CN114236599A - Neutron detector and neutron detection method - Google Patents

Abstract

The present disclosure provides a neutron detector and a neutron detection method. This neutron detector includes absorbing layer and 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 method comprises the following steps that a neutron to be detected and a gamma background of the neutron to be detected are incident from a second side face of a gamma sensitive layer, the first side face is opposite to the second side face, the gamma background deposits in the gamma sensitive layer to generate first scintillation light, and the neutron to be detected deposits in the neutron sensitive layer to generate second scintillation light; the photoelectric detector is arranged on the first side face of the gamma sensitive layer embedded with the neutron sensitive layer and used for detecting the first scintillation light and the second scintillation light so as to realize the detection and identification of the neutron to be detected and the gamma background. The method realizes the improvement of the discrimination effect of the neutron case and the gamma case.

Description

Neutron detector and neutron detection method

Technical Field

The disclosure relates to the technical field of neutron detection, in particular to a neutron detector and a neutron detection method.

Background

Neutron detectors are important tools in nuclear physics and are widely used in the fields of nuclear radiation detection, nuclear safety, material science and the like. Helium-3 (³He) gas detector is a neutron detector which is widely used at present, but because³The scarcity of He gas results in extremely high price, which limits its application. The scintillator detector has the advantages of high detection efficiency, simple structure, stable performance and the like, and the thermal neutron detector based on the scintillator is widely researched and applied, wherein the scintillation crystal neutron detector containing lithium, boron and gadolinium is a current research hotspot.

When detecting neutrons, in most cases, a neutron radiation field always accompanies the existence of gamma background radiation, and a neutron detector usually has a certain response to gamma rays, so that the discrimination between a neutron case and a gamma background case is an urgent problem to be solved when detecting neutrons.

The above information disclosed in this background section is only for enhancement of understanding of the background of the disclosure and therefore it may contain information that does not constitute prior art that is already known to a person of ordinary skill in the art.

Disclosure of Invention

The present disclosure aims to provide a neutron detector and a neutron detection method, which at least overcome the problem of screening a neutron case and a gamma background case in neutron detection to a certain extent.

Additional features and advantages of the disclosure will be set forth in the detailed description which follows, or in part will be obvious from the description, or may be learned by practice of the disclosure.

According to an aspect of the present disclosure, there is provided a neutron detector including an absorption layer and a photodetection device, wherein: the absorbing layer comprises at least one gamma sensitive layer and at least one neutron sensitive layer embedded on a first side of the gamma sensitive layer, wherein: the method comprises the following steps that a neutron to be detected and a gamma background of the neutron to be detected are incident from a second side face of the gamma sensitive layer, the first side face is opposite to the second side face, the gamma background deposits energy in the gamma sensitive layer to generate first scintillation light, and the neutron to be detected deposits energy in the neutron sensitive layer to generate second scintillation light; the photoelectric detection device is arranged at the position embedded with the neutron sensitive layer, and the first side face of the gamma sensitive layer is used for detecting the first scintillation light and the second scintillation light so as to realize that the neutron to be detected and the detection and identification of the gamma background are realized.

According to an embodiment of the present disclosure, a time difference between the luminescence decay time of the gamma sensitive layer and the luminescence decay time of the neutron sensitive layer is greater than a preset threshold.

According to an embodiment of the present disclosure, the gamma sensitive layer is a multi-layer structure.

According to an embodiment of the present 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, bismuth germanate, lead tungstate, cerium-doped lutetium silicate and cerium-doped lanthanum bromide, wherein the neutrons to be detected hardly deposit energy in the gamma sensitive layer.

According to an embodiment of the present disclosure, the neutron to be detected is a thermal neutron, the neutron sensitive layer is at least one neutron sensitive material, and the neutron sensitive material includes but is not limited to: lithium-containing materials, boron-containing materials, gadolinium-containing materials.

According to an embodiment of the present disclosure, the neutron sensitive layer is in a sheet shape, and the thickness of the neutron sensitive layer is between 0.05 mm and 5mm, so that the gamma background deposits all or most of energy in the gamma sensitive layer, and almost no energy is deposited in the neutron sensitive layer.

