JP2002267760A - Neutron detector - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a neutron detector for fast and intermediate neutrons capable of detecting a neutron with lower energy even in a place including γ-ray or β-ray with high energy. SOLUTION: A depletion layer 13a formed on an incident electrode 11a side on which a recoil proton by neutron is incident is not formed in a solid state but formed in a shape where parts having no depletion layer are dispersed. The parts having no depletion part are dispersed, whereby the charge quantity of current pulse by γ-ray or β-ray is reduced, and the discrimination level of a wave height value discrimination circuit for discriminating the current pulse by γ-ray or β-ray can be reduced to lower the minimum energy of the detectable neutron. Examples of the shape include a concentric annular shape, a branched shape and the like.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a personal alarm dosimeter for managing the radiation dose of a worker working in a radiation control area such as a nuclear power plant, and a dose for monitoring an environmental radiation dose. The present invention relates to a neutron detector used for a meter or the like.

[0002]

2. Description of the Related Art Neutrons are radiations having no charge, and have a weak interaction with substances, and are difficult to detect directly. For this reason, a method has been adopted in which neutrons are detected via protons and α rays generated by interaction with a substance having a large cross-sectional area of interaction with neutrons. Fast neutrons and medium neutrons are detected by recoil protons from radiators such as polyethylene containing hydrogen at a high density, and slow neutrons and thermal neutrons are released by nuclear reaction with ¹⁰ B and ⁷ Li.
Detected by line. A semiconductor detection element that utilizes a depletion layer formed in a reverse-biased diode is commonly used as a means for detecting recoil protons or α-rays.

FIG. 9 is a conceptual diagram showing a configuration of a neutron detector having a radiator 2 for high and medium speed neutrons.
FIG. 2 is a pattern diagram showing an example of an electrode shape of the detection element 1 used in the element. The neutron detector, counter 跳陽Ko incident side electrode (in the following abbreviated as incident side electrode) 11 (also referred to as a lower electrode in the following) the opposite side electrode incident side electrode reverse bias is applied between the 12 A semiconductor detecting element (hereinafter, simply referred to as a detecting element) 1 having a depletion layer 13 formed on the side 11 and a material containing hydrogen at a high density such as polyethylene disposed adjacent to the incident side electrode 11. A radiator 2, an amplifier 3 that integrates and amplifies a current pulse flowing through the incident side electrode 11 and outputs a signal corresponding to the amount of charge of the current pulse, and identifies whether the output level of the amplifier 3 is equal to or higher than a predetermined value. a peak value identifying circuit 4, the peak value identifying circuit 4
And a counting circuit (not shown) that counts the outputs of.

As the detection element 1, a heterojunction type silicon diode in which an amorphous silicon layer is formed on a p-type silicon crystal, a pn junction type silicon diode, and the like are generally used. In the case of a hetero-junction type silicon diode, as shown in FIG. 9, the incident side electrode 11 is formed on the entire surface except for the outer peripheral portion of the upper surface to determine a depletion layer formation region. An electrode 12 is formed. In the case of a pn junction type silicon diode, the p ⁺ layer or the n ⁺ layer determines a depletion layer formation region.
Therefore, an electrode for wiring is often formed in a part thereof.

[0005] The radiator 2 is a member for generating recoil protons by elastic collision of neutrons and protons as hydrogen nuclei when neutrons pass through them. for that reason,
As a material of the radiator 2, a material containing hydrogen at a high density, for example, polyethylene is used. The energy of recoil protons depends on the scattering direction after elastic collision, but since the mass of neutrons is almost the same as the mass of protons, the maximum value is when the neutrons are scattered in the same direction as incident, The energy becomes the same as the energy of the neutrons immediately before the collision, and the energy decreases as the angle of inclination from the incident direction decreases, resulting in a continuous distribution up to zero.

[0006] When a recoil proton enters a substance, it interacts with the substance to generate an electron-hole pair and travels through the substance while consuming its energy. Since the mass of the proton is more than three orders of magnitude larger than the mass of the electron, the recoil proton moves through the material without changing its direction, and the electron-hole pair generated by the recoil proton becomes It is distributed only at a very close vicinity of the passage route and at a high density.

