A white light neutron source beamline real-time monitor and monitoring method

Abstract

The present application belongs to the technical field of neutron source beam line measurement, and particularly relates to a white light neutron source beam line real-time monitor and a monitoring method. The white light neutron source beam line real-time monitor comprises a combined parallel plate avalanche detector subsystem for monitoring a wide-spectrum white light neutron beam line of a spallation reaction, and further comprises a low-pressure self-balancing feedback flow gas subsystem and a signal support subsystem connected with the combined parallel plate avalanche detector subsystem. The spallation reaction is obtained by proton targeting generated by an accelerator. The present application adopts multiple neutron detection materials, which can cover wide-energy-area white light neutrons from thermal neutrons to hundreds of MeV neutrons, and meets the needs of most application scenarios. Meanwhile, the selected nuclides have overlapping intervals, which can be mutually checked to ensure the reliability of the neutron measurement results.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of neutron source beamline measurement, and particularly relates to a white light neutron source beamline real-time monitor and a monitoring method. BACKGROUND

[0002] In the field of neutron physics and its application, the accurate description of the neutron radiation field is the primary task, and the main parameters relied on include the neutron energy spectrum, the neutron fluence / yield / flux, and the neutron angular distribution / beam spot profile distribution, which can also be referred to as the neutron beamline characteristic parameters under the collimation constraint condition.

[0003] The neutron energy spectrum refers to the number of neutrons corresponding to different energy neutrons, which represents the energy distribution probability of the neutrons. The neutron fluence refers to the number of neutrons passing through per unit area, which is a concept representing the number of neutrons, and it contains neutrons of different energies. It has two extended concepts, the neutron yield refers to the total number of neutrons emitted by the source into the whole space, and the neutron flux refers to the neutron fluence per unit time, representing the density of the flow. The neutron angular distribution refers to the change of the energy spectrum and the fluence of the neutrons with different emission angles, which is related to the nuclear reaction condition, and generally has anisotropy and angular distribution. Under the collimation constraint condition, more attention is paid to the uniformity of the neutrons after passing through the collimator, including whether the direction is parallel, whether the density is uniform, and whether the energy is consistent at each point in the beam spot.

[0004] The neutron field parameters need accurate experimental results. Generally, the measurement methods of the neutron energy spectrum include the neutron time-of-flight method, the recoil method, and the nuclear reaction method, among which the time-of-flight method is the most accurate because the commonly used detector liquid flash or plastic flash has fast time response and high timing accuracy; the neutron fluence measurement adopts the standard cross-section method or the accompanying particle method; and the neutron beam spot distribution is measured by the mode of scintillator plus CCD.

[0005] The present application is aimed at measuring the spallation neutron source. Since the spallation neutron source is a complex neutron field, it is a collimated constrained neutron field, and the geometry of the neutron source target station is as shown in FIG. Figure 1

[0006] 1.6 GeV high-energy protons are bombarded on a tungsten target through a 15-degree deflection magnet to generate high-brightness white light neutrons. Theoretically, the neutron energy can be up to 1.6 GeV, and the neutron yield can be up to 16 orders of magnitude when the power is 100 kW.

[0007] ​The sub-field characteristics are wide available energy region, which can be from thermal neutron to hundreds of MeV, different from conventional single-energy or quasi-single-energy neutron field, and different from narrow white light neutron field generated by p / d beam and 9Be reaction, and single detection medium cannot accurately measure such a wide energy region. Another characteristic is that the single pulse proton width is about 80 ns, accompanied by 80 ns wide gamma burst. Although the gamma ray is short in time, the fluence is of the same order of magnitude as the generated neutron, so it will make the dead time of ordinary liquid flash and other detectors too large. After tens of microseconds, the detector will gradually recover, but the useful neutron signal cannot be responded because the detector is in the dead time state. SUMMARY

[0008] The purpose of the present application is to provide a monitoring device that can solve the difficulties of eV-hundreds of MeV wide spectrum white light neutron measurement and detector dead time state caused by gamma burst, solve the measurement difficulty caused by too wide neutron energy coverage and too concentrated spallation gamma in a short time during white light neutron source irradiation, and give accurate values of white light neutron energy spectrum, neutron fluence and beam spot distribution in real time.

[0009] To achieve the above purpose, the technical scheme adopted by the present application is a white light neutron source beam line real-time monitor, which comprises a combined parallel plate avalanche detector subsystem for monitoring the wide spectrum white light neutron beam line of spallation reaction, a low-pressure self-balancing feedback flow gas subsystem and a signal support subsystem connected with the combined parallel plate avalanche detector subsystem, and the spallation reaction is obtained by proton targeting generated by an accelerator.

