-rays is provided on the converter layer on the radiation incident side.