For reference, the range of protons in silicon is about 18 μm and 2 MeV when the energy is 1 MeV.
About 48μm, about 150μm at 4MeV, about 730μm at 10MeV
, About 1500 μm at 15 MeV. The range of protons in air is about 20 mm at 1 MeV and about 70 mm at 2 MeV. If the distance between the radiator 2 and the detection element 1 is about 1 mm, the energy loss of recoil protons in the air layer is It is slight.

Therefore, when the material of the detecting element 1 is silicon, if a depletion layer 12 having a thickness of 50 μm is formed, a charge signal corresponding to the total energy can be obtained from protons of 2 MeV or less. In many cases, a charge signal corresponding to 1 MeV or more can be obtained from a proton of 2 MeV or more. Such a neutron detector for high-medium-speed neutrons is used in an environment where not only neutrons but also γ rays and β rays are mixed. In addition, the above-described detection element also generates an electron-hole pair by an electron and the like due to the Compton effect due to γ-rays, generation of an electron pair, and β-ray, and generates a current pulse similarly to the electron-hole pair by the recoil proton. Occurs. In particular, in nuclear power plants, there are 6.1 MeV gamma rays emitted by ¹⁶ N generated by the reaction of nitrogen in water with neutrons, and the signal of this high energy level gamma ray is distinguished from the signal of neutrons. It is necessary to. In the prior art, the discrimination level of the peak value discrimination circuit 4 is set to about 1 MeV to discriminate 6.1 MeV gamma rays from neutrons. This discrimination level is 6.1 MeV γ-rays in a volume of 8 × 8.
This is determined based on the result of measurement by the detection element 1 having a depletion layer of × 0.05 mm ^{3 so} as to prevent the detection element 1 from detecting 6.1 MeV γ-rays.

As described above, in the conventional neutron detector for high-medium-speed neutrons, since the identification level is set to a high energy level corresponding to about 1 MeV, it is necessary to detect neutrons having an energy lower than the identification level. And the sensitivity for detecting neutrons having an energy higher than the discrimination level is also lowered. On the other hand, a neutron detector that detects neutrons using α rays emitted by a nuclear reaction with ¹⁰ B or ⁷ Li is generally called a thermal neutron detector. The cross section of the interaction of neutrons with ¹⁰ B etc. is
The neutron detection sensitivity of thermal neutrons is the largest for thermal neutrons, and decreases gradually as the energy increases. To go.

Generally, the radiator 2 is used to detect neutrons.
A neutron detector for high-medium-speed neutrons and a thermal neutron detector are used in combination, but as described above, when the sensitivity of the neutron detector for high-medium-speed neutrons becomes zero below 1 MeV,
In the neutron detection by this combination, the neutron detection sensitivity near 1 MeV is significantly lower than that in other energy regions, and when measuring an environment with many low energy neutrons, the neutron exposure dose is underestimated. Have the problem of doing it.

[0011]

An object of the present invention is to solve the above-mentioned underestimation of the neutron exposure dose, even in a place where γ-rays and β-rays are mixed, to lower energy neutrons. It is to provide a neutron detector for high and medium speed neutrons that can be detected.

[0012]

SUMMARY OF THE INVENTION The present invention relates to a situation in which recoil protons generated by neutrons generate electron-hole pairs, and a situation in which scattered electrons or generated electrons by gamma rays generate electron-hole pairs. , Based on reducing the amount of charge of the current pulse signal due to γ-rays. The generation position of the electron-hole pair by the recoil proton is, as described above,
The electron-hole pairs generated are very densely distributed only in the vicinity of the proton passage. on the other hand,
The generation state of electron-hole pairs by γ-rays is caused by electrons due to the Compton effect, electron pair generation, and the like, so that electrons having the same mass interact with each other, resulting in a distribution state spread over a wide area.

FIGS. 11 and 12 show such a situation as a model. Radiator 2 by neutrons
The recoiled protons ejected from the detector travel straight in the detection element 1 while keeping the original direction of the ejected ions, move by a range corresponding to the energy, and have a high density of electron-holes in the immediate vicinity of the movement path. Generate pairs. Assuming that the detection element 1 is made of silicon, if the energy of the recoil proton is 1 MeV,
The moving distance is about 18 μm, and in the case of 2 MeV, about 48 μm, which is smaller than the thickness of the depletion layer 13 of the ordinary detection element 1.
Therefore, the recoil protons that have passed through the incident side electrode 11 and entered the depletion layer 13 can generate an electron-hole pair corresponding to an energy of 1 MeV or more in the depletion layer 13.

