CN118915123A - Fast neutron detector, detection device and detection method - Google Patents
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Abstract
The invention discloses a fast neutron detector, a detection device and a detection method, and relates to the technical field of radiation detection. The fast neutron detector includes: the conversion layer is positioned on the outer surface of an incident window of the microstructure gas detector, the blocking layer is positioned between the conversion layer and the incident window, fast neutrons from a neutron source collide with hydrogen atomic nuclei in the conversion layer to generate recoil protons, and the recoil protons corresponding to the scattered neutrons are easily blocked by the blocking layer. The microstructure gas detector determines the hit position, the flight time of fast neutrons and the neutron flux of the neutron source by measuring recoil protons. When the neutron source is a neutron beam, the incidence direction of the neutron beam can be determined, the beam profile can be imaged, and when the neutron source is a pulse neutron generator, the change curve of the flux of the neutron beam with time can be determined. The invention can avoid the influence of gamma background while realizing fast neutron detection, and meet the detection requirements of high flux counting and large-area imaging.
Description
Technical Field
The invention relates to the technical field of radiation detection, in particular to a fast neutron detector based on a novel microstructure gas detector, a detection device and a detection method.
Background
Neutrons are uncharged and cannot ionize a medium through which the neutrons pass, and detection of the neutrons can be realized only after the neutrons react with atomic nuclei. For many application scenes, neutrons to be detected are mainly fast neutrons with energy reaching MeV magnitude and above, and have higher requirements on detector area, detection efficiency, precision and time resolution. The common neutron detector at present mainly adopts 3He、10B、6 Li and other conversion materials sensitive to thermal neutrons, and has extremely low response section to fast neutrons. If fast neutron detection is to be carried out, the fast neutrons need to be firstly slowed down into thermal neutrons and then detected, but only the total flux (namely the number of neutrons passing through a unit area in unit time) can be obtained, and the time information of the fast neutrons is lost.
Liquid scintillator detectors and plastic scintillator detectors are currently the main technical means of fast neutron detection. In order to improve the detection efficiency, the volume of the scintillator needs to be increased, however, the large volume liquid scintillator and the plastic scintillator are easily affected by the gamma background, and neutron-gamma waveform discrimination is necessary to identify effective neutron signals and eliminate the interference of the gamma background. However, the large volume liquid scintillators and plastic scintillators are easy to generate signal accumulation when the incident particle flux is high, so that the discrimination capability of neutron-gamma waveform is reduced, and the measurement accuracy is severely limited when the liquid scintillators and plastic scintillators are used for high-flux fast neutron detection.
The semiconductor detector also has better application prospect in the field of fast neutron detection. For example, a conversion layer rich in hydrogen can be placed on the surface of the SiC detector, and fast neutron detection can be realized by detecting recoil protons generated by the bombardment of neutrons on the conversion layer, so that the method has the advantages of fast time response, insensitivity to gamma and the like. However, the semiconductor detector has a small sensitive area of a single device, and a large number of devices are required to form a large-area detection array in order to improve the detection efficiency, so that the semiconductor detector has the defects of high cost and complex system structure in practical application.
Disclosure of Invention
The invention aims to provide a fast neutron detector, a detection device and a detection method, which avoid the influence of gamma background and can simultaneously meet the counting detection requirement and the large-area imaging detection requirement of high-flux fast neutrons.
In order to achieve the above object, the present invention provides the following solutions:
A fast neutron detector, comprising: a conversion layer and a microstructured gas detector;
the conversion layer is arranged on the outer surface of the incident window of the microstructure gas detector; the conversion layer is a thin film rich in hydrogen;
The microstructure gas detector is used for measuring recoil protons so as to finish detection of fast neutrons; the recoil protons are generated after fast neutrons entering the conversion layer collide with hydrogen nuclei of the conversion layer; the fast neutrons are generated by a neutron source that includes a radiation source, a reactor, an accelerator, and a neutron generator.
In some embodiments, further comprising: a barrier layer; the blocking layer is positioned between the conversion layer and the incident window; the blocking layer is used for blocking low-energy recoil protons corresponding to scattered neutrons with low energy from entering the microstructure gas detector; the scattered neutrons with lower energy are generated after fast neutrons collide with various substances in the field environment.
In some embodiments, the microstructure gas detector is filled with a working gas in a housing, and a space region in the housing is divided into a drift region with a relatively weak electric field and an avalanche region with a relatively strong electric field; the upper surface of the shell is the incident window, the lower surface of the shell is provided with an anode PCB board, and a plurality of electrodes are arranged on the anode PCB board; the recoil protons ionize the working gas in a drift region to generate electrons, the electrons drift into an avalanche region to further ionize the working gas in an avalanche to generate a large number of electrons and ions, and the electrons and ions in the avalanche region move under the action of an electric field to generate induced charge signals on the electrodes of the anode PCB.
