JP5710352B2 - Neutron detector - Google Patents

Description

  Embodiments described herein relate generally to a neutron detector.

  Conventionally, various neutron detectors (neutron two-dimensional detectors) used for neutron transmission imaging, neutron imaging, neutron scattering experiments, and the like have been proposed. Currently, construction of new high-intensity pulsed neutron sources is underway in various countries around the world for the study of physical properties of various substances and basic experiments on nuclei.

Generally, as a neutron detector, a He-3 gas detector using He (helium) isotope ³ He (hereinafter referred to as He-3) gas or a neutron as a detector with high detection efficiency. A scintillation detector using a scintillator that emits light by reacting directly or secondarily is known.

  Here, since neutrons have no electric charge, in order to detect neutrons, a converter that reacts with neutrons and converts them into charged particles or gamma rays is required. As neutron converters, He-3, Li-6, B-10, Cd-113, Gd-155, and Gd-157, which have large neutron absorption cross sections, are known. Therefore, a He-3 gas detector that is a neutron detector using He-3 gas is used.

  Furthermore, in order to efficiently detect high-energy fast neutrons and epithermal neutrons (also known as epithermal), a configuration in which the neutron detector is covered with a neutron moderator such as polyethylene has been studied.

On the other hand, although the scintillation detector has a high counting capability, the density is increased due to the solid and the sensitivity to gamma rays is increased. In order to detect neutrons at a high counting rate, it is essential to use a neutron detection scintillator with a short fluorescence lifetime. Therefore, a neutron detector has been developed in which a scintillator made of a Li ₂ B ₄ O ₇ single crystal is used for neutron detection, and its fluorescence characteristics and a photomultiplier tube are combined. Further, particularly for reducing the influence of gamma rays essential for neutron detection or neutron imaging, a scintillator composed of light elements is preferable. However, since Li, B and O are also light elements, Li ₂ B _A scintillator made of ₄ O ₇ single crystal satisfies the requirements.

Furthermore, neutron scintillators that can be made thinner than conventional neutron scintillators and that are superior in terms of gamma-ray sensitivity and position resolution compared to conventional Li-based scintillators have been developed. This is because at least 950 ° C. or more after mixing Li ₂ B ₄ O ₇ and CeO ₂ using a neutron scintillator in which Ce is added to an oxide composed of B and Li as main constituents to form glass. After heating at a temperature of 1 hour and holding it for 1 hour or longer, it is manufactured by cooling between 800 and 400 ° C. at a rate of 150 ° C./sec or higher.

These LiBO ₃ and Li ₂ B ₄ O ₇ compounds composed only of light elements that are estimated to have low gamma-ray sensitivity emit very little light by neutrons. Furthermore, in the single crystals in which Ce is added to these, the amount of Ce dissolved in the crystal is very small, the emission by neutrons is small, and it is difficult to use as a two-dimensional detector for neutron imaging or neutron radiography. .

  On the other hand, since Li and B use a charged particle generation reaction of several MeV for neutron detection, it is possible to select a scintillator material regardless of gamma ray sensitivity. In particular, B can expect a neutron detection efficiency about four times that of the same amount of Li, so that a thinner scintillator can be produced. For this reason, it is very advantageous in terms of gamma ray sensitivity and position resolution, so it can be said to be an ideal neutron converter. However, B is considered to be disadvantageous in terms of light emission output because the generated charged particle energy is about half that of commercially available Li glass (Li-Glass), and most conventional neutron scintillators convert Li into a converter. It is used as.

  Here, representative examples of neutron scintillators currently in practical use include LiF / ZnS. Although this neutron scintillator has a high light emission amount and is excellent in handling, it is opaque and has limited detection efficiency and counting ability.

  In particular, the resolution in the case of performing high-definition imaging depends on the spread when the reactant and scintillator emit light together, and the resolution of the optical system and imaging device that images the light. Recently, CCDs and CMOS elements used in the imaging system have been dramatically increased in pixel count, so it is considered that the resolution is mainly determined by the configuration of the reaction film and the scintillator. That is, when charged particles are generated by reacting with neutrons in the reaction film and the charged particles and the scintillator react to emit light, the distance (range) of the charged particles and the diffusion distance of the light emitted by the scintillator are determined by the resolution. It becomes a blur related to.

  For this reason, in order to improve the resolution, it is necessary to make the reaction film thinner and to shorten the range of the secondary charged particles to be generated. In the case of LiF / ZnS, Li reacts with neutrons to emit alpha (α) rays, and the αS rays cause the ZnS phosphor to emit light. In an actual configuration, LiF / ZnS is a granular powder, and in many cases, LiF / ZnS powder is applied on an Al plate serving as a substrate with an organic binder and hardened.

