Neutron directional detection device and method based on solid nuclear track detector

Abstract

The invention provides a neutron directional detection device and method based on a solid nuclear track detector, and the device comprises a solid nuclear track detection part which is used for receiving secondary particles generated by the interaction of neutrons and forming observable track signals; the central base is used for reflecting thermal neutron information; and the shell is used for reflecting fast neutron information. The neutron directional detection method comprises the following steps: simulating by using Monte Carlo software to obtain secondary particle information under different incident angles; obtaining a response simulation data set of the neutron directional detection device under the condition of different incident angles by adopting a particle analysis and judgment algorithm; training an artificial neural network model based on the simulation data set; the actual response of the neutron directional detection device is obtained through etching and track reading during measurement; and substituting the actual response of the neutron directional detection device into the artificial neural network model to carry out direction detection. The device has the advantages of light weight, portability, accurate measurement, high detection efficiency, rapidness and simultaneous measurement of the thermal neutron direction.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of neutron detection, in particular to a neutron directional detection device and method based on a solid nuclear track detector. BACKGROUND

[0002] In recent years, China's neutron application technology has developed very rapidly. In medicine, boron neutron capture therapy is used as a new technology to treat malignant tumors. In industry, neutrons are used in metallurgy, coal mining and processing, ore processing and other industries. At the same time, many neutron facilities are also widely used in basic nuclear applications and physical research such as nuclear astrophysics. With the wide application of neutrons, the number of related workers has also gradually increased. Due to the large radiation weight factor of neutrons, even a small amount of neutron exposure can cause great harm. Based on the concept of "people-oriented" development of production, the further development of related application technology puts forward the requirements of precision and comprehensiveness for monitoring the distribution of neutron radiation field

[0003] The incident direction is an important content of neutron radiation field monitoring. On the one hand, there is a large angular response characteristic in the current personal dose measurement and place dose measurement of neutrons. Due to the uncertainty of the incident direction of neutrons, the accuracy of the dose measurement results is difficult to guarantee. On the other hand, only by mastering the incident direction of neutrons can the source of radiation be determined, so that more effective protection adjustment can be made. However, in sharp contrast to the rapid development of China's neutron technology, the monitoring technology for the direction of neutrons is relatively scarce. Especially the comprehensiveness of different energy segments, the portability of personal monitoring, the on-site adaptability of place monitoring, and the long-term stability of cumulative monitoring are important technical problems that need to be solved.

[0004] Since the 1990s, researchers have carried out research on the measurement of the incident direction of neutrons. The commonly used methods for measuring the incident direction of neutrons mainly include three types of coded aperture instrument, neutron scattering camera and time projection chamber:

[0005] (1) The direction measurement of coded aperture instrument is mainly based on the principle that the radiation source in different directions passes through a mask with a certain coding mode, and then forms a specific response on the detection array. The disadvantages of this method are as follows: 1. Since the common coding mask is a plane mask, the range of detectable incident direction is narrow, limited to the direction of the detector array; 2. Since the measurement efficiency of fast neutrons is very low, the combination with a moderator will lose the direction information, so the coded aperture instrument can only measure the incident direction of thermal neutrons; 3. The coded aperture instrument contains a large mask and a detector array, so the volume is large, which makes it difficult to measure on site; 4. The design of complex nuclear electronics and the supporting source direction coding and decoding algorithm make the design of coded aperture instrument more difficult.

[0006] (II) Neutron scattering camera records the energy and position changes of two consecutive scattering events of neutrons in the detector, and calculates the incident direction of the neutrons according to the scattering law. The disadvantages of this method are as follows: 1. Due to the limited volume of the detector, the probability of double scattering of neutrons in the sensitive volume is small, so the number of effective events for direction detection is very small, resulting in low detection efficiency and large error; 2. In the common mixed field of neutrons and photons, the neutron scattering camera needs to separate the two kinds of radiation signals, which brings great difficulty to the measurement; 3. The neutron scattering camera itself is based on the principle of neutron scattering, and the probability of elastic scattering of thermal neutrons is very low, so this method is only suitable for the measurement of the direction of fast neutrons; 4. The cost of instrument manufacturing is high, and frequent maintenance is required.