[0010] Further,

[0011] The combined parallel plate avalanche detector subsystem comprises an aluminum alloy cavity and a plurality of target units arranged in the aluminum alloy cavity, and the target units are used for detecting the wide spectrum white light neutron beam line;

[0012] The aluminum alloy cavity is in a cylindrical shape, a beam window is arranged at the top center position of the aluminum alloy cavity for the wide spectrum white light neutron beam line to enter; the bottom of the aluminum alloy cavity is a cavity panel, and a PCB base is arranged on the upper surface of the cavity panel in the aluminum alloy cavity;

[0013] The target units are arranged on the PCB base and located at the bottom center position of the aluminum alloy cavity, and the wide spectrum white light neutron beam line enters the target units to obtain a detector signal;

[0014] The lower surface of the cavity panel is provided with a power / signal connector connected with the PCB base for transmitting the detector signal to the signal support subsystem, and the signal support subsystem is used for recording, storing and real-time analyzing the detector signal;

[0015] An air inlet and an air outlet are arranged on both sides of the aluminum alloy cavity for connecting the low-pressure self-balancing feedback air supply system, which is used to provide a low-pressure environment containing working gas inside the aluminum alloy cavity.

[0016] Further, the target unit is 5 groups, which are arranged in parallel on the PCB base through target-pole columns; a position collection strip is arranged at the top end of the target-pole column, which is used for measuring the position information of fragments; a fragment isolation target is arranged at the top end of the target-pole column, which is located above the target unit and parallel to the target unit, and is used to isolate the fission fragments from flying to the adjacent unit collection pole to reduce the background noise.

[0017] Further, each group of the target unit includes a thin target at the center position and collection poles on both sides of the thin target; an Au film is arranged between the thin target and the collection pole, and the thickness of the Au film is 10 microns; the collection pole and the Au film are parallel to the thin target, and the distance between the two collection poles is 2 millimeters.

[0018] Further,

[0019] The surfaces of the two sides of the thin target are plated with target material, and the bottom lining of the thin target is a surface-plated metal MYLAR film or metal thin film with a thickness less than 2 microns;

[0020] The target unit is divided into a first target unit, a second target unit, a third target unit, a fourth target unit and a fifth target unit from top to bottom, and the fifth target unit is close to the PCB base;

[0021] The target material on the thin target of the first target unit is 6Li, and the surface density of the target material is less than 10 micrograms per unit area;

[0022] The target material on the thin target of the second target unit is 10B, and the surface density of the target material is less than 10 micrograms per unit area;

[0023] The target material on the thin target of the third target unit is 235U, and the surface density of the target material is less than 100 micrograms per unit area;

[0024] The target material on the thin target of the fourth target unit is 238U, and the surface density of the target material is less than 100 micrograms per unit area;

[0025] The target material on the thin target of the fifth target unit is 235U, and the surface density of the target material is less than 100 micrograms per unit area;

[0026] The collecting electrode of each target unit outputs a signal to the panel through an RC circuit, and the first target unit, the second target unit, the third target unit and the fourth target unit each have one working voltage input and two time signal outputs;

[0027] The thin target of the fifth target unit has a position resolution function and is composed of two groups of strip collecting electrodes perpendicular to each other, has one working voltage input and five signal outputs corresponding to one time signal and four position signals respectively.

[0028] Further,

[0029] The low-pressure self-balancing feedback gas flow subsystem is divided into two parts, which are connected respectively, the first part includes a first needle valve, an inlet valve and a gas cylinder connected in series through pipelines, the first needle valve is connected to the gas inlet; the second part includes a second needle valve, an outlet valve and a vacuum pump connected in series through pipelines, the second needle valve is connected to the gas outlet; further comprising an automatic pressure control instrument, the automatic pressure control instrument is used for controlling the first needle valve and the second needle valve; the working gas provided by the gas cylinder is isobutane / full fluorinated propane;

[0030] The automatic pressure control instrument is also connected with a pressure sensor for monitoring the working gas pressure inside the aluminum alloy cavity; according to the difference between the gas pressure data fed back by the pressure sensor and the set value, the automatic pressure control instrument controls the opening degree of the first needle valve and the second needle valve in real time to ensure the stability of the working gas pressure; the vacuum pump and the combined parallel plate avalanche detector subsystem are electronically insulated.

[0031] Further, the signal support subsystem includes a high-low voltage power supply, a fast amplifier and a data acquisition system connected with the fast amplifier, the fast amplifier is connected with the power / signal connector for amplifying the detector signal and transmitting it to the data acquisition system, the data acquisition system is used to record, store and analyze the detector signal in real time, and the high-low voltage power supply is used to provide power for the fast amplifier and the data acquisition system; the data acquisition system also receives the time-of-flight start signal given by the accelerator at the proton target time, ensures that the detector signal and the time-of-flight start signal work under the same clock, and thus gives the final time-of-flight information.

[0032] The application also discloses a white light neutron source beam line real-time monitoring method for the white light neutron source beam line real-time monitor.

[0033] Step S1, the low-pressure self-balancing feedback gas flow subsystem evacuates the aluminum alloy cavity and performs a gas washing operation;

[0034] Step S2, the detector signal accesses the data acquisition system, the data of the detector signal collected by full waveform is recorded by the back-end computer, the real neutron-induced fission signal is selected by coincidence mode, and the background interference is eliminated.

