Compact solid neutron detector for discriminating fast neutrons, thermal neutrons and gamma rays

Abstract

The invention provides a compact solid neutron detector for discriminating fast neutrons, thermal neutrons and gamma rays. The neutron detector comprises a probe which comprises a PSD plastic flash and a 6Li glass sheet, and the 6Li glass sheet is arranged on the surface where the PSD plastic flash is embedded and used for detecting fluorescence scintillation signals of fast neutrons, thermal neutrons and gamma rays; and the photoelectric device is connected with the probe and is used for converting the fluorescent scintillation signal into an electric signal and carrying out pulse shape discrimination to obtain discrimination information of fast neutrons, thermal neutrons and gamma rays. According to the invention, the lithium glass and the PSD plastic flash are relatively independently designed, so that mutual interference of physical and chemical properties and optical properties caused by polymerization of the two materials is avoided, and on one hand, the phenomena of complex polymerization process, high cost, easy generation of bubbles and the like are avoided; and on the other hand, the problems that the lithium glass content is low and the thermal neutron efficiency is low during polymerization, and the n-gamma discrimination performance is seriously damaged due to rapid reduction of photon scattering and transmittance in PSD plastic flash are solved.

Description

Technical Field

[0001] The invention relates to a compact solid-state neutron detector for detecting fast neutrons, thermal neutrons and gamma rays and a method for distinguishing neutrons, thermal neutrons and gamma rays. Background Art

[0002] Neutron and gamma detection has long been one of the most commonly used technical means in the field of nuclear and radiation safety monitoring. With the rapid development of the nuclear technology industry, the demand for comprehensive measurement of complex gamma and neutron radiation field characteristics and personnel dose monitoring has become increasingly urgent, which has put forward higher requirements on the versatility, reliability and portability of detectors.

[0003] Currently, the most widely used 3 He tube thermal neutron detector and liquid flash fast neutron detector. 3 He tube thermal neutron detector is a kind of detector that uses neutrons and 3 He gas undergoes a nuclear reaction, generating protons and tritium nuclei, and releasing energy. The generated protons and tritium nuclei are emitted in opposite directions, and during the movement, they ionize the working gas, producing a large number of initial electron-ion pairs. The ionized electrons move toward the anode under the action of the electric field, generating an avalanche signal, and thermal neutron events can be identified based on the signal pulse amplitude. The liquid scintillator fast neutron detector is a detector in which charged particles such as recoil protons are generated when neutrons enter the detector and interact with the liquid scintillator. The movement of these charged particles in the liquid scintillator will cause energy deposition, which in turn causes the liquid scintillator to emit a fluorescent flashing signal. The signal pulse is extracted through photoelectric signal conversion, and fast neutron and gamma events are identified by the pulse shape.

[0004] but, 3 He tube thermal neutron detector 3 He gas is expensive and liquid flash is flammable and toxic. 3 He tube thermal neutron detectors and liquid flash fast neutron detectors cannot detect and distinguish fast neutrons, thermal neutrons, and gamma rays at the same time, and cannot meet the requirements of complex radiation environment monitoring. Therefore, it is necessary to develop a neutron detector that can distinguish fast neutrons, thermal neutrons, and gamma rays.

[0005] Currently, if Figure 1a-1b As shown in the figure, the new neutron detector that can detect fast neutrons, thermal neutrons and gamma rays is mainly composed of directly doped 10 B or 6Li compound scintillators (liquid scintillators or plastic scintillators) are used to achieve this. The working principle is as follows: for fast neutrons and thermal neutrons, they respectively undergo nuclear capture reactions with 10B or 6Li and hydrogen nuclei in the liquid or plastic scintillator to produce secondary charged particles and proton recoils. These charged particles move in the scintillator and deposit energy, causing the scintillator molecules to be excited and emit fluorescent scintillation signals. For gamma rays, they interact with the matter in the scintillator, mainly transferring energy to the scintillator molecules through processes such as Compton scattering, electron pair effect or photoelectric effect, causing them to be excited and emit light. The signal pulse is extracted through photoelectric signal conversion, and then the pulse shape is identified. For example Figure 1a-1b The following are the currently commercially available 10 B liquid scintillation and doping 6 Li PSD flashes, but due to direct doping 10 B or 6 The Li compound method will seriously reduce the transmittance of the scintillator and limit the doping concentration, resulting in low thermal neutron detection efficiency and the overlap and mutual interference of thermal neutron and fast neutron events in the discrimination spectrum and making them indistinguishable.