On the other hand, a region where an electron-hole pair may be generated due to electrons or the like scattered or generated by γ-rays is, as a model, shown as a starting point at a position where an electron or the like is generated. The shape of the sphere is a sphere in which the direction in which the particles first jump out is the diameter direction, and the range corresponding to the initial energy of electrons or the like is the diameter. FIGS. 11 and 12 show a case where electrons or the like jump out in the same direction as the incident direction of the γ-ray, which corresponds to a case where electrons having the highest energy are scattered in the case of the Compton effect. A small circle indicates a case where the energy of the γ-ray is small (about 100 KeV), and a large circle indicates a case where the energy of the γ-ray is large (about 5 MeV).

When the γ-rays are incident on the incident side electrode 11 of the detection element 1 almost vertically as shown in FIG. 11, the region where the electron-hole pairs can be generated covers the entire depletion layer 13 of the detection element 1. However, as shown in FIG.
When the light is incident at an angle to 11, the region where electron-hole pairs can be generated may cover the entire depletion layer 13 of the detection element 1. Further, the position at which the γ-rays generate scattered electrons and the like is not limited to the inside of the detection element 1, and the scattered electrons and the like generated by surrounding members fly into the detection element 1 and enter the electron-hole pairs in the depletion layer. May be generated. In this manner, a current pulse is generated by the electron-hole pairs generated in the depletion layer 13, and as described in the section of the prior art, ¹⁶ N is generated.
Is the value close to 1 MeV.

For reference, the range of electrons in silicon is approximately 13 μm when the energy of electrons is 50 KeV.
About 54 μm at 100 KeV, about 190 μm at 200 KeV, 500
About the KeV 770 m, about the 1 MeV 1.7 mm, 2 MeV at about 4.0 mm, the 5MeV about 11 mm, ¹⁶ N is generated 6.1MeV
About the maximum energy of electrons (5.9 MeV) by gamma rays
13 mm.

Here, consider that the detecting element detects a current pulse signal equivalent to 1 MeV at the maximum with ¹⁶ N γ-rays. 5.9 Electrons due to MeV electrons (range 13 mm)
The volume of the region where the hole pairs can be generated is 1150 mm ^{3 because} it is the volume of a sphere having a diameter of 13 mm. On the other hand, the depletion layer volume supra detector element, since it is 8 × 8 × 0.05mm ^3, a 3.2 mm ^3. Comparing the two, the volume of the depletion layer does not reach 0.3% of the volume of the sphere with a diameter of 13 mm, and if the electron-hole pairs are uniformly distributed in the sphere with a diameter of 13 mm, it is included in the depletion layer. The signal level corresponding to the detected electron-hole pair is only about 16 KeV, which is almost two orders of magnitude different from the actually detected maximum value of 1 MeV.

From this difference, it is estimated that the electron-hole pairs generated by scattered electrons and the like will be very unevenly distributed. This non-uniformity can also be predicted by the fact that the range of electrons sharply decreases with decreasing energy. In other words, the generated high-energy electrons interact with passing substances and consume their energy, but most of the energy consumption is due to the interaction with extranuclear electrons. This is the same interaction as the elastic collision of particles of the same mass, and the energy is reduced while generating high-speed secondary, tertiary, and quaternary electrons at each collision. 2 generated by collision
Next, third, fourth, etc. electrons also repeat collisions to reduce their energy.

The range of the electron which was 5.9 MeV at the time of generation is
As mentioned above, it is 13mm, but after repeated collisions, 100 KeV
The range of the converted electrons is 54 μm, and the range of the electrons
The process is 13 μm. Assuming that 5.9 MeV electrons are in the depletion layer
59 100 KeV electrons with the same range as the thickness
Then, the volume of the region where the electron-hole pair can be generated is 4.
86 × 10^-3 mm^ThreeAnd less than the thickness of the depletion layer
Assuming that the range has 118 electrons at 50 KeV,
-The volume of the region where hole pairs can be generated is 1.36 x 10^-Fourmm ^ThreeBecome
Would. Therefore, one generated electron has its energy
Region that may generate electron-hole pairs corresponding to
Is large, but the region that actually generates electron-hole pairs is
It is likely to be ubiquitous and some of such areas will be detected.
When the detector element corresponds to the depletion layer, the detection element is equivalent to 1 MeV
Output the current pulse signal.

