Photoelectric spherical neutron detector, neutron spectrometer and neutron detection method

Abstract

The invention discloses a photoelectric spherical 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 receiving the thermal neutrons and converting the thermal neutrons into optical signals, and a shading 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 the optical signal is transmitted to the photoelectric conversion device through the signal transmission optical fiber to be converted into an electric signal. The outer surface of the moderated ball is covered with the detection layer in the shape of the spherical shell, and spherical detection is achieved. According to the design, the effective detection area is enlarged to be close to the surface area of the whole moderated ball, 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 under 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 photoelectric type spherical 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 energy facilities such as nuclear reactors and fuel assemblies. At present, the traditional spherical neutron detector usually adopts a structure design of installing a point detector (such as a He-3 tube or a semiconductor detector) at the center of a spherical moderator. The fast neutron moderation distance is the radius of the spherical moderator. After the fast neutron enters the moderator, it gradually loses energy through multiple collisions with the moderator material and is gradually moderated into thermal neutrons. Then, the point detector receives the thermal neutrons and converts them into measurable signals to achieve neutron detection. However, this structure of the point detector built-in has the defect of insufficient detection sensitivity, mainly due to the following reasons: 1. Limited effective detection area: the geometric size of the point detector is much smaller than the surface area of the moderator, resulting in that it can only receive a small proportion of thermal neutrons in the moderator. 2. Severe neutron loss: a large number of thermal neutrons are absorbed by the moderator material or diffused to the outside without being detected in time. SUMMARY

[0003] One of the purposes of the present application is to provide a spherical neutron detector that replaces point detection with spherical detection 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 solution: a photoelectric type spherical neutron detector, including a moderator sphere for moderating fast neutrons into thermal neutrons, a detection layer for receiving thermal neutrons and converting them into optical signals, and an outermost light shielding layer, the detection layer covers the outer surface of the moderator sphere in the form of a spherical shell, forming a spherical detection structure, and the optical signals are transmitted to a photoelectric conversion device through a signal transmission optical fiber to be converted into electrical signals.

[0005] Further, the photoelectric conversion device is arranged outside the neutron detector.

[0006] Further, a tapered light guiding structure layer for conducting optical signals is arranged between the detection layer and the signal transmission optical fiber, the structure layer includes a plurality of light cone units, the large end surface of each light cone unit is optically coupled with the surface of the detection layer, and the small end surface is butt jointed with the signal transmission optical fiber.

[0007] Further, the plurality of light cone units are divided into groups, each group adopts an integrated structure or a bundle structure. When adopting an integrated structure, each group of light cone units is integrally formed. When adopting the bundle structure, each light cone unit in each group is arranged independently, and the arrangement mode is that both the large end surface and the small end surface are arranged in a polygonal close-packed or circular arrangement mode.

[0008] Further, the small end surface set of each light cone unit is coupled with an intermediate optical fiber, and the intermediate optical fiber is coupled in any one of the following modes: (a) directly converging to a signal transmission optical fiber through single-stage coupling; (b) gradually converging through multi-stage coupling and finally connecting to a signal transmission optical fiber.

[0009] Further, when the large end surface of each light cone unit is optically coupled with the surface of the detection layer, the coverage is greater than or equal to 95%.

[0010] Further, the detection layer comprises a transparent support layer and a scintillator light-emitting layer arranged on one surface of the transparent support layer, and the conical light guide structure layer is arranged on the other surface of the transparent support layer.

[0011] Further, the scintillator light-emitting 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.

[0012] Further, the light cone unit is an optical fiber cone, which is made by a photocuring 3D printing method or a fusion tapering method. The fusion tapering method comprises the following steps: fixing one end of the optical fiber, heating the middle section of the optical fiber to soften, pulling the other end of the optical fiber in the softened state to uniformly stretch the middle section of the optical fiber to form a conical structure, and shearing the excess part to obtain the required optical fiber cone.

[0013] Further, the moderator sphere comprises a moderator material, and the moderator material is a hydrogen-rich material selected from polyethylene, polypropylene, paraffin, polymethyl methacrylate, water and combinations thereof.

[0014] The second object of the present application is to provide a neutron spectrometer comprising the above-mentioned photoelectric type spherical neutron detector.