[0006] Currently, another technology is based on 6 Li glass and PSD plastic flash are two materials that adopt chemical synthesis method, which chemically polymerizes lithium glass in PSD plastic flash matrix. Figure 1c As shown in the figure, the addition of lithium glass will cause the two materials to interfere with each other in terms of physical, chemical and optical properties. On the one hand, it is very easy to generate bubbles on the surface where lithium glass contacts PSD plastic flash, so the atmosphere is strictly controlled and the preparation process is complicated. On the other hand, the addition of lithium glass (strong self-absorption of ultraviolet fluorescence) reduces the transmittance of fluorescent photons in PSD plastic flash and the difference in refractive index at the interface between the two causes an increase in internal scattering of photons, so the volume proportion of lithium glass is limited. The optical properties inside PSD plastic flash decrease rapidly, and eventually seriously damage the n-γ discrimination performance. At the same time, the process of chemical polymerization is complex, the cost is high, and the detection performance is limited, which cannot meet the requirements of the development and application of related neutron detection technology and equipment. Summary of the invention

[0007] The present invention aims to provide a novel neutron detector for 6 The problem existing in the chemical synthesis method of Li glass and PSD plastic flash is that the addition of lithium glass causes the two materials to interfere with each other in physical, chemical and optical properties, which leads to complicated preparation process, uneven bubbles and rapid decline of optical properties inside PSD plastic flash, and finally seriously damages key technical problems such as n-γ discrimination performance and low thermal neutron efficiency. A compact solid-state neutron detector for detecting fast neutrons, thermal neutrons and gamma rays and a method for discriminating neutrons, thermal neutrons and gamma rays are provided.

[0008] The technical method of the present invention is as follows:

[0009] A compact solid-state neutron detector for identifying fast neutrons, thermal neutrons, and gamma rays, the neutron detector comprising a probe for detecting fluorescent scintillation signals of fast neutrons, thermal neutrons, and gamma rays and a photoelectric device for converting the fluorescent scintillation signals into electrical signals and performing pulse shape identification to obtain identification information of fast neutrons, thermal neutrons, and gamma rays, the probe comprising a PSD plastic flash and 6 Li glass sheet, 6 The Li glass sheet is arranged on the surface of the PSD plastic flash embedded therein; the photoelectric device is connected with the probe.

[0010] Specifically, the PSD plastic scintillator has a scintillator, which includes 2,5-diphenyloxazole (PPO) and a wave shifter; wherein the wave shifter includes 9,10-diphenylanthracene (DPHA) or 1,4-bis(5-phenyloxazole)benzene (POPPOP), and the PPO content is more than 20%wt.

[0011] Specifically, the PSD plastic flash matrix is ​​one of polystyrene (PS), polyvinyl toluene (PVT), and organic glass (PMMA).

[0012] Specifically, 6 Li glass is a special thin sheet design. 6 The thickness of the Li glass sheet is 1 to 1.5 mm. The embedding method is gluing. Optical silicone grease or silicone is used for gluing.

[0013] Specific 6 A plurality of holes or a plurality of thin strips are formed on the Li glass sheet; wherein, when a plurality of holes are formed, the interval between the holes is 1 to 1.5 mm, and when a plurality of thin strips are formed, the interval between the strip width and the strip gap is 1 to 1.5 mm. 6 The Li glass sheet is arranged in a plurality of hole arrays or thin strip arrays.

[0014] The photoelectric device includes a silicon photomultiplier tube, an amplifying circuit, and a signal output connector which are connected in sequence; the silicon photomultiplier tube collects fluorescent flickering signals and converts them into weak current signals to identify detection signals; the amplifying circuit amplifies the detection signals; the signal output connector outputs the detection signals and transmits them to a digital multi-channel analyzer to obtain identification information of fast neutrons, thermal neutrons, and gamma rays.

[0015] The present invention also provides a method for distinguishing fast neutrons, thermal neutrons, and gamma rays, using the above-mentioned neutron detector, the method comprising:

[0016] The probe is used to detect the fluorescent scintillation signals of fast neutrons, thermal neutrons and gamma rays;

[0017] Photoelectric devices are used to convert fluorescent scintillation signals and identify pulse shapes to obtain identification information of fast neutrons, thermal neutrons and gamma rays.

