Spherical sensitive neutron detector, neutron spectrometer and neutron detection method

Abstract

The invention discloses a spherical sensitive neutron detector, a neutron spectrometer and a neutron detection method, and relates to the technical field of neutron detection. The neutron detector comprises a moderation ball used for moderating fast neutrons into thermal neutrons, a detection layer used for detecting the thermal neutrons and a shading outer layer arranged on the outermost layer, and the detection layer covers the outer surface of the moderation ball in a spherical shell form to form a spherical detection structure and can convert the thermal neutrons into electric signals. According to the invention, a spherical surface detection structure is adopted, the effective detection area is enlarged to be close to the surface area of the whole moderated sphere, and compared with a traditional central point arrangement detector mode, the thermal neutron capture probability is greatly improved, so that the detection sensitivity is improved. Meanwhile, the slowing-down distance of the fast neutrons is expanded to the whole diameter from the original slowing-down spherical radius, so that the size of the detector can be remarkably reduced on the premise of keeping the same slowing-down effect.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of neutron detection, and in particular to a spherical sensitive neutron detector, a neutron spectrometer and a neutron detection method. BACKGROUND

[0002] Neutron detection is a key technology for measuring neutron energy spectrum and fluence rate in nuclear power facilities such as nuclear reactors and fuel assemblies. At present, the traditional neutron detector mainly adopts a spherical structure with an embedded point detector, and its typical representative is a neutron sphere dosimeter. The traditional spherical neutron detector is usually composed of a spherical moderator (moderator sphere) and a central point detector (such as a He-3 proportional counter tube or a semiconductor detector), and the fast neutron moderation distance is the radius of the moderator sphere. Its working principle is as follows: after the fast neutron (energy range 0.025 eV-20 MeV) enters the moderator sphere, it loses energy through multiple collisions with the moderator material and is gradually moderated to a thermal neutron. Then the thermal neutron diffuses to the center of the sphere and is captured by the point detector to produce a nuclear reaction, generating an electrical signal which is converted into dose rate or neutron flux data after being processed by a preamplifier. However, although this structure is widely used in radiation protection and neutron energy spectrum measurement, it still has the defect of low detection sensitivity. On the one hand, the geometric size of the point detector is much smaller than the surface area of the moderator sphere, and the effective detection area is limited, resulting in that only a small proportion of thermal neutrons can be captured, and a large number of thermal neutrons are absorbed or leaked by the moderator material without being detected; on the other hand, in a low neutron flux (such as 10 nSv / h) environment, due to the limited sensitive volume which is limited by the physical size of the point detector, the signal-to-noise ratio is low, and it is difficult to achieve high sensitivity measurement. SUMMARY

[0003] One of the purposes of the present application is to provide a spherical neutron detector which replaces point detection with spherical detection, so as to increase the effective detection area, improve the thermal neutron capture probability, and thus improve the detection sensitivity.

[0004] In order to achieve the above purpose, the present application adopts the following technical scheme: a spherical sensitive neutron detector, comprising a moderator sphere for moderating fast neutrons into thermal neutrons and a detection layer for detecting thermal neutrons, and a light-shielding outer layer arranged at the outermost layer, wherein the detection layer covers the outer surface of the moderator sphere in the form of a spherical shell, forms a spherical detection structure, and can convert thermal neutrons into electrical signals.

[0005] Further, the moderator sphere contains a moderator material, and the moderator material is a hydrogen-rich material selected from polyethylene, polypropylene, paraffin, polymethyl methacrylate, water and combinations thereof.

[0006] In the above scheme, the detection layer can adopt any one of the following conversion structures: a semiconductor direct conversion structure which directly converts the charged particles generated by the nuclear reaction of thermal neutrons into electrical signals; The photoelectric indirect conversion structure converts thermal neutrons into light signals through a scintillator, and then converts the light signals into electric signals through a photoelectric conversion device.

[0007] As a preferred mode, the detection layer adopts a semiconductor direct conversion structure. Specifically, the detection layer comprises a first semiconductor detection layer and a neutron reaction layer connected (e.g., coupled) thereto; the neutron reaction layer is used to absorb thermal neutrons and generate heavy charged particles through nuclear reaction; the first semiconductor detection layer is used to detect the heavy charged particles and output a first electric signal.

[0008] Further, the detection layer can also integrate a gamma ray detection function, specifically as follows: The detection layer further comprises a second semiconductor detection layer disposed on the side of the first semiconductor detection layer away from the neutron reaction layer, and the first semiconductor detection layer and the second semiconductor detection layer are separated by a barrier layer; the second semiconductor detection layer is used to detect gamma rays and output a second electric signal.

[0009] Further, the thickness of the barrier layer is greater than the maximum range of the heavy charged particles (e.g., alpha particles) in the material, so that the second semiconductor detection layer only responds to gamma rays.

[0010] Among them, the first semiconductor detection layer is mainly used to detect the heavy charged particles (e.g., alpha particles) generated by the neutron reaction layer. Since the range of alpha particles is short and cannot penetrate the barrier layer, the second semiconductor detection layer cannot detect the alpha particle signal. The main function of the barrier layer is to separate the first semiconductor detection layer and the second semiconductor detection layer to prevent signal interference between the two layers. The second semiconductor detection layer is used to detect the background gamma ray signal in the environment. By comparing the signals of the first semiconductor detection layer and the second semiconductor detection layer, differential processing can be performed to ensure more accurate detection of neutron signals.

[0011] Further, the neutron reaction layer comprises a neutron conversion material, and the neutron conversion material comprises a neutron reactant selected from 10 B、 6 Li、 157 Gd、 14 N、 35 Cl and compounds thereof.

[0012] Further, the first semiconductor detection layer and the second semiconductor detection layer are both silicon semiconductor detection layers. The silicon semiconductor detection layer can be a PIPS detector or a gold-silicon surface barrier detector.