  Li, which reacts with neutrons, is usually an isotope Li-6 that is used to increase the reaction efficiency. However, since the number density of atoms in the whole including the binder is small, the applied thickness is about several hundred μm. It has become. Therefore, the resolution is determined by the applied thickness and is not high. In particular, when the energy of neutron is increased, the reaction ratio with Li-6 is further decreased and the efficiency is also deteriorated. Although it is conceivable to increase the thickness in order to increase the reaction rate, LiF / ZnS is opaque and the emitted light is scattered by LiF / ZnS and does not pass through.

  As a method for solving these problems, a neutron detector is composed of a capillary plate having a plurality of openings penetrating in the thickness direction and filled with a liquid scintillator that reacts with neutrons in the openings and an imaging detector. However, a two-dimensional detector that measures scintillation light has been proposed. However, the capillary plate portion does not react, and neutrons are lost from this portion, so that the high-definition and high-efficiency two-dimensional detector cannot be obtained. Further, it is difficult to manufacture the scintillator uniformly in the holes of all the capillary plates, and it has not been put into practical use yet.

  On the other hand, image intensifiers (or electron multipliers) have been developed that combine a reaction film and scintillator to achieve high definition and increase sensitivity, and convert the light of the scintillator to electrons with a photoelectric conversion film to amplify the electrons. (For example, refer to Patent Document 1). However, in order to make this structure high definition, the reaction film is only about 5 μm, the reaction efficiency with neutrons is about 10% in the case of B-10, and the remaining 90% of neutrons are transmitted and used. Not. Furthermore, the reaction efficiency decreases further as the energy of neutrons increases. For this reason, in the case of high definition, the reaction efficiency is poor, and when the number of neutrons generated is small (the flux is small), it must be accumulated over time.

Republished patent WO2008 / 132849

  As described above, in neutron detectors that use neutrons, pass through the state of matter and structures, image non-destructively with high definition and high sensitivity, and detect scattered neutrons in two dimensions In particular, the development of a neutron detector capable of high-definition and high-efficiency detection, particularly up to the high-energy neutron region, has been desired.

  The present invention has been made in view of the above-mentioned problems of the prior art, and its purpose is to detect a wide range of neutron energy, particularly high energy, with high definition and high efficiency. Is to provide.

  The neutron detector according to the embodiment extends along the incident direction of neutrons, and has a metal film serving as a reflective layer that reflects light, and is formed on the metal film and extends along the incident direction of neutrons. A first vapor-deposited film that reacts with neutrons and emits radiation; and extends along an incident direction of the neutron and is disposed adjacent to the first vapor-deposited film and reflects light A second vapor-deposited film made of a reflective material; and the radiation generated in the first vapor-deposited film, extending along the incident direction of neutrons and disposed adjacent to the second vapor-deposited film And a scintillator layer that generates light from a multi-layered structure in which a plurality of layers are stacked, and the light generated by the scintillator layer is reflected by the metal film and the second deposited film. While propagating through the scintillator layer and leading out to the outside. Characterized in that it has a detection unit.

  According to the present invention, it is possible to provide a neutron detector that can detect a wide range of neutron energy, particularly high energy, with high definition and high efficiency.

The figure which shows the principal part schematic structure of the neutron detector which concerns on one Embodiment. The figure which expands and shows the principal part schematic structure of the neutron detector of FIG. The figure which expands and shows the principal part schematic structure of the neutron detector which concerns on other embodiment. The figure which expands and shows the principal part schematic structure of the neutron detector which concerns on other embodiment. The graph which shows the relationship between neutron energy and neutron absorption cross section. The graph which shows the relationship between thickness and the transmittance | permeability of a thermal neutron. The figure which shows the whole structure of the neutron detector which concerns on one Embodiment. The figure which shows the whole structure of the neutron detector which concerns on other embodiment. The figure which shows the whole structure of the neutron detector which concerns on other embodiment. The figure which shows the whole structure of the neutron detector which concerns on other embodiment. The figure which shows the whole structure of the neutron detector which concerns on other embodiment. The figure which shows the principal part schematic structure of the conventional neutron detector. The figure which shows the principal part schematic structure of the conventional neutron detector.

  Hereinafter, embodiments of a neutron detector according to the present invention will be described with reference to the drawings.

  FIG. 1 is a diagram illustrating a schematic cross-sectional configuration of a main part of a neutron detector according to an embodiment of the present invention. 12 and 13 are diagrams showing a schematic cross-sectional configuration of a main part of a conventional neutron detector.

  The conventional neutron detector shown in FIG. 12 uses a granular scintillator 4 (for example, LiF / ZnS phosphor). In general, the granular scintillator 4 is transparent in order to fix the granular scintillator 4 and efficiently transmit emitted light 5 to an aluminum substrate 3 made of aluminum (a material through which neutrons can easily pass). Binder 6 is used. The binder 6 fixes the granular scintillator 4 to the aluminum substrate 3 to form a neutron detector.