[0015] Further, the number of the neutron detectors is multiple, and the diameters of the respective neutron detectors are different, the respective neutron detectors are arranged independently of each other to form a multi-sphere structure, or are arranged in a radial nesting mode to form a multi-layer moderator-detection structure.

[0016] A third object of the present application is to provide a neutron detection method employing the above-mentioned photoelectric type spherical neutron detector, and comprising the following steps: S1. Fast neutrons are slowed down by a moderator sphere and interact with a detection layer to generate optical signals; S2. The optical signals are transmitted to a photoelectric conversion device through a signal transmission optical fiber; S3. The optical signals are converted into electrical signals by the photoelectric conversion device, and the parameters of the electrical signals are analyzed to achieve neutron detection.

[0017] The present application breaks through the structural limitation of the existing spherical neutron detector in which point detectors are embedded in the moderator sphere. The present application uses a spherical shell-shaped detection layer to cover the outer surface of the moderator sphere to achieve spherical detection. By expanding the effective detection area to nearly the entire surface area of the moderator sphere, the present application significantly increases the capture probability of thermal neutrons compared to the conventional method of arranging detectors at the center of the moderator sphere, thereby improving the detection sensitivity of the neutron detector. At the same time, the present application changes the fast neutron slowing-down distance from the original moderator sphere radius to the current moderator sphere diameter, which significantly reduces the volume of the detector under the same moderation effect. BRIEF DESCRIPTION OF DRAWINGS

[0018] Figure 1 FIG. 1 is a front view of a photoelectric type spherical neutron detector; Figure 2 FIG. 2 is a perspective view of a photoelectric type spherical neutron detector, with the signal transmission optical fiber omitted; Figure 3 FIG. 3 is a structural schematic diagram of a conical light guide structure layer when it is arranged on the inner surface of a transparent support layer; Figure 4 FIG. 4 is a perspective view of a single group of light cone units with the large end face and the small end face arranged in a hexagonal close-packed manner; Figure 1 Figure 5 FIG. 5 is a perspective view of a single group of light cone units with the large end face and the small end face arranged in a hexagonal close-packed manner; Figure 2 Figure 6 FIG. 6 is a top view of a single group of light cone units with the large end face and the small end face arranged in a hexagonal close-packed manner; Figure 7 FIG. 7 is a schematic diagram of the beam combining method of each group of light cone units; Figure 8 FIG. 8 is a structural schematic diagram of a single photoelectric type spherical neutron detector; Figure 1 Figure 9 FIG. 9 is a structural schematic diagram of a single photoelectric type spherical neutron detector; Figure 2 Figure 10 FIG. 10 is a structural schematic diagram of a neutron spectrometer with a multi-layer moderation-detection structure; Figure 1 ​​​​, which contains three detection spheres; Figure 11 Structure diagram of a neutron spectrometer with a multi-layer slowing-detection structure Figure 2 , which contains three detection spheres.

[0019] In the figure: 1 - detection sphere 1a - slowing sphere 1b - detection layer 1b1 - transparent support layer 1b2 - scintillator light-emitting layer 1c - conical light guide structure layer 1c1 - light cone unit 1d - light shielding layer 1e - central hole 2 - signal transmission optical fiber 3 - intermediate optical fiber. DETAILED DESCRIPTION

[0020] 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 of the present application, see Figures 1-11 .

[0021] In view of the technical bottleneck of low detection sensitivity of the conventional spherical neutron detector, the embodiment discards the previous structure design of embedding a point-like detector (such as a He-3 tube or a semiconductor detector) in the slowing sphere, and instead adopts an external detection structure, i.e., a detection layer 1b is arranged on the outer surface of the slowing sphere 1a to realize spherical surface detection. In this way, the point-like surface detection can be extended to spherical surface detection, the effective detection area is increased, compared with the conventional method of arranging a detector at the center point of the slowing 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 slowing distance from the original slowing sphere radius to the current slowing sphere diameter, so that the detector volume can be significantly reduced under the same slowing effect.