[0013] As another preferred mode, the detection layer adopts a photoelectric indirect conversion structure. Specifically, the detection layer comprises a first photoelectric conversion layer and a scintillator layer connected (e.g., coupled) thereto; the scintillator layer is used for absorbing thermal neutrons and converting them into optical signals; and the first photoelectric conversion layer is used for absorbing the optical signals generated by the scintillator layer and converting them into first electrical signals.

[0014] Further, the detection layer can also integrate a gamma ray detection function, specifically as follows: The detection layer further comprises a second photoelectric conversion layer arranged on the side of the first photoelectric conversion layer away from the scintillator layer, and the first photoelectric conversion layer and the second photoelectric conversion layer are separated by an intermediate light shielding layer; the intermediate light shielding layer is used for blocking the optical signals generated by the scintillator layer; and the second photoelectric conversion layer is used for detecting gamma rays and outputting second electrical signals.

[0015] Further, the scintillator layer comprises a neutron conversion material, and the neutron conversion material comprises a neutron reactant selected from 10 B、 6 Li、 157 Gd、 14 N、 35 Cl and compounds thereof, and a scintillator matrix selected from ZnS(Ag), LiF(Eu), CaF2(Eu), YAG(Ce), LaF3(Ce), Gd2O2S(Tb) and combinations thereof.

[0016] Further, the first photoelectric conversion layer and the second photoelectric conversion layer each comprise a photoelectric conversion material selected from perovskite, copper indium gallium selenide (CIGS), indium gallium (InGaP), organic semiconductor (P3HT or P3BP), lead sulfide (PbSe), lead selenide (PbS), indium gallium arsenide (InGaAs), gallium arsenide (GaAs), silicon nitride (SiN) and combinations thereof.

[0017] The light shielding outer layer is composed of a light shielding material and is used for shielding environmental light interference.

[0018] The connection mode between the layers includes but is not limited to direct contact or connection through an optical coupling agent.

[0019] The second purpose of the present application is to provide a neutron spectrometer comprising the spherical sensitive neutron detector of any one of the above structures.

[0020] Further, the number of the neutron detectors is multiple and the diameters of the respective neutron detectors are different, and the respective neutron detectors are arranged independently of each other or in a radial nested manner.

[0021] The third object of the present application is to provide a neutron spectrometer comprising a plurality of neutron detectors with different diameters, each of which is arranged in a radial nested manner, at least one (for example, one) of which is a spherical sensitive neutron detector with a detection layer comprising an integrated gamma-ray detection function semiconductor direct conversion structure as described above, and the rest of which are spherical sensitive neutron detectors with a detection layer comprising a non-integrated gamma-ray detection function semiconductor direct conversion structure as described above.

[0022] The fourth object of the present application is to provide a neutron spectrometer comprising a plurality of neutron detectors with different diameters, each of which is arranged in a radial nested manner, at least one (for example, one) of which is a spherical sensitive neutron detector with a detection layer comprising an integrated gamma-ray detection function photoelectric indirect conversion structure as described above, and the rest of which are spherical sensitive neutron detectors with a detection layer comprising a non-integrated gamma-ray detection function photoelectric indirect conversion structure as described above.

[0023] The fifth object of the present application is to provide a neutron detection method using any one of the spherical sensitive neutron detectors described above, which comprises the following steps: The fast neutrons interact with the detection layer (for example, nuclear reactions or scintillation effects occur) after being moderated by the moderator sphere to generate an electrical signal, and neutron detection is achieved through signal processing.

[0024] The present application breaks through the structural limitation of existing spherical neutron detectors with point detectors built-in the moderator sphere, and uses a spherical shell-shaped detection layer to cover the outer surface of the moderator sphere to achieve spherical detection. This design expands the effective detection area to close to the entire surface area of the moderator sphere, compared with the traditional method of arranging detectors at the center point of the moderator sphere, significantly increases the capture probability of thermal neutrons, and thus improves the detection sensitivity of the neutron detector. At the same time, this design also changes the fast neutron moderation distance from the original moderator sphere radius to the current moderator sphere diameter, which can significantly reduce the volume of the detector while maintaining the same moderation effect. BRIEF DESCRIPTION OF DRAWINGS

[0025] Figure 1 Structure diagram of the neutron detector in the embodiment Figure 1 , whose detection layer adopts a photoelectric indirect conversion structure; Figure 2 Structure diagram of the neutron detector in the embodiment Figure 2 , whose detection layer adopts a photoelectric indirect conversion structure; Figure 3 Structure diagram of the neutron spectrometer with a multi-layer nested structure in the embodiment Figure 1 ; Figure 4Structure diagram of a neutron spectrometer with a multi-layer nested structure in an embodiment Figure 2 ; Figure 5 Structure diagram of a neutron spectrometer with a multi-layer nested structure in an embodiment Figure 3 ; Figure 6 Structure diagram of a neutron spectrometer with a multi-layer nested structure in an embodiment Figure 4 ; Figure 7 Structure diagram of a neutron detector in an embodiment Figure 3 , which uses a semiconductor direct conversion structure for the detection layer Figure 8 Structure diagram of a neutron detector in an embodiment Figure 4 , which uses a semiconductor direct conversion structure for the detection layer Figure 9 Flowchart of the working process of a neutron spectrometer in an embodiment.

[0026] In the figure: 1 - Moderator sphere 2 - Detection layer 2a - Second sandwich structure 2a1a - First photoelectric conversion layer 2a1b - Second photoelectric conversion layer 2a2 - Intermediate light shielding layer 2b - Scintillator layer 2c - First sandwich structure 2c1a - First semiconductor detection layer 2c1b - Second semiconductor detection layer 2c2 - Spacer layer 2d - Neutron reaction layer 3 - Light shielding outer layer 4 - Detection sphere DETAILED DESCRIPTION

[0027] For the convenience of those skilled in the art, the present application will be further described below in conjunction with the embodiments and the accompanying drawings, and the content mentioned in the embodiments is not a limitation on the present application.

