System for testing comprehensive performance of microstructure neutron detector

Abstract

The invention provides a system for testing the comprehensive performance of a microstructure neutron detector, and the system comprises a neutron slowing-down body, and the front side of the neutron slowing-down body is provided with a mixed radioactive source and a switchable gamma shielding body. A standard neutron detector, a silicon-based microstructure neutron detector and a standard gamma detector are arranged in the neutron moderator, and the silicon-based microstructure neutron detector is placed in a constant temperature box; the standard neutron detector, the silicon-based microstructure neutron detector and the standard gamma detector are respectively connected with a front-end electronic device, and each front-end electronic device is connected with the multichannel counter. Radiation performance testing is carried out on a developed silicon-based microstructure neutron detector chip prototype system, the thermal neutron detection efficiency, the n / gamma discrimination ratio, the applicable temperature range and the counting rate are included, and the blank of testing of a three-dimensional structure silicon-based neutron detector is filled.

Description

Technical Field

[0001] The invention provides a system for testing the comprehensive performance of a microstructure neutron detector, belonging to the technical field of radiation detection. Background Art

[0002] Semiconductor neutron detectors are radiation detectors that use semiconductor materials as detection media. They differ from gas detectors in that semiconductor materials replace the gas in gas detectors. Since the average ionization energy of silicon is 3.6eV, which is nearly an order of magnitude smaller than the average ionization energy of gas, 30eV, it can produce more electron-hole pairs when depositing the same energy, and has a higher energy resolution. At the same time, the mature manufacturing process and low manufacturing cost of silicon materials make it one of the semiconductor materials with the most types and the most extensive applications in the preparation of neutron detectors.

[0003] As for silicon-based neutron detectors, foreign countries started earlier, while domestic research is relatively weak and has not yet achieved commercialization. The huge demand still relies on foreign imports; at the same time, with the 3 The shortage of He resources can be alleviated by the research of silicon-based neutron detectors. 3 The supply of He proportional counters is insufficient to meet the demand. Therefore, the research and testing of three-dimensional silicon-based neutron detectors has great scientific research and application value, and is of great significance for the commercialization of silicon-based neutron detectors. Summary of the invention

[0004] The present invention provides a system for testing the comprehensive performance of a microstructure neutron detector, and performs radiation performance tests on a developed silicon-based microstructure neutron detector (MSND) chip prototype system, including thermal neutron detection efficiency, n / γ discrimination ratio, applicable temperature range and counting rate, so as to fill the gap in the test of three-dimensional structure silicon-based neutron detectors.

[0005] The specific technical solution is:

[0006] A system for testing the comprehensive performance of a microstructure neutron detector, comprising a neutron moderator, wherein a mixed radioactive source and a switchable gamma shield are arranged at the front side of the neutron moderator;

[0007] The neutron moderator is provided with a standard neutron detector, a silicon-based microstructure neutron detector and a standard γ detector, wherein the silicon-based microstructure neutron detector is placed in a constant temperature box; the standard neutron detector, the silicon-based microstructure neutron detector and the standard γ detector are respectively connected to a front-end electronic device, and each front-end electronic device is connected to a multi-channel counter.

[0008] The mixed radioactive source is used for radiating neutrons and gamma rays.

[0009] The neutron moderator is made of high-density polyethylene with a density of 0.962 g / cm 3 The whole is a hollow cylindrical structure with an inner diameter of 160mm; the neutron moderator includes a front half and a rear half, and the front half and the rear half are connected by a mortise and tenon structure; the front end face of the front half is a closed structure with a thickness of 130mm; the rear end face of the rear half is open and is provided with a cover plate, and the cover plate is provided with a central through hole and multiple small through holes for the wires to pass through.

[0010] A circular hole is arranged on the switchable gamma shielding body.