[0022] Based on the above idea, the embodiment provides a photoelectric type spherical neutron detector. As shown in Figure 1 , 2As shown in FIGS. 1, 8, and 9, the neutron detector can be regarded as a detection sphere 1, which comprises, from inside to outside, a spherical moderator (i.e., a moderator sphere la), a detection layer lb, and a light shielding layer ld in a radially nested manner, i.e., the detection layer lb is wrapped outside the moderator sphere la, and the light shielding layer ld is wrapped outside the detection layer lb. The moderator sphere la is arranged at the center of the detection sphere 1 and is used to slow down fast neutrons into thermal neutrons. The detection layer lb is used to receive thermal neutrons and convert them into optical signals, and is in the form of a spherical shell covering the outer surface of the moderator sphere la to form a spherical detection structure, thereby achieving spherical detection, expanding the effective detection area, increasing the capture probability of thermal neutrons, and thus improving the detection sensitivity. The detection layer lb is connected to a photoelectric conversion device through a signal transmission optical fiber 2, and the optical signals are transmitted to the photoelectric conversion device through the signal transmission optical fiber 2 to be converted into electrical signals. The light shielding layer ld is arranged at the outermost layer of the detection sphere 1 and is used to shield the interference of external light.

[0023] The photoelectric conversion device can be built-in in the neutron detector or arranged outside the neutron detector. Preferably, the photoelectric conversion device is arranged outside the neutron detector, which has the following advantages: moving the photoelectric conversion device outside the neutron detector and performing photoelectric conversion by the external photoelectric conversion device. This improvement of external photoelectric conversion can greatly reduce the interference of environmental gamma rays on neutron detection and improve the detection accuracy. Meanwhile, the operation of separately distinguishing gamma rays is no longer needed, which further improves the detection efficiency. Moreover, the photoelectric conversion device arranged outside is convenient for shielding treatment, which can minimize the interference of gamma rays.

[0024] It should be noted that the neutron detector according to the present embodiment adopts a spherical detection structure and realizes signal conversion by a photoelectric conversion device. Based on this feature, it can be named as a "photoelectric spherical neutron detector". In addition, the neutron detector expands the traditional point-like plane detection mode to spherical detection, greatly increases the capture probability of thermal neutrons, and thus improves the detection sensitivity of the neutron detector. Therefore, from the perspective of performance advantages of improving the detection sensitivity, the neutron detector can be called a "spherical sensitive neutron detector".

[0025] In view of the problem that the order of magnitude of the super-large light output area of the spherical detection layer lb does not match the limited receiving core diameter of a single optical fiber, the present embodiment adopts a tapered light guide structure layer lc to realize efficient coupling and transmission of optical signals. Specifically, the tapered light guide structure layer lc comprises a plurality of light cone units lc1 (referred to as "light cones" for short), the large end surface of each light cone unit lc1 is optically coupled to the surface of the detection layer lb, and the small end surface is connected to the signal transmission optical fiber 2. These light cone units lc1 are usually uniformly distributed on the surface of the detection layer lb in the form of an array to achieve high-density coverage, ensuring that the coverage rate is not less than 95% (i.e., the coverage rate ≥ 95%), thereby realizing omnidirectional optical signal acquisition.

[0026] For the selection of the light cone unit 1c1, it is made of light-guiding material, such as plastic optical fiber material or other light-guiding material. In this embodiment, the plastic optical fiber material is selected to make the optical fiber cone as the light cone unit 1c1, and this is taken as an example for description. The optical fiber cone is a special optical fiber structure, which realizes efficient transmission of optical signals between optical fibers of different diameters by gradually changing the diameter of the optical fiber. The structure of the optical fiber cone is as follows: 1. Large end face: one end of the optical fiber cone has a larger diameter, which is usually used to receive optical signals; 2. Small end face: the other end of the optical fiber cone has a smaller diameter, which is usually used to output optical signals; 3. Conical structure: the middle part of the optical fiber cone gradually tapers, forming a conical structure, which helps to efficiently transmit optical signals.