In some embodiments, the working gas is an inert gas doped with a quenching gas or the working gas is carbon tetrafluoride doped with a quenching gas.
A fast neutron detection device, comprising: readout electronics system and fast neutron detector as in any of the above; the fast neutron detector comprises a conversion layer and a microstructure gas detector;
The readout electronics system is electrically connected with the electrode of the microstructure gas detector; the readout electronics system is used for processing the induced charge signals on the electrodes to obtain fast neutron detection information; the induced charge signal is an induced signal generated on the electrode by ionizing the working gas in the drift region of the microstructure gas detector by recoil protons and then enabling the working gas to generate avalanche ionization after electrons generated by ionization drift to the avalanche region of the microstructure gas detector; the recoil protons are generated after fast neutrons which are incident on the conversion layer collide with hydrogen atomic nuclei of the conversion layer, and the fast neutrons are emitted by a neutron source; the fast neutron detection information includes a hit position of a fast neutron, a flight time, and a neutron flux of a neutron source.
In some embodiments, when the neutron source is a neutron beam, the fast neutron detection information further includes: imaging results of the incidence direction of the neutron beam and the neutron beam profile.
In some embodiments, when the neutron source is a pulsed neutron generator, the fast neutron detection information further includes: neutron flux profile of a pulsed neutron generator over time.
In some embodiments, the readout electronics system includes: the device comprises a pre-amplifying and shaping circuit, a data acquisition circuit and a data processing circuit;
The pre-amplifying and shaping circuit is electrically connected with the electrode; the pre-amplifying and shaping circuit is used for amplifying and shaping and filtering the induced charge signal to obtain an amplified signal;
The data acquisition circuit is electrically connected with the pre-amplifying and shaping circuit; the data acquisition circuit is used for digitizing the amplified signals to obtain digitized signals;
the data processing circuit is in communication connection with the data acquisition circuit; the data processing module is used for processing the digital signals to obtain fast neutron detection information.
A fast neutron detection method is applied to the fast neutron detection device and comprises the following steps:
Acquiring an induced charge signal; the induced charge signal is an induced signal generated on the electrode by ionizing the working gas in the drift region of the microstructure gas detector by recoil protons and then enabling the working gas to generate avalanche ionization after electrons generated by ionization drift to the avalanche region of the microstructure gas detector; the recoil protons are generated after fast neutrons which are incident to the conversion layer collide with hydrogen atomic nuclei of the conversion layer, and the fast neutrons are emitted by a neutron source;
Processing the induced charge signal to obtain fast neutron detection information; the fast neutron detection information includes a hit position of a fast neutron, a flight time, and a neutron flux of a neutron source.
According to the specific embodiment provided by the invention, the invention discloses the following technical effects:
The invention provides a fast neutron detector, a detection device and a detection method, wherein the fast neutron detector comprises: the conversion layer is arranged on the outer surface of an incident window of the micro-structure gas detector, fast neutrons in the neutron source collide with hydrogen atomic nuclei of the conversion layer after being incident on the conversion layer to generate recoil protons, and the micro-structure gas detector measures the recoil protons to finish detection of the fast neutrons. Because the action cross section of the fast neutrons and hydrogen nuclei is relatively large, higher fast neutron detection efficiency can be obtained. Since the sensitivity of the microstructure gas detector to gamma rays is very low, gamma rays are hardly detected by the microstructure gas detector, and thus the influence of gamma background can be almost directly ignored. As long as the positions of the two fast neutrons which are simultaneously incident hit the fast neutron detector are far away from each other, signals of the two fast neutrons can be formed on different electrodes without influencing each other, the upper measurement limit of neutron flux is improved, and the counting and detecting requirements of the high-flux fast neutrons can be met. Because the micro-structure gas detector is easier to realize large-area processing and manufacturing, the sensitive area of the fast neutron detector is easy to increase only by adopting the micro-structure gas detector with larger size and the conversion layer with corresponding size, and the micro-structure gas detector also has better position resolution, so that the high-efficiency fast neutron flux detection can be realized, and the large-area imaging measurement of the fast neutron beam profile can be realized.
Drawings
In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings that are needed in the embodiments will be briefly described below, and it is obvious that the drawings in the following description are only some embodiments of the present invention, and other drawings may be obtained according to these drawings without inventive effort for a person skilled in the art.