According to another aspect of the present disclosure, there is provided a neutron detection method, which employs the neutron detector, wherein: the method comprises the following steps: acquiring an example waveform detected by the photoelectric detection device according to the signals of the gamma background and the neutrons to be detected by the photoelectric detection device; according to the signals of the gamma background and the neutrons to be detected by the photoelectric detection device, obtaining energy deposition spectrums of the gamma background and the neutrons to be detected in the absorption layer; and screening neutron cases and gamma background cases according to the case waveforms and/or the energy deposition spectrum.

According to an embodiment of the present disclosure, screening neutron cases and gamma background cases according to the case waveform and/or the energy deposition spectrum includes: and carrying out multiple screening on neutron cases and gamma background cases according to the case waveforms and the energy deposition spectrum.

According to an embodiment of the present disclosure, screening neutron cases and gamma background cases according to the case waveform and/or the energy deposition spectrum includes: screening the neutron case and the gamma background case according to the rising time and the falling time in the case waveform; or screening the neutron case and the gamma background case according to the pulse width in the case waveform; or screening the neutron case and the gamma background case according to the multiplicity information in the case waveform.

According to an embodiment of the present disclosure, screening neutron cases and gamma background cases according to the case waveform and/or the energy deposition spectrum includes: and screening the neutron case and the gamma background case according to the characteristic peak in the energy deposition spectrum.

According to the neutron detector provided by the embodiment of the disclosure, the absorption layer is set as the nested gamma sensitive layer and the neutron sensitive layer, the neutron sensitive layer is embedded on the first side surface of the gamma sensitive layer, a neutron to be detected and a gamma background are incident from the second side surface of the gamma sensitive layer opposite to the first side surface, the gamma background is deposited in the gamma sensitive layer to generate first scintillation light, the neutron to be detected is deposited in the neutron sensitive layer to generate second scintillation light, and the photoelectric detector is set on the first side surface 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 to realize detection and identification of the neutron and the gamma background, so that the discrimination effect of the neutron case and the gamma case is improved.

It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory only and are not restrictive of the disclosure.

Drawings

The above and other objects, features and advantages of the present disclosure will become more apparent by describing in detail exemplary embodiments thereof with reference to the attached drawings.

Fig. 1 shows a graph of the response of cerium-doped gadolinium aluminum gallium garnet crystals of different thicknesses to gamma rays in an embodiment of the present disclosure.

Fig. 2 shows a schematic diagram of a cerium-doped gadolinium aluminum gallium garnet crystal slab in an embodiment of the present disclosure.

Fig. 3 shows a schematic view of a photo-detection device in an embodiment of the disclosure.

Fig. 4 shows a schematic diagram of a thermal neutron test experimental apparatus in an embodiment of the present disclosure.

Fig. 5 shows a thermal neutron test result diagram of a cerium-doped gadolinium aluminum gallium garnet crystal in an embodiment of the present disclosure.

FIG. 6 is a schematic diagram illustrating a neutron detector configuration according to an exemplary embodiment.

FIG. 7 is a schematic diagram illustrating another neutron detector configuration according to an exemplary embodiment.

Fig. 8 is a schematic diagram illustrating a thermal neutron detector structure in a simulation calculation according to an exemplary embodiment.

FIG. 9 is a graph illustrating the deposition energy of different energy gamma rays in a lead tungstate crystal in a simulation calculation, according to an exemplary embodiment.

FIG. 10 is a schematic flow diagram illustrating a method of neutron detection according to an exemplary embodiment.

Fig. 11 is a graph of the deposition energies of different energy gamma rays in a cerium doped gadolinium aluminum gallium garnet crystal in a simulation calculation according to an exemplary embodiment.

Fig. 12 is a deposition energy spectrum of 2MeV gamma rays in a cerium-doped gadolinium aluminum gallium garnet crystal in a simulation calculation shown according to an exemplary embodiment.

Fig. 13 is a graph comparing output waveforms of a crystalline lead tungstate and a cerium-doped gadolinium aluminum gallium garnet crystal shown according to an exemplary embodiment.

FIG. 14 illustrates a neutron-gamma waveform discrimination result according to an exemplary embodiment.

Detailed Description

Example embodiments will now be described more fully with reference to the accompanying drawings. Example embodiments may, however, be embodied in many different forms and should not be construed as limited to the examples set forth herein; rather, these embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the concept of example embodiments to those skilled in the art. The drawings are merely schematic illustrations of the present disclosure and are not necessarily drawn to scale. The same reference numerals in the drawings denote the same or similar parts, and thus their repetitive description will be omitted.