[0007] (III) Time projection chamber records the position and drift time of particles hitting the readout block in the detector to obtain the projection position and drift distance of particles in the anode plate plane, thereby realizing the measurement of the incident direction. The disadvantages of this method are as follows: 1. The readout plane of the time projection chamber is divided into multiple small signal readout blocks, which leads to the reconstructed track being affected by factors such as electric field stability, plane uniformity, and complex radiation field, resulting in poor system stability; 2. The direction principle of the time projection chamber is mainly based on recording secondary electrons generated in the sensitive volume, and this primary particle is mainly generated by fast neutrons, so it is currently mainly used for the measurement of fast neutrons; 3. The design of the time projection chamber needs to ensure that the particles are incident from the front surface of the detector to accurately measure the energy deposition path, and there is a problem of detection blind area.

[0008] Overall, the above three methods have the problem of limited sensitive range when detecting the direction of neutrons due to the influence of the energy response and angular response of the detector. This is manifested in the following aspects:

[0009] (I) There is a visual angle blind area in the measurement: various detectors that use electronic systems for real-time processing have electronic systems that block part of the detection area in their design structure, which limits the measurement angle and makes it difficult to detect neutrons from some directions. This part of the area is the visual angle blind area.

[0010] (II) The measurement cannot achieve energy zone measurement: neutrons and matter have complex interactions, and in actual working conditions, their energy distribution is wide, and due to the different interaction methods of different energies and matter, they exhibit different spatial distributions, so the direction of neutrons of different energies at the same position is often different. The previous neutron directional detector usually only uses the reaction characteristics of neutrons in a certain energy range for detection, which results in a narrow sensitive energy range and cannot reflect the different direction characteristics of neutrons in different energy ranges.

[0011] (Three) measurement cannot achieve a wide range of measurement: directional detection in a large range of scenes needs to collect direction information at multiple points at the same time, and the joint tracing is realized through multi-point data, the complex process and high cost of the existing directional detector make it difficult to achieve this purpose. In some areas where the measurement space is limited, the larger volume also limits the application of the existing directional detector. SUMMARY

[0012] The present application is to solve the above problems, and aims to provide a neutron directional detection device and method based on a solid nuclear track detector.

[0013] The present application provides a neutron directional detection device based on a solid nuclear track detector, which has the following characteristics: a solid nuclear track detection part, including six CR-39 solid nuclear track detectors; a center base made of boron nitride ceramic material, used to reflect thermal neutron information, the center base is surrounded by six CR-39 solid nuclear track detectors; and a shell made of polyethylene material, used to reflect fast neutron information, including two symmetrical and tightly connected groove shells, the shell is used to place the center base and the six CR-39 solid nuclear track detectors.

[0014] In the neutron directional detection device based on a solid nuclear track detector provided by the present application, the following features can also be present: the peripheral size of each groove shell is 24mm*24mm*12mm, after the two groove shells are tightly connected, an accommodation space for placing the center base and the six CR-39 solid nuclear track detectors is formed inside, and the six CR-39 solid nuclear track detectors are arranged on the groove shells and surround the six faces of the center base.

[0015] In the neutron directional detection device based on a solid nuclear track detector provided by the present application, the following features can also be present: the size of the center base is 14mm*14mm*14mm, and the size of each of the six CR-39 solid nuclear track detectors is 10mm*10mm*1mm.

[0016] In the neutron directional detection device based on a solid nuclear track detector provided by the present application, the following features can also be present: the two surfaces of the CR-39 solid nuclear track detector are tightly attached to the shell and the center base respectively, the contact surface with the shell is used for fast neutron detection, and the secondary protons generated by the interaction between the fast neutron and the polyethylene material are used to realize the detection, and the contact surface with the center base is used for thermal neutron detection, and the secondary alpha particles generated by the interaction between the thermal neutron and the boron nitride ceramic material are used to realize the detection.