Fig. 1 is a schematic structural diagram of a fast neutron detector provided in embodiment 1 of the present invention.
Fig. 2 is a schematic diagram showing the comparison of the detection efficiency of the fast neutron detector at different polyethylene thicknesses according to example 1 of the present invention.
Fig. 3 is a schematic diagram illustrating the working principle of the barrier layer according to embodiment 1 of the present invention.
Fig. 4 is a schematic diagram showing the comparison of the detection efficiency of the fast neutron detector with the barrier layer and the unobstructed layer according to embodiment 1 of the present invention.
Fig. 5 is a schematic structural diagram of a fast neutron detecting device according to embodiment 2 of the present invention.
Fig. 6 is a schematic waveform diagram of embodiment 2 of the present invention.
Symbol description:
1-a conversion layer; 2-a housing; 3-working gas; 4-an entrance window; 5-anode PCB board; 6-electrode; 7-barrier layer.
Detailed Description
The following description of the embodiments of the present invention will be made clearly and completely with reference to the accompanying drawings, in which it is apparent that the embodiments described are only some embodiments of the present invention, but not all embodiments. All other embodiments, which can be made by those skilled in the art based on the embodiments of the invention without making any inventive effort, are intended to be within the scope of the invention.
The invention aims to provide a fast neutron detector, a detection device and a detection method, which avoid the influence of gamma background and can simultaneously meet the counting detection requirement and the large-area imaging detection requirement of high-flux fast neutrons.
In order that the above-recited objects, features and advantages of the present invention will become more readily apparent, a more particular description of the invention will be rendered by reference to the appended drawings and appended detailed description.
Example 1
The microstructure gas detector (such as Micromegas, GEM and the like) is a novel gas detector developed from the eighth nineties of the last century, and is vigorously developed in recent years, and the microstructure gas detector has the advantages of high counting rate, high spatial resolution, irradiation resistance, large-area manufacturing and the like, so that the microstructure gas detector becomes a novel neutron measurement technical means. At present, a plurality of domestic and foreign scientific research institutions are pushing to utilize the microstructure gas detector to conduct neutron measurement research, but the existing work is mainly to combine the microstructure gas detector with a thermal neutron sensitive material to realize thermal neutron detection. For example, GEM detector-based thermal neutron detectors using 10 B as a thermal neutron conversion layer were proposed and successfully developed by germany university; university of france improves the efficiency of thermal neutron detection by coating 10 B on both sides of the micro-mesh and the cathode of the microstructured gas detector and stacking multiple layers; a special THGEM film for neutron detection using ceramics as a base material is developed by a certain institute of China and is used for a GEM detector to finish thermal neutron detection; a micro-structure gas detector adopting a thermocompression bonding process is combined with a neutron sensitive material (such as 10 B) in a certain laboratory in China, so that researches on neutron beam spot measurement of a spallation white light neutron source and a neutron nuclear data measurement time projection room are carried out, and applications such as a boron neutron capture treatment beam monitor are carried out. However, no report of directly performing fast neutron detection by using a large-area microstructure gas detector at home and abroad exists at present.
As shown in fig. 1, the present embodiment provides a fast neutron detector, including: a conversion layer 1 and a microstructured gas detector. The conversion layer 1 is mounted on the outer surface of the entrance window 4 of the microstructured gas detector. The micro-structure gas detector is used for measuring recoil protons to finish detection of fast neutrons, the recoil protons are generated after the fast neutrons which are incident to the conversion layer 1 collide with hydrogen nuclei of the conversion layer 1, the fast neutrons are emitted by a neutron source, and the neutron source comprises a radiation source, a reactor, an accelerator and a neutron generator.
In this embodiment, the conversion layer 1 is a hydrogen-containing film, i.e., the conversion layer 1 is a hydrogen-rich film material, and the thickness of the conversion layer 1 is from hundred micrometers to several millimeters, i.e., the thickness of the conversion layer 1 is from 100 micrometers to 10 millimeters. In this embodiment, the conversion layer 1 may cover the incident window 4 completely or partially, and the length of the conversion layer 1 may be 20cm and the width may be 20cm, so that the detection area of the fast neutron detector is 20×20cm 2. Of course, since the size of the micro-structural gas detector is flexible, and the size of the conversion layer 1 can be changed according to the size change of the micro-structural gas detector, the detection area of the fast neutron detector can be designed according to the needs, and taking 20×20cm 2 is only an example given by the embodiment, and should not be construed as limiting the invention.