[0027] For the preparation of the optical fiber cone, it can be directly printed by light-curing 3D printing, or it can be prepared by fusion tapering method. The appropriate tapering process can be selected as needed during actual preparation. The fusion tapering method mainly includes the following steps: one end of the optical fiber is fixed, and the middle section of the optical fiber is heated to softening; in the softening state, the other end of the optical fiber is pulled to uniformly stretch the middle section of the optical fiber to form a conical structure; the excess part is cut off to obtain the required optical fiber cone. Specifically: one end of the optical fiber is fixed on a clamping fixture that can be clamped and released, and the other end is wound around a roller. The middle section of the optical fiber is placed in a temperature-controlled zone of 160±2℃ to soften it. In the softening state, the optical fiber is placed vertically, and the clamping fixture uniformly stretches the middle section of the optical fiber to form a conical structure. The excess part is cut off to obtain the required optical fiber cone. Multiple optical fibers can be tapered at the same time to improve production efficiency. Then, the effective optical fiber cones are selected, and their tips (small ends) are clamped and gathered to form a tight arrangement. The large and small end faces of the optical fiber cones can be arranged in a hexagonal or circular dense stacking manner. A large-diameter optical fiber that has not been tapered is coupled (glued) to the gathering surface to ensure efficient transmission of optical signals. Each optical fiber cone is coupled to an optical fiber, and n optical fiber cones are gathered and coupled again, and finally pass out from the center hole 1e of the detection sphere 1.

[0028] For the light cone units 1c1 distributed on the surface of the detection layer 1b, in order to facilitate production and assembly, these light cone units 1c1 are usually divided into groups to form small groups, each group adopts an integrated structure or a bundle structure. When adopting an integrated structure, each group of light cone units is integrally formed. These groups of light cone units with an integrated structure can be regarded as large light cones with an integrated structure. When adopting a bundle structure, each light cone unit 1c1 in each group is independently arranged, and the arrangement manner is that the large end face and the small end face are arranged in a polygonal dense arrangement or a circular arrangement. These groups of light cone units with a bundle structure can be regarded as large light cones with a combined structure.

[0029] Among them, the arrangement mode such as polygon dense arrangement and circular arrangement can improve the collection efficiency of optical signals, and can also ensure the uniform distribution of the light cone unit 1c1 on the surface of the transparent support layer 1b1. The polygon dense arrangement mode includes but is not limited to hexagonal dense arrangement, pentagonal dense arrangement, etc. For example, as shown in Figure 3 some groups of light cone units 1c1 adopt hexagonal dense arrangement for the large end face and the small end face, and the remaining groups of light cone units 1c1 adopt pentagonal dense arrangement for the large end face and the small end face. These hexagonal and pentagonal dense arrangement groups of light cone units are spliced in a manner similar to the structure of a football to form an overall spherical arrangement structure. Figures 4-6 The structure of a single group of light cone units arranged in a hexagonal dense arrangement for the large end face and the small end face is shown.

[0030] For the connection mode between each group of light cone units and the signal transmission optical fiber 2, the beam combining mode is usually used for connection. Specifically, the small end face set of each group of light cone units is coupled with an intermediate optical fiber 3. The intermediate optical fiber 3 can be directly converged to the signal transmission optical fiber 2 through single-stage beam combining, or can be gradually converged (equivalent to gradually combining in steps, i.e. combining n times at a time) through multi-stage beam combining, and finally connected to the signal transmission optical fiber 2. The specific selection can be made as needed.

[0031] The detection layer 1b includes a transparent support layer 1b1 (such as a PMMA transparent layer) and a scintillator luminescent layer 1b2 arranged on one surface of the transparent support layer 1b1, and a conical light guide structure layer 1c arranged on the other surface of the transparent support layer 1b1. Among them, the transparent support layer 1b1 is sandwiched between the scintillator luminescent layer 1b2 and the conical light guide structure layer 1c. The scintillator luminescent layer 1b2 can be coated on one surface of the transparent support layer 1b1, and the conical light guide structure layer 1c can be coupled on the other surface of the transparent support layer 1b1 through optical glue.

[0032] The detection layer 1b has two structures to choose from: The first structure: the scintillator luminescent layer 1b2 is arranged on the outer surface of the transparent support layer 1b1, and the conical light guide structure layer 1c is arranged on the inner surface of the transparent support layer 1b1.

[0033] The second structure: the scintillator luminescent layer 1b2 is arranged on the inner surface of the transparent support layer 1b1, and the conical light guide structure layer 1c is arranged on the outer surface of the transparent support layer 1b1.