In order to examine the state of uneven distribution, the same depletion layer thickness (50 μm) as the above-described detection element and the depletion layer area of 1.
A prototype of a detector element of 5 × 1.5 mm ² was fabricated, and γ by ¹⁶ N
As a result of measuring the current pulse detected by the line, the maximum value was 70% for the above-described detection element in which the area of the depletion layer was 8 × 8 mm ^2.
%Met. Depletion layer area from 8 × 8mm ² to 1.5 × 1.5mm
Despite the significant reduction to ^two , the charge of the current pulse is only reduced by 30%. In other words, 70% of the electron-hole pairs corresponding to a current pulse signal corresponding to a maximum of 1 MeV detected by the conventional detection element are 3 × 8 × 8 mm ² .
Only 5% exists within a 1.5 × 1.5 mm ^2, the remaining 30
% Of electron-hole pairs are present in an area of 96.5%. This result confirmed that the model in which electron-hole pairs generated by scattered electrons and the like are very unevenly distributed is correct.

According to the present invention, a γ of 6.1 MeV that generates ¹⁶ N
The electron-hole pairs due to high energy γ-rays such as lines are distributed over a wide area, but the distribution density is extremely non-uniform, based on the above-mentioned situation. In other words, the present invention does not form the depletion layer in a solid state, but forms a shape in which portions where the depletion layer does not exist are scattered, so that the depletion layer existing in the region where the electron-hole pairs are densely distributed is formed. It is intended to reduce the volume ratio, reduce the number of electron-hole pairs separated by the depletion layer and detected as a current pulse, and reduce the maximum peak value.

According to the first aspect of the present invention, a recoil proton generated by the interaction between a radiator containing hydrogen at a high density and a neutron generates an electron-hole pair generated in a detection element by an electric field in a depletion layer of the detection element. In a neutron detector that detects neutrons by measuring the amount of charge of this current pulse by separating it as a current pulse, the shape of the depletion layer of the detection element viewed from the recoil proton incident side (hereinafter the plane of the depletion layer) (Referred to as a shape) is a shape in which portions where no depletion layer exists are scattered.

Since the plane shape of the depletion layer is a shape in which portions where no depletion layer is present are scattered, as is apparent from the above description, the charge amount of the current pulse due to the γ-ray is reduced as compared with the case of the solid electrode. Can be done. On the other hand, even if the area where the depletion layer does not exist is scattered, the recoil proton detection sensitivity, that is, the neutron detection sensitivity hardly changes unless the area of the depletion layer is changed. Furthermore, if the amount of charge of the current pulse due to γ-rays is reduced and its maximum peak value is reduced, the set value of the identification level of the peak value identification circuit can be reduced. In this case, the minimum detectable neutrons Energy levels are reduced and neutron detection sensitivity is increased. In particular, the rate of increase at low energy levels is large.

According to a second aspect of the present invention, in the first aspect of the present invention, the shape in which the portion where the depletion layer does not exist is scattered,
It is shaped with branches multiple branches. In the shape having a plurality of branches, the depletion layer is integrated, so that the current takeout portion can be provided at one place. The invention of claim 3 is
According to the second aspect of the present invention, the plurality of branch branches have a tree shape, a comb tooth shape, or a concentric arc shape. Branches having these shapes are easy to form and are most suitable as the shape of the depletion layer.

According to a fourth aspect of the present invention, in the first aspect of the present invention, the shape in which the portion where the depletion layer does not exist is scattered is
It has a concentric annular or polygonal shape. Such a shape is the most suitable shape for obtaining excellent directional characteristics. According to a fifth aspect of the present invention, in the first aspect of the present invention, the portion where the depletion layer does not exist is scattered in a point-symmetrical shape or a rotationally symmetrical shape with its center as a center of symmetry. By forming the shape of the depletion layer into a point-symmetric shape or a rotationally symmetric shape when viewed from the recoil proton incident side, excellent directional characteristics can be obtained.