  The basic neutron detection mechanism is as follows. Neutron (n) 1 passes through the aluminum substrate 3 and reacts with Li in the granular scintillator 4. Strictly speaking, Li is an isotope of Li-6, and Li-6 and neutron (n) 1 react to emit alpha (α) rays 2. This reaction is described as (n, α). The emitted α-ray 2 is emitted from the ZnS phosphor of the granular scintillator 4 and becomes light 5.

  The α-ray 2 is emitted in all directions in the granular scintillator 4 and has a range of about 5 μm to 10 μm (distance traveled by radiation). The particle size of the granular scintillator 4 is approximately the same as the range of the α-ray 2, and the light 5 emitted inside the granular scintillator 4 is absorbed and attenuated in the granular scintillator 4, while Come out. The light 5 passes through the other granular scintillator 4 or is reflected by the granular scintillator 4, passes through the binder 6, and comes out of the neutron detector. Li-6 atoms that react with neutrons account for a quarter of the atomic ratio of LiF / ZnS in the entire granular scintillator 4, and considering the number of atoms of the binder 6, the overall reaction efficiency deteriorates.

  Therefore, in order to increase the efficiency, it is necessary to increase the thickness to which the granular scintillator 4 is applied. However, the light 5 emitted on the incident side of the neutron 1 is transmitted through the granular scintillator 4, reflected by the granular scintillator 4, or transmitted through the binder 6 and comes out of the neutron detector. , The transmittance of light is deteriorated, and the resolution is also deteriorated because the light is further diffused and transmitted.

  The scintillator having this configuration actually used for imaging has a thickness of about several hundred μm. For fast neutrons with high neutron energy, the reaction cross-section with Li-6 is even smaller than that of thermal neutrons. For this reason, in order to increase the reaction efficiency, the thickness must be further increased, and therefore the resolution becomes worse.

The method shown in FIG. 13 has been put to practical use as a method for obtaining a bright image image by increasing the resolution. In this method, B-10 (thermal neutron cross section: 3838 barn), which is four times larger in thermal neutron cross section than Li-6 (thermal neutron cross section: 940 barn), is used as a reactant with neutrons. . Further, the ratio of the number of reacting atoms is 4/5 in the ¹⁰ B ₄ C vapor deposition film 7, and since it can be manufactured by vapor deposition without a binder, the proportion of B-10 present in the unit volume is also large, Even if it is thin, the efficiency can be increased.

However, B-10, like Li-6, has a range of α rays 2 emitted by the (n, α) reaction of about 4 to 5 μm, so if it is thicker than 5 μm, it will be incident upon reaction with neutron 1. The α ray 2 emitted on the side cannot pass through the ¹⁰ B ₄ C vapor deposition film 7 and reach the CsI phosphor 8. ^When the thickness of the ¹⁰ B ₄ C vapor-deposited film 7 is 5 μm, about 80% of thermal neutrons are transmitted when viewed comprehensively, and only about 20% is effectively used. However, compared with the configuration of FIG. 12, the atomic density per unit volume on the reaction surface is high, and the reaction film is about 5 μm, which enables high-definition imaging.

  Moreover, the reacted α-ray 2 is emitted by the highly transparent needle-like CsI phosphor 8 to become light 5, and further becomes an electron 10 by the photoelectric conversion film 9. As a result, the transmission efficiency is increased, and the sensitivity shown in FIG. However, as shown in the graph of FIG. 5 where the vertical axis represents the neutron absorption cross section and the horizontal axis represents the neutron energy, in the case of high energy neutrons (fast neutrons), the neutron absorption cross section is larger than that of thermal neutrons. Since it is two orders of magnitude smaller, the reaction rate becomes extremely small.

  Next, the configuration of the neutron detector according to one embodiment of the present invention will be described with reference to FIGS.

  1 and 2 are enlarged views of the main configuration of the detection unit of the neutron detector according to the first embodiment of the present invention. As shown in FIG. 1, the neutron detector according to one embodiment of the present invention includes an aluminum substrate 3 made of aluminum so as to be located on the incident side of the neutron 1. Adjacent to the aluminum substrate 3, a multi-stage laminated structure is formed in which each layer extends along the incident direction of the neutron 1.

In the first embodiment, the multi-layered structure includes an Al (aluminum) film 12, a ¹⁰ B ₄ C (concentrated boron carbide enriched with boron 10 isotope) vapor deposition film 7 as a first vapor deposition film, and a second The multi-layered laminated structure is formed by repeatedly laminating a laminated structure composed of an Al (aluminum) vapor-deposited film 13 as the vapor-deposited film and the scintillator 11 in multiple stages (for example, several hundred to several thousand stages). When viewed from the incident surface side of the neutron 1, this multi-layered laminated structure is alternately arranged in a grid pattern (grid shape) so that the laminating directions are different by 90 °, thereby expanding two-dimensionally. A detection unit (two-dimensional neutron reaction scintillator) of a neutron detector having a neutron incident surface is configured.