Furthermore, the described features, structures, or characteristics may be combined in any suitable manner in one or more embodiments. In the following description, numerous specific details are provided to give a thorough understanding of embodiments of the disclosure. One skilled in the relevant art will recognize, however, that the subject matter of the present disclosure can be practiced without one or more of the specific details, or with other methods, apparatus, steps, etc. In other instances, well-known structures, methods, devices, implementations, or operations are not shown or described in detail to avoid obscuring aspects of the disclosure.

Furthermore, the terms "first", "second", etc. are used for descriptive purposes only and are not to be construed as indicating or implying relative importance or implicitly indicating 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 the present disclosure, "a plurality" means at least two, e.g., two, three, etc., unless explicitly specifically limited otherwise. The symbol "/" generally indicates that the former and latter associated objects are in an "or" relationship.

In the present disclosure, unless otherwise expressly specified or limited, the terms "connected" and the like are to be construed broadly, e.g., as meaning electrically connected or in communication with each other; may be directly connected or indirectly connected through an intermediate. The specific meaning of the above terms in the present disclosure can be understood by those of ordinary skill in the art as appropriate.

As mentioned above, lithium-6 (⁶Li) and boron-10: (¹⁰B) Due to the large thermal neutron capture cross section, the method has wide application in neutron detectors. In addition, gadolinium-155 (gadolinium-155) of gadolinium element¹⁵⁵Gd and gadolinium-157 (¹⁵⁷Gd) has a very large thermal neutron capture cross section, and Gd-containing scintillators have become hot spots for thermal neutron detection in recent years. After thermal neutrons are captured by Gd, degaussing produces gamma photons, low energy X-rays and internal conversion electrons (internal conversion electrons), and two isotopes of Gd react with neutrons by nuclear reactions as follows:

n+¹⁵⁵Gd→¹⁵⁶Gd*→¹⁵⁶Gd+γ(8.5MeV)+e^- _IC(0.039～0.19MeV)+X

n+¹⁵⁷Gd→¹⁵⁸Gd*→¹⁵⁸Gd+γ(7.9MeV)+e^- _IC(0.029～0.20MeV)+X

¹⁵⁵gd and¹⁵⁷gd generates an unstable excited state with a very short lifetime after absorption of neutrons¹⁵⁶Gd and¹⁵⁸gd, total excitation energy 8.53MeV and 7.94MeV, respectively, and thermal neutron capture cross-sections 60800b and 253929b, respectively. The two emit a series of gamma rays in the process of gradually exciting to the ground state; there is a great chance that the excess energy is transferred to the inner shell electrons of the atoms when the last stage is de-excited, so that the electrons are separated from the orbit and are emitted out, and inner conversion electrons are formed. All three secondary particles produced by Gd capture thermal neutron degaussing can be used as signals to label thermal neutron cases. The gamma photon energy is high, only a part of energy can be deposited in the gamma sensitive crystal, and the probability of forming a full energy peak is low. The low-energy X-ray and the internal conversion electron have great probability of depositing all energy in the gamma sensitive crystal to form a full energy peak, and the full energy peak structure corresponds to the thermal neutron captureThe signal is obtained and can be used as a characteristic peak of the thermal neutron signal.

Inorganic crystal GAGG: Ce (cerium doped gadolinium aluminum gallium garnet, molecular formula Ce: Gd)₃Al₂Ga₃O₁₂) As a new developed scintillator, the red fluorescent powder has the characteristics of high density, high light yield, quick luminescence decay time, no deliquescence and the like, and is widely researched. The GAGG-Ce emission spectrum peak is about 540nm, can be well matched with the absorption spectrum of a Silicon photomultiplier (Silicon photomultiplier, SiPM), and is an excellent material for detecting gamma rays. Meanwhile, the GAGG: Ce crystal contains gadolinium (Ga) element, and the absorption cross section of the element on thermal neutrons is very large, so the GAGG: Ce crystal is also an ideal thermal neutron detection material. However, the GAGG-Ce crystal is sensitive to gamma rays, so that how to realize effective identification of neutron/gamma cases is a very important key technology. Since the absorption cross section of gadolinium on thermal neutrons is very large, even though the detection efficiency of the GAGG: Ce thin slice on thermal neutrons is very high, the detection efficiency of the crystal on gamma is reduced along with the reduction of the thickness of the crystal, and therefore, the identification of neutron/gamma cases can be realized by matching the thin GAGG: Ce crystal with a proper gamma sensitive crystal as a thermal neutron detector.