[0011] The present invention determines the optimal thickness of the polyethylene of the neutron moderator through MCNNP5 simulation, and redesigns the neutron moderator physically and mechanically to maximize the proportion of thermal neutrons incident on the detector. A switchable γ shield is added in front of the neutron moderator to implement the performance test of the detector in different radiation fields, so as to obtain an important indicator for measuring the performance of the detector (n / γ discrimination ratio). The constant temperature box in this test system can simulate the detector working in different temperature environments, so as to obtain another important indicator for measuring the performance of the detector (the usable temperature range). The use of a multi-channel counter can record the counts of different detectors under the same experimental conditions.

[0012] The silicon-based microstructure neutron detector MSND of the present invention is to etch some grooves on the silicon-based material by wet etching, and then fill the neutron conversion material by centrifugal method, thereby increasing the 6 The filling amount of LiF and 6 The contact surface area between LiF and the semiconductor material Si.

[0013] The relevant performance parameters of domestic silicon-based microstructure neutron detectors are only obtained by simulation, and there is no actual test data. The present invention designs a comprehensive performance test system for microstructure neutron detectors, which can test several major performance parameters of the detector (thermal neutron detection efficiency, n / γ discrimination ratio, applicable temperature range and counting rate), filling the gap in the test system solution for three-dimensional silicon-based neutron detectors and verifying the performance superiority of MSND.

[0014] When measuring the intrinsic detection efficiency of thermal neutrons, the equipment included should include a neutron source, a polyethylene moderator, a silicon-based microstructure neutron detector, and a calibrated standard neutron detector. 3 Proportional counter tube, preamplifier, main amplifier, multi-channel counter, DT5730 signal acquisition card, RDT counting module and 640-bit oscilloscope.

[0015] The function of the polyethylene moderator is to slow down high-energy neutrons to the thermal energy zone. The silicon-based microstructure neutron detector is a thermal neutron detector. During the test, the thermal neutron counts measured within a certain time range are recorded. 3 The function of the He proportional counter is to record the total number of thermal neutrons emitted by the neutron source and incident on the sensitive surface of the detector within the same time interval. The comparison between the two is the intrinsic detection efficiency of thermal neutrons. The function of the preamplifier is to preliminarily amplify and process the detector signal, but the pulse amplitude output by the preamplifier is small, so the main amplifier is required to further amplify the signal, and after processing and forming, it is input into the multi-channel analyzer. The multi-channel analyzer can pre-process the signal, such as denoising, filtering, etc., to improve the quality of the signal. Since the signal is divided into multiple channels for analysis, the multi-channel analyzer can realize parallel processing and improve processing efficiency. The DT5730 data acquisition card has multiple high-speed analog input channels and can collect multiple analog signals at the same time. It also has high-speed analog signal conversion capability, and performs analog-to-digital conversion on analog signals at high sampling rates to ensure high-precision acquisition and accurate recording of signals. The 640Zi oscilloscope has the advantages of high sensitivity, wide bandwidth, high sampling rate, and versatility. It can convert electrical signals that are invisible to the naked eye into visible images. Its large screen display can clearly display waveforms and measurement results. In addition, it has advanced triggering and analysis functions, supporting a variety of waveform analysis and measurement functions, such as spectrum analysis, time domain analysis, eye diagram analysis, etc. Among them, the trigger function of the oscilloscope can help users quickly find signals of interest and improve measurement efficiency. The trigger function can be time, voltage, waveform, etc. After setting the trigger conditions, the oscilloscope will automatically start sampling when the conditions are met. The RDT module has high-speed data acquisition capabilities, which can quickly and accurately record the occurrence time and counting information of events. It is suitable for real-time monitoring and control scenarios that require high frequency and high-precision counting.