[0018] The beneficial effects of the present invention are:

[0019] 1. The probe of the present invention is 6 The Li glass sheet is arranged on the surface of the embedded PSD plastic flash. Since the lithium glass is on the surface, its fluorescence transmittance is high and the internal scattering and refraction of the PSD plastic flash is small, it can increase the thermal neutron detection efficiency while maintaining its PSD discrimination ability. Moreover, the lithium glass and the PSD plastic flash are designed relatively independently. On the one hand, it avoids the mutual interference in the physical, chemical and optical properties caused by the polymerization of the two materials, resulting in the problem of low content of polymerized lithium glass and low thermal neutron efficiency. On the other hand, it avoids the complex atmosphere control and process preparation due to the easy generation of bubbles on the contact surface. At the same time, the addition of lithium glass (strong self-absorption of ultraviolet fluorescence) reduces the transmittance of fluorescent photons in the PSD plastic flash and the difference in refractive index at the interface between the two causes increased internal scattering of photons, which will cause the optical performance transmittance inside the PSD plastic flash to drop rapidly and eventually seriously damage the n-γ discrimination performance. In addition, the embedded 6 The problem of complex process of Li glass and PSD plastic flash synthesis method.

[0020] Second, the present invention 6 Li glass sheets and PSD plastic flash can be combined according to different application scenarios.

[0021] 3. The present invention 6 The Li glass sheet and PSD plastic flash are independent of each other and do not affect each other. The process is simple and the reliability is high.

[0022] Fourth, the lithium glass sheet of the present invention adopts a plurality of hole arrays or strip arrays, which can greatly reduce the gamma sensitivity and improve the discrimination performance of the thermal neutron peak. At the same time, the improvement of the PSD plastic flash performance can be developed independently, avoiding the increase in the complexity of the polymerization process control and the generation of bubbles and the decrease in transparency caused by the addition of lithium glass, resulting in poor n-γ discrimination and low thermal neutron efficiency.

[0023] 5. The present invention uses a silicon photomultiplier tube (SIPM, about 4 mm thick) for readout instead of the traditional commonly used photomultiplier tube (PMT, at least 5 cm long), which can greatly reduce the volume of the probe and enhance its vibration resistance. This is a relatively innovative design, because there are currently no reports of other neutron detectors that use SIPM for readout and have triple discrimination capabilities. It has high functional integration and lightweight structure, and is of great significance in the development of practical applications such as portable neutron detection equipment. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1a Direct doping 10Pulse shape discrimination spectrum of liquid scintillator of compound B;

[0025] Figure 1b Direct doping 6 Pulse shape discrimination spectrum of PSD plastic flash of Li compound;

[0026] Figure 1c This is a detector test image of chemical polymerization of lithium glass and PSD plastic scintillating matrix;

[0027] Figure 2 It is the probe diagram of the present invention;

[0028] Figure 3 It is a shape diagram of the strip-shaped hole of the present invention;

[0029] Figure 4 It is the shape diagram of the circular hole of the present invention;

[0030] Figure 5 is a large-scale detector diagram of the present invention;

[0031] FIG6 shows the SIPM readout of the detector of the present invention in the open source and slowing down 252 Pulse shape discrimination spectrum under Cf; where, Figure 6a Read out the pulse shape discrimination spectrum of the detector of the present invention at an open source for SIPM, Figure 6b The detector of the present invention is slowed down for SIPM reading 252 Pulse shape discrimination spectrum at Cf. DETAILED DESCRIPTION

[0032] The technical solution of the present invention is described clearly and completely below. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0033] The present invention provides a compact solid-state neutron detector for distinguishing fast neutrons, thermal neutrons and gamma rays. Figure 2 As shown, the neutron detector includes a probe for detecting the fluorescence scintillation signals of fast neutrons, thermal neutrons and gamma rays and a photoelectric device for converting the fluorescence scintillation signals into electrical signals and performing pulse shape discrimination to obtain discrimination information of fast neutrons, thermal neutrons and gamma rays. The probe includes a PSD plastic flash and 6 Li glass sheet, 6 The Li glass sheet is arranged on the surface of the PSD plastic flash embedded therein; the photoelectric device is connected with the probe.

[0034] here, 6 Li glass sheets include ordinary thin sheets, round hole sheets or slit sheets.6 Li glass sheets can be obtained through mechanical cutting and laser processing. PSD plastic flash can be selected from mature commercial products. PSD plastic flash can be processed into strips and the surface is polished.