In this embodiment, the micro-structure gas detector is filled with the working gas 3 in the housing 2, the space area in the housing 2 includes a drift area with a relatively weak electric field and an avalanche area with a relatively strong electric field, the upper surface of the housing 2 is an incident window 4, the lower surface of the housing 2 is provided with an anode PCB 5, a plurality of electrodes 6 are arranged on the anode PCB 5, when recoil protons move in the drift area in the micro-structure gas detector, the working gas 3 is ionized by interaction with the working gas 3 to generate electron-ion pairs (i.e., electrons and ions), the electrons drift toward the anode under the action of the electric field, the ions drift toward the opposite direction, the electrons drift downward in the drift area (as shown by the dotted line in fig. 1), the working gas 3 is further ionized by avalanche after entering the avalanche area to generate a large amount of electrons and ions, and the electrons and ions in the avalanche area move under the action of the electric field to generate induced charge signals on the electrodes 6, and then the fast neutron detection information can be obtained by analyzing the induced charge signals.
The main component of the working gas 3 may be inert gas such as argon or carbon tetrafluoride, and a quenching gas such as carbon dioxide and isobutane is mixed in the main component in a certain proportion, that is, the working gas is inert gas mixed with the quenching gas, or the working gas is carbon tetrafluoride mixed with the quenching gas. The working gas 3 had a thickness of 1cm and a pressure of 1 atmosphere. Of course, the thickness of the working gas 3 may be designed as desired, taking 1cm as just one example given in this embodiment, and should not be construed as limiting the invention.
The working process of the fast neutron detector of the embodiment is as follows: fast neutrons emitted by a neutron source are incident into the conversion layer 1, the fast neutrons collide with hydrogen nuclei in the conversion layer 1 to generate recoil protons, the recoil protons enter the microstructure gas detector through the incident window 4, the recoil protons interact with the working gas 3 in the microstructure gas detector to enable the working gas 3 to generate electron-ion pairs, electrons in the electron-ion pairs drift downwards to enter an avalanche region to enable the working gas 3 to further generate avalanche ionization, a large number of generated electrons and ions move under the action of an electric field to generate induced charge signals on the electrode 6, and the read-out electronics system reads out the induced charge signals and performs corresponding analysis and treatment to obtain fast neutron detection information.
The fast neutron detector is characterized in that a layer of thin film material rich in hydrogen elements (namely high in hydrogen content) is added above the micro-structure gas detector to serve as a conversion layer 1, and fast neutrons are detected by measuring recoil protons generated after fast neutrons collide with hydrogen atomic nuclei in the conversion layer 1 through the micro-structure gas detector. Because the action cross section (namely the occurrence probability) of the fast neutrons and the hydrogen nuclei is relatively large, by utilizing the characteristic, when the neutron sources containing the same number of fast neutrons are incident on the conversion layer 1, compared with the existing detector, more fast neutrons can be detected, higher fast neutron detection efficiency is obtained, and neutron flux measurement with higher precision is realized.
The neutron detection is often accompanied by higher gamma background, larger interference is easy to generate in the neutron detection process, the sensitivity of the working gas 3 of the micro-structure gas detector to gamma rays is very low, and the gamma rays are hardly detected by the micro-structure gas detector, so that when the fast neutron detector based on the micro-structure gas detector is used for detecting fast neutrons, the influence of the gamma background can be almost directly ignored, the influence of neutron gamma identification and gamma background subtraction on neutron flux measurement accuracy is avoided, and the measurement accuracy is improved.
The microstructure gas detector used in this embodiment uses a plurality of electrodes 6 and a plurality of readout channels (i.e., channels used in reading out the induced charge signals on the electrodes 6 of the electronic system) to detect the incident neutrons over a larger area, and can measure the higher flux of the incident neutrons. This is because if the time difference between the two fast neutrons detected by the detector is small, for the scintillator detector, the signals are piled up and are difficult to distinguish, so that statistics of the number of fast neutrons is affected, but for the fast neutron detector of this embodiment, as long as the two fast neutrons hit the fast neutron detector at a far distance, the signals of the two fast neutrons are formed at different electrodes 6 and are read out through different read-out channels, so that the fast neutrons with a short time interval but different hit positions can be distinguished by increasing the number of read-out channels, the measurement upper limit of neutron flux is improved, and the neutron measurement requirement of a higher flux can be met.
In this embodiment, the electrode 6 on the bottom surface of the micro-structure gas detector is used to generate an induced charge signal, and then the induced charge signal is analyzed to complete fast neutron detection, so that for a large-area detection requirement, the detection area can be increased by only increasing the sizes of the conversion layer 1 and the micro-structure gas detector, the sensitive area of the fast neutron detector can be easily increased, and the number of the electrodes 6 and the number of the readout channels are correspondingly increased, so that large-area measurement can be realized at lower cost.