[0017] The application provides a neutron directional detection method based on a solid nuclear track detector, and specifically comprises the following steps: S1, using Monte Carlo simulation software, a geometric model of a neutron directional detection device is established, neutron radiation sources at different angles are simulated, and the energy and incident angle information of secondary particles passing through the contact surface of the solid nuclear track detection unit and the conversion layer under the corresponding incident angle condition are recorded; the conversion layer contact surface is a polyethylene contact surface and a boron nitride contact surface, and the secondary particles include protons passing through the polyethylene contact surface and alpha particles passing through the boron nitride contact surface; S2, a particle analysis and judgment algorithm is used to judge whether the secondary particles can form a response on the CR-39 solid nuclear track detector according to the comparison between the incident angle of the secondary particles and the critical angle, wherein the critical angle is calculated using a track growth theory model according to the energy of the secondary particles, and finally the response of the neutron directional detection device formed under different incident angles is obtained; S3, the response of the neutron directional detection device after irradiation of the neutron radiation source at different angles is used as a simulation data set. The response of the neutron directional detection device is used as an input layer, the incident angle of the neutron radiation source is used as an output layer, two hidden layers are added to construct an artificial neural network model, and the artificial neural network model is trained based on the simulation data set. S4, during actual measurement, after the neutron directional detection device is irradiated by the neutron radiation source, the solid nuclear track unit is taken out for chemical etching to form visible tracks, and then an optical microscope is used to read the track density to obtain the response of the neutron directional detection device; S5, the response of the neutron directional detection device is used as an input into the artificial neural network model to detect the direction of neutron incidence.

[0018] Effects of the application

[0019] According to the neutron directional detection device and method based on the solid nuclear track detector, the application has good on-site applicability of the equipment, namely portability and high mobility; the neutron directional detector has high precision and can accurately judge the incident direction; the application proposes a scheme for simultaneously measuring two energies by wide-energy-range neutron measurement, aiming at the case that the direction distribution of fast neutrons and thermal neutrons needs to be measured respectively in actual situations; the application simplifies the assembly process of the detector, reduces the operation difficulty and personnel training cost; and the application has good popularization, the detector structure is designed to have a fixed size and be compatible with the existing commercial CR-39, so that batch production and popularization of the detector can be ensured.

[0020] The dual-surface detection method proposed in this invention can effectively utilize the two detection surfaces of the detector to simultaneously measure fast neutrons and thermal neutrons. This invention significantly simplifies the detector structure. Compared to traditional methods that use sheet-like polyethylene or boron nitride as the conversion layer, this invention directly designs polyethylene as the outer shell, which simultaneously serves as both a fast neutron detection conversion layer and a protective shell. Furthermore, due to the isotropic nature of the nuclear reaction emission products of thermal neutrons, using boron nitride ceramic as the internal cubic block can simultaneously serve as both a thermal neutron detection conversion layer and a base. Traditional neutron direction detection systems often use active detectors. While these detectors offer timely responses, passive solid-state nuclear track detectors are more suitable for applications requiring cumulative measurements or personal dose monitoring due to their smaller size and better long-term stability. Attached Figure Description

[0021] Figure 1 This is a structural diagram of the neutron orientation detection device in an embodiment of the present invention; and

[0022] Figure 2 This is a flowchart of the neutron directional detection method in an embodiment of the present invention. Detailed Implementation

[0023] In the description of this application, it should be noted that, unless otherwise expressly specified and limited, the terms "installation," "connection," and "linking" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral connection; they can refer to a mechanical connection, an electrical connection, or a connection that allows communication between them; they can refer to a direct connection or an indirect connection through an intermediate medium; they can refer to the internal communication between two components or the interaction between two components. Those skilled in the art can understand the specific meaning of the above terms in this application according to the specific circumstances.