[0035] Further,

[0036] In the step S1, the gas washing operation includes the following steps:

[0037] Step S1.1, first pass: close the gas inlet valve and the first needle valve, open the gas outlet valve and the second needle valve of the gas outlet, start pumping with the vacuum pump, and pump the internal gas pressure of the aluminum alloy cavity to 100 Pa. Close the gas outlet valve and the second needle valve; open the gas inlet valve and the first needle valve to provide working gas until the internal gas pressure of the aluminum alloy cavity reaches 1500 Pa, close the gas inlet valve and the first needle valve, open the gas outlet valve and the second needle valve, and start pumping with the vacuum pump to pump the internal gas pressure of the aluminum alloy cavity to 100 Pa.

[0038] Step S1.2, second pass: close the gas outlet valve and the second needle valve; open the gas inlet valve and the first needle valve to provide working gas until the internal gas pressure of the aluminum alloy cavity reaches 1500 Pa, close the gas inlet valve and the first needle valve, open the gas outlet valve and the second needle valve, and start pumping with the vacuum pump to pump the internal gas pressure of the aluminum alloy cavity to 100 Pa.

[0039] Step S1.3, third pass: close the gas outlet valve and the second needle valve; open the gas inlet valve and the first needle valve to provide working gas until the internal gas pressure of the aluminum alloy cavity reaches 2000 Pa, close the gas inlet valve and keep the first needle valve open, open the gas outlet valve, slowly open the second needle valve until the internal gas pressure of the aluminum alloy cavity decreases to 820 Pa, close the second needle valve, and then adjust the second needle valve until the internal gas pressure of the aluminum alloy cavity slowly decreases. Close the first needle valve and adjust the first needle valve. Fully open the gas inlet valve; adjust the second needle valve to stabilize the internal gas pressure of the aluminum alloy cavity at the set working gas pressure. At this time, the combined parallel plate avalanche detector subsystem reaches the normal working state.

[0040] In the step S2,

[0041] The working voltage of the combined parallel plate avalanche detector subsystem is adjusted to within +600V; the detector signal output is connected to the fast amplifier, and after amplification and shaping, it is directly connected to the back-end data acquisition system. The frequency of the data acquisition system is greater than 1GHz.

[0042] If two of the time signals of the output of each group of the first target unit to the fourth target unit are coincident, if the two time signals arrive at the same time, it is determined to be a normal signal, and one of the time signals is given as a time-of-flight stop signal; if multiple simultaneous signals occur within the group, it is considered to be multiple events; all constitute a complete time-of-flight event with the time-of-flight start signal; if there is no coincident signal, it is determined that there is no valid event in the current period; if all outputs of each group produce signals at the same time, it is determined that the combined parallel plate avalanche detector subsystem is fired, and the gas washing operation of the steps S1.1 to S1.3 is repeated.

[0043] Further, after the step S1.3, a gas tightness measurement is also needed, and the specific steps are: close the gas inlet valve, use the vacuum pump to pump, close the gas outlet valve when the internal gas pressure of the aluminum alloy cavity is reduced to 100 Pa, and then record the internal gas pressure value of the aluminum alloy cavity once every set time interval.

[0044] The beneficial effects of the present application are:

[0045] 1. The present application adopts multiple neutron detection materials, which can cover a wide energy range of white light neutrons from thermal neutrons to hundreds of MeV neutrons, meeting the needs of most application scenarios, and the selected nuclides have overlapping intervals that can verify each other to ensure the reliability of the neutron measurement results.

[0046] 2. The present application adopts a low-pressure gas flow detection system, and the working gas pressure (the internal gas pressure of the aluminum alloy cavity 15) is between one hundredth and one thousandth of atmospheric pressure; the total thickness of the backing and structural material of the target unit used is less than 0.5 mm, greatly reducing the generation of gamma bursts.

[0047] 3. The present application can measure multiple parameter values at a time, including neutron energy spectrum, neutron fluence, and beam spot distribution, improving efficiency and providing users with more comprehensive, real-time information, which is beneficial to the analysis of measurement results.

[0048] 4. The backing thickness of the neutron conversion material (target material) in the present application is less than 2 microns, and the background signal generation is greatly reduced by using time coincidence technology.

[0049] 5. The detector (combined parallel plate avalanche detector subsystem) of the present application has fast response and high timing accuracy, which can be better than 1 ns, improving the energy resolution.

[0050] 6. The real-time online data generated by the present application provides normalized data for scientific experiments, and can also provide cumulative fluence for process and non-destructive testing neutron irradiation, and can also provide data basis for radiation dosimetry research and neutron detector calibration. BRIEF DESCRIPTION OF DRAWINGS

[0051] Figure 1 is a schematic diagram of the target station geometry of the spallation neutron source described in the background of the invention;

[0052] Figure 2 is a schematic diagram of a white neutron source beamline real-time monitor described in the detailed description of the invention;

[0053] Figure 3 is a schematic diagram of a measurement unit described in the detailed description of the invention (collecting electrode 16 and thin target 17 are in a dispersed state);

[0054] Figure 4 is a schematic diagram of a measurement unit described in the detailed description of the invention (collecting electrode 16 and thin target 17 are in a combined state);

[0055] Figure 5 is a schematic diagram of a parallel-plate avalanche detector subsystem described in the detailed description of the invention;