In the research of simulating response of Geant4 to GAGG with area of 5mm x 5mm and different thickness to gamma rays with different energy, setting 20keV as the energy threshold value of crystal response, the simulation result is shown in FIG. 1, FIG. 1 shows that the deposition energy of the gamma rays with different energy in the GAGG: Ce crystals with different thickness is greater than 20keV, the response probability of the crystals to the gamma rays is reduced along with the reduction of the thickness of the crystals and the increase of the energy of the gamma rays, when the thickness of the crystals is 0.2mm, the response efficiency to the gamma rays with energy greater than 300keV is less than 2%, but the response probability to the gamma rays with energy less than 200keV is larger. Therefore, when the GAGG: Ce crystal is used for thermal neutron detection, the effect on the high-energy gamma background can be effectively reduced by cutting the GAGG into slices, but certain response probability still exists on gamma rays with energy lower than 200keV, so that the neutron/gamma case identification effect is poor due to the interference of low-energy gamma rays when the slice GAGG: Ce crystal is used as a thermal neutron detector for identifying the neutron/gamma case. It is therefore desirable to shield the low energy portion of the gamma background that accompanies the neutrons.

FIG. 2 shows a schematic diagram of a cerium-doped gadolinium aluminum gallium garnet (GAGG: Ce) crystal slab in an embodiment of the present disclosure. Fig. 3 shows a schematic diagram of a photo-detection device SiPM in an embodiment of the disclosure. Fig. 4 shows a schematic diagram of a thermal neutron test experimental apparatus in an embodiment of the present disclosure. As shown in fig. 4, in the thermal neutron detection experiment, the GAGG: Ce crystal is cut into crystal pieces 402 with thickness of 1mm or thinner as shown in fig. 2, and is coupled with the photoelectric device SiPM 404 with sensitive area of 6mm × 6mm as shown in fig. 3 to form a thermal neutron detector. The GAGG is characterized in that a Ce crystal 402 captures thermal neutrons to generate secondary gamma photons, X rays and internal conversion electrons, secondary particles deposit in the crystal to generate scintillation light, the scintillation light is absorbed by a photodetector SiPM 404, and an electric signal is generated and amplified by a reading circuit on a SiPM driving board 406 and transmitted to a data acquisition system to realize thermal neutron detection. The detector is wrapped with 2mm thick lead 408 and 2mm thick stainless steel 410, aluminum 412 (or copper), where lead is used to shield low energy gamma rays and stainless steel 410 and aluminum 412 are used to shield the characteristic X-rays (-70 keV) produced by gamma rays on lead. As shown in fig. 4, the neutrons generated by an americium-beryllium (Am-Be) neutron source 414 are fast neutrons with High energy, and a High Density Polyethylene (HDPE) 416 with a thickness of 5cm is used to moderate the fast neutrons into thermal neutrons. The SiPM 404 provides functions of high voltage, signal amplification, temperature correction and the like through a driving board 406, and waveform signals of the SiPM 404 are acquired through a waveform sampling plug-in DT5751 and stored in a computer for offline analysis.

As shown in fig. 5, fig. 5 shows the results of the thermal neutron test of the Ce crystal of fig. 2, which is 6mm by 1mm GAGG, obtained by using the experimental apparatus of fig. 4, wherein the solid line shows the thermal neutron signal spectrum, and the dotted line shows the background signal spectrum. From the figure, GAGG can be seen, wherein the low-energy X-ray and the internal conversion electron generated after the Ce crystal captures the thermal neutron deposit the total energy in the crystal to form two total energy peaks, and the energy corresponding to the two total energy peaks is 33keV and 77keV respectively through the calibration of a radioactive source. The 33keV peak is formed by the deposition energy of the inner conversion electrons at 33keV and the 77keV peak is formed by the superposition of the inner conversion electrons at 33keV and the X-rays at 44 keV. The two full energy peaks can be used as characteristic peaks of a thermal neutron capture signal, and the identification of thermal neutrons and a background signal is effectively realized. The ratio of 77keV high energy peak signal to background case number in this test result was 5.65.

