Neutron detector and neutron detection method

Abstract

The present disclosure provides a neutron detector and a neutron detection method. The neutron detector comprises an absorption layer and a photoelectric detection device, wherein: the absorption layer comprises at least one gamma sensitive layer and at least one neutron sensitive layer, the neutron sensitive layer is embedded in the first side of the gamma sensitive layer, wherein: the to-be-detected neutron and the gamma background of the to-be-detected neutron are incident from the second side of the gamma sensitive layer, the first side is opposite to the second side, the gamma background deposits energy in the gamma sensitive layer to generate first scintillation light, and the to-be-detected neutron deposits energy in the neutron sensitive layer to generate second scintillation light; the photoelectric detection device is arranged on the first side of the gamma sensitive layer embedded with the neutron sensitive layer, and is used for detecting the first scintillation light and the second scintillation light, so as to realize the detection and discrimination of the to-be-detected neutron and the gamma background. The method realizes the improvement of the discrimination effect of neutron events and gamma events.

Description

Technical Field

[0001] This disclosure relates to the field of neutron detection technology, and more specifically, to a neutron detector and a neutron detection method. Background Technology

[0002] Neutron detectors are important tools in nuclear physics, and are widely used in fields such as nuclear radiation detection, nuclear safety, and materials science. Helium-3 ( 3 He gas detectors are currently the most widely used neutron detectors, but due to... 3 The scarcity of helium gas makes it extremely expensive, limiting its application. Scintillator detectors have advantages such as high detection efficiency, simple structure, and stable performance. Scintillator-based thermal neutron detectors have been widely studied and applied, with lithium-containing, boron-containing, and gadolinium-containing scintillator crystal neutron detectors being current research hotspots.

[0003] When detecting neutrons, the neutron radiation field is always accompanied by gamma background radiation in most cases. Neutron detectors usually have a certain response to gamma rays. Therefore, the distinction between neutron events and gamma background events is an urgent problem to be solved when detecting neutrons.

[0004] The information disclosed in the background section is only intended to enhance the understanding of the background of this disclosure, and therefore may include information that does not constitute prior art known to those skilled in the art. Summary of the Invention

[0005] The purpose of this disclosure is to provide a neutron detector and a neutron detection method that overcomes, to some extent, the problem of distinguishing between neutron events and gamma background events in neutron detection.

[0006] Other features and advantages of this disclosure will become apparent from the following detailed description, or may be learned in part by practice of this disclosure.

[0007] According to one aspect of this disclosure, a neutron detector is provided, comprising an absorption layer and a photodetector, wherein: the absorption layer comprises at least one gamma-sensitive layer and at least one neutron-sensitive layer, the neutron-sensitive layer being embedded in a first side of the gamma-sensitive layer, wherein: a neutron to be detected and its gamma background are incident from a second side of the gamma-sensitive layer, the first side being opposite to the second side, the gamma background depositing energy in the gamma-sensitive layer to generate a first scintillation, and the neutron to be detected depositing energy in the neutron-sensitive layer to generate a second scintillation; the photodetector is disposed on the first side of the gamma-sensitive layer in which the neutron-sensitive layer is embedded, for detecting the first scintillation and the second scintillation, thereby realizing the detection and identification of the neutron to be detected and the gamma background.

[0008] According to one embodiment of this disclosure, the time difference between the emission decay time of the gamma-sensitive layer and the emission decay time of the neutron-sensitive layer is greater than a preset threshold.

[0009] According to one embodiment of this disclosure, the gamma-sensitive layer has a multilayer structure.

[0010] According to one embodiment of this disclosure, the gamma-sensitive layer is at least one gamma-photon-sensitive material, including but not limited to: at least one of thallium-doped sodium iodide, barium fluoride, thallium-doped cesium iodide, cesium iodide, bismuth germanate, lead tungstate, cerium-doped lutetium silicate, and cerium-doped lanthanum bromide, wherein the neutron to be detected hardly deposits energy in the gamma-sensitive layer.

[0011] According to one embodiment of this disclosure, the neutron to be detected is a thermal neutron, and the neutron-sensitive layer is at least one neutron-sensitive material, including but not limited to: lithium-containing materials, boron-containing materials, and gadolinium-containing materials.

[0012] According to one embodiment of this disclosure, the neutron-sensitive layer is sheet-like, and the thickness of the neutron-sensitive layer is between 0.05 mm and 5 mm, so that the gamma background deposits all or most of the energy in the gamma-sensitive layer, while almost no energy is deposited in the neutron-sensitive layer.