[0028] In view of the technical bottleneck of low detection sensitivity of traditional spherical neutron detectors, the present embodiment abandons the previous structure design of embedding a point-like detector (such as a He-3 tube or a semiconductor detector) in the center of the moderator sphere, and instead adopts an external detection structure, i.e., a detection layer 2 is arranged on the outer surface of the moderator sphere 1 to realize spherical surface detection. In this way, point-like surface detection can be extended to spherical surface detection, the effective detection area is increased, and compared with the traditional method of arranging a detector at the center of the moderator sphere, the capture probability of thermal neutrons is greatly increased, thereby improving the detection sensitivity of the neutron detector. At the same time, this design can also change the fast neutron moderation distance from the original moderator sphere radius to the entire diameter of the moderator sphere, so that the volume of the detector can be significantly reduced under the same moderation effect.

[0029] Based on the above concept, the embodiment provides a spherical sensitive neutron detector. As shown in Figure 1 、 2 The neutron detector can be regarded as a detection sphere 4, which includes a spherical moderator (i.e. a moderator sphere 1), a detection layer 2 and a light-shielding outer layer 3 from inside to outside, which are arranged in a radial nested manner, that is, the detection layer 2 is wrapped outside the moderator sphere 1, and the light-shielding outer layer 3 is wrapped outside the detection layer 2. Among them, the moderator sphere 1 is used to slow down fast neutrons to thermal neutrons, and is arranged at the center of the detection sphere 4. The detection layer 2 covers the outer surface of the moderator sphere 1 in the form of a spherical shell, forms a spherical detection structure, and can absorb thermal neutrons and directly or indirectly convert them into electrical signals. The light-shielding outer layer 3 is used to shield the interference of external light, and is arranged at the outermost layer of the detection sphere 4.

[0030] The embodiment not only covers the outer surface of the moderator sphere 1 with the detection layer 2 in the form of a spherical shell to form a spherical detection structure, realize spherical detection, expand the effective detection area, increase the capture probability of thermal neutrons, and improve the detection sensitivity, but also realizes the spatial integration of each functional unit through the radial superposition arrangement of the functional layers (the moderator layer (i.e. the moderator sphere 1), the detection layer 2 and the light-shielding outer layer 3), while ensuring the detection performance, making the overall structure of the detector more compact and lightweight.

[0031] It should be noted that the neutron detector involved in the embodiment greatly increases the capture probability of thermal neutrons by expanding the traditional point-like plane detection method to spherical detection, thereby improving the detection sensitivity of the neutron detector. Therefore, from the perspective of performance advantage of improving the detection sensitivity, the neutron detector can be called a "spherical sensitive neutron detector".

[0032] The moderator sphere 1 is mainly composed of a moderator material (such as a hydrogen-rich material containing a large amount of hydrogen elements), which is used to slow down high-energy fast neutrons to low-energy thermal neutrons. The moderator material can be selected from at least one of polyethylene, polypropylene, paraffin, polymethyl methacrylate and water (for example, one of them). The embodiment selects a polyethylene moderator sphere. In addition, according to the requirements, the moderator sphere 1 can adopt a solid structure or a hollow structure. For example, in an independent single neutron detector, the moderator sphere 1 adopts a solid structure; in a plurality of neutron detectors nested layer by layer, the moderator sphere 1 of the neutron detector of the base layer (i.e. the innermost layer) adopts a solid structure, and the moderator sphere 1 of the neutron detector of the expansion layer (i.e. the outer layer) adopts a hollow structure, the inner diameter of which is adapted to the outer diameter of the adjacent inner layer detector.

[0033] The light-shielding outer layer 3 is composed of a non-transparent material, such as a metal material or plastic, for example, aluminum. These materials can shield the interference of ambient light.

[0034] Regarding the structure of the detection layer 2, it can adopt any of the following structures to realize the direct or indirect conversion of thermal neutrons into electrical signals.

[0035] The first type is a semiconductor direct conversion structure, which directly converts the charged particles generated by the nuclear reaction of thermal neutrons into an electrical signal.

[0036] The second type is a photoelectric indirect conversion structure, which first converts thermal neutrons into a light signal through a scintillator, and then outputs an electrical signal through a photoelectric conversion device.

[0037] As a preferred mode, the detection layer 2 adopts a semiconductor direct conversion structure to realize the direct conversion of thermal neutrons into an electrical signal. Specifically, as shown in Figure 7 8 The first semiconductor detection layer 2c1a and the neutron reaction layer 2d can be connected through an optical coupling mode to form a basic detection unit. Among them: the neutron reaction layer 2d is used to absorb thermal neutrons and generate heavy charged particles through nuclear reaction; the first semiconductor detection layer 2c1a is used to detect heavy charged particles and output a first electrical signal.

[0038] However, the environmental background gamma rays may have some impact on the detection results, so the gamma ray detection function can be integrated in the detection layer 2. Specifically as follows: The detection layer 2 further includes a second semiconductor detection layer 2c1b arranged on the side of the first semiconductor detection layer 2c1a away from the neutron reaction layer 2d. The second semiconductor detection layer 2c1b can be used as an auxiliary detection unit. The first semiconductor detection layer 2c1a and the second semiconductor detection layer 2c1b are arranged apart by a separation layer 2c2 to form a first sandwich structure 2c. The first sandwich structure 2c and the neutron reaction layer 2d together constitute the detection layer 2. Among them, the second semiconductor detection layer 2c1b is used to detect gamma rays and output a second electrical signal; the separation layer 2c2 is used to separate the two semiconductor detection layers to prevent heavy charged particles generated by the first semiconductor detection layer 2c1a from entering the second semiconductor detection layer 2c1b. By measuring the signals of neutrons and gamma rays through the two semiconductor detection layers (the first semiconductor detection layer 2c1a and the second semiconductor detection layer 2c1b) respectively, and then calculating the difference to reduce the interference of gamma rays, a more accurate neutron signal can be obtained.