[0034] As shown in Figure 1 , 2As shown, the detection sphere 1 has a central hole 1e. Specifically, both the detection layer 1b and the light-shielding layer 1d are provided with central holes 1e, and the two holes are coaxially aligned. Central hole 1e serves as both an infusion hole for injecting moderator material and an exit hole for the optical fiber bundle (i.e., the signal transmission optical fiber 2). Moderator material is filled into the detection layer 1b through central hole 1e, forming a spherical moderator, also referred to as moderator sphere 1a. The primary function of moderator sphere 1a is to moderate high-energy fast neutrons into low-energy thermal neutrons. Hydrogen-rich moderator materials such as polyethylene, polypropylene, paraffin wax, polymethyl methacrylate, and water can be used as the moderator. In this embodiment, polyethylene is used as the moderator.

[0035] The detection sphere 1 is a concentric spherical structure as a whole, and each layer of structure covering the moderation sphere 1a can be regarded as a spherical shell structure. For example, the detection layer 1b can be regarded as a detection spherical shell, the light-shielding layer 1d can be regarded as a light-shielding spherical shell, the conical light-guiding structure layer 1c can be regarded as a conical light-guiding structure spherical shell, the transparent support layer 1b1 can be regarded as a transparent support spherical shell, and the scintillator light-emitting layer 1b2 can be regarded as a scintillator light-emitting spherical shell. Among them, the light-shielding spherical shell can be made of opaque materials such as aluminum or plastic, and its outer wall is painted black to reduce interference from external light. All spherical shells can be assembled by two hemispherical shells. These assembled structures can adopt a detachable design, for example, through slot positioning and sealing structure to achieve precise assembly, so as to reduce assembly difficulty and improve assembly efficiency.

[0036] The detection layer 1b is used to generate and transmit optical signals. The transparent support layer 1b1 provides an optically transparent medium, supporting the other layers and ensuring efficient transmission of optical signals. The scintillator luminescent layer 1b2 converts the energy generated by the interaction between neutrons and matter into optical signals. The tapered light-guiding structure layer 1c efficiently transmits these optical signals to the signal transmission fiber 2.

[0037] The scintillator light emitting layer 1b2 comprises a neutron conversion material for converting thermal neutrons into light signals. The neutron conversion material comprises a material selected from 10 B. 6 Li, 157 Gd, 14 N. 35 Neutron reactants of Cl and its compounds, and a scintillator matrix selected from ZnS (Ag), LiF (Eu), CaF2 (Eu), YAG (Ce), LaF3 (Ce), Gd2O2S (Tb) and combinations thereof. 10 B+ZnS(Ag) is used as the scintillator luminescent layer material, that is, the neutron conversion material contains 10 The neutron reactant of element B and the scintillator matrix (i.e., luminescent body) with ZnS (Ag). During the detection process, the thermal neutrons react with the scintillator luminescent layer 1b2. 10B nuclear reaction occurs, generating charged particles. These charged particles deposit energy in the ZnS(Ag) scintillator, emitting photons.

[0038] The following describes a neutron detector in which the conical light guide structure layer 1c is disposed on the inner surface or the outer surface of the transparent support layer 1b1. The technical means in the two structures can be borrowed from and replaced by each other, and the embodiment does not limit the technical means to a single structure.

[0039] 1. The conical light guide structure layer 1c is disposed on the inner surface of the transparent support layer 1b1.

[0040] In this structure, the inner wall of the transparent support layer 1b1 can be polished, and the optical epoxy resin is used to bond the light cone unit array along the curved surface, ensuring that the coverage rate is not less than 95%, so as to realize omnidirectional light signal acquisition. The outer surface of the transparent support layer 1b1 is uniformly coated with a scintillator light-emitting layer 1b2 by a spin coating process to form a radiation-photon conversion interface. The equatorial plane of the transparent support layer 1b1 is reserved with a perfusion hole (i.e., a central hole 1e), and after assembly, the perfusion hole is used to perfuse the moderator material to form a moderator body. Finally, a black light shield 1d is compounded on the outer layer of the transparent support layer 1b1.