The Al film 12 has a thickness (length in the vertical direction in FIGS. 1 and 2) of 5 μm or more, extends along the incident direction of the neutron 1 and acts as a reflective layer that reflects light. ^{The 10} B ₄ C vapor deposition film 7 is formed by vapor deposition on the Al film 12 and extends along the incident direction of the neutron 1. The ¹⁰ B ₄ C vapor deposition film 7 has a thickness (length in the vertical direction in FIGS. 1 and 2) of, for example, about 4 to 5 μm. ^{In the 10} B ₄ C deposited film 7, boron 10 reacts with neutron 1 and emits radiation (α rays 2).

Al deposited film 13 has a thickness (length in the vertical direction in FIGS. 1 and 2) are about 0.1 .mu.m to 0.5 ^.mu.m, on 10 _{B 4} C deposited film ^7, 10 _{B 4} C deposited film 7 is formed by vapor deposition so as to be adjacent to 7. Therefore, this Al vapor deposition film 13 also has a configuration extending along the incident direction of the neutron 1. The Al vapor deposition film 13 functions as a reflective film that reflects light.

The scintillator 11 is made of a plastic scintillator or the like, and is disposed adjacent to the Al vapor deposition film 13 so as to extend along the incident direction of the neutron 1. The scintillator 11 has a thickness (vertical length in FIGS. 1 and 2) of 5 μm or more, for example, about several tens of μm to 100 μm. The scintillator 11 emits light by the α rays 2 emitted in the ¹⁰ B ₄ C vapor deposition film 7 and generates light 5.

A large number of the above laminated structures are further laminated to constitute a detection unit of the neutron detector. Further, in the present embodiment, in the above laminated structure, each layer such as ¹⁰ B ₄ C vapor deposition film 7 has a configuration that is inclined in the laminating direction with respect to the incident direction of neutron 1, that is, in FIGS. The rear end side (right side in the figure) is configured to rise upward.

As described above, in the neutron detector of this embodiment, the scintillator 11 is sandwiched between the Al vapor deposition film 13 and the Al film 12, and the ¹⁰ B ₄ C vapor deposition film 7 is also composed of the Al vapor deposition film 13 and the Al film. The structure is sandwiched between the films 12.

^{Since the 10} B ₄ C vapor deposition film 7 is black and has low light reflectivity, when the ¹⁰ B ₄ C vapor deposition film 7 and the scintillator layer 11 are directly laminated, the light 5 generated in the scintillator layer 11 is efficiently transmitted. Can not do it. On the other hand, the scintillator layer 11 has a sandwich structure sandwiched between the Al vapor deposition film 13 and the Al film 12 as in the present embodiment, so that reflection by the Al vapor deposition film 13 and the Al film 12 is utilized. The light 5 generated in the scintillator layer 11 can be transmitted efficiently, and can be extracted outside.

That is, α rays 2 emitted by (n, α) reaction at each point in the ¹⁰ B ₄ C vapor deposition film 7 are emitted in a direction substantially perpendicular to the neutron 1 (thickness direction of 4 to 5 μm). The component emits light from the scintillator 11 and becomes light 5. The emitted light 5 travels through the highly transparent scintillator 11 (plastic scintillator) while being reflected by the Al vapor deposition film 13 and the Al film 12, and can be taken out to the outside.

Further, the Al film 12 having a thickness of 5 μm or more absorbs α rays 2 emitted downward in the ¹⁰ B ₄ C vapor deposition film 7 in FIGS. 1 and 2, and prevents light emission from the lower scintillator 11. This improves the position resolution.

Furthermore, in this embodiment, the ¹⁰ B ₄ C vapor deposition film 7 is formed to extend along the incident direction of the neutron 1 as described above. The neutron 1, rather than perpendicular to the ^{10 B} 4 _C deposited film 7, nearly horizontal, and the disposed with an inclination ^{10 B} 4 in _C deposited film 7, to move diagonally Therefore, the reaction efficiency can be greatly improved.

  As described above, the neutron detector according to the present embodiment can greatly improve the utilization efficiency of neutrons, and can efficiently propagate the emitted light 5 without diffusing the light. This makes it possible to obtain a two-dimensional detector for neutrons that can be efficiently and precisely imaged.

The relationship between the thickness of the reaction material and the transmittance of thermal neutrons is shown in the graph of FIG. As shown in FIG. 6, in the case of ¹⁰ B ₄ C, thermal neutrons having a thickness of 50 μm and about 90% react. Therefore, by making the length of the ¹⁰ B ₄ C vapor deposition film 7 (the length in the horizontal direction in FIGS. 1 and 2) about 50 μm, it is possible to react with about 90% of thermal neutrons.