[0056] Figure 6 is an enlarged schematic diagram of a collecting electrode 16 and a thin target 17 of a parallel-plate avalanche detector subsystem described in the detailed description of the invention (in an installed state);

[0057] Figures 2-6 In the figure: 1 - automatic pressure controller, 2 - cavity back panel, 3 - first needle valve, 4 - gas inlet valve, 5 - gas cylinder, 6 - second needle valve, 7 - gas outlet valve, 8 - vacuum pump, 9 - fast amplifier, 10 - data acquisition system, 11 - gas flow inlet, 12 - beam window, 13 - target-electrode stand, 14 - position collection strip, 15 - aluminum alloy cavity, 16 - collecting electrode, 17 - thin target, 18 - PCB base, 19 - cavity panel, 20 - power / signal connector, 21 - Au film, 22 - gas flow outlet. DETAILED DESCRIPTION

[0058] The invention will be further described below in conjunction with the accompanying drawings and examples.

[0059] The invention provides a white neutron source beamline real-time monitor (see Figure 2 ), comprising a combined parallel-plate avalanche detector subsystem for monitoring a wide-spectrum white neutron beamline of a spallation reaction, and further comprising a low-pressure self-balancing feedback gas flow subsystem and a signal support subsystem connected to the combined parallel-plate avalanche detector subsystem, the spallation reaction being obtained by proton targeting generated by an accelerator.

[0060] The combined parallel-plate avalanche detector subsystem is the core component of the white neutron source beamline real-time monitor, and its design idea is to use a time-of-flight method for measurement,

[0061]

[0062] The energy E of the neutron and the time of flight tn are directly related, and the energy of the neutron can be inversely deduced by obtaining the time spectrum.

[0063] The combined parallel-plate avalanche detector subsystem (see Figure 5 ) comprises an aluminum alloy cavity 15 and a plurality of target units (see Figure 6 ) arranged in the aluminum alloy cavity 15, the target units being used for detecting a wide-spectrum white neutron beam line;

[0064] The aluminum alloy cavity 15 is in a cylindrical shape, and a beam window 12 is arranged at the top center position of the aluminum alloy cavity 15 for the wide-spectrum white neutron beam line to enter; the bottom of the aluminum alloy cavity 15 is a cavity panel 19, and a PCB base 18 is arranged on the upper surface of the cavity panel 19 in the aluminum alloy cavity 15;

[0065] The target units are arranged on the PCB base 18 and located at the bottom center position of the aluminum alloy cavity 15, and the wide-spectrum white neutron beam line enters the target units to obtain a detector signal;

[0066] The lower surface of the cavity panel 19 (that is, the outer surface of the bottom of the aluminum alloy cavity) is provided with a power / signal connector 20 connected with the PCB base 18, which is used for transmitting the detector signal to a signal support subsystem, and the signal support subsystem is used for recording, storing and real-time analyzing the detector signal;

[0067] An air inlet 11 and an air outlet 22 are further arranged on both sides of the aluminum alloy cavity 15 for connecting a low-pressure self-balancing feedback air system, which is used for providing a low-pressure environment containing working gas in the aluminum alloy cavity 15.

[0068] As shown in Figure 6 , the target units are 5 groups and are arranged in parallel on the PCB base 18 through target-pole columns 13; a position collection strip 14 is further arranged at the top end of the target-pole column 13, which is used for measuring the position information of fragments (that is, measuring the distribution of the neutron beam spot); a fragment isolation target is further arranged at the top end of the target-pole column 13, which is located above the target units and parallel to the target units, and is used for isolating the fission fragments from flying to the adjacent collection poles of the units to reduce the background noise (that is, isolating the crosstalk of the fission fragments of the adjacent measurement units to reduce the background noise).

[0069] As shown in Figure 3 , 4As shown, each group of target units includes a thin target 17 located at the center position, a collector 16 located on both sides of the thin target 17; an Au film 21 is also arranged between the thin target 17 and the collector 16, and the thickness of the Au film 21 is 10 microns (the Au film 21 is used as a barrier layer to prevent fission fragments, charged particles from entering another parallel plate avalanche detector subsystem from one parallel plate avalanche detector subsystem, and to prevent secondary triggering); the collector 16 and the Au film 21 are parallel to the thin target 17, and the distance between the two collectors 16 is 2 millimeters; the thin target 17 is connected to a positive voltage, and the collector 16 is grounded, and the ground connection is finally connected to the laboratory ground.