[0039] According to the requirements, the position distribution of each functional layer can be that the neutron reaction layer 2d is arranged immediately adjacent to the moderator sphere 1, and the second semiconductor detection layer 2c1b is arranged immediately adjacent to the light-shielding outer layer 3, which can be seen from Figure 7 ; or vice versa, the neutron reaction layer 2d is arranged immediately adjacent to the light-shielding outer layer 3, and the second semiconductor detection layer 2c1b is arranged immediately adjacent to the moderator sphere 1, which can be seen from Figure 8 .

[0040] Among them, the thickness of the separation layer 2c2 is greater than the maximum range of heavy charged particles (such as alpha particles) in the material, so that the second semiconductor detection layer 2c1b only responds to gamma rays.​

[0041] The first semiconductor detection layer 2c1a is mainly used to detect the heavy charged particles (such as alpha particles) generated by the neutron reaction layer 2d. Since the range of alpha particles is short and cannot penetrate the barrier layer 2c2, the second semiconductor detection layer 2c1b cannot detect the alpha particle signal. The main function of the barrier layer 2c2 is to separate the first semiconductor detection layer 2c1a and the second semiconductor detection layer 2c1b to prevent signal interference between the two layers. The second semiconductor detection layer 2c1b is used to detect the background gamma ray signal in the environment. By comparing the signals of the first semiconductor detection layer 2c1a and the second semiconductor detection layer 2c1b, differential processing can be performed to ensure more accurate detection of the neutron signal.

[0042] In the detection layer 2 using a semiconductor direct conversion structure, the neutron reaction layer 2d contains a neutron conversion material, and the neutron conversion material contains a neutron reactant selected from 10 B、 6 Li、 157 Gd、 14 N、 35 Cl and compounds thereof, and the selected reactant can react with thermal neutrons to generate charged particles. The first semiconductor detection layer 2c1a and the second semiconductor detection layer 2c1b are both silicon semiconductor detection layers, which can be PIPS detectors or gold-silicon surface barrier detectors.

[0043] As another preferred mode, the detection layer 2 uses a photoelectric indirect conversion structure to realize the indirect conversion of thermal neutrons into electrical signals. Specifically, as shown in Figure 1 、 2 The detection layer 2 includes a first photoelectric conversion layer 2a1a and a scintillator layer 2b connected thereto. The first photoelectric conversion layer 2a1a and the scintillator layer 2b can be connected by optical coupling to form a basic detection unit. Among them: the scintillator layer 2b is used to capture thermal neutrons and convert them into optical signals; the first photoelectric conversion layer 2a1a is used to absorb the optical signals and convert them into first electrical signals. This structure can realize the functions of capturing thermal neutrons and converting them into optical signals and converting the optical signals into electrical signals.

[0044] However, the environmental background gamma rays may have some impact on the detection results, so the gamma ray detection function can be integrated into the detection layer 2. Specifically as follows: The detection layer 2 also includes a second photoelectric conversion layer 2a1b, located on the side of the first photoelectric conversion layer 2a1a away from the scintillator layer 2b. The second photoelectric conversion layer 2a1b serves as an auxiliary detection unit. The first and second photoelectric conversion layers 2a1a and 2a1b are separated by an intermediate light-shielding layer 2a2 (referred to as the "light-shielding layer"), forming a second sandwich structure 2a. The intermediate light-shielding layer 2a2 blocks the optical signal generated by the scintillator layer 2b. The second photoelectric conversion layer 2a1b detects background gamma rays and outputs a second electrical signal. Neutron and gamma-ray signals are measured separately by the two photoelectric conversion layers (the first and second photoelectric conversion layers 2a1a and 2a1b). The difference is then calculated to reduce gamma-ray interference, thereby obtaining a more accurate neutron signal.

[0045] The scintillator layer 2b contains a neutron conversion material for converting thermal neutrons into light signals. The neutron conversion material includes a scintillator matrix (i.e., a luminescent material) and a neutron reactant. The scintillator matrix can be selected from ZnS (Ag), LiF (Eu), CaF2 (Eu), YAG (Ce), LaF3 (Ce), Gd2O2S (Tb), and combinations thereof. The selected scintillator is sensitive to α and β rays and can absorb them and convert them into photons. The neutron reactant can be selected from 10 B. 6 Li, 157 Gd, 14 N. 35 Cl and its compounds, the selected reactants can react with thermal neutrons to produce charged particles. 10 B compound + ZnS(Ag) scintillator, such as ZnS(Ag): 10 B composite scintillator or 10 Layered structure of B coating + independent ZnS(Ag) layer.

[0046] Both photoelectric conversion layers (first photoelectric conversion layer 2a1a and second photoelectric conversion layer 2a1b) contain photoelectric conversion materials, which can be the same. The photoelectric conversion material can be selected from perovskites, copper indium gallium selenide (CIGS), indium gallium (InGaP), organic semiconductors (P3HT or P3BP), lead sulfide (PbSe), lead selenide (PbS), indium gallium arsenide (InGaAs), gallium arsenide (GaAs), silicon nitride (SiN), and combinations thereof. The selected material is capable of converting optical signals into electrical signals. Perovskite is the preferred material.

[0047] The intermediate light shielding layer 2a2 is made of a light-proof material and is used to block the light signal generated by the scintillator layer 2b. The light-proof material can be a black insulating film (such as a black PET film) or aluminum foil (after insulation treatment).

[0048] It should be noted that the connection methods between the various functional layers include but are not limited to direct contact or connection via an optical coupling agent.

[0049] The following mainly describes in detail the structure of the detection layer 2 using indirect photoelectric conversion as an example.