[0013] According to another aspect of this disclosure, a neutron detection method is provided, employing the aforementioned neutron detector, wherein the method includes: obtaining an event waveform detected by the photodetector based on the signals of the gamma background and the neutron to be detected detected by the photodetector; obtaining the energy deposition spectrum of the gamma background and the neutron to be detected in the absorption layer based on the signals of the gamma background and the neutron to be detected detected by the photodetector; and distinguishing between neutron events and gamma background events based on the event waveform and / or the energy deposition spectrum.

[0014] According to one embodiment of this disclosure, distinguishing neutron events and gamma background events based on the event waveform and / or the energy deposition spectrum includes: performing multiple identification of neutron events and gamma background events based on the event waveform and the energy deposition spectrum.

[0015] According to one embodiment of this disclosure, identifying neutron events and gamma background events based on the event waveform and / or the energy deposition spectrum includes: identifying neutron events and gamma background events based on the rise time and fall time in the event waveform; or identifying neutron events and gamma background events based on the pulse width in the event waveform; or identifying neutron events and gamma background events based on multiplicity information in the event waveform.

[0016] According to one embodiment of this disclosure, identifying neutron events and gamma background events based on the event waveform and / or the energy deposition spectrum includes: identifying neutron events and gamma background events based on characteristic peaks in the energy deposition spectrum.

[0017] The neutron detector provided in the embodiments of this disclosure sets the absorption layer as a nested gamma-sensitive layer and a neutron-sensitive layer. The neutron-sensitive layer is embedded in the first side of the gamma-sensitive layer. The neutron to be detected and the gamma background are incident from the second side of the gamma-sensitive layer opposite to the first side. The gamma background deposits energy in the gamma-sensitive layer to generate a first scintillation light, and the neutron to be detected deposits energy in the neutron-sensitive layer to generate a second scintillation light. The photodetector is set on the first side of the gamma-sensitive layer with the embedded neutron-sensitive layer to detect the first scintillation light and the second scintillation light to achieve the detection and identification of neutrons and gamma background, thereby improving the differentiation effect between neutron events and gamma events.

[0018] It should be understood that the above general description and the following detailed description are merely exemplary and do not limit this disclosure. Attached Figure Description

[0019] The above and other objects, features and advantages of this disclosure will become more apparent from a detailed description of exemplary embodiments thereof with reference to the accompanying drawings.

[0020] Figure 1 The diagram illustrates the response of cerium-doped gadolinium aluminum gallium garnet crystals of different thicknesses to gamma rays in embodiments of this disclosure.

[0021] Figure 2 This diagram illustrates a cerium-doped gadolinium aluminum gallium garnet crystal thin film according to an embodiment of the present disclosure.

[0022] Figure 3 A schematic diagram of a photodetector device according to an embodiment of the present disclosure is shown.

[0023] Figure 4 A schematic diagram of a thermal neutron testing experimental apparatus according to an embodiment of this disclosure is shown.

[0024] Figure 5 The diagram shows the thermal neutron test results of a cerium-doped gadolinium aluminum gallium garnet crystal according to an embodiment of this disclosure.

[0025] Figure 6 This is a schematic diagram of a neutron detector structure according to an exemplary embodiment.

[0026] Figure 7 This is a schematic diagram of another neutron detector structure according to an exemplary embodiment.

[0027] Figure 8This is a schematic diagram of a thermal neutron detector structure in a simulation calculation, according to an exemplary embodiment.

[0028] Figure 9 This is a simulation calculation illustrating the deposition energy of gamma rays of different energies in a lead tungstate crystal, according to an exemplary embodiment.

[0029] Figure 10 This is a flowchart illustrating a neutron detection method according to an exemplary embodiment.

[0030] Figure 11 This is a simulation diagram illustrating the deposition energy of gamma rays of different energies in a cerium-doped gadolinium aluminum gallium garnet crystal, according to an exemplary embodiment.

[0031] Figure 12 This is a simulated energy spectrum of 2MeV gamma rays deposited in a cerium-doped gadolinium aluminum gallium garnet crystal, according to an exemplary embodiment.

[0032] Figure 13 This is a comparison diagram of the output waveforms of crystalline lead tungstate and cerium-doped gadolinium aluminum gallium garnet crystals, according to an exemplary embodiment.