[0070] The two side surfaces of the thin target 17 are plated with target material, and the bottom lining of the thin target 17 is a surface-plated metal MYLAR film or a metal thin film with a thickness of less than 2 microns, which ensures that the particles in the wide-spectrum white neutron beam line can pass through the metal MYLAR film or the metal thin film to generate ionization and signal collection;

[0071] The target units are divided into first target units, second target units, third target units, fourth target units and fifth target units from top to bottom, and the fifth target units are close to the PCB base 18;

[0072] The target material on the thin target 17 of the first target unit is 6Li, and the areal density of the target material is less than 10 micrograms per unit area;

[0073] The target material on the thin target 17 of the second target unit is 10B, and the areal density of the target material is less than 10 micrograms per unit area;

[0074] The target material on the thin target 17 of the third target unit is 235U, and the areal density of the target material is less than 100 micrograms per unit area;

[0075] The target material on the thin target 17 of the fourth target unit is 238U, and the areal density of the target material is less than 100 micrograms per unit area;

[0076] The target material on the thin target 17 of the fifth target unit is 235U, and the areal density of the target material is less than 100 micrograms per unit area;

[0077] The collector 16 of each target unit outputs a signal to the panel through an RC circuit, and the first target unit, the second target unit, the third target unit and the fourth target unit each have one working voltage input and two time signal outputs;

[0078] The thin target 17 of the fifth target unit has a position resolution function and is composed of two groups of strip collectors perpendicular to each other, has one working voltage input, and five signal outputs corresponding to one time signal and four position signals, and the four position signals include X1, X2, Y1 and Y2, which are given through a delay line;

[0079] X=(X1-X2) / (X1+X2) Formula (2)

[0080] Y = (Y1 - Y2) / (Y1 + Y2) Formula (3).

[0081] The set value of the surface density of the target material can ensure that the self-absorption correction of the outgoing charged particles is small, which is beneficial to accurate measurement.

[0082] The formula measurement is combined by four target materials (i.e. four standard nuclei, see Table 1) to achieve full-energy region coverage and verification.

[0083] Table 1 (IAEA recommended standard)

[0084]

[0085] Through the above four nuclei, the energy region from thermal neutron to 200 MeV high-energy neutron can be fully covered, and overlapping coverage is formed in most regions, which is beneficial to mutual verification of data of different nuclei. The form of low-pressure parallel plate avalanche detector can achieve fast response and be immune to γ-flash impact.

[0086] After the neutrons in the wide-spectrum white neutron beam line react with the target material, fission fragments or charged particles are released. For heavy target U, the neutrons in the Th target cause the target material to fission, and the fission product nuclei are emitted; for light target 6Li, 10B target, after reacting with neutrons, T, α, Li and other charged particles are released. After the parallel plate avalanche detector subsystem receives the fission product nuclei and charged particle sensing signals, the time and position information of the reaction of neutrons with the target can be given, and the flight time spectrum and corresponding position of the neutrons can be given through the time-of-flight method. After inversion calculation, the neutron energy spectrum, neutron flux and beam spot distribution and other beam line characteristic parameter values can be obtained according to the detection efficiency and other conditions, realizing the real-time monitoring function of the neutron beam line.

[0087] The low-pressure self-balancing feedback flow gas subsystem is divided into two parts, which are connected respectively, the first part includes the first needle valve 3, the inlet valve 4 (pressure reducing valve) and the gas cylinder 5 (the gas cylinder 5 needs to be set to a safe distance far enough) connected in series through the pipeline, the first needle valve 3 is connected with the flow gas inlet 11; the second part includes the second needle valve 6, the outlet valve 7 (shutoff valve) and the vacuum pump 8 connected in series through the pipeline, the second needle valve 6 is connected with the flow gas outlet 22; it also includes an automatic pressure control instrument 1 (model VCC500), the automatic pressure control instrument 1 is used to control the first needle valve 3 and the second needle valve 6; the working gas provided by the gas cylinder 5 is isobutane / full fluorinated propane;

[0088] The automatic pressure control instrument 1 is also connected with a pressure sensor for monitoring the working gas pressure inside the aluminum alloy cavity 15; according to the difference between the gas pressure data fed back by the pressure sensor and the set value, the automatic pressure control instrument 1 controls the opening degree of the first needle valve 3 and the second needle valve 6 in real time to ensure the stability of the working gas pressure; the vacuum pump 8 is electronically insulated from the combined parallel-plate avalanche detector subsystem, otherwise the output signal of the parallel-plate avalanche detector subsystem will be affected.

[0089] The signal support subsystem includes a high-low voltage power supply, a fast amplifier 9 and a data acquisition system 10 connected with the fast amplifier 9, the fast amplifier 9 is connected with a power / signal joint 20 for amplifying the detector signal and then transmitting the amplified signal to the data acquisition system 10, the data acquisition system 10 is used for recording, storing and analyzing the detector signal in real time, and the high-low voltage power supply is used for providing power supply for the fast amplifier 9 and the data acquisition system 10; the working voltage required by the detector is provided by the high-low voltage power supply (ISEG power supply); the detector signal is directly output to the fast amplifier 9, and then output to the data acquisition system 10 after shaping; meanwhile, the data acquisition system 10 also receives a time-of-flight start signal given by the accelerator at the proton hitting moment (i.e. the pulse generation moment), so that the detector signal and the time-of-flight start signal work under the same clock, and the final time-of-flight information can be given.

[0090] The application further discloses a white light neutron source beam line real-time monitoring method for the white light neutron source beam line real-time monitor.

[0091] In step S1, the low-pressure self-balancing feedback gas flow subsystem performs vacuumization on the aluminum alloy cavity 15 and performs gas washing operation.