[0050] Take an independent single neutron detector as an example. Based on the original spherical moderator (i.e., moderator sphere 1), the point-shaped detectors inside are removed and filled to form a solid moderator sphere 1. Then, the following functional layers (four layers in total) are coated on the spherical surface of the moderator sphere 1: a mixed scintillator layer (such as 10 B compound + ZnS (Ag) scintillator), a photoelectric conversion layer, an intermediate light-shielding layer 2a2, another photoelectric conversion layer, and then a light-shielding outer layer 3 is coated on the outermost layer. Among them, the two photoelectric conversion layers (i.e., the first photoelectric conversion layer 2a1a and the second photoelectric conversion layer 2a1b) and the intermediate light-shielding layer 2a2 between them constitute a second sandwich structure 2a. The second sandwich structure 2a and the mixed scintillator layer (i.e., the scintillator layer 2b described above) together constitute the detection layer 2. According to requirements, the position distribution of each functional layer can be such that the scintillator layer 2b is set adjacent to the moderator sphere 1, and the second photoelectric conversion layer 2a1b is set adjacent to the light-shielding outer layer 3. Figure 1 Or vice versa, the scintillator layer 2b is arranged adjacent to the light-shielding outer layer 3, and the second photoelectric conversion layer 2a1b is arranged adjacent to the moderation ball 1, see Figure 2 .

[0051] Taking the structure in which the scintillator layer 2b is disposed adjacent to the moderator sphere 1 and the second photoelectric conversion layer 2a1b is disposed adjacent to the light-shielding outer layer 3 as an example (i.e., the scintillator layer 2b, the first photoelectric conversion layer 2a1a, the intermediate light-shielding layer 2a2, the second photoelectric conversion layer 2a1b, and the light-shielding outer layer 3 are disposed on the surface of the moderator sphere 1 from the inside to the outside), the operating principle of the neutron detector is as follows: 1. Neutron moderation: After fast neutrons enter the moderation sphere 1, they are slowed down into thermal neutrons.

[0052] 2. Nuclear reaction and photon production: thermal neutrons and scintillator layer 2b 10 B undergoes a nuclear reaction, generating charged particles. These charged particles deposit energy in the ZnS (Ag) scintillator and emit photons.

[0053] 3. Photon conversion into electrical signals: These photons are absorbed by the first photoelectric conversion layer 2a1a and converted into electrical signals for output.

[0054] 4. Photon shielding: The intermediate light shielding layer 2a2 shields the photons generated by the scintillator layer 2b, preventing these photons from interfering with the second photoelectric conversion layer 2a1b.

[0055] 5. Signal correction: The second photoelectric conversion layer 2a1b detects the environmental background gamma rays and outputs the corresponding electrical signal. The output signal is used to correct the excess counts generated by the first photoelectric conversion layer 2a1a due to the influence of gamma rays.

[0056] 6. Environmental light shielding: The outermost light-shielding layer 3 shields the environmental photons, preventing these external photons from interfering with the internal photoelectric conversion layers.

[0057] This embodiment mainly uses nuclear reaction method for fast neutron detection. Specifically, fast neutrons are first slowed down to thermal neutrons by a slowing-down material such as a polyethylene slowing-down sphere. Subsequently, these thermal neutrons undergo nuclear reactions with a reaction material such as 10 B) to produce charged particles. These charged particles excite photons in the scintillator, which are then absorbed by the photoelectric conversion layer and converted into electrical signals. By processing these electrical signals, the relevant parameters of the fast neutrons can be obtained, thereby realizing the detection of fast neutrons.

[0058] Wherein, the thermal neutron and 10 B reaction process is as follows: 94% probability: 10 B+n→ 7 Li * (0.84 MeV) + α (1.47 MeV); 7 Li * → 7 Li + γ (0.48 MeV).

[0059] 6% probability: 10 B+n→ 7 Li (1.02 MeV) + α (1.78 MeV).

[0060] In a neutron detector with a photoelectric indirect conversion structure in the detection layer 2, according to the position distribution of the functional layers, there are mainly the following two structures.

[0061] The first structure (see Figure 1 ): With the slowing-down sphere 1 as the center, the following five layers are distributed from inside to outside.

[0062] The first layer is the scintillator layer 2b( 10 B + ZnS(Ag)): Since 10 B has a high thermal neutron capture cross-section, thermal neutrons undergo reactions with 10 B to produce charged particles, and the charged particles deposit energy in ZnS(Ag) and are converted into photons, which enter the second layer.

[0063] The second layer is a photoelectric conversion layer (i.e., the first photoelectric conversion layer 2a1a). Since the first layer of the scintillator absorbs thermal neutrons through a reaction and emits photons, the purpose of this layer is to absorb the visible photons generated by the first layer and convert the optical signal into an electrical signal for output.

[0064] The third layer is an intermediate light shielding layer 2a2. The visible photons generated in the reaction of the first layer may pass through the second layer into the fourth layer. Therefore, an intermediate light shielding layer 2a2 is added between the second layer and the fourth layer to avoid the visible photons generated by the reaction from causing miscounting of the data of the fourth layer, thereby causing deviation of the results.

[0065] The fourth layer is a photoelectric conversion layer (i.e., the second photoelectric conversion layer 2a1b). Since the environmental background gamma rays will cause additional counting of the photoelectric conversion layer, a separate photoelectric conversion layer is used to collect the data generated by the gamma rays alone, and the interference caused by the gamma rays to the device is reduced by taking the difference.

[0066] The fifth layer is a light shielding outer layer 3. The light shielding outer layer 3 is used to shield light and avoid additional counting or large counting deviation caused by natural light.

[0067] The second structure (see Figure 2 ): The five layers are arranged in the order of inside to outside with the moderator sphere 1 as the center.

[0068] The first layer is a photoelectric conversion layer (i.e., the second photoelectric conversion layer 2a1b). Since the environmental background gamma rays will cause additional counting of the photoelectric conversion layer, a separate photoelectric conversion layer is used to collect the data generated by the gamma rays alone, and the interference caused by the gamma rays to the device is reduced by taking the difference.