The thickness of the GAGG to Ce crystal can be changed, and the following table shows the thermal neutron test results of the GAGG to Ce crystal with different thicknesses:

it can be seen that the ratio of the neutron signal to the background case number is gradually increased along with the reduction of the thickness of the crystal, and the result shows that the sensitivity of the crystal to the gamma signal can be effectively suppressed by reducing the thickness of the crystal, thereby being beneficial to realizing better neutron/gamma distinction. However, as the thickness of the crystal decreases, the number of detected neutron instances also decreases, and in the development of a specific detector, the crystal thickness needs to be optimally designed according to the actual test environment requirements.

Therefore, based on the excellent neutron/gamma discrimination capability of the GAGG: Ce crystal thin sheet obtained in the above experiment, the present disclosure provides a neutron detector, in which an absorption layer is provided as a nested gamma sensitive layer and a neutron sensitive layer, the neutron sensitive layer is embedded on a first side of the gamma sensitive layer, a neutron and a gamma background are incident from a second side of the gamma sensitive layer opposite to the first side, the gamma background is deposited in the gamma sensitive layer to generate a first scintillation light, the neutron is deposited in the neutron sensitive layer to generate a second scintillation light, a photoelectric detector is provided on the first side of the gamma sensitive layer embedded with the neutron sensitive layer to detect the first scintillation light and the second scintillation light to realize the detection and discrimination of the neutron and the gamma background, the gamma sensitive layer is used to shield a low-energy part in the background gamma accompanied by the neutron and detect a non-low-energy part in the gamma background, thereby improving the discrimination effect of neutron case and gamma case.

FIG. 6 is a schematic diagram illustrating a neutron detector configuration according to an exemplary embodiment. As shown in fig. 6, the neutron detector includes an absorber layer 602 and a photodetector device 604. The absorption layer 602 is formed by stacking and nesting at least one gamma sensitive layer 6022 and at least one neutron sensitive layer 6024, wherein the neutron sensitive layer 6024 is embedded at a first side of the gamma sensitive layer 6022, neutrons to be detected and a gamma background are incident from a second side of the gamma sensitive layer 6022, the first side is opposite to the second side, the gamma background is deposited in the gamma sensitive layer 6022 to generate first scintillation light, the neutrons are deposited in the neutron sensitive layer 6024 to generate second scintillation light, and scintillation light signals of the gamma sensitive layer 6022 and the neutron sensitive layer 6024 are read by the same photoelectric detection device 604 such as SiPM or PMT. The gamma sensitive layer 6022 and the neutron sensitive layer 6024 may be crystals, plastic scintillators, ceramics, and coatings containing specific substances, and the like. The neutron sensitive layer is not necessarily transparent to light and may contain at least one neutron sensitive substance of Gd, B, Li, etc., for example, a flake-form GAGG: Ce crystal with a thickness of 0.2 millimeters (mm) to 5mm, and even thinner, for example, 0.05mn, 0.07mm, etc., for detecting thermal neutron signals, and for example, a coating of a compound containing gadolinium or a gadolinium-doped resistive coating. The outer layer of the GAGG: Ce crystal may be surrounded by a crystal sensitive to gamma signals, and the gamma sensitive layer 6022 may not necessarily be transparent to light and non-responsive to thermal neutron signals, and may be, for example, a gamma sensitive scintillator. The gamma sensitive layer 6022 has two functions, namely, detecting gamma signals accompanied by thermal neutrons and counting the gamma signals; and the second is used for shielding low-energy gamma signals, realizing full absorption of low-energy gamma rays and avoiding neutron case misjudgment caused by energy deposition of the gamma rays in the GAGG: Ce crystal.

Through the structural design of the detector, the simultaneous detection of neutrons and gamma cases can be realized, wherein peripheral gamma sensitive crystals are used for detecting the gamma cases, and GAGG (gamma-gamma. Neutron and gamma instances can be identified by energy discrimination and pulse shape discrimination. The deposition energy of the thermal neutron case in the GAGG-Ce crystal presents a characteristic peak, the continuous spectrum formed by the gamma case can be screened, in addition, the pulse shape screening can be realized for the two particles by optimizing the luminescence decay time of the peripheral crystal, and the two screening modes are combined together, so that the screening efficiency can be effectively improved.