[0035] In one embodiment, 6 The working principle of Li glass-PSD plastic scintillator: First, the PSD plastic scintillator in the detector has a detection and slowing effect on fast neutrons. Fast neutrons can produce recoil protons by colliding with hydrogen atoms in it. The recoil protons deposit energy in the plastic scintillator to produce fluorescent scintillation signals. Their decay time is relatively slow. After conversion by photoelectric devices and pulse shape discrimination, the corresponding identification band of fast neutrons is formed. Similar to the corresponding gamma rays, they produce fluorescence through Compton scattering of electrons in PSD plastic scintillator. Their decay time is relatively faster. After conversion by photoelectric devices and pulse shape discrimination, the corresponding identification band of gamma rays is formed. 6 Li glass captures thermal neutrons directly incident on it and after plastic flash moderation 6 Li(n, 3H+4He, 4.8MeV), reaction product 3 H+ 4 He produces near-ultraviolet fluorescence in lithium glass, which has the longest decay time. After conversion by photoelectric devices and pulse shape discrimination, it forms a full-energy deposition peak for thermal neutron events. 252 The PSD identification test spectrum of Cf fission neutron source is as follows Figure 3 The results show that the detector can clearly distinguish fast neutrons and gamma rays, and the thermal neutron peak deposition energy is relatively high, which is very effective for polyethylene slowdown. 252 The Cf source also has a high thermal neutron detection efficiency. Here, it can also be said that the relative count of thermal neutron peak events is high, indicating that the thermal neutron efficiency is high. The above shows that the optical and detection performance of the detector is good.

[0036] In the prior art, the chemical polymerization method is used to obtain 6 Li glass-PSD plastic flash, such as Figure 1c As shown in Figure 2, the addition of lithium glass (strong UV fluorescence self-absorption) leads to a decrease in the photon transmittance and an increase in photon scattering inside the PSD plastic flash. 6 The scintillation performance of Li glass-PSD decreases rapidly with the high proportion of lithium glass, resulting in low thermal neutron detection efficiency (for example, in existing studies, when lithium glass is added with a mass fraction generally less than 6% @ 1 inch, the detector becomes foggy and opaque, and the detector is small in size, and the polymerization process such as controlling bubbles is difficult) and little difference in the fluorescence characteristics of charged particles induced by fast and thermal neutrons, so that the thermal neutron peaks overlap and interfere with each other in the fast neutron PSD spectrum.

[0037] Therefore, the probe of the present invention is to 6The Li glass sheet is set on the surface embedded with PSD plastic flash. Since the lithium glass is on the surface, its fluorescence transmittance is high and the internal scattering and refraction are small, it can increase the efficiency of thermal neutron detection while maintaining its PSD discrimination ability.

[0038] Preferably, the 6 The relative mass of the Li glass sheet is relatively high. 6 The relative mass of the Li glass sheet can reach up to about 15%, which is higher than that of similar 1-inch cylindrical detectors by the polymerization method, avoiding the doping concentration and 6 The content of Li glass flakes is limited, and the thermal neutron detection efficiency can be increased while maintaining its PSD discrimination capability.

[0039] In addition, comparison Figure 1c As can be seen from the results in Figure 6, 6 The Li glass sheet is arranged on the surface of the PSD plastic flash embedded therein to realize the detector with better performances than the PSD plastic flash (EJ276 plastic flash identification) and lithium glass chemical polymerization, such as fast, thermal neutron, gamma ray discrimination, and thermal neutron efficiency, and at the same time facilitates the assembly of large-sized detectors.

[0040] Specifically, the embedding method is gluing. The gluing method uses silicone grease or silicone that is generally UV-transmissive. The cost and process complexity of gluing are much lower than those of chemical polymerization methods, making it an economically feasible option for further use in products such as portable neutron detectors and neutron dose rate meters.

[0041] Specifically, the PSD plastic scintillator has a scintillator. The scintillator includes 2,5-diphenyloxazole and a wave shifter, wherein the wave shifter includes 9,10-diphenylanthracene or 1,4-bis(5-phenyloxazole)benzene. PSD plastic scintillator refers to a plastic scintillator with a higher scintillator (2,5-Diphenyloxazole, PPO) content (generally 20%wt, even reaching more than 30%wt) than ordinary plastic scintillators. Since the PPO content is generally 20%wt, or even reaches more than 30%wt, it will cause the fast neutron fluorescence decay time to be longer than the gamma pulse, thereby achieving pulse shape discrimination.

[0042] Specifically, the PSD plastic flash matrix is ​​one of polystyrene (PS), polyvinyl toluene (PVT), and organic glass (PMMA).