[0041] In this structure, the optical fiber cone is embedded in the moderator sphere 1a, and the optical fiber cone is made of plastic optical fiber material, the main component of which is polymethyl methacrylate (PMMA), which has certain contribution to the moderation process due to its hydrogen content, but the overall moderation mainly depends on the moderator sphere 1a. The overall moderation is still mainly dependent on the moderator sphere 1a, and the plastic optical fiber is auxiliary. The large end face of the optical fiber cone is arranged in a hexagonal dense arrangement or a circular arrangement to increase the area of the received light signal and ensure the uniform distribution of the optical fiber cone on the inner wall of the transparent support layer 1b1. After the inner wall of the transparent support layer 1b1 is filled with the optical fiber cone, the small end face of each group of optical fiber cones is directly combined and coupled to the signal transmission optical fiber 2, or is combined in multiple n-in-one multi-stage manner step by step, and then connected to the signal transmission optical fiber 2, to ensure the effective transmission of the light signal. Specifically, the multiple n-in-one combining manner refers to the process of gradually combining multiple optical fibers into one optical fiber. First, a certain number of optical fibers are combined into one intermediate optical fiber 3, and then these intermediate optical fibers 3 are further combined, and finally an output optical fiber is formed. See Figure 7 This step-by-step combination can reduce high-order mode loss and improve the transmission efficiency of the light signal.

[0042] 2. The conical light guide structure layer 1c is disposed on the outer surface of the transparent support layer 1b1.

[0043] In the structure, the large end faces of each group of fiber tapers are tightly adhered to the outer wall of the transparent support layer 1b1 by ultraviolet curing optical glue or radiation-resistant epoxy resin, ensuring the reliability and durability of the adhesion and reducing the loss of optical signals. The small end faces of each group of fiber tapers are collectively coupled to an intermediate optical fiber 3. This intermediate optical fiber 3 can be directly combined with the intermediate optical fibers 3 collectively coupled to the small end faces of the remaining groups of fiber tapers (also known as beam combining), and connected to the signal transmission optical fiber 2, or combined by multiple n-beam combining methods, and finally connected to the signal transmission optical fiber 2. All fiber tapers are evenly distributed on the entire outer spherical surface of the transparent support layer 1b1, ensuring efficient collection of optical signals. The inner wall of the transparent support layer 1b1 is coated with a scintillator luminescent material to achieve radiation-photon conversion. On the basis of not affecting the luminescent material, the transparent support layer 1b1 is filled with a moderator material to form a moderator. The outermost layer is also provided with a light shielding layer 1d to reduce external light interference.

[0044] The working principle of the neutron detector will be briefly described below.

[0045] In the detection process, the scintillator material reacts with 10 B to deposit energy and excite electrons, producing visible light. The reaction process is as follows: Fast neutrons enter the moderator sphere 1a and undergo elastic scattering with hydrogen nuclei. The fast neutron moderation range is the thickness of the moderator sphere 1a with a diameter of 1a. After collision, the energy of the fast neutron gradually decreases, and finally it is moderated to a thermal neutron. The thermal neutron diffuses to 10 B+ZnS(Ag) scintillator layer, and (n, α) reaction occurs (reaction cross section 3837 barns): 10 B+n→ 7 Li+α+2.79 MeV (total energy) The α particle (1.47 MeV) and 7 Li (0.84 MeV) recoil nucleus produce ionization tracks in the ZnS(Ag) crystal lattice, ionize Ag⁺ luminescent centers, and emit blue light with a wavelength of 450 nm. The fluorescence signal is transmitted in the tapered optical fiber (i.e., fiber taper) in a total reflection mode. The high numerical aperture of the large end face captures a wide range of scattered photons. In the tapered region, the transmission mode is converted from multi-mode to single-mode due to the gradual reduction in diameter, effectively suppressing high-order mode loss and ensuring efficient transmission of optical signals.

[0046] The neutron detector in the embodiment can also be applied to a neutron spectrometer as a component thereof. Specifically, the neutron spectrometer can include one or more neutron detectors with different diameters. If the neutron spectrometer includes only one neutron detector, it can generally only measure neutrons in a fixed energy range; when it includes multiple neutron detectors with different diameters, the energy range can be widened. Therefore, the neutron spectrometer preferably includes multiple neutron detectors with different diameters, which is referred to as a multi-sphere neutron spectrometer.

[0047] In the multi-sphere neutron spectrometer, the multiple neutron detectors included therein can be arranged independently of each other to form a multi-sphere structure. These neutron detectors have different diameters, and each of the detectors corresponds to a specific neutron energy range. However, the multi-sphere structure has the problem of occupying too much space. Therefore, the embodiment proposes a new structure with a smaller volume. Specifically, the multiple neutron detectors in the neutron spectrometer are arranged in a radial nested manner to form a multi-layer moderation-detection structure (which can be referred to as a "multi-layer nested structure"), which can be seen in Figure 10 、 11 . This structure not only widens the energy range, but also maintains a small volume. In the multi-layer moderation-detection structure, the adjacent detection spheres 1 are arranged in a radial nested manner, i.e., each sphere is nested inside another sphere, similar to the hierarchical structure of an onion. Each layer has moderation and detection functions, 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.