Next, a neutron detector according to the second embodiment will be described with reference to FIG. In the neutron detector of the second embodiment, an Al film 12 having a thickness of 5 μm or more so as to extend along the neutron incident surface on the neutron incident side (left side in FIG. 3), ¹⁰ B ₄ The C vapor deposition film 7 and the Al vapor deposition film 13 having a thickness of about 0.1 μm to 0.5 μm are disposed for light reflection. The other parts are configured in the same manner as in the first embodiment shown in FIGS. 1 and 2, so that the corresponding parts are denoted by the same reference numerals and redundant description is omitted.

  In the neutron detector of the second embodiment, in addition to the functions and effects of the neutron detector of the first embodiment, the reaction efficiency with the neutron 1 on the neutron input surface can be increased. As a result, the size of the neutron detector through which neutrons pass (the horizontal direction in FIG. 3) can be shortened and made compact.

Next, referring to FIG. 4, a neutron detector according to a third embodiment suitable for fast neutron measurement will be described. In the neutron detector of the third embodiment, thermal neutrons are absorbed between the ¹⁰ B ₄ C deposited film 7 and the Al film 12 having a thickness (length in the vertical direction in FIG. 4) of 5 μm or more. Gd ₂ O ₃ vapor deposition film 14 (thickness of 5 μm or more) is inserted.

Further, in the third embodiment, the plastic scintillator 16 is used as the scintillator and has a thickness of 5 μm or more so as to extend along the incident surface of the neutron 1 on the incident side of the neutron 1 (left side in FIG. 4). The Al film 12, the ¹⁰ B ₄ C vapor deposition film 7, and the Al vapor deposition film 13 having a thickness of about 0.1 μm to 0.5 μm are disposed. The other parts are configured in the same manner as in the first embodiment shown in FIGS. 1 and 2, so that the corresponding parts are denoted by the same reference numerals and redundant description is omitted.

In the neutron detector according to the third embodiment having the above configuration, fast neutrons 9 which are neutrons of high energy components react in the ¹⁰ B ₄ C vapor deposition film 7 to emit α rays 2, and the α rays 2 Reacts in the plastic scintillator 16 to emit light, and becomes light 5. However, the (n, α) reaction in the ¹⁰ B ₄ C vapor-deposited film 7 is concentrated boron shown in the graph of FIG. 5 with the ordinate indicating the neutron absorption cross section and the abscissa indicating the neutron energy when the neutron energy increases. The absorption cross section is attenuated in the order of digits like the line of neutron absorption cross section. That is, the reaction probability (efficiency) is deteriorated. For this reason, it is necessary to make the length of the ¹⁰ B ₄ C vapor deposition film 7 (the length in the left-right direction in FIG. 3) longer in the order of digits than in the case of thermal neutrons.

Therefore, focusing on hydrogen that is scattered at a substantially constant rate with respect to the neutron energy in the reaction with neutrons, in the third embodiment, in the case of a plastic scintillator 16 (or a glass scintillator or a crystal scintillator that does not contain hydrogen). The scintillator is covered with a resin containing hydrogen), and the fast neutron 9 is decelerated with hydrogen. The decelerated neutron 15 diffuses in the same direction from the plastic scintillator 16. Neutrons 15 decelerated by the ¹⁰ B ₄ C deposited film 7 below the plastic scintillator 16 react to emit α rays 2, and the α rays 2 react with the plastic scintillator 16 to generate light 5.

On the other hand, when the decelerated neutron 15 reacts with the ¹⁰ B ₄ C vapor deposition film 7 on the upper side of the plastic scintillator 16, light is emitted from the upper and lower plastic scintillators 16 and the light 5 is emitted, resulting in poor resolution. Therefore, Gd ₂ containing gadolinium (Gd) having a large absorption cross section in the thermal neutron region under the upper ¹⁰ B ₄ C vapor deposition film 7 so as not to react with the upper ¹⁰ B ₄ C vapor deposition film 7 of the plastic scintillator 16. By providing the O ₃ vapor deposition film 14, it is possible to prevent the lower neutron from entering.

As described above, in the third embodiment, particularly in the case of high-energy neutrons, the reaction distance with the ¹⁰ B ₄ C vapor deposition film 7 becomes long, so that the fast neutrons 9 are decelerated by the hydrogen atoms of the plastic scintillator 16. The neutron 15 is converted to react with the ¹⁰ B ₄ C deposited film 7. Since the range of the decelerated neutron 15 is several centimeters or more and diffuses, the Gd ₂ O ₃ vapor deposition film 14 (thickness of about 5 μm to several tens of μm) is placed on one side of the ¹⁰ B ₄ C vapor deposition film 7 (FIG. 4). The neutron 15 that has been diffused is absorbed by being formed on the middle and lower side. As a result, the resolution of the detector can be improved while increasing the detection efficiency.

  Next, the overall configuration of the neutron detector having the detection unit configured as described above will be described.