[0016] The test steps of thermal neutron intrinsic detection efficiency are as follows: put the polyethylene moderator on the platform, adjust the height of the platform, make the laser, radiation hole and detector on the same horizontal line, and then put the MSND and the scaled standard neutron detector 3The He proportional counter tube is placed inside the moderator, the holes of the switchable γ shield are closed, and the detector is connected to the front-end electronic devices (preamplifier and main amplifier). The cables are led out through the back cover of the moderator and connected to the multi-channel counter. The storage port of the multi-channel counter should be set to read-write mode, while the data output port should be set to read-only mode. The storage port address of the multi-channel counter adopts the signal amplitude value, and the input data is the address storage value plus 1. Connect the digital spectrometer, oscilloscope and data acquisition card, start RDT MSND on the laptop, turn on the power, observe the preamplifier signal, and connect the main amplifier signal if the signal meets the expectation. After connecting the high-voltage power supply to the amplifier, leave the radiation room, close the shielding door, and then control the pan-tilt to increase the power. The preamplifier signal and the main amplifier signal are connected to the channel 1 (ch1) and channel 2 (ch2) input channels of the oscilloscope through the oscilloscope probe. Using the measurement function provided by the oscilloscope, the amplitude, frequency, period, duty cycle, rise time, fall time and other parameters of the signal can be accurately measured. Slowly adjust the oscilloscope until you see a perfect waveform on the oscilloscope, recording the counts of both detectors in the same time.

[0017] When measuring the n / γ discrimination ratio, the equipment included includes a neutron-γ hybrid source, a switchable γ shield, a polyethylene moderator, a silicon-based microstructure neutron detector, a preamplifier, a main amplifier, a DT5730 signal acquisition card, an RDT counting module and a 640Zi oscilloscope.

[0018] The hybrid source can radiate neutrons and gamma rays. During the test, the gamma shield is opened first to allow neutrons and gamma rays to enter the sensitive volume of the detector together. When particles (neutrons or gamma rays) interact with the detector, they will produce different signals or responses. Neutrons usually interact with the detector material through nuclear reactions, such as elastic scattering, inelastic scattering or nuclear fission, while gamma rays interact with the detector material through processes such as photoelectric effect, Compton scattering or electron pair generation. The silicon-based microstructure neutron detector processes and records the electrical signals formed by these secondary charged particles. The preamplifier performs preliminary amplification and processing of the signal, outputs the pulse amplitude and waveform, and the main amplifier further amplifies and shapes the signal (filtering and shaping to improve the signal-to-noise ratio). The waveform is observed on the 640Zi oscilloscope, and the multi-channel counter and DT5730 signal acquisition card analyze and count the signal. Then, the holes of the gamma shield are closed to shield the gamma rays. Under the same conditions, the pulse signal count is obtained, and the n / gamma discrimination ratio is calculated by the number of neutrons correctly identified as neutrons / the number of gamma rays incorrectly identified as neutrons.

[0019] The steps of n / γ discrimination ratio test are as follows: put the polyethylene moderator on the platform, adjust the height of the platform, let the laser, radiation hole and detector be on the same horizontal line, then put the MSND and standard γ detector into the moderator, open the hole of the γ shield first, connect the detector to the front-end electronic device (preamplifier and main amplifier), and lead the cable through the back cover of the moderator to the DT5730 signal acquisition card and 640Zi oscilloscope. Start RDTMSND on the laptop, and after turning on the power, observe the preamplifier signal first. If the signal meets the expectation, the main amplifier signal can be connected. After connecting the high-voltage power supply to the amplifier, the researchers leave the radiation room, close the shielding door, and then control the PTZ to raise the source, and then slowly debug the oscilloscope until a perfect waveform is seen on the oscilloscope, and record the detector counts within a certain period of time. The second step is to close the hole of the γ shield to shield the γ rays, repeat the above steps, and record the detector counts within the same period of time.

[0020] When testing the applicable temperature range, use the temperature control equipment to process the MSND, then wrap it with thermal insulation film, repeat the measurement process under the same source intensity, observe whether the oscilloscope waveform is normal, and record the pulse count. Then change the temperature, repeat the above process, and record the pulse count vs. temperature curve until the oscilloscope waveform becomes abnormal and the pulse count drops sharply, so as to obtain the applicable temperature range of the detector.