[0033] Figure 14 The waveform identification result of neutron-gamma is shown according to an exemplary embodiment. Detailed Implementation

[0034] Exemplary embodiments will now be described more fully with reference to the accompanying drawings. However, these exemplary embodiments can be implemented in many forms and should not be construed as limited to the examples set forth herein; rather, they are provided so that this disclosure will be more comprehensive and complete, and will fully convey the concept of the exemplary embodiments to those skilled in the art. The drawings are merely illustrative of this disclosure and are not necessarily drawn to scale. The same reference numerals in the drawings denote the same or similar parts, and therefore repeated descriptions of them will be omitted.

[0035] Furthermore, the described features, structures, or characteristics can be combined in any suitable manner in one or more embodiments. Numerous specific details are provided in the following description to give a thorough understanding of embodiments of this disclosure. However, those skilled in the art will recognize that the technical solutions of this disclosure can be practiced with one or more of the specific details omitted, or other methods, apparatuses, steps, etc., can be employed. In other instances, well-known structures, methods, apparatuses, implementations, or operations are not shown or described in detail to avoid obscuring various aspects of this disclosure.

[0036] Furthermore, the terms "first," "second," etc., are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of technical features indicated. Thus, a feature defined as "first" or "second" may explicitly or implicitly include one or more of that feature. In the description of this disclosure, "multiple" means at least two, such as two, three, etc., unless otherwise explicitly specified. The symbol " / " generally indicates that the preceding and following objects are in an "or" relationship.

[0037] In this disclosure, unless otherwise expressly specified and limited, the term "connection" and similar terms should be interpreted broadly, for example, it can refer to an electrical connection or the ability to communicate with each other; it can refer to a direct connection or an indirect connection through an intermediate medium. Those skilled in the art can understand the specific meaning of the above terms in this disclosure according to the specific circumstances.

[0038] As mentioned above, lithium-6 ( 6 Li) and Boron-10 ( 10 B) Due to its large thermal neutron capture cross section, it has found wide application in neutron detectors. In addition, gadolinium-155 (Gadolinium) is another element in gadolinium. 155 Gd) and gadolinium-157 157 Gd has a very large thermal neutron capture cross section, making Gd-containing scintillators a hot research topic in thermal neutron detection in recent years. After capturing a thermal neutron, Gd de-excites and produces gamma photons, low-energy X-rays, and internal conversion electrons. Two isotopes of Gd undergo nuclear reactions with neutrons through the following reaction equation:

[0039] n+ 155 Gd→ 156 Gd*→ 156 Gd+γ(8.5MeV)+e - IC (0.039~0.19MeV)+X

[0040] n+ 157 Gd→ 158 Gd*→ 158 Gd+γ(7.9MeV)+e - IC (0.029~0.20MeV)+X

[0041] 155 Gd and 157 Gd generates unstable excited states with very short lifetimes after absorbing neutrons. 156 Gd* and 158Gd*, with total excitation energies of 8.53 MeV and 7.94 MeV, and thermal neutron capture cross-sections of 60800 Å and 253929 Å, respectively, emit a series of gamma rays during their successive de-excitation to the ground state. During the final de-excitation stage, there is a high probability that excess energy is transferred to the inner-shell electrons of the atom, causing them to escape their orbits and form internally converted electrons. These three secondary particles produced by the de-excitation of Gd-captured thermal neutrons can all be used as signals to characterize thermal neutron events. Gamma photons, with their higher energy, can only deposit a portion of their energy in gamma-sensitive crystals, resulting in a lower probability of forming a full-energy peak. In contrast, low-energy X-rays and internally converted electrons have a high probability of depositing their full energy in gamma-sensitive crystals, forming a full-energy peak. This full-energy peak structure corresponds to the thermal neutron capture signal and can be used as a characteristic peak of the thermal neutron signal.

[0042] Inorganic crystal GAGG:Ce (cerium-doped gadolinium aluminum gallium garnet, molecular formula Ce:Gd3Al2Ga3O) 12 As a newly developed scintillator, GAGG:Ce has been widely studied due to its high density, high light yield, fast emission decay time, and non-hygroscopic properties. The emission spectrum peak of GAGG:Ce is around 540 nm, which matches well with the absorption spectrum of silicon photomultiplier tubes (SiPMs), making it an excellent material for gamma-ray detection. Furthermore, because GAGG:Ce crystals contain gadolinium (Ga), which has a very large absorption cross-section for thermal neutrons, they are also ideal thermal neutron detection materials. However, GAGG:Ce crystals themselves are sensitive to gamma rays, so achieving effective neutron / gamma event identification is a crucial technology. Due to the very large absorption cross-section of gadolinium for thermal neutrons, even thin sheets of GAGG:Ce have very high detection efficiency for thermal neutrons. However, the detection efficiency for gamma rays decreases as the crystal's thickness decreases. Therefore, using thin-sheet GAGG:Ce crystals in conjunction with suitable gamma-sensitive crystals as thermal neutron detectors can achieve neutron / gamma event identification.