[0092] In step S2, the detector signal is input to the data acquisition system 10, the data of the detector signal collected in the full waveform mode is recorded by a rear-end computer and can also be analyzed online, and the real neutron-induced fission signal is selected through coincidence, so that the background interference is eliminated.

[0093] In step S1, the gas washing operation includes the following steps.

[0094] In step S1.1, first pass: the gas inlet valve 4 and the first needle valve 3 are closed, the gas outlet valve 7 and the second needle valve 6 of the gas flow outlet 22 are opened, the vacuum pump 8 is started to pump gas, the internal gas pressure of the aluminum alloy cavity 15 is pumped to 100 Pa, the gas outlet valve 7 and the second needle valve 6 are closed, the gas inlet valve 4 and the first needle valve 3 are opened to provide working gas, until the internal gas pressure of the aluminum alloy cavity 15 reaches about 1500 Pa, the gas inlet valve 4 and the first needle valve 3 are closed, and the gas outlet valve 7 and the second needle valve 6 are opened, and the vacuum pump 8 is started to pump gas, so that the internal gas pressure of the aluminum alloy cavity 15 is pumped to 100 Pa.

[0095] Step S1.2, second pass: close the outlet valve 7 and the second needle valve 6; open the inlet valve 4 and the first needle valve 3 to provide working gas until the internal air pressure of the aluminum alloy cavity 15 reaches about 1500 Pa, close the inlet valve 4 and the first needle valve 3, open the outlet valve 7 and the second needle valve 6, start pumping with the vacuum pump 8, and pump the internal air pressure of the aluminum alloy cavity 15 to 100 Pa;

[0096] Step S1.3, third pass: close the outlet valve 7 and the second needle valve 6; open the inlet valve 4 and the first needle valve 3 to provide working gas until the internal air pressure of the aluminum alloy cavity 15 reaches about 2000 Pa, close the inlet valve 4 and keep the first needle valve 3 open, open the outlet valve 7, slowly open the second needle valve 6 until the internal air pressure of the aluminum alloy cavity 15 decreases to about 820 Pa, close the second needle valve 6, and then adjust the second needle valve 6 (open the second needle valve 6 slightly) until the internal air pressure of the aluminum alloy cavity 15 slowly and stably decreases, close the first needle valve 3, and then adjust the first needle valve 3 (open the first needle valve 3 slightly) and fully open the inlet valve 4; adjust the second needle valve 6 to stabilize the internal air pressure of the aluminum alloy cavity 15 at about the set working air pressure, and at this time the combined parallel-plate avalanche detector subsystem reaches the normal working state;

[0097] In step S2,

[0098] The working voltage of the combined parallel-plate avalanche detector subsystem is generally adjusted to within +600 V, and specific fine tuning is required. The working voltage power supply is a commercial power supply, and ISEG with good voltage stability is generally selected. The voltage value can be tested by pre-installing Am241, which has an energy of 5.4 MeV, to estimate the corresponding different voltages of the reaction charged particle energy and ensure that the output signals of each unit are greater than the threshold value to effectively distinguish. After the detector signal output is connected to the fast amplifier 9, the signal is amplified and shaped and directly connected to the back-end data acquisition system 10. The frequency of the data acquisition system 10 is preferably greater than 1 GHz, which can more effectively collect data because the time response of the detector is very fast, usually below ns.

[0099] The two time signals of the output of each group of the first to fourth target units are made to coincide. If the two time signals arrive at the same time, it is determined to be a normal signal, and one of the time signals is given as a time-of-flight stop signal. If multiple signals are generated at the same time in the group, it is considered to be multiple events. Both must form a complete time-of-flight event with the time-of-flight start signal (that is, the accelerator pickup signal). If there is no coincident signal, it is determined that there is no effective event in this period. If all the outputs of each group produce signals at the same time, it is determined that the combined parallel-plate avalanche detector subsystem is on fire, and the gas washing operation of steps S1.1 to S1.3 is repeated.

[0100] The time-of-flight and neutron energy relationship can be calculated according to Formula 1, and after the energy spectrum is obtained, Formula 4 is referred to

[0101] A=N x σ x Φ x η Formula (4)

[0102] Wherein A is the number of events of each energy partition, N is the number of target nuclei, σ is the standard reaction cross section, Φ is the neutron fluence, and η is the detection efficiency. Among them, the neutron fluence is to be measured, and the others can be obtained through experiment or simulation or table lookup, so as to obtain the final neutron energy spectrum and fluence.

[0103] After normal operation, a sufficient number of nuclear reaction events are accumulated, and considering that the total number of channels is 10000000, 100 events are generated per second per unit, and it takes more than 1 day to complete the energy spectrum test.

[0104] For the 5th group, the time lead is taken as a reference and is not processed. The position output is given according to Formulas 2 and 3, and the event generation position is finally obtained to obtain the profile beam spot information.