  In order to provide a neutron detector that can be imaged as a high-definition and highly efficient two-dimensional detector for a wide range of neutron energy, particularly for high energy, a two-dimensional neutron reaction scintillator that is a detector having the above-described configuration. It is necessary to adjust the image of the light emitted by the optical lens with an optical lens or the like and image it with an imaging device such as a CCD or CMOS of the imaging camera. In particular, in order to image with neutrons, it is necessary to efficiently image the light of the two-dimensional neutron reaction scintillator. If the neutron intensity is weak, the light emitted is also weak, and it is necessary to reduce the optical loss as much as possible. For that purpose, it is necessary to devise a technique for amplifying the light emitted by the two-dimensional neutron reaction scintillator to reduce the loss and increase the detection efficiency.

  The optical image intensifier tube 103 shown in FIG. 7 is effective as an image amplification tube having a large diameter. Further, if the neutron directly hits the imaging camera 106, the imaging device may be damaged, and it is necessary to devise an approach to keep the imaging device away from the neutron irradiation line. Therefore, in the embodiment shown in FIG. 7, the image image emitted from the output phosphor 103c of the optical image intensifier tube 103 is reflected by the optical reflector 104 in a direction perpendicular to the neutron irradiation line, and then optically reflected. Two-dimensional detection is performed by the imaging camera 106 through the lens 105.

  In the embodiment shown in FIG. 7, an image of light emitted from the two-dimensional neutron reaction scintillator 101 that is the detection unit having the above-described configuration is efficiently introduced into the image sensor, and damage to the image sensor due to radiation such as neutrons and gamma rays. The two-dimensional detector imaging with less noise is realized by combining the optical lens 102, the optical image intensifier tube 103, the optical reflector 104, the optical lens 105, and the imaging camera 106.

In the two-dimensional neutron reaction scintillator 101, as shown in FIGS. 1 and 3, neutrons pass through the aluminum substrate 3 and the Al film 12, which are scintillator-constituting substrates having little reaction with neutrons, and have a thickness of about 4 to 5 μm. Reacts with ¹⁰ B ₄ C vapor deposition film 7. The ¹⁰ B ₄ C vapor deposition film 7 has a structure in which an Al film 12 and an Al vapor deposition film 13 having a thickness of about 0.1 to 0.5 μm are sandwiched. ^{When the 10} B ₄ C deposited film 7 reacts with neutrons, alpha rays are emitted and react with the scintillator 11 to emit light. Many emit light from blue to green.

  A two-dimensional image image emitted by the two-dimensional neutron reaction scintillator 101 is formed on the photoelectric conversion film 103 a of the optical image intensifier tube 103 by the optical lens 102. The input surface of the optical image intensifier tube 103 is made of glass. The input surface size of the optical image intensifier tube 103 ranges from 4 inches to a maximum diameter of 20 inches. The larger the diameter, the more efficiently the light emission of the two-dimensional neutron reaction scintillator 101 geometrically and efficiently. Can be imaged. In particular, the efficiency increases as the diameter (size) of the two-dimensional neutron reaction scintillator 101 is smaller than the diameter of the optical lens 102.

  It is converted into electrons by the photoelectric conversion film 103a, imaged on the output phosphor 103c by the electron lens 103b, and emitted again as an image image. In the optical image intensifier tube 103, electrons are amplified by a high voltage applied between the electrodes, and a minute image is also brightly output. The output image is captured by the imaging camera 106 with the optical lens 105 adjusted in focus. However, there are many imaging devices of the imaging camera 106 that are generally used, such as a CCD and a CMOS, which are damaged by radiation such as neutrons and gamma rays and leave noise in the image. Therefore, the optical reflecting mirror 104 is used so as to install the imaging camera 106 away from the neutron beam line to be irradiated. As a result, it is possible to prevent the imaging camera 106 from being directly irradiated with radiation, and damage to the imaging camera 106 can be reduced.

  The amount of light emitted by the two-dimensional neutron reaction scintillator 101 varies depending on the intensity of the irradiated neutrons, but is generally not bright enough to be confirmed with the naked eye. Therefore, an optical image intensifier tube 103 is used, in particular, it is converted into electrons using a photoelectric conversion film 103a having a high conversion efficiency in accordance with the wavelength emitted by the two-dimensional neutron reaction scintillator 101, and is amplified to be output phosphor. The light is amplified so that it can be confirmed with the naked eye by emitting light at 103c. By taking this image with the imaging camera 106 installed so as to be shifted from the irradiation line of neutrons and gamma rays, it is possible to reduce damage to the imaging device as much as possible, and it is possible to take a two-dimensional image image with less noise due to radiation. . Note that this effect can be further improved by providing a structure capable of shielding neutrons and gamma rays around the imaging camera 106.