[0043] In a simulation study using the mature Monte Carlo simulation software Geant4 in the field of high-energy physics, the response of 5mm*5mm GAGG:Ce crystals of different thicknesses to gamma rays of different energies was investigated. 20keV was set as the energy threshold for the crystal to respond. The simulation results are as follows: Figure 1 As shown, Figure 1The diagram shows the proportion of gamma rays with energies greater than 20 keV deposited in GAGG:Ce crystals of different thicknesses. The crystal's response probability to gamma rays decreases with decreasing crystal thickness and increasing gamma ray energy. When the crystal thickness is 0.2 mm, the response efficiency to gamma rays with energies greater than 300 keV is less than 2%, but the response probability to gamma rays with energies below 200 keV is relatively high. Therefore, when using GAGG:Ce crystals for thermal neutron detection, slicing GAGG into thin slices can effectively reduce the impact on the high-energy gamma background. However, there is still a certain response probability to gamma rays with energies below 200 keV. Thus, using thin-slice GAGG:Ce crystals as thermal neutron detectors results in poor neutron / gamma event identification due to interference from low-energy gamma rays. Therefore, it is necessary to shield the low-energy portion of the gamma background accompanying neutrons.

[0044] Figure 2 This diagram illustrates a cerium-doped gadolinium aluminum gallium garnet (GAGG:Ce) crystal sheet according to an embodiment of the present disclosure. Figure 3 A schematic diagram of a photodetector SiPM according to an embodiment of the present disclosure is shown. Figure 4 A schematic diagram of a thermal neutron testing experimental apparatus according to an embodiment of this disclosure is shown. Figure 4 As shown, in the thermal neutron detection experiment, the GAGG:Ce crystal was cut into pieces as follows: Figure 2 The crystal sheet 402 shown has a thickness of 1 mm or even less, and Figure 3 The photoelectric device SiPM404, with a sensitive area of ​​6mm*6mm, is coupled into a thermal neutron detector. The GAGG:Ce crystal 402 traps thermal neutrons, generating secondary gamma photons, X-rays, and internally converted electrons. These secondary particles deposit energy within the crystal, producing scintillation light. This scintillation light is absorbed by the SiPM404 photodetector, generating an electrical signal that is amplified by the readout circuit on the SiPM driver board 406 and transmitted to the data acquisition system, thus achieving thermal neutron detection. The detector is encased in 2mm thick lead 408 and 2mm thick stainless steel 410, aluminum 412 (or copper). The lead shields against low-energy gamma rays, while the stainless steel 410 and aluminum 412 shield against the characteristic X-rays (~70keV) generated by the gamma rays on the lead. Figure 4 As shown, the neutrons produced by the americium-beryllium (Am-Be) neutron source 414 are high-energy fast neutrons. A 5cm thick layer of high-density polyethylene (HDPE) 416 is used to slow down the fast neutrons into thermal neutrons. The SiPM 404 is provided with high voltage, signal amplification, and temperature correction functions by the driver board 406. The waveform signal of the SiPM 404 is acquired by the waveform sampling plug-in DT5751 and saved to the computer for offline analysis.

[0045] like Figure 5 As shown, Figure 5 To utilize Figure 4 The experimental setup obtained Figure 2 The thermal neutron test results for a 6mm*6mm*1mm GAGG:Ce crystal are shown in the figure. The solid line represents the thermal neutron signal energy spectrum, and the dashed line represents the background signal energy spectrum. The figure shows that after the GAGG:Ce crystal captures a thermal neutron, the low-energy X-rays and internal conversion electrons deposit all their energy within the crystal, forming two full-energy peaks. According to the radiometric source calibration, these two full-energy peaks correspond to energies of 33keV and 77keV, respectively. The 33keV peak is formed by the energy deposition of 33keV internal conversion electrons, while the 77keV peak is formed by the superposition of 33keV internal conversion electrons and 44keV X-rays. These two full-energy peaks can be used as characteristic peaks of the thermal neutron capture signal, effectively distinguishing between thermal neutrons and background signals. In this test result, the ratio of the 77keV high-energy peak signal to the number of background events is 5.65.