In some embodiments, the gamma sensitive layer may be a multi-layer structure, as shown in FIG. 7, where FIG. 7 is a schematic view of another neutron detector structure shown according to an exemplary embodiment. The gamma sensitive layer 7022 in fig. 7 is a plurality of layers, each of which may be: at least one gamma photon sensitive material selected from thallium doped sodium iodide, barium fluoride, thallium doped cesium iodide, bismuth germanate, lead tungstate, cerium doped lutetium silicate, and cerium doped lanthanum bromide.

In some embodiments, the time difference between the luminescence decay time of the gamma sensitive layer 6022 and the luminescence decay time of the neutron sensitive layer 6024 is greater than a preset threshold. For example, the gamma sensitive crystal adopts the GAGG of the Ce crystal with the luminescence decay time of 100ns in the neutron sensitive layer 6024, and in order to realize the effective discrimination of neutron signals and gamma signals, the gamma sensitive crystal should select the crystal with the luminescence decay time and the GAGG of the Ce crystal with the larger difference, so that the pulse shape discrimination of neutron and gamma cases can be realized by utilizing the different luminescence decay times of the two crystals. The scintillation luminescence decay time of different crystals is greatly different, for example, the luminescence decay time of Bismuth Germanate (BGO) crystal is 300ns, the luminescence decay time of thallium-doped cesium iodide (CsI (Tl)) crystal is 1300ns, and the luminescence decay time of lead tungstate (PWO or PbWO4) crystal is 30ns, and the crystals can be used as peripheral gamma sensitive crystals. The difference between the luminescence decay time of the gamma sensitive crystal and the luminescence decay time of the neutron sensitive crystal can be made to be larger than a preset threshold, for example, for the GAGG: Ce crystal, the gamma sensitive crystal with the difference larger than the preset threshold of 100ns can be selected, such as the luminescence decay time of BGO crystal is 300ns, and the luminescence decay time of CsI (Tl) crystal is 1300 ns; the difference between the luminescence decay time of the neutron sensitive crystal and the luminescence decay time of the gamma sensitive crystal can also be larger than a predetermined threshold value of 50ns, for example, the luminescence decay time of the PbWO4 crystal is 30 ns. The larger the difference between the luminescence decay times of the two crystals is, the better the identification effect is obtained.

The gamma sensitive crystal adopts PbWO4 crystal and BGO crystal as examples, and the simulation research of the performance of the thermal neutron detector is carried out. A simulated thermal neutron detector structure of a gamma sensitive crystal adopting PbWO4 crystals is shown in figure 8, wherein the size of the GAGG: Ce crystals is 5mm 0.2mm, the size of the PWO crystals is 20mm, a groove of 5mm 0.2mm is dug on the surface of the PWO crystals, and the GAGG: Ce crystals are nested in the PWO crystals. Fig. 9 shows the result of energy deposition of gamma rays of different energies in the PWO crystal, and it can be seen that the PWO crystal disposed at the periphery can absorb gamma rays of energies less than 300keV with very high efficiency. Gamma rays with incident energies of 100keV, 200keV and 300keV, respectively, are absorbed in total in PWO crystals in proportions of 99.3%, 99.2% and 96.4%, respectively, so that the peripheral PWO crystals can achieve highly efficient detection of gamma rays and very good shielding of the internal GAGG: Ce crystals.

FIG. 10 is a schematic flow diagram illustrating a method of neutron detection according to an exemplary embodiment. The neutron detection method shown in fig. 10 may employ the neutron detector of fig. 6 or fig. 7 described above. Referring to fig. 10, a neutron detection method provided by an embodiment of the present disclosure may include the following steps.

In step S1002, an instance waveform detected by the photodetector is obtained according to signals of the neutron to be detected and the gamma background detected by the photodetector.

In step S1004, an energy deposition spectrum of the gamma background and the neutron to be detected in the absorption layer is obtained according to signals of the gamma background and the neutron to be detected by the photoelectric detection device.

In step S1006, neutron instances and gamma background instances are discriminated from the instance waveforms and/or the energy deposition spectra.