[0024] To make the technical means, creative features, objectives and effects of the present invention easy to understand, the following embodiments, in conjunction with the accompanying drawings, specifically illustrate a neutron directional detection device and method based on a solid-state nuclear track detector.

[0025] Figure 1 This is a structural diagram of the neutron orientation detection device in an embodiment of the present invention.

[0026] like Figure 1As shown, the neutron directional detection device 10 based on the solid nuclear track detector in the embodiment includes three parts of a solid nuclear track detection part 11, a center base 12 and a shell 13. The solid nuclear track detection part is used to receive secondary particles generated by the interaction of neutrons and form observable track signals. The center base is used as a thermal neutron conversion layer to form alpha particles that can be detected by the solid nuclear track. The shell is used as a fast neutron conversion layer to form protons that can be detected by the solid nuclear track.

[0027] The solid nuclear track detection part 11 includes six CR-39 solid nuclear track detectors, and the material is C 12 H 18 The size of the six CR-39 solid nuclear track detectors is 10mm*10mm*1mm.

[0028] The center base 12 is a cubic boron nitride ceramic material, which is used to reflect the information of thermal neutrons. The size of the center base 13 is 14mm*14mm*14mm, and the center base is surrounded by the six CR-39 solid nuclear track detectors.

[0029] The shell 13 is made of polyethylene material, which is used to reflect the information of fast neutrons. The shell includes two symmetrical and tightly connected groove shells. The shell is used to place the center base and the six CR-39 solid nuclear track detectors.

[0030] The size of each groove shell is 24mm*24mm*12mm. After the two groove shells are tightly connected, an accommodation space for placing the center base and the six CR-39 solid nuclear track detectors is formed in the interior. The six CR-39 solid nuclear track detectors are arranged on the groove shells and surround the six surfaces of the center base.

[0031] Figure 2 It is the flowchart of the neutron directional detection method in the embodiment of the application.

[0032] As Figure 2 shown, the application also discloses a neutron directional detection method based on a solid nuclear track detector, which specifically includes the following steps:

[0033] Step 1, using Monte Carlo simulation software, a geometric model of the neutron directional detection device 10 is established, different angle neutron radiation sources are simulated, and the energy and incident angle information of the secondary particles passing through the contact surface of the solid nuclear track detection part and the conversion layer under the corresponding incident angle condition are recorded. The energy and incident angle information of the secondary particles are input into the particle analysis and judgment algorithm to obtain the simulation data set of the response of the neutron directional detection device formed under different incident angle conditions. Based on the simulation data set, the artificial neural network model is trained to obtain the optimal model as the detection model.

[0034] Step 2, in-situ measurement, the neutron directional detection device 10 is irradiated under the neutron radiation field, after receiving the irradiation, the solid nuclear track part 11 is taken out to form visible tracks by chemical etching, and then the track density is read by using an optical microscope to obtain the response of the neutron directional detection device;

[0035] Step 3, the response of the neutron directional detection device is substituted into the artificial neural network model as input to detect the direction of neutron incidence. The response of the contact surface of the solid nuclear track part 11 and the central base 12 is used for the detection of the direction of thermal neutron incidence, and the response of the contact surface of the shell 13 is used for the detection of the direction of fast neutron incidence.

[0036] The neutron directional detection device 10 of the present application can be applied to a neutron directional detection system based on solid nuclear tracks.

[0037] The neutron directional detection system comprises a neutron directional detection device, a track automatic reading device, a track extraction analysis device, a multi-scenario incidence simulation device, a particle analysis judgment device, and a neutron incidence direction reconstruction device.

[0038] The track automatic reading device comprises a neutron emission module and an optical microscope reading module. The neutron emission module emits neutrons to the neutron directional detection device to etch and generate tracks. The optical microscope reading module analyzes the etched neutron directional detection device, reads the tracks, and obtains track reading results.