[0026]

DESCRIPTION OF THE PREFERRED EMBODIMENTS A neutron detector according to the present invention
It has the same configuration as the conventional neutron detector for high-medium-speed neutrons shown in FIG. 9, and a reverse bias is applied between the incident electrode and the lower electrode on the opposite side to form a depletion layer on the incident electrode side. The formed detection element, a radiator made of a material containing hydrogen at high density such as polyethylene disposed adjacent to the incident side electrode, and a current pulse flowing through the incident side electrode by integrating and amplifying the current pulse. An amplifier that outputs a signal corresponding to the charge amount, a peak value identification circuit that determines whether the output level of the amplifier is equal to or higher than a predetermined value, and a counting circuit that counts the output of the peak value identification circuit. ing.

The present invention is different from the prior art in that the shape of the depletion layer of the detecting element is different from that of the prior art in that the plane shape of the depletion layer is a shape in which portions where no depletion layer is present are scattered. The planar shape of the depletion layer is determined by the shape of the incident-side electrode in the case of a heterojunction detection element, and the p ⁺ layer or n ⁺ for forming a junction in the case of a pn junction detection element.
⁺ Depends on the shape of the layer.

Hereinafter, the present invention will be described in more detail with reference to an embodiment of a heterojunction type detecting element. In the first to third embodiments, the shape of the incident side electrode is formed by photolithography, and in the fourth to seventh embodiments, the shape is formed by masking. According to the mask vapor deposition, the incident-side electrode patterned directly by vapor deposition or sputtering using a metal mask or the like can be formed, so that the number of steps for forming the incident-side electrode can be much smaller than in the case of photolithography. On the other hand, the width of an electrode that can be formed cannot be made as narrow as that by photolithography due to the manufacturing limit of a metal mask or the like.

Incidentally, the incident side electrode of these embodiments is p ⁺
If it is replaced with a layer or an n ⁺ layer, it becomes a pn junction type detection element. [First Embodiment of Detecting Element] FIG. 1 is a conceptual diagram showing the structure of a first embodiment 1a of a detecting element used in a neutron detector according to the present invention, and FIG. It is a pattern diagram which shows the shape of.

The detecting element 1a has an incident side electrode 11a composed of a central circle and four concentric rings having the same center, and has the same lower electrode 12 as in the prior art. Since the incident side electrode 11a is composed of five independent parts,
When connecting 1a to an amplifier, each of the five parts is wired and connected integrally to the amplifier. As an example of the dimensions of the detection element 1a, the area is 10 × 10 mm ² , the diameter of the central circle of the incident side electrode 11a is φ0.5 mm, and the interval and width of the four concentric rings are both 0.5 mm. Note that the thickness of the depletion layer 13a is set to 50 μm.

For reference, the energy of an electron having a range of 0.5 mm is about 400 KeV. By adopting the plane-side incident side electrode 11a shown in FIG. 2, the depletion layer 1a and the portion without the depletion layer coexist over the entire surface of the detection element 1a. In the electrode, part of the electron-hole pairs separated as the charge signal is not separated, the signal level by the γ-ray is reduced, and the peak value of the peak value identifying circuit can be set low.

Since the lowering of the peak value of the discrimination corresponds to the occurrence position of the detectable recoil protons in the radiator extending to the inside of the radiator, the detection sensitivity of the neutrons is increased. The detection sensitivity of neutrons having energy close to the discrimination peak value is greatly increased, and neutrons having energies between the conventional discrimination peak value and the new discrimination peak value can be detected. As a result, the energy characteristics of the neutron detectors is improved.

The feature of this pattern is that it is a perfect concentric pattern, so that it has the best directional characteristics. The effect is more reliable as the dimensions of the pattern such as the diameter of the circle, the width of the ring, and the interval are reduced, but the number of steps in the wiring step increases, and if the width is too narrow, the work becomes difficult. Therefore, the dimensions are determined in consideration of the effect and the number of steps. Further, in the above-described embodiment, the width and the interval are the same, but if it is desired to set the identification peak value lower, the ratio of the interval to the width may be increased.

[Second Embodiment of Detecting Element] FIG. 3 is a pattern diagram showing the shape of the incident side electrode 11b of the second embodiment 1b of the detecting element. The pattern of this embodiment has a detection element 1b
Are connected by thin connecting portions. In order to complete the wiring of many places in one place as in the first embodiment,
Since they are integrated by thin connecting portions, the number of assembling steps is reduced as compared with the first embodiment. This embodiment also has the best directional characteristics, as in the first embodiment, since the thin connection does not significantly affect the directional characteristics.