[0105] After step S1.3, airtightness measurement is also needed, and the specific steps are: closing the inlet valve 4, using the vacuum pump 8 to pump, closing the outlet valve 7 when the internal pressure of the aluminum alloy cavity 15 is reduced to about 100 Pa, and then recording the internal pressure value of the aluminum alloy cavity 15 once every set time interval (when the combined parallel plate avalanche detector subsystem has obvious air leakage, it is difficult to reduce the vacuum to below 100 Pa on the one hand; on the other hand, even if the pumping time is increased to make the air pressure reach about 100 Pa, the air pressure will be greater than 300 Pa after 0.5 h).

[0106] The device described in the present application is not limited to the embodiments described in the specific embodiments, and other embodiments can be derived by those skilled in the art according to the technical solutions of the present application, which also belong to the technical innovation range of the present application.

Claims

1. A white light neutron source beamline real-time monitor characterized by: The application relates to a white neutron source beam line real-time monitor The combined parallel-plate avalanche detector subsystem for monitoring the wide-spectrum white neutron beam line of a spallation reaction is also connected with a low-pressure self-balancing feedback flow gas subsystem and a signal support subsystem, and the spallation reaction is obtained by proton targeting generated by an accelerator; The combined parallel-plate avalanche detector subsystem comprises an aluminum alloy cavity (15) and a plurality of target units arranged in the aluminum alloy cavity (15) and used for detecting the wide-spectrum white neutron beam line; The aluminum alloy cavity (15) is in a cylindrical shape, a beam window (12) is arranged at the top center position of the aluminum alloy cavity (15) and used for the wide-spectrum white neutron beam line to enter; the bottom of the aluminum alloy cavity (15) is a cavity panel (19), and a PCB base (18) is arranged on the upper surface of the cavity panel (19) in the aluminum alloy cavity (15); The target units are arranged on the PCB base (18) and located at the bottom center position of the aluminum alloy cavity (15), the wide-spectrum white neutron beam line enters the target units to obtain a detector signal; The lower surface of the cavity panel (19) is provided with a power / signal connector (20) connected with the PCB base (18) and used for transmitting the detector signal to the signal support subsystem, and the signal support subsystem is used for recording, storing and real-time analyzing the detector signal; A flow gas inlet (11) and a flow gas outlet (22) are further arranged on both sides of the aluminum alloy cavity (15) and used for connecting the low-pressure self-balancing feedback flow gas subsystem, and the low-pressure self-balancing feedback flow gas subsystem is used for providing a low-pressure gas environment containing working gas in the aluminum alloy cavity (15); The target units are 5 groups and are arranged in parallel on the PCB base (18) through target-pole stand columns (13); a position collection strip (14) is further arranged at the top end of the target-pole stand column (13) and used for measuring fragment position information; a fragment isolation target is further arranged at the top end of the target-pole stand column (13) and located above and parallel to the target units and used for isolating fission fragments from flying to adjacent unit collection poles and reducing background noise.

2. A real-time monitor for a white source beam line as defined in claim 1, characterized in that: Each group of the target units comprises a thin target (17) at the center position and collection poles (16) located on both sides of the thin target (17); an Au film (21) is further arranged between the thin target (17) and the collection poles (16), the thickness of the Au film (21) is 10 micrometers, the collection poles (16) and the Au film (21) are parallel to the thin target (17), and the spacing between the two collection poles (16) is 2 millimeters.

3. The white neutron source beam line real-time monitor according to claim 2, wherein: The surfaces of the thin target (17) on both sides are plated with target material, and the bottom lining of the thin target (17) is a surface plated metal MYLAR film or metal thin film with a thickness less than 2 micrometers. The target unit is divided into first target unit, second target unit, third target unit, fourth target unit and fifth target unit from top to bottom, and the fifth target unit is close to the PCB base (18); The target material on the thin target (17) of the first target unit is 6Li, and the surface density of the target material is less than 10 micrograms per unit area; The target material on the thin target (17) of the second target unit is 10B, and the surface density of the target material is less than 10 micrograms per unit area; The target material on the thin target (17) of the third target unit is 235U, and the surface density of the target material is less than 100 micrograms per unit area; The target material on the thin target (17) of the fourth target unit is 238U, and the surface density of the target material is less than 100 micrograms per unit area; The target material on the thin target (17) of the fifth target unit is 235U, and the surface density of the target material is less than 100 micrograms per unit area; The collecting electrode (16) of each target unit outputs a signal to the panel through an RC circuit, and the first target unit, the second target unit, the third target unit and the fourth target unit each have one working voltage input and two time signal outputs; The thin target (17) of the fifth target unit has a position resolution function and is composed of two groups of strip collecting electrodes perpendicular to each other, has one working voltage input and five signal outputs, respectively corresponding to one time signal and four position signals.

4. The real-time monitor of the white light neutron source beamline according to claim 3, characterized in that: The low-pressure self-balancing feedback flow gas system is divided into two parts and connected to the first part includes a first needle valve (3), an inlet valve (4) and a gas cylinder (5) connected in series through pipelines, the first needle valve (3) is connected to the flow gas inlet (11); the second part includes a second needle valve (6), an outlet valve (7) and a vacuum pump (8) connected in series through pipelines, the second needle valve (6) is connected to the flow gas outlet (22); further comprising an automatic pressure control instrument (1), the automatic pressure control instrument (1) is used for controlling the first needle valve (3) and the second needle valve (6); the working gas provided by the gas cylinder (5) is isobutane / full fluoropropane; The automatic pressure control instrument (1) is also connected with a pressure sensor for monitoring the working gas pressure inside the aluminum alloy cavity (15); according to the difference between the gas pressure data fed back by the pressure sensor and the set value, the automatic pressure control instrument (1) controls the opening degree of the first needle valve (3) and the second needle valve (6) in real time to ensure the stability of the working gas pressure; the vacuum pump (8) and the combined parallel plate avalanche detector subsystem are electronically insulated.