[0039] The optical microscope reading module comprises an optical microscope and a digital camera. The resolution of the optical microscope is 0.6um / pixel, and the 2D image of the track is captured by the digital camera.

[0040] The track extraction analysis device comprises an accurate ellipse fitting module. The long axis and the short axis of the track reading result are analyzed by the accurate ellipse fitting module to obtain track extraction analysis results.

[0041] The multi-scenario incidence simulation device comprises FLUKA Monte Carlo simulation software. The FLUKA Monte Carlo simulation software is used to establish a geometric model of the neutron directional detection device. By changing the incidence angle of the neutron emission module, the information of the secondary particles generated in the sensitive volume of the solid nuclear track detection part and the conversion layer contact surface under different incidence angles is recorded. The conversion layer contact surface is a boron nitride contact surface and a polyethylene contact surface. The secondary particles include alpha particles for the boron nitride contact surface and protons for the polyethylene contact surface. The alpha particles are used to reflect the information of thermal neutrons, and the protons are used to reflect the information of fast neutrons.

[0042] The particle analysis judgment device calculates the critical angle of incidence of the secondary particles of different energies through the information of the secondary particles and the V function, judges whether the particles on the boron nitride contact surface can form a track according to the relationship between the energy and the critical angle of incidence, finally obtains a response matrix, and obtains the final incident simulation result.

[0043] The neutron incident direction reconstruction device includes an artificial neural network model, reconstructs the neutron incident direction based on the track extraction analysis result and the incident simulation result, and uses the artificial neural network model.

[0044] The artificial neural network model obtains the output by building an input layer, a hidden layer and an output layer, and calculating the result of each neuron layer by layer from the input layer using formulas (1) and (2).

[0045]

[0046]

[0047] wherein, represents the linear sum of the neuron vector group of the j-1th layer, represents the i-th neuron of the j-1th layer, wij represents the weight of the connection between the neurons of the j-1th layer and the jth layer, bj is the bias of the jth neuron hidden layer, g() is the corresponding activation function, and y represents the output of the neuron.

[0048] In order to remove the influence of different neutron field intensities and backgrounds, the response of the solid nuclear track detector is standardized as formulas (3)-(5).

[0049]

[0050]

[0051]

[0052] wherein represents the result of the i-th face under the j-th situation, represents the average response under the j-th situation, represents the standard deviation of the six faces under the j-th situation, represents the corrected result of the i-th face under the j-th situation.

[0053] Effects of the embodiment

[0054] The solid nuclear track detector-based neutron directional detection device and method have good field applicability of equipment, namely portability and high maneuverability; the neutron directional detector has high precision and can accurately judge the incident direction; the wide-energy-range neutron measurement is used to meet the requirement of measuring the directional distribution of fast neutrons and thermal neutrons respectively; the assembling process of the detector is simplified, and the operation difficulty and personnel training cost are reduced; and the detector structure is designed to have a fixed size and be compatible with the existing commercial CR-39, so that batch production and popularization of the detector can be ensured.

[0055] The detector structure is simplified, and compared with the traditional method of using sheet polyethylene or boron nitride as a conversion layer, the polyethylene is directly designed as an outer shell to simultaneously serve as a fast neutron detection conversion layer and a protective shell.

[0056] The detector can realize accurate measurement, the solid nuclear track detectors are arranged on six surfaces of the cube, the design ensures high specificity of incident irradiation results in different directions, and the spatial resolution is high; compared with the traditional detector with a large volume, the detector has a small volume, can only represent the incident direction of the point in space during measurement, and can realize accurate measurement of the point.

[0057] The detector has high detection efficiency, most of the neutrons are blocked by the traditional coded aperture instrument, and only a small part of the double-scattering events is used by the neutron scattering camera, so the detection efficiency is low; in the present application, all the neutrons incident on the detector can be used as judgment information for directional measurement, so the detection efficiency can be greatly improved.