[0069] The second layer is an intermediate light shielding layer 2a2. The visible photons generated in the reaction of the fourth layer may pass through the third layer into the first layer. Therefore, an intermediate light shielding layer 2a2 is added between the first layer and the third layer to avoid the visible photons generated by the reaction from causing miscounting of the data of the first layer, thereby causing deviation of the results.

[0070] The third layer is a photoelectric conversion layer (i.e., the first photoelectric conversion layer 2a1a). Since the fourth layer of the scintillator absorbs thermal neutrons through a reaction and emits photons, the purpose of this layer is to absorb the visible photons generated by the fourth layer and convert the optical signal into an electrical signal for output.

[0071] The fourth layer is a scintillator layer 2b ( 10 B+ZnS(Ag)): Since 10 B has a high thermal neutron capture cross section, thermal neutrons react with 10 B to generate charged particles, and the charged particles deposit energy in ZnS(Ag) and are converted into photons, which enter the third layer.

[0072] The fifth layer is a light-shielding outer layer 3: for light shielding, to avoid additional counting or too much counting deviation caused by natural light.

[0073] For the above two structures, the photoelectric conversion layer is arranged on the inner and outer sides of the scintillator layer 2b respectively: the photoelectric conversion channel directly connected to the scintillator layer 2b (i.e. the connected side channel) is connected to a charge preamplifier, and the photoelectric conversion signal is output after being amplified by the charge preamplifier; the photoelectric conversion channel (i.e. the back side channel) of the scintillator layer 2b (i.e. the scintillator layer 2b is spaced apart from the intermediate light-shielding layer 2a2) outputs the signal through another route of charge preamplifier; the two signals are respectively calculated for dose rate and the difference is calculated, and the γ interference in the connected side original signal is deducted, to output the neutron dose rate.

[0074] The above neutron detector can be directly used for neutron detection. The neutron detection method mainly includes the following steps: The fast neutrons are slowed down by the moderator sphere 1 and interact with the detection layer 2 (for example, nuclear reaction or scintillation effect) to generate an electric signal, and the neutron detection is realized through signal processing.

[0075] The following takes the neutron detector with a detection layer 2 containing an integrated γ-ray detection function and a photoelectric indirect conversion structure as an example to describe the specific steps of the neutron detection method: (1) Slow down the fast neutrons into thermal neutrons by the moderator sphere 1; (2) Capture the thermal neutrons by the scintillator layer 2b and generate a light signal; (3) Collect the light signal by the first photoelectric conversion layer 2a1a and convert it into a first electric signal; (4) Block the light signal generated by the scintillator layer 2b by the intermediate light-shielding layer 2a2; (5) Collect the γ-ray signal of the environmental background by the second photoelectric conversion layer 2a1b alone and convert it into a second electric signal; (6) Perform differential processing on the two electric signals to output the neutron counting result.

[0076] In addition, the above neutron detector can also be applied to a neutron spectrometer as a component thereof. Specifically, the neutron spectrometer can contain one or more (different diameters) neutron detectors. If the neutron spectrometer contains only one neutron detector, it can usually only measure neutrons in a fixed energy range; and when it contains multiple neutron detectors with different diameters, the energy domain range can be widened. Therefore, it is preferred that the neutron spectrometer contains multiple neutron detectors with different diameters, which is called a multi-sphere neutron spectrometer.

[0077] In a multi-sphere neutron spectrometer, the multiple neutron detectors contained therein can be arranged independently of each other to form a multi-sphere structure. These neutron detectors have different diameters, and each detector corresponds to a specific neutron energy range. However, this multi-sphere structure has the problem of occupying too much volume. Therefore, this embodiment proposes a new structure with a smaller volume. Specifically, the multiple neutron detectors in the neutron spectrometer are arranged in a radially nested manner to form a multi-layer nested structure. This structure can not only relax the energy range, but also maintain a small volume. In the multi-layer nested structure, adjacent detection spheres are arranged in a radially nested manner, that is, each sphere is nested inside another sphere, similar to the hierarchical structure of an onion. Each layer has a moderation and detection function, and each layer is an independent neutron detector, corresponding to a specific neutron energy range. This structure helps to improve the efficiency and sensitivity of the detector.

[0078] In a neutron spectrometer with only one neutron detector, the moderator sphere 1 is a solid structure. In a neutron spectrometer with a multi-layer nested structure containing multiple neutron detectors, the detection spheres 4 are nested from the inside out according to their diameter. Specifically, the central detection sphere 4 is a solid structure, and the outer detection spheres 4 are hollow structures. The hollow detection spheres 4 are nested concentrically outside the solid detection spheres 4, forming a multi-layer concentric sphere structure. Figure 3 、 4 This structural design allows each hollow sphere to fit tightly against the outside of the adjacent inner sphere, sharing the same center, thus ensuring compactness of the structure and efficient signal transmission.

[0079] In the neutron spectrometer with the above-mentioned multi-layer nested structure, each detection sphere 4 is configured with a photoelectric conversion layer (or semiconductor detection layer) for measuring gamma rays, but in fact, only one photoelectric conversion layer (or semiconductor detection layer) for measuring gamma rays is required in the neutron spectrometer. For this reason, the present embodiment also provides another neutron spectrometer with a multi-layer nested structure that is different from the neutron spectrometer with the above-mentioned multi-layer nested structure. The difference is that some neutron detectors are configured with a double photoelectric conversion layer + an intermediate light shielding layer 2a2 (or a double semiconductor detection layer + a neutron reaction layer 2d), while some neutron detectors are configured with a single photoelectric conversion layer + an intermediate light shielding layer 2a2 (or a single semiconductor detection layer + a neutron reaction layer 2d). Specifically, the neutron spectrometer includes a plurality of neutron detectors with different diameters, and each neutron detector is arranged in a radially nested manner. At least one (for example, one) neutron detector uses a neutron detector with a detection layer 2 of a semiconductor direct conversion structure that includes an integrated gamma ray detection function, and the remaining neutron detectors use a neutron detector with a detection layer 2 of a semiconductor direct conversion structure that does not include an integrated gamma ray detection function. For details, see. Figure 5 、 6Alternatively, the neutron spectrometer may include multiple neutron detectors of varying diameters, arranged in a radially nested manner. At least one (e.g., one) neutron detector may include a detection layer 2 comprising a photoelectric indirect conversion structure with an integrated gamma-ray detection function, while the remaining neutron detectors may include a detection layer 2 comprising a photoelectric indirect conversion structure without an integrated gamma-ray detection function. A neutron spectrometer may be configured with only one neutron detector comprising a detection layer 2 with an integrated gamma-ray detection function to simplify the structure and reduce costs.