[0046] The thickness of GAGG:Ce crystals can be varied. The table below shows the thermal neutron test results for GAGG:Ce crystals with different thicknesses:

[0047]

[0048] As the crystal thickness decreases, the ratio of neutron signal to background event count gradually increases. This result indicates that reducing the crystal thickness can effectively suppress the crystal's sensitivity to gamma signals, which is beneficial for achieving better neutron / gamma differentiation. However, as the crystal thickness decreases, the number of detected neutron events also decreases. In specific detector development, the crystal thickness needs to be optimized according to the actual testing environment requirements.

[0049] Therefore, based on the excellent neutron / gamma discrimination capability of the GAGG:Ce crystal thin film obtained in the above experiments, this disclosure provides a neutron detector. By setting the absorption layer as a nested gamma-sensitive layer and neutron-sensitive layer, with the neutron-sensitive layer embedded on the first side of the gamma-sensitive layer, neutrons and gamma background incident from the second side of the gamma-sensitive layer opposite to the first side. The gamma background deposits energy in the gamma-sensitive layer to generate a first scintillation, and the neutron deposits energy in the neutron-sensitive layer to generate a second scintillation. A photodetector is placed on the first side of the gamma-sensitive layer with the embedded neutron-sensitive layer to detect the first and second scintillations, thereby achieving the detection and discrimination of neutrons and gamma background. The gamma-sensitive layer shields the low-energy portion of the gamma background accompanying the neutron and detects the non-low-energy portion, thus improving the discrimination effect between neutron and gamma events.

[0050] Figure 6This is a schematic diagram of a neutron detector structure according to an exemplary embodiment. Figure 6 As shown, the neutron detector includes an absorption layer 602 and a photodetector 604. The absorption layer 602 is composed of at least one gamma-sensitive layer 6022 and at least one neutron-sensitive layer 6024, both made of stacked and nested materials. The neutron-sensitive layer 6024 is embedded in a first side of the gamma-sensitive layer 6022. The neutrons to be detected and the gamma background are incident from a second side of the gamma-sensitive layer 6022, with the first and second sides facing each other. The gamma background deposits energy in the gamma-sensitive layer 6022 to generate a first scintillation, and the neutrons deposit energy in the neutron-sensitive layer 6024 to generate a second scintillation. The scintillation signals of the gamma-sensitive layer 6022 and the neutron-sensitive layer 6024 are read out by the same photodetector 604, such as a SiPM or PMT. The gamma-sensitive layer 6022 and the neutron-sensitive layer 6024 can be crystals, plastic scintillators, ceramics, or coatings containing specific substances, etc. The neutron-sensitive layer is not necessarily transparent and may contain at least one neutron-sensitive material such as Gd, B, or Li. For example, it can be a thin sheet-like GAGG:Ce crystal with a thickness of 0.2 mm to 5 mm, or even thinner, such as 0.05 mm or 0.07 mm, for detecting thermal neutron signals. Alternatively, it can be a coating containing gadolinium compounds or a gadolinium-doped resistive coating. The outer layer of the GAGG:Ce crystal can be surrounded and covered by a crystal sensitive to gamma signals. The gamma-sensitive layer 6022 is not necessarily transparent and does not respond to thermal neutron signals; for example, it can be a gamma-sensitive scintillator. This gamma-sensitive layer 6022 has two functions: first, to detect the gamma signal accompanying thermal neutrons and count the gamma signals; second, to shield low-energy gamma signals, achieving full absorption of low-energy gamma rays and preventing gamma rays from depositing energy in the GAGG:Ce crystal, which could lead to misjudgments of neutron events.

[0051] The detector structure design described above enables simultaneous detection of neutron and gamma events. The outer gamma-sensitive crystal is used for gamma event detection, while the GAGG:Ce crystal is used for thermal neutron detection. Neutron and gamma events can be distinguished through energy discrimination and pulse shape discrimination. The deposition energy of thermal neutron events in the GAGG:Ce crystal exhibits characteristic peaks, which can be discriminated from the continuous spectrum formed by gamma events. Furthermore, by optimizing the emission decay time of the outer crystal, pulse shape discrimination can be achieved for both types of particles. Combining these two discrimination methods effectively improves the discrimination efficiency.