In this embodiment, the trace of the recoil proton can be measured by using the microstructure gas detector, and the hit position and hit time of the fast neutron can be reversely deduced according to the trace of the recoil proton, and for the case of the known fast neutron generation time, the flight time of the fast neutron can be obtained. And for the neutron source, calculating the neutron flux of the fast neutrons emitted by the neutron source according to the measured fast neutron count, and obtaining the neutron flux of the neutron source. For a neutron beam, the neutron beam can be regarded as one of neutron sources, the neutron beam has a direction, so that emitted fast neutrons have overall directivity, imaging of a neutron beam profile can be achieved under the condition that the hitting positions of the fast neutrons are known, and the incidence direction of the neutron beam can be calculated by using the angle distribution result of the track of the recoil protons.
Specifically, recoil protons generated after different fast neutrons in the neutron source collide with hydrogen nuclei interact with the working gas 3 in the microstructure gas detector to ionize the working gas 3, electron-ion pairs are generated, electrons in the electron-ion pairs generate induced charge signals at the electrodes 6 through drifting and avalanche amplification, and then three-dimensional tracks of different recoil protons can be determined by analyzing the induced charge signals generated by all the electrodes 6, wherein the three-dimensional tracks are tracks of the recoil protons in the working gas 3.
The method for determining the three-dimensional track comprises the following steps: based on the time at which the induced charge signals are generated by the electrodes 6 and the positions of the electrodes 6, all the induced charge signals corresponding to each recoil proton are determined on the basis of the principle of time continuity and position continuity, and for each recoil proton, the position of the recoil proton in the X-Y direction can be determined based on the position of the electrode 6 involved in all the induced charge signals corresponding to the recoil proton, so that the position of the recoil proton in the X-Y direction can be accurately measured using a high position resolution detector (i.e., the electrodes 6) at the anode plane. After positioning in the X-Y direction, a track projection of the recoil protons in the X-Y direction can be obtained. Because of the correlation between the drift velocity of electrons and the internal field intensity of the microstructure gas detector, a uniform electric field can be maintained in most areas of the drift region, so that the electrons have constant drift velocity, and after the electrons drift at a uniform velocity in the drift region, the electrons reach the avalanche region to generate avalanche amplification, induced charge signals are mainly generated by a large amount of electrons and ions generated by the avalanche amplification, the difference of ionization positions in the Z direction can cause the drift time of the electrons in the drift region to be different, the relative values of the Z-direction positions of recoil proton tracks corresponding to different electrodes can be obtained according to the difference of the generation time of waveforms of all channels, the microstructure gas detector is thinner, the recoil protons can pass through the microstructure gas detector, the length of the track in the Z direction is approximately equal to the thickness of the working gas 3, namely, the track at the start and stop positions of the Z direction corresponds to the upper bottom surfaces and the lower bottom surfaces of the drift region, and therefore the track of the recoil protons in the Z direction can be completely determined, and the three-dimensional track of the recoil protons can be obtained.
For fast neutrons, the method for determining the hit position and the flight time of the fast neutrons comprises the following steps: the hitting position of fast neutrons corresponding to the recoil protons can be determined by analyzing the three-dimensional tracks of the recoil protons, the starting points of the three-dimensional tracks are the hitting positions, the hitting positions are the incidence positions of the fast neutrons in the conversion layer 1, the time corresponding to the starting points of the three-dimensional tracks is the hitting time, the hitting time is the time when the fast neutrons are incident in the conversion layer 1, and the flight time of the fast neutrons can be obtained by calculating the difference between the fast neutron generation time and the hitting time due to the known fast neutron generation time.
For the neutron source, the number of the three-dimensional tracks is the number of recoil protons, the number of the recoil protons is the number of the detected fast neutrons, the number of the detected fast neutrons is divided by the total efficiency of the fast neutron detector, and the fast neutron emission number is the neutron flux of the fast neutrons emitted by the neutron source in the embodiment. The total efficiency can be determined experimentally, which is the product of the space geometrical efficiency and the absolute detection efficiency of the fast neutron detector.