In some embodiments, the case waveform can provide a variety of information, such as rise time, fall time, amplitude, pulse width, charge integration, time delay, multiplicity, etc., from one or more of which neutron cases and gamma background cases can be discriminated. For example, neutron and gamma background instances can be discriminated based on the rise and fall times in the instance waveform. As shown in fig. 13, fig. 13 is a waveform diagram showing a gamma background case and neutron case comparison of outputs of the PWO crystal and the GAGG: Ce crystal, and in the waveform diagram, it can be defined that a time from the start of rising to the peak of the waveform is a rising time, and a time falling to a predetermined proportion of the peak (for example, 50%, 20%, 10%, or the like) is a falling time.

In other embodiments, neutron and gamma background instances are discriminated, for example, based on the pulse width in the instance waveform. The pulse width can be defined as a parameter related to the rise time and the fall time, for example, a time interval between a time of rising to a half of the peak value and a time of falling to a half of the peak value, as shown in fig. 13, and also because the pulse widths of the gamma background case and the neutron case waveform are different due to the difference in the light emission decay time between the PWO crystal and the GAGG: Ce crystal, thereby enabling the discrimination between the gamma background case and the neutron case.

In other embodiments, for example, neutron cases and gamma background cases are discriminated based on the multiplicity information in the case waveform. When the Time accuracy of the detector is high enough (e.g. fast Time photomultiplier tube, rise Time <100ps, single photon TTS (transit Time Spread) <50ps), the detector can generate multiple waveform signals with a single trigger, and fig. 13 shows a gamma background case waveform of a signal output and a neutron case waveform of a signal output. When the detector with high time precision is adopted, if a threshold value is set for the waveform, a plurality of over-threshold signals under single trigger can be obtained, the number of the over-threshold signals is called the multiplicity of the waveform, and the multiplicity of the waveforms of neutrons and gamma also has difference. The neutron-gamma signals can be discriminated by utilizing the difference of the multiplicity of the plurality of waveform signals under single trigger, so that the particle discrimination efficiency is further improved.

In some embodiments, for example, neutron and gamma background events may be discriminated from characteristic peaks in the energy deposition spectra. As shown in FIG. 5, the GAGG: Ce crystal captures thermal neutrons to form two full energy peaks, the energy corresponding to the two full energy peaks is 33keV and 77keV respectively, and the deposition energy of the gamma background does not form the full energy peaks, so that the gamma background case and the neutron case can be discriminated.

In some embodiments, for example, neutron cases and gamma background cases can be multiply screened based on the case waveforms and the energy deposition spectra; or multiple discrimination is carried out on neutron cases and gamma background cases according to pulse width in case waveforms and characteristic peaks in energy deposition spectrums.

FIG. 11 shows the energy deposition results of gamma rays with different energies in a GAGG: Ce crystal with a thickness of 0.2mm, and from the simulation results, it can be seen that the probability of the gamma rays with an energy less than 300keV depositing energy more than 20keV in a GAGG: Ce crystal lamella is less than 0.1% in the case of peripheral crystal shielding, that is, the probability of the low-energy gamma rays being misinterpreted as thermal neutron cases is less than 0.1%. The probability of depositing energy greater than 20keV in a GAGG: Ce crystal for high energy gamma rays is less than 1%. In order to further reduce the probability of misjudging the high-energy gamma case as a neutron in the GAGG: Ce crystal, further discrimination can be realized by utilizing energy threshold judgment and selection. The energy of the full energy peak deposited by thermal neutrons in the GAGG: Ce crystal is 33keV and 77keV respectively, 20-150keV can be set as an energy threshold, and the case that the deposition energy is not at the threshold can be judged as a gamma case. By taking the deposition energy spectrum of the gamma ray of 2MeV in the GAGG: Ce crystal as shown in FIG. 12 as an example, the gamma background resolution capability of the detector can be further improved through energy threshold selection. FIG. 13 shows a comparison of the output waveforms of a PWO crystal and a GAGG: Ce crystal, showing that the difference in waveforms can be used to discriminate between gamma and neutron signals.

Fig. 14 shows the distribution of two signals obtained after the neutron and gamma signal waveforms are analyzed by Pulse Shape Discrimination (PSD), and it can be seen that the detector with this structure can effectively discriminate the neutron and gamma signals.