[0048] In the neutron spectrometer including only one neutron detector, the moderation sphere 1a is a solid structure. In the neutron spectrometer including multiple neutron detectors in the multi-layer moderation-detection structure, the detection spheres 1 are arranged in a nested manner from the inside to the outside according to the diameters. Specifically, the central detection sphere 1 is a solid structure, and the outer detection sphere 1 is a hollow structure. The hollow detection spheres 1 are nested in a concentric manner outside the solid detection spheres 1 to form a multi-layer concentric sphere structure, which can be seen in Figure 10 、 11 . This structure design makes each hollow sphere closely fit outside the adjacent inner sphere, sharing the same sphere center, thereby ensuring the compactness of the structure and the efficiency of signal transmission.

[0049] It is worth mentioning that the different diameter detectors of the multi-ball system are integrated into a single ball in a radial nested manner in the embodiment, 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 compressed. 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 the diameter size (that is, the central detector is a solid ball structure, and the outer detector is a hollow ball structure, and the hollow ball detector is nested on the solid ball detector from the inside out layer by layer), so that multiple detectors of different diameters are integrated in a single ball structure, thereby meeting the detection requirements of different neutron energy regions while greatly compressing the size of the entire neutron spectrometer. Moreover, due to the spherical detection design of the single-ball structure neutron spectrometer (which can also be regarded as a single neutron detector containing a slow ball 1a and a detection layer 1b of different diameters), the solid angle coverage is close to 4π, and the neutron capture rate per unit time is greatly improved, so that the irradiation time can be greatly shortened, and the full spectrum measurement of the neutron energy spectrum can be completed in a single exposure, completely avoiding the serial measurement defects of the multi-ball system. In summary, the radial nested design of multiple detectors in the embodiment realizes "single-ball multi-energy region" detection, and the spherical detection replaces point detection, the solid angle coverage is increased to 4π, and the volume and performance are optimized.

[0050] In addition, the embodiment also provides a neutron detection method, which adopts the neutron detector described above and comprises the following steps: S1. The neutron is slowed down by the slow ball 1a and interacts with the scintillator light-emitting layer 1b2 of the detection layer 1b to generate a light signal; S2. The light signal is conducted to the signal transmission optical fiber 2 through the light cone unit 1c1; S3. The light signal is transmitted to the photoelectric conversion device through the signal transmission optical fiber 2; S4. The parameters of the light signal are analyzed after the light signal is converted into an electric signal by the photoelectric conversion device, and neutron detection is realized.

[0051] In general, the embodiment breaks through the structural limitation of existing spherical neutron detectors in which point detectors are embedded in the moderator sphere. The detection layer 1b in the form of a spherical shell covers the outer surface of the moderator sphere 1a, realizing spherical detection. This design expands the effective detection area to close to the entire surface area of the moderator sphere 1a, significantly increasing the capture probability of thermal neutrons compared to the conventional arrangement of detectors at the center of the moderator sphere, thereby improving the detection sensitivity of the neutron detector and 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 changes 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, allowing the volume of the detector to be significantly reduced under the same slow-down effect. Moreover, the external design of the detection layer 1b eliminates the need for internal detectors to occupy space in the moderator sphere 1a, allowing the entire detection device to be more compact. In addition, the spherical detection structure can simultaneously capture neutrons at different incident angles, obtaining nearly 4π omnidirectional response data in a single measurement, thereby improving detection efficiency.

[0052] Furthermore, the embodiment moves the photoelectric conversion device to the outside of the neutron detector and performs photoelectric conversion through the external photoelectric conversion device. This improvement can significantly reduce the interference of environmental gamma rays on neutron detection, improving detection accuracy. At the same time, the need for separate gamma ray discrimination in the past is eliminated, further improving detection efficiency. Moreover, the external photoelectric conversion device is convenient for shielding, which can minimize the interference of gamma rays.