[Third Embodiment of Detecting Element] FIG. 4 is a pattern diagram showing the shape of the incident side electrode 11c of the third embodiment 1c of the detecting element. The pattern of this embodiment is obtained by replacing the concentric ring of the second embodiment with a concentric square cross-girder. Since the concentric ring has been replaced by a concentric girder, the directional characteristics are not as excellent as those of the second embodiment, but have sufficiently excellent directional characteristics.

The feature of this pattern is that, in the case of detecting elements having the same area, the electrode area can be made larger than that of the second embodiment, so that the neutron sensitivity can be increased by the extent that the electrode area can be made larger. It is. In this embodiment, a square cross-girder is used, but a polygonal cross-girder other than a square may be used.

[Fourth Embodiment of Detecting Element] FIG. 5 is a pattern diagram showing the shape of the incident side electrode 11d of the fourth embodiment of the detecting element 1d. The shape of the incident-side electrode 11d is a rotationally symmetric dendritic pattern rotated by 90 ° with respect to the center of the detecting element 1d as the center of symmetry, and is also a point-symmetric dendritic pattern. The width of the branch portion and the interval between the branches are both set to be the same (for example, 0.5 mm).

According to this embodiment, since the incident-side electrode 11d is formed in a tree shape, a depletion layer and a portion without a depletion layer coexist over the entire surface of the detection element 1d, as in the first embodiment. As a result, the detection element 1d also reduces the signal level due to γ-rays, and allows the identification peak value of the peak value identification circuit to be set low. Further, since the pattern is rotationally symmetric at 90 °, the pattern has good symmetry and excellent directional characteristics.

Since the input electrode 11d of this embodiment can be formed by vapor deposition using a metal mask, the number of steps for forming the electrode is the same as that of the prior art. [Fifth Embodiment of Detecting Element] FIG. 6 is a pattern diagram showing the shape of the incident side electrode 11e of the fifth embodiment 1e of the detecting element.

The shape of the incident side electrode 11e is obtained by replacing the dendritic pattern of the fourth embodiment with a comb-like pattern. The characteristics of this embodiment and the man-hours for forming the electrode
Is completely equivalent to the embodiment. [Sixth Embodiment of Detecting Element] FIG. 7 is a pattern diagram showing the shape of the incident side electrode 11f of the sixth embodiment 1f of the detecting element.

The shape of the incident side electrode 11f is obtained by replacing the dendritic pattern of the fourth embodiment with a concentric arc pattern. In this embodiment, since the envelope area of the electrode is reduced because of the arc-shaped pattern, the width of the branch portion is made larger than the interval between the branches, and the electrode area is made the same as the previous two embodiments. . For this reason, the ratio of the electrode area to the envelope area of the electrodes of the detection element is larger than that of the previous two embodiments, and the peak value of the peak value discriminating circuit is somewhat larger than that of the previous two embodiments. However, the feature of this pattern is
It is an arc shape, compared to the previous two embodiments,
Better directional characteristics.

[Seventh Embodiment of Detecting Element] FIG. 8 is a pattern diagram showing the shape of the incident side electrode 11g of the seventh embodiment of the detecting element 1g. The pattern of this embodiment is a comb-like pattern extending only in the horizontal direction. Although this is the simplest shape among the embodiments, the directional characteristics are slightly inferior to those of the fourth and fifth embodiments, but are practically acceptable. Other characteristics than the directional characteristics are almost the same as those of the fourth and fifth embodiments.

[0043]

According to the first aspect of the present invention, the shape of the depletion layer of the detection element as viewed from the recoil proton incident side is a shape in which portions where no depletion layer is present are scattered. as apparent from the description of the section means "
The charge amount of the current pulse due to γ-rays can be reduced as compared with the case of a solid electrode. On the other hand, even if the area where the depletion layer does not exist is scattered, the recoil proton detection sensitivity, that is, the neutron detection sensitivity hardly changes unless the area of the depletion layer is changed. Furthermore, if the amount of charge of the current pulse due to γ-rays is reduced and its maximum peak value is reduced, the set value of the identification level of the peak value identification circuit can be reduced. In this case, the minimum detectable neutrons Energy levels are reduced and neutron detection sensitivity is increased. In particular, the rate of increase at low energy levels is large.