[0080] The following is a further explanation of the multi-sphere structure neutron spectrometer and the multi-layer nested structure neutron spectrometer.

[0081] First, traditional multi-sphere neutron spectrometers usually use Bonner spheres of different specifications to measure neutron energy spectra. The moderating sphere center of each detector is generally configured 3 He proportional counter. However, 3 He resources are scarce and expensive, and if scintillator detection is used instead, the detection efficiency is low. Therefore, this embodiment abandons the central point detector (such as He-3 proportional counter tube, scintillator detector), and sets a detection layer 2 on the outer surface of the moderator sphere 1 to form a spherical detection structure. This new spherical detector design uses a spherical covered detection layer 2 to avoid the need for 3 The reliance on He materials reduces costs. Furthermore, the traditional spherical point detection has been improved to a spherical detection design, transforming the original small-scale detection area at the center of the sphere into a large-scale detection area across the entire sphere. Replacing point detection with spherical detection not only significantly increases the probability of thermal neutron capture, thereby improving detection sensitivity, but also achieves full coverage of nearly 4π solid angles, significantly increasing the neutron capture rate per unit time, and thus significantly improving the detection efficiency of fast neutrons. This allows for the collection of more data and makes it easier to measure the neutron energy spectrum.

[0082] Secondly, the traditional multi-ball neutron spectrometer needs to use multiple independent neutron detectors (different diameters) to measure in combination, which has some shortcomings: (1) multiple detectors arranged independently of each other need to occupy a large space, resulting in a large system volume; (2) each detector needs to be measured individually, which is a cumbersome operation process, resulting in low measurement efficiency. Therefore, in the embodiment, the different diameter detectors of the traditional multi-ball system are integrated into a single ball in a radial nested manner, and a single ball can cover the neutron detection requirements in a wide energy range (from fast neutrons to thermal neutrons). In this way, not only can the detection requirements of different neutron energy regions be met at the same time, but the overall size of the neutron spectrometer can also be greatly reduced. The diameters of the various neutron detectors can be determined in advance through simulation, and then these detectors are arranged in a nested manner from the inside out according to their diameters (i.e., the central detector is a solid sphere structure, and the outer layer of the detector is a hollow sphere structure, and the hollow sphere detector is nested on the solid sphere detector from the inside out), so that multiple detectors of different diameters are integrated in a single spherical structure, thereby meeting the detection requirements of different neutron energy regions while greatly reducing the size of the entire neutron spectrometer. Moreover, due to the spherical detection design of the single-ball neutron spectrometer (which can also be regarded as a single neutron detector containing a slow neutron ball 1 and a detection layer 2 of different diameters), the solid angle coverage is close to 4π, and the neutron capture rate per unit time is greatly improved, which can greatly shorten the exposure time, and the full spectrum measurement of the neutron energy spectrum can be completed in a single exposure, completely avoiding the defects of serial measurement of the multi-ball system. In summary, through the radial nesting design of multiple detectors, the embodiment realizes "single-ball multi-energy region" detection, and by using spherical detection instead of point detection, the solid angle coverage is increased to 4π, achieving dual optimization of volume and performance.

[0083] Of course, in the multi-ball structure neutron spectrometer and the multi-layer nested structure neutron spectrometer, only one of the above structures (mainly referring to the position distribution of each functional layer) of the neutron detector can be applied, or both structures of the neutron detector can be applied, which can be selected as needed.

[0084] The working process of the neutron spectrometer (see Figure 9 ) will be briefly introduced below, mainly including: 1. Neutron radiation field: the starting end of the measurement, providing the measured neutron radiation source.

[0085] 2. Slow neutron system: slow down high-energy neutrons (fast neutrons) into thermal neutrons / epithermal neutrons to improve detection efficiency.

[0086] 3. Detector array: slow down the neutrons after the slow neutron system, and the detector array absorbs the neutrons, and the detector converts the neutron signal into a measurable electrical signal.

[0087] 4. Signal preprocessing module: the signal output by the detector is preliminarily processed, such as amplification, filtering or denoising, to improve the signal quality.

[0088] 5. Data acquisition system: convert the pre-processed signal into digital data, and store and preliminarily arrange.

[0089] 6. Dose rate, deduct γ influence: measure the neutron dose rate, and deduct the interference of γ rays by technical means to ensure the accuracy of the data.

[0090] 7. Deconvolution software: analyze the collected data by using the deconvolution software, generate the neutron spectrum or other related results, and complete the whole measurement process.

[0091] The system realizes the whole process from the neutron radiation field to the data analysis through the modular design, and ensures the accuracy and reliability of the measurement.