[0052] In some embodiments, the gamma-sensitive layer can be a multilayer structure, such as... Figure 7 As shown, Figure 7 This is a schematic diagram of another neutron detector structure according to an exemplary embodiment. Figure 7The gamma-sensitive layer 7022 is multilayered, and each layer can be at least one of the following gamma-photon-sensitive materials: sodium thallium iodide, barium fluoride, cesium thallium iodide, cesium iodide, bismuth germanate, lead tungstate, lutetium silicate doped with cerium, and lanthanum bromide doped with cerium.

[0053] In some embodiments, the time difference between the emission decay time of the gamma-sensitive layer 6022 and the emission decay time of the neutron-sensitive layer 6024 is greater than a preset threshold. For example, the emission decay time of the GAGG:Ce crystal used in the neutron-sensitive layer 6024 is ~100ns. To achieve effective discrimination between neutron and gamma signals, the gamma-sensitive crystal here should be selected with a significant difference in emission decay time compared to the GAGG:Ce crystal. This allows for the identification of the pulse shape of neutron and gamma events by utilizing the different emission decay times of the two crystals. There are significant differences in the scintillation emission decay times between different crystals. For example, the emission decay time of bismuth germanate (BGO) crystal is 300ns, that of thallium-doped cesium iodide (CsI(Tl)) crystal is 1300ns, and that of lead tungstate (PWO or PbWO4) crystal is 30ns. These crystals can all be used as peripheral gamma-sensitive crystals. The difference between the emission decay time of the gamma-sensitive crystal and the emission decay time of the neutron-sensitive crystal can be made greater than a predetermined threshold. For example, for GAGG:Ce crystals, a gamma-sensitive crystal with a difference greater than the predetermined threshold of 100 ns can be selected, such as BGO crystal with an emission decay time of 300 ns and CsI(Tl) crystal with an emission decay time of 1300 ns. Similarly, the difference between the emission decay time of the neutron-sensitive crystal and the emission decay time of the gamma-sensitive crystal can be made greater than the predetermined threshold of 50 ns, such as PbWO4 crystal with an emission decay time of 30 ns. The greater the difference in emission decay times between the two crystals, the better the discrimination effect.

[0054] Taking PbWO4 and BGO crystals as examples of gamma-sensing crystals, a simulation study of the performance of thermal neutron detectors was conducted. The simulated thermal neutron detector structure using PbWO4 crystal as the gamma-sensing crystal is shown below. Figure 8 As shown, the GAGG:Ce crystal has a size of 5mm*5mm*0.2mm, and the PWO crystal has a size of 20mm*20mm*20mm. A 5mm*5mm*0.2mm groove is cut on the surface of the PWO crystal, and the GAGG:Ce crystal is nested in the PWO crystal. Figure 9The energy deposition results of gamma rays with different energies in a PWO crystal are shown. It can be seen that the PWO crystal at the periphery can absorb gamma rays with energies less than 300 keV with very high efficiency. The absorption rates of gamma rays with incident energies of 100 keV, 200 keV, and 300 keV in the PWO crystal are 99.3%, 99.2%, and 96.4%, respectively. Thus, the peripheral PWO crystal can achieve high-efficiency detection of gamma rays and provide excellent shielding for the internal GAGG:Ce crystal.

[0055] Figure 10 This is a flowchart illustrating a neutron detection method according to an exemplary embodiment. Figure 10 The neutron detection method shown can be implemented using the methods described above. Figure 6 or Figure 7 The neutron detector. (Reference) Figure 10 The neutron detection method provided in this disclosure may include the following steps.

[0056] In step S1002, the event waveform detected by the photodetector is obtained based on the gamma background and the signal of the neutron to be detected detected by the photodetector.

[0057] In step S1004, the energy deposition spectrum of the gamma background and the neutron to be detected in the absorption layer is obtained based on the signal of the gamma background and the neutron to be detected detected by the photoelectric detection device.

[0058] In step S1006, neutron events and gamma background events are identified based on the event waveform and / or energy deposition spectrum.