[0043] In one embodiment, the 6 The thickness of the Li glass sheet is 1 to 1.5 mm. 6 A plurality of holes or a plurality of thin strips are formed on the Li glass sheet. When a plurality of holes are formed, the interval between the holes is 1 to 1.5 mm. When a plurality of thin strips are formed, the interval between the strip width and the strip gap is 1 to 1.5 mm. Here, Figure 3 and Figure 4As shown, it can be a circular hole or a thin strip array. This is mainly because the range of Compton electrons generated by high-energy gamma rays above 1.5 MeV in lithium glass is about 1.5 mm, so 6 Reducing the pore or slit unit size of Li glass to below about 1.5 mm can reduce gamma energy deposition, thereby enabling effective discrimination of neutron gamma amplitudes.

[0044] Furthermore, the plurality of holes are arranged in an array or a thin strip array. Through the array design, the thermal neutron layer is on the surface of the detector, and the thermal neutron detection (lithium glass) and the fast neutron detection (PSD plastic flash) are better separated, which will greatly improve the photon transmittance and reduce internal scattering, so that the fluorescence and detection performance can be kept independent to the greatest extent, so that the performance of n-γ discrimination spectrum and thermal neutron peak resolution (equivalent light yield) and thermal neutron efficiency is improved. Because the PSD material and lithium glass material are easy to shape and can be combined according to different application production, their performance is more independent and does not affect each other, the process is simpler, and the reliability is high.

[0045] The present invention uses PSD plastic flash glue to bond lithium glass material and adopts circular hole arrays or strip holes, which can be carried out independently without interfering with each other, and can greatly reduce its process cost and improve its performance, making it practical and having good fast thermal neutron and gamma ray discrimination and detection capabilities.

[0046] Furthermore, if Figure 5 As shown, in order to meet the requirements of neutron detection and radiation field feature analysis in various scenarios, the above method can be repeatedly used to form a large-size detector array to increase the thermal neutron detection efficiency. 6 According to physical simulation, as shown in Figure 6, the 8cm*8cm*12.7cm composite detector (composed of 16 20mm*20mm*120cm strip-shaped lithium glass-PSD plastic flash arrays) has an intrinsic efficiency of more than 50% for 1-6MeV fast neutrons. 252 The thermal neutron peak intrinsic efficiency of the Cf neutron source exceeds 5%, even under heavy polyethylene shielding. 252 Cf sources also have a high thermal neutron detection efficiency.

[0047] In one embodiment, a lithium glass sheet may be embedded with a PSD plastic flash side and then wrapped with a reflective layer material, such as MgO powder or aluminum-plated film.

[0048] Specifically, the photoelectric device includes a silicon photomultiplier tube, an amplifier circuit, and a signal output connector connected in sequence. The silicon photomultiplier tube collects the fluorescent flashing signal and converts it into a weak current signal to identify the detection signal; the amplifier circuit amplifies the detection signal; the signal output connector outputs the detection signal and transmits it to the digital multi-channel analyzer to obtain the identification information of fast neutrons, thermal neutrons, and gamma rays.

[0049] The present invention uses a semiconductor silicon photodiode (SIPM) to replace a vacuum glass device (PMT), further compressing the probe volume and having high light quantum efficiency, and can produce a high-performance, low-cost all-solid-state portable neutron detector with high neutron detection efficiency, strong gamma discrimination, stability, and strong vibration resistance, and can be used for neutron metrology and radiation monitoring equipment, neutron measurement systems and other engineering requirements.

[0050] At the same time, the detector design using SIPM readout in the present invention and the test results of fast, thermal neutron and gamma ray discrimination show that its detection performance is good, and its size, vibration resistance and portability are greatly improved.

[0051] Compared with the prior art, the photoelectric converters commonly used at the back end of the scintillator detector include PMT and SIPM. The former is a vacuum electronic device with low noise, wide temperature range but large size, while the latter is a semiconductor device with high noise but small size and high light quantum efficiency. The present invention uses SIPM for fluorescence readout of the detector, converts it into a weak current signal, and enters the back-end digital multi-channel spectrometer for digital multi-channel analyzer after a fast amplifier, which can obtain fast, thermal neutron, gamma ray discrimination spectrum and other information in real time. Using a compact SIPM readout design to replace the traditional commonly used PMT can reduce the volume of the probe and enhance its vibration resistance and portability.