  Next, another embodiment will be described with reference to FIG. In this embodiment, a two-dimensional neutron reaction scintillator 111 corresponding to the two-dimensional neutron reaction scintillator 101 in FIG. 7 is formed on the neutron input reaction surface in the neutron image intensifier tube 113. For this reason, the input surface of the optical image intensifier tube 103 in FIG. 7 is made of transparent glass for the purpose of transmitting light, whereas in the case of the neutron image intensifier tube 113 shown in FIG. It is made of aluminum that is easy to penetrate. The two-dimensional neutron reaction scintillator 111 disposed inside the neutron image intensifier tube 113 is formed by directly coating a photoelectric conversion film 113a. As a result, light emitted from the two-dimensional neutron reaction scintillator 111 can be more efficiently converted into electrons, amplified by the electron lens 113b, and imaged on the output phosphor 113c.

  According to the neutron detector having the above-described configuration, not only can the light emitted from the two-dimensional neutron reaction scintillator 111 be efficiently used without geometrical loss due to the optical lens, but also the number of parts can be reduced and the adjustment time can be shortened. Mistakes can be reduced.

  Next, another embodiment will be described with reference to FIG. In this embodiment, the microchannel type image intensifier 123 is used for light amplification instead of the image intensifier amplification by the electron lens.

  The light emitted from the two-dimensional neutron reaction scintillator 101 can be used by being integrated into the input surface of the microchannel type image intensifier 123 with an optical lens. In the embodiment shown in FIG. The taper fiber 112 with less adjustment and less adjustment is coupled to the input surface of the microchannel type image intensifier 123. In FIG. 9, reference numeral 123a denotes a photoelectric conversion film.

  In the embodiment shown in FIG. 9, since the size of the two-dimensional neutron reaction scintillator 101 is larger than the input surface of the microchannel type image intensifier 123, the tapered fiber 112 is used, but conversely, the two-dimensional neutron reaction scintillator 101 is used. If the size of the fiber is small, reverse taper fiber or straight bundle fiber is used. In the embodiment shown in FIG. 9, the output phosphor screen 123 c of the microchannel type image intensifier 123 is configured to capture an image by combining the optical lens 105 and the imaging camera 106, but the microchannel type image intensifier 123 is configured. A CCD element or a CMOS element may be directly coupled to the output phosphor screen 123c via a bundle-type fiber or a tapered fiber.

  According to the neutron detector having the above-described configuration, the light input from the two-dimensional neutron reaction scintillator 101 is efficiently input by the tapered fiber 112 (or bundle type fiber) without any geometrical loss to the input surface of the microchannel type image intensifier 123. In addition to image formation, the number of parts can be reduced, the adjustment time can be shortened, and adjustment errors can be reduced. Further, the microchannel type image intensifier 123 can be used to make the whole compact. However, since the resolution is determined by the channel interval of the microchannel type image intensifier 123, the resolution is limited.

  Next, another embodiment will be described with reference to FIG. In this embodiment, the high-sensitivity imaging camera 116 is used instead of amplification by the microchannel type image intensifier 123 shown in FIG. The high-sensitivity imaging camera 116 uses an HARP (High-gain Avalanche Rushing amorphous Photoconductor) photoelectric conversion film 107 having an electron amplification function as a photoelectric conversion film of the imaging mechanism, and further uses a HEED (High-efficiency Electron) as a cold cathode electron source. Emission Device) A cold cathode electron source 108 is used.

  According to the neutron detector having the above-described configuration, light emitted from the two-dimensional neutron reaction scintillator 101 is efficiently imaged on the input surface of the HARP photoelectric conversion film 107 by the tapered fiber 112 (or bundle type fiber) without geometric loss. Not only can the imaging system be integrated, but the number of parts and the adjustment time can be reduced, and adjustment errors can be reduced. In addition, the overall size is further reduced as compared with the case where the optical image intensifier tube 103, the neutron image intensifier tube 113, the microchannel type image intensifier 123, and the like are used. However, the sensitivity is lowered by the reduction of the amplification function by the image intensifier.

  Next, another embodiment will be described with reference to FIG. In this embodiment, the neutron image intensifier tube 113 is used instead of amplification by the microchannel type image intensifier, but the HARP photoelectric conversion film 107 and the HEED cold cathode electron source 108 having an electronic amplification function are used. It is installed immediately after the output phosphor 113c (relative to the neutron incident direction) and has an imaging function. By adopting such a configuration, the electronic amplification function is enhanced and high-definition imaging can be performed.

  Both the HARP photoelectric conversion film 107 and the HEED cold cathode electron source 108 need to be arranged in a vacuum vessel, and the neutron image intensifier tube 113 is also a vacuum vessel, and can be installed in the inside. . However, there are cases where it is better to place the HARP photoelectric conversion film 107 and the HEED cold cathode electron source 108 inside the neutron image intensifier tube 113 after enclosing the glass further because of the potential.