And for the neutron beam, the shooting positions of all fast neutrons successfully entering the conversion layer 1 in the neutron beam are drawn, so that the function of neutron beam profile imaging can be realized. Because the recoil protons carry the momentum of the incident fast neutrons, the deflection angle of the recoil protons relative to the incident fast neutrons has certain characteristics, the correlation between the incidence direction of the neutron beam and the statistical calculation result of the incidence angle of the three-dimensional track of the recoil protons is determined in advance through experiments, the incidence angle of a large number of the three-dimensional tracks of the recoil protons (namely, the included angle between the direction of the track starting point and the vertical line) is calculated in a statistical way, and the direction information of the incident neutron beam can be obtained according to the statistical calculation result, so that the incidence direction of the neutron beam is obtained.
The charged particles such as cosmic ray muon in the environment can be detected by the microstructure gas detector, so that the detection accuracy of neutron flux is further influenced, and the influence is larger when the neutron flux is lower, and as the average energy loss rate and scattered degree of different charged particles in the working gas 3 are different, the particles are greatly different from the track of recoil protons, the particle identification can be performed by utilizing the track measurement function of the microstructure gas detector, and specifically, the particle identification can be performed by selecting indexes such as total energy, hit channel number, track incidence point, track drift time difference, maximum ionization energy loss position, total energy and track length relation, and the like, so that the interference of the cosmic ray muon and the like is eliminated, and the neutron flux detection accuracy is further improved.
The embodiment provides a fast neutron detector for measuring fast neutron flux based on a microstructure gas detector, which can meet the measurement requirements of large area and high time precision, avoid the influence of gamma background and other charged particles in the environment, improve the detection precision, reach higher flux measurement upper limit and meet the monitoring requirement of high flux neutrons.
In order to study the detection efficiency achieved by the fast neutron detector of this embodiment, a Monte Carlo physical simulation was performed using a computer program, using polyethylene rich in hydrogen elements as the conversion layer 1 (other materials rich in hydrogen elements may be used in practical applications), and the conversion layer 1 was placed on the outer surface of the incident window 4 above the cuboid-shaped working gas 3, and bombarded with 14MeV high-energy neutrons (i.e., fast neutrons) from the front. The high-energy neutrons are detected by striking recoil protons in the polyethylene, which are detected in a manner that energy is deposited in the working gas 3, and when the deposition energy is greater than 50keV, the fast neutron instance is considered to be detected, and fig. 2 shows the results of simulation of the detection efficiency of the fast neutron detector obtained under different polyethylene thicknesses, and when polyethylene with the thickness of 2mm is used as the conversion layer 1, the detection efficiency for the fast neutrons can reach the maximum, which is close to 0.35 per mill.
As shown in fig. 3, the fast neutron detector of the present embodiment further includes: the blocking layer 7 is arranged between the conversion layer 1 and the incident window 4, the blocking layer 7 is arranged on the outer surface of the incident window 4, the blocking layer 7 is used for blocking recoil protons (i.e. low-energy recoil protons in fig. 3) corresponding to low-energy scattered neutrons (i.e. low-energy fast neutrons in fig. 3) from entering the microstructure gas detector, the scattered neutrons are generated after the fast neutrons collide with various substances in the field environment, and the recoil protons corresponding to the scattered neutrons are recoil protons with low energy generated after the scattered neutrons interact with the conversion layer 1. The material of the barrier layer 7 may be selected from metals such as aluminum and the like.
When measuring high-energy fast neutrons (namely fast neutrons), various substances in the field environment can be hit by the high-energy fast neutrons to generate low-energy scattered neutrons, the energy of the scattered neutrons is approximately below 4MeV, if the scattered neutrons are detected, the measurement accuracy of the high-energy fast neutron flux can be affected, and the influence of the low-energy scattered neutrons can be effectively reduced by adding a layer of metal material (such as Al) capable of blocking low-energy recoil protons between the conversion layer 1 and the microstructure gas detector. Fig. 4 shows simulation results obtained using Geant4 software, which can reduce the detection efficiency by more than an order of magnitude for neutrons below 4MeV, but by only about 17% for neutrons below 14 MeV.
Example 2
As shown in fig. 5, the present embodiment provides a fast neutron detection apparatus, including: the readout electronics system and the fast neutron detector described in example 1, the fast neutron detector comprising a conversion layer 1 and a microstructured gas detector.
The readout electronics system is electrically connected with the electrode 6 of the microstructure gas detector, and the readout electronics system is used for processing the induced charge signal generated on the electrode 6 to obtain fast neutron detection information. The induced charge signal is an induced signal generated on the electrode 6 by ionizing the working gas 3 in the drift region of the microstructure gas detector by recoil protons, which are generated after fast neutrons incident on the conversion layer 1 collide with hydrogen nuclei of the conversion layer 1, and the electrons generated by ionization drift to the avalanche region to further ionize the working gas 3, and the fast neutrons are emitted by a neutron source. The fast neutron detection information includes the hit location of the fast neutrons, the time of flight, and the neutron flux of the neutron source.