[0052] Specifically, most of the current neutron dosimetry equipment uses a "neutron moderator absorber + thermal neutron detector" structure, but this structure is large in size, low in sensitivity, and has a single function. 6 The Li glass-PSD plastic flash detector does not require an additional moderator and is small in size. In addition to realizing the functions of the above-mentioned traditional thermal neutron detector-based neutron dose equipment, it can also simultaneously realize the measurement of gamma dose rate and fast neutron pulse amplitude spectrum (for example, the measurement of fast neutron pulse amplitude spectrum can invert and analyze the energy spectrum information of the neutron radiation field to a certain extent). It can be used for radiation field and source term characteristic analysis in complex scenes, so it has considerable development potential and application prospects.

[0053] Furthermore, the optoelectronic device also includes a power supply module for providing power.

[0054] The present invention also provides a method for distinguishing fast neutrons, thermal neutrons and gamma rays, using the above-mentioned neutron detector, the method comprising: using a probe to detect the fluorescent scintillation signals of fast neutrons, thermal neutrons and gamma rays; using a photoelectric device to convert the fluorescent scintillation signals and distinguish the pulse shape, and obtain the fast neutrons, thermal neutrons and gamma rays. Identification information.

[0055] Furthermore, a silicon photomultiplier tube is used to collect fluorescent flicker signals and convert them into weak current signals to identify detection signals; an amplifier circuit is used to amplify the detection signals; a signal output connector is used to output the detection signals and transmit them to a digital multi-channel analyzer to obtain identification information of fast neutrons, thermal neutrons, and gamma rays.

[0056] Although embodiments of the present invention have been shown and described, it will be appreciated by those skilled in the art that various changes, modifications, substitutions and variations may be made to the embodiments without departing from the principles and spirit of the present invention, and that the scope of the present invention is defined by the appended claims and their equivalents.

Claims

1. A compact solid-state neutron detector for identifying fast neutrons, thermal neutrons, and gamma rays, characterized in that: The neutron detector includes a probe for detecting the fluorescence scintillation signals of fast neutrons, thermal neutrons and gamma rays and a photoelectric device for converting the fluorescence scintillation signals into electrical signals and performing pulse shape discrimination to obtain discrimination information of fast neutrons, thermal neutrons and gamma rays. The probe includes a PSD plastic flash and 6 Li glass sheet, 6 The Li glass sheet is arranged on the surface of the PSD plastic flash embedded therein; the photoelectric device is connected with the probe.

2. The neutron detector according to claim 1, characterized in that: The PSD plastic scintillator has a scintillator, wherein the scintillator includes 2,5-diphenyloxazole and a wave shifter, wherein the wave shifter includes 9,10-diphenylanthracene or 1,4-bis(5-phenyloxazole)benzene, and the content of 2,5-diphenyloxazole is more than 20%wt.

3. The neutron detector according to claim 2, characterized in that: The PSD plastic flash matrix includes one of polystyrene, polyvinyl toluene and organic glass.

4. The neutron detector according to claim 1, characterized in that: The embedding method is gluing.

5. The neutron detector according to claim 4, characterized in that: The adhesive is optical silicone grease or silicone.

6. The neutron detector according to claim 1, characterized in that: Said 6 The thickness of the Li glass sheet is 1 to 1.5 mm.

7. The neutron detector according to claim 1, characterized in that: 6 A plurality of holes or a plurality of thin strips are formed on the Li glass sheet; wherein, when a plurality of holes are formed, the interval between the holes is 1 to 1.5 mm, and when a plurality of thin strips are formed, the interval between the strip width and the strip gap is 1 to 1.5 mm.

8. The neutron detector according to claim 7, characterized in that: Said 6 The Li glass sheet is arranged in a plurality of hole arrays or thin strip arrays.

9. The neutron detector according to any one of claims 1 to 8, characterized in that: The photoelectric device includes a silicon photomultiplier tube, an amplifying circuit, and a signal output connector connected in sequence; Silicon photomultiplier tube, collects fluorescent flash signals and converts them into weak current signals to identify detection signals; An amplifier circuit amplifies the detection signal; The signal output connector outputs the detection signal and transmits it to the digital multi-channel analyzer to obtain the identification information of fast neutrons, thermal neutrons and gamma rays.

10. A method for distinguishing fast neutrons, thermal neutrons and gamma rays, characterized in that: Using the neutron detector according to any one of claims 1 to 9, the method comprises: The probe is used to detect the fluorescent scintillation signals of fast neutrons, thermal neutrons and gamma rays; Photoelectric devices are used to convert fluorescent scintillation signals into electrical signals and perform pulse shape identification to obtain identification information of fast neutrons, thermal neutrons, and gamma rays.

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