[0021] When measuring the count rate, the equipment included should include a neutron source, a polyethylene moderator, a silicon-based microstructure neutron detector, a preamplifier, a main amplifier, a multi-channel counter, a stopwatch, a DT5730 signal acquisition card, an RDT counting module, and a 640Zi oscilloscope. The count rate can be calculated using the following formula: Count rate = number of events recorded by the counter / statistical time. The number of events recorded by the counter refers to the number of particles received by the detector within the statistical time; the statistical time refers to the length of time that the particles are measured by the detector. Therefore, the count rate can be obtained by calculating the pulse signal collected within a unit time.

[0022] Compared with the traditional system, the radiation source of this system is a mixed source instead of a single source. There is a shield in front of the polyethylene moderator, which can choose whether to shield the gamma rays according to the needs. The polyethylene moderator contains a standard neutron detector, a self-developed MSND detector and a standard gamma detector. The test results are led out through multiple holes of the wire and recorded by a multi-channel counter, making the system more powerful.

[0023] The moderator design used in the present invention is determined after a large number of simulations. The proportion of thermal neutrons after high-energy neutrons pass through the moderator is higher, and the thermal neutron detection efficiency of the neutron detector is higher. The moderator has an appropriate size and is easy to operate.

[0024] The present invention can realize that different detectors work and record at the same time under the same radiation field, which is more comparative and the radiation field is also variable.

[0025] The silicon-based microstructure neutron detector (MSND) of the present invention is provided with a constant temperature box outside, so that the detector can work at different temperatures.

[0026] The data acquisition equipment of the present invention includes a DT5730 signal acquisition card and an RDT counting module, which can simultaneously acquire multiple analog signals. These channels can be connected to various types of sensors or detectors for real-time acquisition of analog signals generated in particle physics experiments or nuclear physics experiments. At the same time, it also has high-speed analog signal conversion capabilities, and can digitally process analog signals at an extremely high sampling rate, ensuring high-precision acquisition and accurate recording of signals. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1 It is the overall framework diagram of the system of the present invention;

[0028] Figure 2 It is a schematic diagram of the structure of the neutron moderator of the present invention;

[0029] Figure 3 It is a cross-sectional view of the neutron moderator of the present invention. DETAILED DESCRIPTION

[0030] The technical solutions in the embodiments of the present invention will be described clearly and completely below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, rather than all the embodiments.

[0031] like Figure 1 As shown, a system for testing the comprehensive performance of a microstructure neutron detector comprises a neutron moderator 6, wherein a mixed radioactive source 1 and a switchable gamma shield 2 are provided at the front side of the neutron moderator 6;

[0032] The neutron moderator 6 is provided with a standard neutron detector 3, a silicon-based microstructure neutron detector 7 and a standard γ detector 5, wherein the silicon-based microstructure neutron detector 7 is placed in a constant temperature box 4; the temperature preservation range is 0-45°C. The standard neutron detector 3, the silicon-based microstructure neutron detector 7 and the standard γ detector 5 are respectively connected to a front-end electronic device 8, and each front-end electronic device 8 is connected to a multi-channel counter 9. The counter is multi-channel, and the test results of different detectors are simultaneously drawn out after passing through the front-end electronic device 8 and recorded by the multi-channel counter 9.

[0033] The matching counting equipment includes DT5730 signal acquisition card, RDT counting module and 640Zi oscilloscope.

[0034] The mixed radioactive source 1 is used for radiating neutrons and gamma rays.

[0035] like Figure 2 and Figure 3 As shown, the neutron moderator 6 is made of high-density polyethylene material with a density of 0.962 g / cm 3 The overall structure is a hollow cylindrical structure with an inner diameter of 160mm, which can be loaded with detectors and electronic devices.