In this embodiment, the readout electronics system includes: the device comprises a pre-amplifying and shaping circuit, a data acquisition circuit and a data processing circuit. The pre-amplifying and shaping circuit is electrically connected with the electrode and is used for amplifying and shaping and filtering the induced charge signal to obtain an amplified signal. The data acquisition circuit is electrically connected with the pre-amplifying and shaping circuit and is used for digitizing the amplified signals to obtain digitized signals. The data processing circuit is in communication connection with the data acquisition circuit and is used for processing the digital signals to obtain fast neutron detection information.
When the neutron source is a neutron beam, the fast neutron detection information of the embodiment further includes: imaging results of the incidence direction of the neutron beam and the neutron beam profile. When the neutron source is a pulse neutron generator, the fast neutron detection information of the embodiment further includes: neutron flux profile of a pulsed neutron generator over time.
The multichannel read-out electronic system adopted in the embodiment has higher time resolution, and can finally achieve nanosecond time resolution by matching with the microstructure gas detector adopted in the embodiment, so that the hit time of fast neutrons hitting the fast neutron detector can be accurately measured, and the flight time of the fast neutrons can be obtained by calculating the difference between the fast neutron generation time and the hit time under the condition of known fast neutron generation time. When high flux incident fast photons are measured, the monitoring of the change of the neutron flux in a short time can be realized, and for a pulse type neutron source (i.e. a pulse neutron generator), the pulse width can reach microsecond magnitude, the detection device of the embodiment not only can measure the neutron flux emitted by each pulse, but also can monitor the change of the neutron flux in a single pulse period along with time, and can better meet the requirement of analyzing the performance of the pulse neutron generator.
For a pulsed neutron generator, as shown in fig. 6, the embodiment can also accurately measure the trigger time (i.e. hit time) T n (e.g. T 1、T2、...、T6 in fig. 6) of each fast neutron signal waveform, and the accuracy can reach nanosecond level. For a pulse neutron generator, knowing the trigger time T 0 of a neutron pulse, the hit time of each fast neutron signal detected by a detector during each neutron pulse can be accurately measured, so if the neutron flux of a certain period of time during one pulse is calculated, the number of detected fast neutrons in the period of time can be directly counted, the number of detected fast neutrons can be obtained by dividing the total efficiency of the fast neutron detector, the number of fast neutrons emitted in the period of time can be obtained, the number of fast neutrons emitted is the neutron flux of a neutron source in the period of time, and the neutron flux of each period of time is sequentially determined, so that the change curve of the neutron flux of the pulse neutron generator during one pulse along with time can be obtained.
The electrode 6 of the microstructure gas detector of this embodiment may adopt a strip structure or a pixel array structure to read out, the induced charge signal output by each electrode 6 is amplified, shaped and filtered by a pre-amplifying and shaping circuit, and then digitized by a data acquisition circuit, and the physical information of the signal waveform is extracted to obtain the amplitude, hit time, channel number, etc. of each signal waveform, and finally the data is transmitted to a computer. By writing a data analysis computer program, according to the amplitude, the hit time and the channel number of each signal waveform, the three-dimensional track of the recoil protons and the ionization energy loss density (dE/dx) can be reversely deduced, on the basis, particle identification can be carried out, background cases except the recoil protons and the recoil nuclei are removed, the neutron flux measurement precision is improved, and meanwhile, fast neutron detection information can be obtained according to the data analysis result, and the flux measurement of fast neutrons is realized. For pulsed neutron generators, a fine time structure of neutron pulse flux over time can also be obtained.
Example 3
The present embodiment provides a fast neutron detection method, which is applied to the fast neutron detection device described in embodiment 1, and includes:
Acquiring an induced charge signal; the induced charge signal is an induced signal generated on the electrode by ionizing the working gas in the drift region of the microstructure gas detector by recoil protons and then enabling the working gas to generate avalanche ionization after electrons generated by ionization drift to the avalanche region of the microstructure gas detector; the recoil protons are generated after fast neutrons incident on the conversion layer collide with hydrogen nuclei of the conversion layer, and the fast neutrons are emitted by a neutron source.
Processing the induced charge signal to obtain fast neutron detection information; the fast neutron detection information includes a hit position of a fast neutron, a flight time, and a neutron flux of a neutron source.
The technical features of the above embodiments may be arbitrarily combined, and all possible combinations of the technical features in the above embodiments are not described for brevity of description, however, as long as there is no contradiction between the combinations of the technical features, they should be considered as the scope of the description.