[0059] In some embodiments, the event waveform can provide a wealth of information, such as rise time, fall time, amplitude, pulse width, charge integral, time delay, multiplicity, etc., and neutron events and gamma background events can be distinguished based on one or more of this information. For example, neutron events and gamma background events can be distinguished based on the rise time and fall time in the event waveform. Figure 13 As shown, Figure 13 The diagram shows a comparison of gamma background event and neutron event waveforms output by PWO crystal and GAGG:Ce crystal. In the waveform diagram, the time from the start of the rise to the peak value can be defined as the rise time, and the time to fall back to a predetermined percentage of the peak value (e.g., 50%, 20%, or 10%, etc.) can be defined as the fall time. It can be seen that due to the different emission decay times of PWO crystal and GAGG:Ce crystal, the rise time and fall time of the gamma background event and neutron event waveforms are also different, which allows for the differentiation between gamma background events and neutron events.

[0060] In other embodiments, for example, neutron events and gamma background events are distinguished based on the pulse width in the event waveform. The pulse width can be defined as a parameter related to the rise and fall times, such as the time interval between the time it takes to rise to half the peak value and the time it takes to fall to half the peak value. Figure 13 As shown, the pulse widths of gamma background events and neutron events are also different due to the different emission decay times of PWO crystals and GAGG:Ce crystals, which can be used to distinguish between gamma background events and neutron events.

[0061] In other embodiments, for example, neutron events and gamma background events are distinguished based on multiplicity information in the event waveforms. When the detector's timing accuracy is sufficiently high (e.g., fast-time photomultiplier tube, rise time <100 ps, ​​single-photon TTS (transient time spread) <50 ps), the detector can generate multiple waveform signals in a single trigger. Figure 13 The diagram shows the waveforms of a gamma background event and a neutron event from a single signal output. When using this type of high-time-accuracy detector, setting a threshold for the waveform yields multiple over-threshold signals from a single trigger. The number of over-threshold signals is called the multiplicity of the waveform. The multiplicity differs between neutron and gamma waveforms. Therefore, the differences in the multiplicity of multiple waveforms from a single trigger can be used to distinguish between neutron and gamma signals, further improving the efficiency of particle identification.

[0062] In some embodiments, for example, neutron events and gamma background events can be distinguished based on characteristic peaks in the energy deposition spectrum. Figure 5 As shown, GAGG:Ce crystals trap thermal neutrons to form two full-energy peaks, with corresponding energies of 33keV and 77keV, respectively. In contrast, the deposition energy of gamma background does not form a full-energy peak. Therefore, gamma background events and neutron events can be distinguished.

[0063] In some embodiments, for example, neutron events and gamma background events can be multiplexed based on the event waveform and energy deposition spectrum; or based on the pulse width in the event waveform and the characteristic peaks in the energy deposition spectrum.

[0064] Figure 11The results show the energy deposition of gamma rays of different energies in a 0.2 mm thick GAGG:Ce crystal. The simulation results indicate that, with external crystal shielding, the probability of gamma rays with energies less than 300 keV depositing at energies greater than 20 keV in a GAGG:Ce crystal sheet is less than 0.1%, meaning the probability of low-energy gamma rays being misidentified as thermal neutron events is less than 0.1%. For high-energy gamma rays, the probability of depositing at energies greater than 20 keV in a GAGG:Ce crystal is less than 1%. To further reduce the probability of high-energy gamma events being misidentified as neutrons in GAGG:Ce crystals, energy threshold selection can be used for further differentiation. The full-energy peak energies of thermal neutrons deposited in GAGG:Ce crystals are 33 keV and 77 keV, respectively. An energy threshold of 20-150 keV can be set; events with deposition energies outside this threshold can be identified as gamma events. Figure 12 Taking the deposition energy spectrum of 2MeV gamma rays in GAGG:Ce crystal as an example, the gamma background resolution of the detector can be further improved by selecting the energy threshold. Figure 13 The output waveforms of PWO crystal and GAGG:Ce crystal are shown in the comparison diagram. It can be seen that the waveform difference can be used to distinguish gamma signals and neutron signals.

[0065] Figure 14 The distribution of the two signals after pulse shape discrimination (PSD) analysis of the neutron and gamma signal waveforms is presented. It can be seen that the detector with this structure can effectively distinguish between neutron and gamma signals.