[0058] The traditional measurement method mainly focuses on the incident direction of neutrons in a certain energy range, and the simultaneous measurement of fast neutrons and thermal neutrons is less studied.

[0059] Those skilled in the art should understand that the present application is not limited to the above-mentioned embodiments, and the above-mentioned embodiments and descriptions in the specification are only to illustrate the principles of the present application, and various changes and improvements can be made without departing from the spirit and scope of the present application, and these changes and improvements all fall within the scope of the claimed present application. The scope of protection of the present application is defined by the appended claims and their equivalents.

Claims

1. A neutron directional detection apparatus based on a solid state nuclear track detector, characterized in that, It comprises: a solid nuclear track detection unit, comprising six CR-39 solid nuclear track detectors; a center base made of boron nitride ceramic material for reflecting thermal neutron information, which is surrounded by the six CR-39 solid nuclear track detectors; and a shell made of polyethylene material for reflecting fast neutron information, comprising two symmetrical and tightly connected groove shells, which is used to place the center base and the six CR-39 solid nuclear track detectors.

2. The neutron directional detection device based on solid nuclear track detector according to claim 1, wherein: wherein the peripheral size of each groove shell is 24mm*24mm*12mm, and after the two groove shells are tightly connected, an accommodation space for placing the center base and the six CR-39 solid nuclear track detectors is formed inside, and the six CR-39 solid nuclear track detectors are arranged on the inner wall of the groove shell and around the six surfaces of the center base.

3. The neutron directional detection device based on solid nuclear track detector according to claim 2, wherein: wherein the size of the center base is 14mm*14mm*14mm, and the size of each of the six CR-39 solid nuclear track detectors is 10mm*10mm*1mm.

4. The neutron directional detection device based on solid nuclear track detector according to claim 2, wherein: wherein the two surfaces of the CR-39 solid nuclear track detector are tightly attached to the shell and the center base respectively, the contact surface with the shell is used for fast neutron detection, and the secondary protons generated by the interaction between the fast neutron and the polyethylene material are used for detection, and the contact surface with the center base is used for thermal neutron detection, and the secondary alpha particles generated by the interaction between the thermal neutron and the boron nitride ceramic material are used for detection.

5. A method of neutron directional detection based on a solid state nuclear track detector, characterized in that Specifically comprising the following steps: S1, using Monte Carlo simulation software, a geometric model of the neutron directional detection device is established, different angle neutron radiation source irradiation is simulated, and the energy and incident angle information of the secondary particles passing through the contact surface of the solid nuclear track detection unit and the conversion layer under the corresponding incident angle condition are recorded, the contact surface of the conversion layer is the polyethylene contact surface and the boron nitride contact surface, and the secondary particles include protons passing through the polyethylene contact surface and alpha particles passing through the boron nitride contact surface; S2, using particle analysis judgment algorithm, whether the secondary particles can form a response on the CR-39 solid nuclear track detector is judged according to the comparison between the incident angle of the secondary particles and the critical angle, wherein the critical angle is calculated using the track growth theory model according to the energy of the secondary particles, and finally the response of the neutron directional detection device formed under different incident angle conditions is obtained; S3, the response of the neutron directional detection device after the neutron radiation source irradiation at different angles is taken as the simulation data set. The response of the neutron directional detection device is taken as the input layer, the incident angle of the neutron radiation source is taken as the output layer, two hidden layers are added to construct an artificial neural network model, and the artificial neural network model is trained based on the simulation data set. S4, in actual measurement, after the neutron directional detection device is irradiated by a neutron radiation source, a solid nuclear track part is taken out to perform chemical etching to form visible tracks, and then an optical microscope is used to read the track density to obtain a response of the neutron directional detection device; S5, the response of the neutron directional detection device is taken as input into the artificial neural network model to detect the neutron incident direction.

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