The principles and embodiments of the present invention have been described herein with reference to specific examples, the description of which is intended only to assist in understanding the methods of the present invention and the core ideas thereof; also, it is within the scope of the present invention to be modified by those of ordinary skill in the art in light of the present teachings. In view of the foregoing, this description should not be construed as limiting the invention.
Claims (9)
1. A fast neutron detector, comprising: a conversion layer and a microstructured gas detector;
the conversion layer is arranged on the outer surface of the incident window of the microstructure gas detector; the conversion layer is a thin film rich in hydrogen;
The microstructure gas detector is used for measuring recoil protons so as to finish detection of fast neutrons; the recoil protons are generated after fast neutrons entering the conversion layer collide with hydrogen nuclei of the conversion layer; the fast neutrons are generated by a neutron source that includes a radiation source, a reactor, an accelerator, and a neutron generator.
2. The fast neutron detector of claim 1, further comprising: a barrier layer; the blocking layer is positioned between the conversion layer and the incident window; the blocking layer is used for blocking recoil protons corresponding to the scattered neutrons from entering the microstructure gas detector; the scattered neutrons are generated after fast neutrons collide with various substances in the field environment.
3. The fast neutron detector of claim 1, wherein the microstructured gas detector is filled with a working gas in a housing, a spatial region in the housing comprises a drift region and an avalanche region, the upper surface of the housing is the entrance window, the lower surface of the housing is provided with an anode PCB board on which a plurality of electrodes are arranged; the recoil protons ionize the working gas in a drift region to generate electrons, the electrons drift into an avalanche region to enable the working gas to generate avalanche ionization to generate electrons and ions, and the electrons and the ions in the avalanche region move under the action of an electric field to enable the electrodes to generate induced charge signals.
4. A fast neutron detector according to claim 3, wherein the working gas is an inert gas doped with a quenching gas or the working gas is carbon tetrafluoride doped with a quenching gas.
5. A fast neutron detection device, comprising: readout electronics system and fast neutron detector according to any of claims 1-4; the fast neutron detector comprises a conversion layer and a microstructure gas detector;
The readout electronics system is electrically connected with the electrode of the microstructure gas detector; the readout electronics system is used for processing the induced charge signals on the electrodes to obtain fast neutron detection information; the induced charge signal is an induced signal generated on the electrode by ionizing the working gas in the drift region of the microstructure gas detector by recoil protons and then enabling the working gas to generate avalanche ionization after electrons generated by ionization drift to the avalanche region of the microstructure gas detector; the recoil protons are generated after fast neutrons which are incident on the conversion layer collide with hydrogen atomic nuclei of the conversion layer, and the fast neutrons are emitted by a neutron source; the fast neutron detection information includes a hit position of a fast neutron, a flight time, and a neutron flux of a neutron source.
6. The fast neutron detection device of claim 5, wherein when the neutron source is a neutron beam, the fast neutron detection information further comprises: imaging results of the incidence direction of the neutron beam and the neutron beam profile.
7. The fast neutron detection device of claim 5, wherein when the neutron source is a pulsed neutron generator, the fast neutron detection information further comprises: neutron flux profile of a pulsed neutron generator over time.
8. The fast neutron detection device of claim 5, wherein the readout electronics system comprises: the device comprises a pre-amplifying and shaping circuit, a data acquisition circuit and a data processing circuit;
The pre-amplifying and shaping circuit is electrically connected with the electrode; the pre-amplifying and shaping circuit is used for amplifying and shaping and filtering the induced charge signal to obtain an amplified signal;
The data acquisition circuit is electrically connected with the pre-amplifying and shaping circuit; the data acquisition circuit is used for digitizing the amplified signals to obtain digitized signals;
the data processing circuit is in communication connection with the data acquisition circuit; the data processing circuit is used for processing the digitized signals to obtain fast neutron detection information.
9. A fast neutron detection method applied to the fast neutron detection device according to any one of claims 5 to 8, comprising:
Acquiring an induced charge signal; the induced charge signal is an induced signal generated on the electrode by ionizing the working gas in the drift region of the microstructure gas detector by recoil protons and then enabling the working gas to generate avalanche ionization after electrons generated by ionization drift to the avalanche region of the microstructure gas detector; the recoil protons are generated after fast neutrons which are incident to the conversion layer collide with hydrogen atomic nuclei of the conversion layer, and the fast neutrons are emitted by a neutron source;
Processing the induced charge signal to obtain fast neutron detection information; the fast neutron detection information includes a hit position of a fast neutron, a flight time, and a neutron flux of a neutron source.
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