[0066] This disclosure provides a thermal neutron detector based on two crystals. This detector can simultaneously detect neutron and gamma signals, and possesses excellent waveform and energy discrimination capabilities for both neutron and gamma signals. It achieves high-efficiency simultaneous detection of gamma and neutron signals, and enables simultaneous discrimination of gamma and neutron signals based on energy and waveform differences. Furthermore, the energy and waveform information of the gamma signal can be adjusted by changing the peripheral crystals, meeting the needs of various applications. Specifically, the luminescence decay time of the GAGG crystal used for neutron signal detection is approximately 100 ns. To achieve different neutron / gamma discrimination requirements, the peripheral gamma detection crystal can be selected according to specific needs. For example, a CsI(Tl) crystal with a very long luminescence decay time (1300 ns) can be selected, as well as a cerium-doped lanthanum bromide (LaBar3(Ce)) crystal with a relatively short luminescence decay time (320 ns), or even a scintillator with a very short luminescence decay time (a few ns). This feature is unattainable for neutron / gamma discrimination using conventional neutron detection crystals.

[0067] Exemplary embodiments of this disclosure have been specifically shown and described above. It should be understood that this disclosure is not limited to the detailed structures, arrangements, or implementations described herein; rather, this disclosure is intended to cover various modifications and equivalent arrangements contained within the spirit and scope of the appended claims.

Claims

1. A neutron detector, characterized in that, Includes an absorption layer and a photodetector, wherein: The absorbing layer includes at least one gamma-sensitive layer and at least one neutron-sensitive layer. The neutron-sensitive layer is embedded in a groove on a first side of the gamma-sensitive layer. The neutron-sensitive layer is sheet-like and has a thickness between 0.05 mm and 5 mm. The gamma-sensitive layer at least partially surrounds the neutron-sensitive layer, wherein: The neutron to be detected and its gamma background are incident from the second side of the gamma-sensitive layer, with the first side facing the second side. The gamma background deposits energy in the gamma-sensitive layer to generate a first scintillation, and the neutron to be detected deposits energy in the neutron-sensitive layer to generate a second scintillation. The gamma-sensitive layer absorbs low-energy gamma rays more efficiently than a preset value. The photodetector is disposed on the first side of the gamma-sensitive layer embedded with the neutron-sensitive layer. The same photodetector is used to detect both the first scintillation light and the second scintillation light, thereby enabling the detection and identification of the neutron to be detected and the gamma background; wherein: The time difference between the emission decay time of the gamma-sensitive layer and the emission decay time of the neutron-sensitive layer is greater than a preset threshold; and... The neutron-sensitive layer can capture the neutron to be detected to form a full-energy peak, while the deposition energy of the gamma background will not form a full-energy peak.

2. The neutron detector according to claim 1, characterized in that, The gamma-sensitive layer has a multi-layer structure.

3. The neutron detector according to claim 1 or 2, characterized in that, The gamma-sensitive layer is at least one gamma-photon-sensitive material, including but not limited to: sodium thallium-doped iodide, barium fluoride, cesium thallium-doped iodide, cesium iodide, bismuth germanate, lead tungstate, lutetium silicate doped with cerium, and lanthanum bromide doped with cerium.

4. The neutron detector according to claim 3, characterized in that, The neutron to be detected is a thermal neutron, and the neutron-sensitive layer is at least one neutron-sensitive material, including but not limited to: lithium-containing materials, boron-containing materials, and gadolinium-containing materials.

5. A neutron detection method, characterized in that, The method, employing a neutron detector as described in any one of claims 1 to 4, comprises: Based on the signals detected by the photodetector device for the gamma background and the neutron to be detected, the event waveform detected by the photodetector device is obtained; Based on the signals of the gamma background and the neutron to be detected detected by the photoelectric detection device, the energy deposition spectrum of the gamma background and the neutron to be detected in the absorption layer is obtained; Neutron events and gamma background events are identified based on the waveforms of the events and the energy deposition spectra.

6. The method according to claim 5, characterized in that, The neutron event and gamma background event are distinguished based on the waveform and energy deposition spectrum of the event, including: Multiple screening is performed on neutron events and gamma background events based on the waveforms of the events and the energy deposition spectrum.

7. The method according to claim 5, characterized in that, The neutron event and gamma background event are distinguished based on the waveform and energy deposition spectrum of the event, including: Neutron events and gamma background events are distinguished based on the rise and fall times in the waveforms of the aforementioned events; or based on the pulse width in the waveforms of the aforementioned events; or Neutron events and gamma background events are distinguished based on the multiplicity information in the waveforms of the events.

8. The method according to claim 5, characterized in that, The neutron event and gamma background event are distinguished based on the waveform and energy deposition spectrum of the event, including: Neutron events and gamma background events are identified based on the characteristic peaks in the energy deposition spectrum.

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