[0036] The neutron moderator 6 includes a front section 63 and a rear section 64, which are connected by a mortise and tenon structure 65 and can be disassembled and spliced; the front end face 61 of the front section 63 is a closed structure with a thickness of 130 mm; at this thickness, the proportion of thermal neutrons after neutron moderation is the highest, which is obtained by simulation. The rear end face of the rear section 64 is open and provided with a cover plate 62, which is provided with a central through hole 621 and a plurality of small through holes 622 for wires to pass through. The diameter of the central through hole 621 is 50 mm, and the diameter of the small through holes 622 next to it is 35 mm, which can be used for wires and inserting helium-3 proportional counter tubes, and the commonly used diameters are 19 mm, 25.4 mm, 32 mm, 38 mm, and 50 mm.

[0037] A circular hole is provided on the switchable γ shield 2. The switchable γ shield 2 is made of lead, iron or concrete, and the circular hole can be controlled to switch, thereby realizing the conversion of the neutron field, the γ-ray field and the mixed field, and measuring the n / γ discrimination ratio of the silicon-based microstructure neutron detector 7.

[0038] The present invention is used to test the comprehensive performance of a microstructure neutron detector. During the test, a neutron and γ mixed radiation source is used as a mixed radiation source 1. Whether to close the round hole on the switchable γ shielding body 2 is selected according to the need. The silicon-based microstructure neutron detector 7 to be tested is put on a constant temperature box 4, the temperature is set, and the detector is placed in a neutron moderator 6. Each detector is connected to a front-end electronic device, and the cable is led out through the round hole on the disk, and recorded by a multi-channel counter 9. After the amplifier is connected to a high-voltage power supply, the researcher leaves the radiation room, closes the shielding door, and increases the source in the control room. Finally, a signal acquisition card, a counting module, and an oscilloscope are used to record and process the signal, and calculate the relevant performance.

[0039] In the actual thermal neutron detection test, the radiation source should be directly in front of the switchable γ shield 2 and the neutron moderator 6. The distance between the radiation source and the detector and the test temperature should be selected according to actual needs. A layer of aluminum film can be added to the side surface inside the neutron moderator 6 to shield neutrons incident from the side into the moderator.

[0040] Through experiments, it is shown that this test system can test the comprehensive performance of microstructure neutron detectors.

Claims

1. A system for testing the comprehensive performance of a microstructure neutron detector, characterized in that: It comprises a neutron moderator (6), wherein a mixed radioactive source (1) and a switchable gamma shield (2) are arranged on the front side of the neutron moderator (6); The neutron moderator (6) is provided with a standard neutron detector (3), a silicon-based microstructure neutron detector (7) and a standard gamma detector (5), wherein the silicon-based microstructure neutron detector (7) is placed in a constant temperature box (4); the standard neutron detector (3), the silicon-based microstructure neutron detector (7) and the standard gamma detector (5) are respectively connected to a front-end electronic device (8), and each front-end electronic device (8) is connected to a multi-channel counter (9).

2. A system for testing the comprehensive performance of a microstructure neutron detector according to claim 1, characterized in that: The mixed radioactive source (1) is used for radiating neutrons and gamma rays.

3. A system for testing the comprehensive performance of a microstructure neutron detector according to claim 1, characterized in that: The neutron moderator (6) is made of high-density polyethylene material with a density of 0.962 g / cm 3 The neutron moderator (6) is a hollow cylindrical structure with an inner diameter of 160 mm. The neutron moderator (6) includes a front half (63) and a rear half (64), and the front half (63) and the rear half (64) are connected by a mortise and tenon structure (65). The front end face (61) of the front half (63) is a closed structure with a thickness of 130 mm. The rear end face of the rear half (64) is open and is provided with a cover plate (62). The cover plate (62) is provided with a central through hole (621) and a plurality of small through holes (622) for the wires to pass through.

4. A system for testing the comprehensive performance of a microstructure neutron detector according to claim 1, characterized in that: The switchable gamma shielding body (2) is provided with a circular hole.

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