  According to the embodiment having the above configuration, the light emitted from the two-dimensional neutron reaction scintillator 101 disposed in the neutron image intensifier tube 113 can be converted into electrons more efficiently, amplified, and used. Further, since there is no optical loss due to the taper fiber or the bundle type fiber, the sensitivity becomes high and an image with little quantum noise can be obtained. Furthermore, compared with a microchannel type image intensifier, there is no limitation on the microchannel interval, and high-definition detection becomes possible. In addition, the image pickup system is integrated, so that the number of parts can be reduced and the adjustment time can be shortened, adjustment errors can be reduced, and if the focus adjustment is performed at the initial stage of manufacture, it can be used as it is.

  Instead of disposing the HARP photoelectric conversion film 107 and the HEED cold cathode electron source 108, it is also possible to use a HARP imaging tube of the same vacuum tube in combination in the vacuum vessel. In this embodiment, the production is complicated in that the production in a vacuum is increased, but there is no need to adjust the optical part outside, and a simple imaging tube is obtained, and there is no fear that the focus is shifted after assembly adjustment.

  As mentioned above, although some embodiment of this invention was described, these embodiment is shown as an example and is not intending limiting the range of invention. These novel embodiments can be implemented in various other forms, and various omissions, replacements, and changes can be made without departing from the scope of the invention. These embodiments and modifications thereof are included in the scope and gist of the invention, and are included in the invention described in the claims and the equivalents thereof.

1 ...... neutrons, 2 ...... alpha rays, 5 ...... light, 6 ...... aluminum substrate, 7 ^...... 10 _{B 4} C deposited film, 11 ...... scintillator, 12 ...... Al film, 13 ...... Al evaporated film.

Claims (11)

A metal film extending along the incident direction of neutrons and acting as a reflective layer for reflecting light;
A first deposited film formed on the metal film, extending along an incident direction of neutrons, and reacting with the neutrons to emit radiation;
A second vapor deposition film made of a reflective material extending along the incident direction of neutrons and disposed adjacent to the first vapor deposition film and reflecting light;
A scintillator layer extending along the incident direction of neutrons and disposed adjacent to the second vapor deposition film and generating light from the radiation generated in the first vapor deposition film;
Has a multi-stage laminated structure in which a multi-layer laminated structure is laminated,
A neutron detection device comprising: a detector configured to propagate the light generated in the scintillator layer through the scintillator layer while being reflected by the metal film and the second vapor deposition film, and to lead out to the outside. vessel. The neutron detector according to claim 1,
The detection unit has a configuration in which the multistage stacked structure is combined in a cross-beam shape. A neutron detector according to claim 1 or 2,
An incident side neutron reaction layer that extends along the neutron incident surface on the neutron incident side of the detection unit and emits radiation by reacting with neutrons,
It is disposed on the neutron incident side of the detection unit and adjacent to the rear side in the neutron incident direction of the incident side neutron reaction layer, and is made of a reflective material that extends along the neutron incident surface and reflects light. An neutron detector comprising an incident-side reflection layer. The neutron detector according to any one of claims 1 to 3,
The neutron detector according to claim 1, wherein the multi-layer stacked structure of the detector is disposed with an inclination in the stacking direction with respect to the incident direction of neutrons. The neutron detector according to any one of claims 1 to 4,
The first deposition layer is composed of boron 10 concentrated boron carbide to the isotope was concentrated ^{(10 B 4} _C), said second deposition film, neutron detection, characterized by being composed of an aluminum vessel. The neutron detector according to any one of claims 1 to 5,
A third vapor deposition film that extends along the incident direction of neutrons and absorbs thermal neutrons is formed between the metal film of the detection unit and the first vapor deposition film. A neutron detector. The neutron detector according to claim 6,
The neutron detector, wherein the third vapor deposition film is made of gadolinium oxide (Gd ₂ O ₃ ). A neutron detector according to claim 6 or 7,
A neutron detector, wherein the scintillator layer is composed of either a plastic scintillator containing hydrogen atoms, a glass scintillator sandwiched between resin layers containing hydrogen atoms, or a crystal scintillator. A neutron detector according to any one of claims 1 to 8,
The light emission image of the detection unit is formed on an optical image intensifier tube by an optical lens, photoelectrically converted and amplified, and the imaging camera for imaging the image of the optical image intensifier tube is shifted from the neutron irradiation line. A neutron detector characterized by installation. A neutron detector according to any one of claims 1 to 8,
The detection unit is formed on the input surface of the image intensifier tube, and a neutron image intensifier tube in which a photoelectric conversion film is formed in a vacuum atmosphere on the rear side in the neutron incident direction of the detection unit, A neutron detector, wherein a luminescence image is photoelectrically converted and amplified, and an image pickup camera for picking up an image of the neutron image intensifier tube is shifted from a neutron irradiation line. A neutron detector according to any one of claims 1 to 8,
From the light output surface of the detection unit, a light emission image is introduced into a microchannel type image intensifier through a bundle type optical fiber or a taper fiber, and is optically amplified, and an output image of the microchannel type image intensifier is captured. A neutron detector characterized by taking a picture with a camera.

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