Therefore, according to the present invention, a neutron detector for high-medium-speed neutrons capable of detecting even a neutron at a lower energy level than a conventional neutron detector for high-medium-speed neutrons without reducing the sensitivity of neutron detection for high-energy neutrons. A neutron detector can be provided. According to the second aspect of the present invention, the shape in which the portion where the depletion layer does not exist is scattered is a shape having a plurality of branches. In the shape having a plurality of branches, the depletion layer is integrated, so that the current takeout portion can be provided at one place. Therefore, in the assembling process of the neutron detector, the number of steps of the wiring process for connecting the detection element and the circuit is not increased.

According to the third aspect of the present invention, the plurality of branches are formed in a tree shape, a comb-like shape or a concentric arc shape. Branches having these shapes are easy to form and are most suitable as the shape of the depletion layer. In the invention according to claim 4, the shape in which the portion where the depletion layer does not exist is scattered is a concentric annular shape or a concentric polygonal shape. Such a shape
Since the shape is most suitable for obtaining excellent directional characteristics, particularly excellent directional characteristics can be obtained.

According to the fifth aspect of the present invention, the portion where the depletion layer does not exist is scattered in a point-symmetrical or rotationally symmetrical shape with its center as a center of symmetry. Since a point-symmetric shape or a rotationally symmetric shape is a shape suitable for obtaining excellent directional characteristics, excellent directional characteristics can be obtained.

[Brief description of the drawings]

FIG. 1 is a conceptual diagram showing the structure of a first embodiment of a detecting element used in a neutron detector according to the present invention.

FIG. 2 is a pattern diagram showing a shape of an incident side electrode of the first embodiment of the detection element.

FIG. 3 is a pattern diagram showing the shape of an incident-side electrode according to a second embodiment of the detection element.

FIG. 4 is a pattern diagram showing the shape of an incident-side electrode according to a third embodiment of the detection element.

FIG. 5 is a pattern diagram showing the shape of an incident-side electrode according to a fourth embodiment of the detection element.

FIG. 6 is a pattern diagram showing the shape of an incident-side electrode according to a fifth embodiment of the detection element.

FIG. 7 is a pattern diagram showing the shape of an incident side electrode of a sixth embodiment of the detection element.

FIG. 8 is a pattern diagram showing the shape of an incident-side electrode according to a seventh embodiment of the detection element.

FIG. 9 is a conceptual diagram showing a configuration of a neutron detector according to the related art.

FIG. 10 is a pattern diagram showing an example of an electrode shape of a detection element according to the related art.

FIG. 11 is a conceptual diagram illustrating the detection of neutrons and γ-rays by a detection element.

FIG. 12 is a conceptual diagram for explaining a problem of the detection element according to the related art.

[Explanation of symbols]

 1, 1a, 1b, 1c, 1d, 1e, 1f, 1g Detector 11a, 11b, 11c, 11d, 11e, 11f, 11g Incident electrode 12 Lower electrode 13, 13a Depletion layer 2 Radiator 3 Amplifier 4 Peak value discriminator

Claims (5)

[Claims] An electron-hole pair generated in a detecting element by a recoil proton generated by an interaction between a radiator containing hydrogen at a high density and a neutron is separated by an electric field of a depletion layer of the detecting element. In a neutron detector that detects neutrons by extracting the current pulse as a pulse and measuring the amount of charge of this current pulse, the shape of the depletion layer of the detection element as seen from the recoil proton incident side is the shape where the depletion layer does not exist A neutron detector, characterized in that: 2. The neutron detector according to claim 1, wherein the portion where the depletion layer does not exist is scattered to have a plurality of branches. 3. The neutron detector according to claim 2, wherein the plurality of branch branches have a tree shape, a comb tooth shape, or a concentric arc shape. 4. The neutron detector according to claim 1, wherein the shape in which the portion where the depletion layer does not exist is scattered is a concentric annular shape or a concentric polygonal shape. 5. The neutron according to claim 1, wherein the shape in which the portion where the depletion layer does not exist is scattered is a point-symmetric shape or a rotationally-symmetric shape with its center as a center of symmetry. Detector.