[0092] In summary, the embodiment breaks through the structural limitation of the existing spherical neutron detector in embedding a point detector in the moderator sphere 1, adopts a spherical shell shaped detection layer 2 to cover the outer surface of the moderator sphere 1, and realizes spherical detection. This design expands the effective detection area to close to the surface area of the moderator sphere 1, greatly increases the capture probability of thermal neutrons compared with the traditional method of arranging detectors at the center of the moderator sphere, and thus improves the detection sensitivity of the neutron detector, providing a new technical solution for high-sensitivity measurement in a low-flux environment (such as 10 nSv / h). At the same time, this design can change the slow-down distance of fast neutrons from the radius of the moderator sphere to the diameter of the moderator sphere at the present stage, so that the volume of the detector can be significantly reduced while maintaining the same moderation effect. Moreover, the external design of the detection layer 2 of the embodiment eliminates the space occupation requirement of the internal detector for the moderator sphere 1, so that the whole detection device can be more miniaturized. In addition, the spherical detection structure can capture neutrons of different incident angles at the same time, and can obtain omnidirectional response data close to 4π solid angle in a single measurement, thereby improving the detection efficiency.

[0093] Moreover, the spherical detection structure of the embodiment realizes the spatial integration of each functional unit through the radial superposition arrangement of the functional layers (the moderator layer (i.e. the moderator sphere 1), the detection layer 2, and the light-shielding outer layer 3), ensures the detection performance, and makes the overall structure of the detector more compact and lightweight.

[0094] In addition, the embodiment realizes a breakthrough reduction in the volume of the neutron spectrometer while maintaining high performance through a single-sphere structure and a spherical detection design. By using the neutron detector of the embodiment, a neutron spectrometer with a single-sphere structure (i.e., a "multi-layer nested structure") containing multiple neutron detectors is constructed, effectively reducing the device volume and simplifying the operation process, making the device more portable and facilitating on-site deployment and real-time monitoring. It is worth mentioning that the spherical structure detector can realize omnidirectional response of nearly 4π solid angle. Through the global surface scintillator coverage design, the detector can simultaneously capture neutrons incident at multiple angles, and only a single measurement is required to obtain omnidirectional distribution data. This is significantly better than the limited solid angle response of traditional point detectors, thereby enabling more accurate measurement of the neutron spectrum, improving detection efficiency and shortening the measurement time.

[0095] The above embodiment is a preferred implementation scheme of the present application, in addition to this, the present application can be implemented in other ways, any obvious replacement without departing from the technical scheme concept of the present application is within the protection scope of the present application.

[0096] Finally, it should be emphasized that in order to make it more convenient for ordinary skilled in the art to understand the improvements of the present application relative to the prior art, some descriptions of the present application have been simplified, and some other elements have also been omitted from the present application file for the sake of clarity, and those skilled in the art should realize that these omitted elements can also constitute the content of the present application.

Claims

1. Spherical sensitive neutron detector, characterized by: The invention comprises a moderation sphere (1) for slowing down fast neutrons into thermal neutrons, a detection layer (2) for detecting thermal neutrons, and a light-shielding outer layer (3) arranged at the outermost layer. The detection layer (2) covers the outer surface of the moderation sphere (1) in the form of a spherical shell to form a spherical detection structure, and is capable of converting thermal neutrons into electrical signals.

2. The spherical sensitive neutron detector according to claim 1, characterized in that: The detection layer (2) comprises a first semiconductor detection layer (2c1a) and a neutron reaction layer (2d) connected thereto; The neutron reaction layer (2d) is used to absorb thermal neutrons and generate heavy charged particles through nuclear reactions; The first semiconductor detection layer (2c1a) is used to detect heavy charged particles and output a first electrical signal.

3. The spherical sensitive neutron detector according to claim 2, characterized in that: The detection layer (2) further comprises a second semiconductor detection layer (2c1b) provided on a side of the first semiconductor detection layer (2c1a) away from the neutron reaction layer (2d), wherein the first semiconductor detection layer (2c1a) and the second semiconductor detection layer (2c1b) are separated by a spacer (2c2); The second semiconductor detection layer (2c1b) is used to detect gamma rays and output a second electrical signal.

4. The spherical sensitive neutron detector according to claim 1, characterized in that: The detection layer (2) comprises a first photoelectric conversion layer (2a1a) and a scintillator layer (2b) connected thereto; The scintillator layer (2b) is used to absorb thermal neutrons and convert them into light signals; The first photoelectric conversion layer (2a1a) is used to absorb the optical signal generated by the scintillator layer (2b) and convert it into a first electrical signal.

5. The spherical sensitive neutron detector according to claim 4, characterized in that: The detection layer (2) further comprises a second photoelectric conversion layer (2a1b) provided on a side of the first photoelectric conversion layer (2a1a) away from the scintillator layer (2b), wherein the first photoelectric conversion layer (2a1a) and the second photoelectric conversion layer (2a1b) are separated by an intermediate light shielding layer (2a2); The intermediate light shielding layer (2a2) is used to block the light signal generated by the scintillator layer (2b); The second photoelectric conversion layer (2a1b) is used to detect gamma rays and output a second electrical signal.

6. A neutron spectrometer, characterized in that: The spherical sensitive neutron detector comprises the spherical sensitive neutron detector according to any one of claims 1 to 5.

7. The neutron spectrometer according to claim 6, characterized in that: There are multiple neutron detectors, each with a different diameter, and each neutron detector is arranged independently of each other or in a radially nested manner.

8. A neutron spectrometer, characterized in that: It comprises a plurality of neutron detectors with different diameters, each neutron detector is arranged in a radially nested manner, at least one neutron detector is a spherical sensitive neutron detector as claimed in claim 3, and the remaining neutron detectors are spherical sensitive neutron detectors as claimed in claim 2.

9. A neutron spectrometer, characterized in that: It comprises a plurality of neutron detectors with different diameters, each neutron detector is arranged in a radially nested manner, at least one neutron detector is a spherical sensitive neutron detector as claimed in claim 5, and the remaining neutron detectors are spherical sensitive neutron detectors as claimed in claim 4.

10. A neutron detection method, characterized in that: Using the spherical sensitive neutron detector according to any one of claims 1 to 5, the method comprises the following steps: After being slowed down by the slowing ball (1), the fast neutrons interact with the detection layer (2) to generate electrical signals, and neutron detection is achieved through signal processing.

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