[0053] In addition, the embodiment realizes a breakthrough in the volume of the neutron spectrometer while maintaining high performance through the single-sphere architecture and spherical detection design. By using the neutron detector of the embodiment, a single-sphere architecture (i.e., a "multi-layer slow-down-detection structure") neutron spectrometer containing multiple neutron detectors is constructed, effectively reducing the device volume and simplifying the operation process, making the device more portable and convenient for on-site deployment and real-time monitoring. It is worth mentioning that the spherical structure detector can achieve nearly 4π omnidirectional response. Through the global surface scintillator coverage design, this detector can simultaneously capture neutrons at multiple incident angles, obtaining omnidirectional distribution data in a single measurement. This is significantly better than the limited solid angle response of traditional point detectors, thereby enabling more accurate measurement of neutron energy spectrum, improving detection efficiency, and shortening measurement time.

[0054] The above embodiment is a preferred implementation of the present application. In addition to this, the present application can be implemented in other ways, and any obvious substitutions within the concept of the present technical solution are within the protection scope of the present application.

[0055] Finally, it should be emphasized that some of the description of the present application has been simplified and that, for the sake of clarity, the present application document also omits some other elements, which the person skilled in the art should be aware of, and which can also constitute the content of the present application.

Claims

1. Photoelectric spherical neutron detector, characterized by: The invention comprises a moderation sphere (1a) for slowing down fast neutrons into thermal neutrons, a detection layer (1b) for receiving thermal neutrons and converting them into optical signals, and a light shielding layer (1d) arranged on the outermost layer. The detection layer (1b) covers the outer surface of the moderation sphere (1a) in the form of a spherical shell to form a spherical detection structure, and transmits the optical signal to the photoelectric conversion device through the signal transmission optical fiber (2) to convert it into an electrical signal.

2. The photoelectric spherical neutron detector according to claim 1, characterized in that: The photoelectric conversion device is arranged outside the neutron detector.

3. The photoelectric spherical neutron detector according to claim 1 or 2, characterized in that: A conical light-guiding structure layer (1c) for transmitting light signals is provided between the detection layer (1b) and the signal transmission optical fiber (2). The structure layer comprises a plurality of light cone units (1c1). The large end face of each light cone unit (1c1) is optically coupled to the surface of the detection layer (1b), and the small end face is butted against the signal transmission optical fiber (2).

4. The photoelectric spherical neutron detector according to claim 3, characterized in that: The light cone units (1c1) are divided into multiple groups, each group adopting an integrated structure or a bundle structure; When an integrated structure is adopted, each group of light cone units is formed as a whole; When a bundle structure is adopted, each light cone unit (1c1) in each group is arranged independently, and the arrangement method is: the large end face and the small end face are both arranged in a polygonal close-packed or circular manner.

5. The photoelectric spherical neutron detector according to claim 4, characterized in that: The small end faces of each group of light cone units are collectively coupled to an intermediate optical fiber (3), and the intermediate optical fibers (3) are bundled in any of the following ways: (a) Directly converge to the signal transmission optical fiber (2) through single-stage beam combining; (b) The beams are gradually converged through multi-stage beam combining and finally connected to the signal transmission optical fiber (2).

6. The photoelectric spherical neutron detector according to claim 3, characterized in that: When the large end surface of each light cone unit (1c1) is optically coupled with the surface of the detection layer (1b), the coverage rate is ≥95%.

7. The photoelectric spherical neutron detector according to claim 3, characterized in that: The detection layer (1b) comprises a transparent support layer (1b1) and a scintillator light-emitting layer (1b2) provided on one surface of the transparent support layer (1b1), and the tapered light-guiding structure layer (1c) is provided on the other surface of the transparent support layer (1b1).

8. A neutron spectrometer, characterized in that: The photoelectric spherical neutron detector comprises the photoelectric spherical neutron detector according to any one of claims 1 to 7.

9. The neutron spectrometer according to claim 8, 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.

10. A neutron detection method, characterized in that: Using the photoelectric spherical neutron detector according to any one of claims 1 to 7, the method comprises the following steps: S1. After being slowed down by the moderation sphere (1a), fast neutrons interact with the detection layer (1b) to generate optical signals; S2. The optical signal is transmitted to the photoelectric conversion device through the signal transmission optical fiber (2); S3. The optical signal is converted into an electrical signal by a photoelectric conversion device and its parameters are analyzed to achieve neutron detection.

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