The utility model provides a thermal neutron detector based on two kinds of crystals, this detector can survey neutron and gamma signal simultaneously to possess the waveform discrimination and the energy discrimination ability of excellent neutron and gamma signal, realized high efficiency detection when gamma signal and neutron signal, realized gamma signal and neutron signal adopt energy and waveform difference to distinguish simultaneously, and the accessible is changed peripheral crystal and has been realized the adjustment of gamma signal energy information and waveform information, can satisfy different application occasion demands. Specifically, the light emitting decay time of the GAGG crystal for neutron signal detection is about 100ns, and peripheral gamma detection crystals can be selected according to specific requirements in order to realize neutron/gamma discrimination with different requirements. For example, a CsI (Tl) crystal (1300ns) with very long luminescence decay time can be selected, a cerium-doped lanthanum bromide (LaBar3(Ce)) crystal (320ns) with relatively short luminescence decay time can be selected, and even a scintillator (a few ns) with very short luminescence decay time can be selected. This feature is not achievable with conventional neutron detection crystals for neutron/gamma discrimination.

Exemplary embodiments of the present disclosure are specifically illustrated and described above. It is to be understood that the present disclosure is not limited to the precise arrangements, instrumentalities, or instrumentalities described herein; on the contrary, the disclosure is intended to cover various modifications and equivalent arrangements included within the spirit and scope of the appended claims.

Claims (10)

1. A neutron detector, comprising an absorber layer and a photodetector device, wherein:

the absorbing layer comprises at least one gamma sensitive layer and at least one neutron sensitive layer embedded on a first side of the gamma sensitive layer, wherein:

the method comprises the following steps that a neutron to be detected and a gamma background of the neutron to be detected are incident from a second side face of the gamma sensitive layer, the first side face is opposite to the second side face, the gamma background deposits energy in the gamma sensitive layer to generate first scintillation light, and the neutron to be detected deposits energy in the neutron sensitive layer to generate second scintillation light;

the photoelectric detection device is arranged at the position embedded with the neutron sensitive layer, and the first side face of the gamma sensitive layer is used for detecting the first scintillation light and the second scintillation light so as to realize that the neutron to be detected and the detection and identification of the gamma background are realized.

2. The neutron detector of claim 1, wherein a time difference between the luminescence decay time of the gamma sensitive layer and the luminescence decay time of the neutron sensitive layer is greater than a preset threshold.

3. The neutron detector of claim 1, wherein the gamma sensitive layer is a multilayer structure.

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

5. The neutron detector of claim 4, wherein the neutrons to be detected are thermal neutrons, and the neutron sensitive layer is at least one neutron sensitive material, including but not limited to: lithium-containing materials, boron-containing materials, gadolinium-containing materials.

6. The neutron detector of claim 1, wherein the neutron-sensitive layer is sheet-like, and the neutron-sensitive layer has a thickness between 0.05 millimeters and 5 millimeters.

7. A neutron detection method, characterized in that the neutron detector of any of claims 1 to 6 is used, the method comprising:

acquiring an example waveform detected by the photoelectric detection device according to the signals of the gamma background and the neutrons to be detected by the photoelectric detection device;

according to the signals of the gamma background and the neutrons to be detected by the photoelectric detection device, obtaining energy deposition spectrums of the gamma background and the neutrons to be detected in the absorption layer;

and screening neutron cases and gamma background cases according to the case waveforms and/or the energy deposition spectrum.

8. The method of claim 7, wherein screening neutron instances and gamma background instances from the instance waveforms and/or the energy deposition spectra comprises:

and carrying out multiple screening on neutron cases and gamma background cases according to the case waveforms and the energy deposition spectrum.

9. The method of claim 7, wherein screening neutron instances and gamma background instances from the instance waveforms and/or the energy deposition spectra comprises:

screening the neutron case and the gamma background case according to the rising time and the falling time in the case waveform; or

Screening neutron cases and gamma background cases according to the pulse width in the case waveform; or

And screening the neutron case and the gamma background case according to the multiplicity information in the case waveform.

10. The method of claim 7, wherein screening neutron instances and gamma background instances from the instance waveforms and/or the energy deposition spectra comprises:

and screening the neutron case and the gamma background case according to the characteristic peak in the energy deposition spectrum.

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