5. A white source beamline real-time monitor according to claim 4, characterized in that: The signal support subsystem comprises a high-low voltage power supply, a fast amplifier (9) and a data acquisition system (10) connected to the fast amplifier (9), the fast amplifier (9) is connected to the power / signal connector (20) for amplifying the detector signal and transmitting it to the data acquisition system (10), the data acquisition system (10) is used to record, store and analyze the detector signal in real time, and the high-low voltage power supply is used to provide power for the fast amplifier (9) and the data acquisition system (10); the data acquisition system (10) also receives the time-of-flight start signal given by the accelerator when the protons are targeted, ensures that the detector signal and the time-of-flight start signal work under the same clock, and thus gives the final time-of-flight information.

6. A white light neutron source beamline real-time monitoring method for the white light neutron source beamline real-time monitor of claim 5, comprising the following steps: Step S1, the low-pressure self-balancing feedback flow gas subsystem evacuates the aluminum alloy cavity (15), and performs a gas washing operation; Step S2, the detector signal is input into the data acquisition system (10), the data of the detector signal collected by the full waveform is recorded by a backend computer, and the real neutron-induced fission signal is selected by coincidence, so that the background interference is eliminated.

7. The white light neutron source beamline real-time monitoring method of claim 6, characterized in that: In the step S1, the gas washing operation comprises the following steps: Step S1.1, first pass: close the gas inlet valve (4) and the first needle valve (3), open the gas outlet valve (7) and the second needle valve (6) of the gas outlet (22), start pumping with the vacuum pump (8), and pump the internal gas pressure of the aluminum alloy cavity (15) to 100 Pa, close the gas outlet valve (7) and the second needle valve (6); open the gas inlet valve (4) and the first needle valve (3) to provide working gas, until the internal gas pressure of the aluminum alloy cavity (15) reaches 1500 Pa, close the gas inlet valve (4) and the first needle valve (3), open the gas outlet valve (7) and the second needle valve (6), and start pumping with the vacuum pump (8) to pump the internal gas pressure of the aluminum alloy cavity (15) to 100 Pa; Step S1.2, second pass: close the gas outlet valve (7) and the second needle valve (6); open the gas inlet valve (4) and the first needle valve (3) to provide working gas, until the internal gas pressure of the aluminum alloy cavity (15) reaches 1500 Pa, close the gas inlet valve (4) and the first needle valve (3), open the gas outlet valve (7) and the second needle valve (6), and start pumping with the vacuum pump (8) to pump the internal gas pressure of the aluminum alloy cavity (15) to 100 Pa; Step S1.3, the third time: close the outlet valve (7) and the second needle valve (6); open the inlet valve (4) and the first needle valve (3), provide working gas until the internal gas pressure of the aluminum alloy cavity (15) reaches 2000Pa, close the inlet valve (4) and keep the first needle valve (3) open, open the outlet valve (7), slowly open the second needle valve (6) until the internal gas pressure of the aluminum alloy cavity (15) decreases to 820Pa, close the second needle valve (6), and then adjust the second needle valve (6) until the internal gas pressure of the aluminum alloy cavity (15) slowly decreases, close the first needle valve (3), and then adjust the first needle valve (3), fully open the inlet valve (4); adjust the second needle valve (6) to stabilize the internal gas pressure of the aluminum alloy cavity (15) at the set working gas pressure, at which time the combined parallel-plate avalanche detector subsystem reaches a normal working state; In the step S2, The working voltage of the combined parallel-plate avalanche detector subsystem is adjusted to within +600V, the detector signal output is connected to the fast amplifier (9), and after amplification and shaping, it is directly connected to the data acquisition system (10) in the back end; the frequency of the data acquisition system (10) is greater than 1GHz; The two time signals of the output of each group of the first to fourth target units are coincided, if the two time signals arrive at the same time, it is judged as a normal signal, and one of the time signals is given as a time-of-flight stop signal; if multiple signals are generated at the same time in this group, it is considered as multiple events; all of them must form a complete time-of-flight event with the time-of-flight start signal; if there is no coincident signal, it is judged as no valid event in this period; if all outputs of each group produce signals at the same time, it is determined that the combined parallel-plate avalanche detector subsystem is on fire, and the gas washing operation of the steps S1.1 to S1.3 is repeated.

8. A method of real-time monitoring of a beamline of a white source of neutrons according to claim 7, characterized in that, in After the step S1.3, gas tightness measurement is also needed, the specific steps are: close the inlet valve (4), use the vacuum pump (8) to pump, when the internal gas pressure of the aluminum alloy cavity (15) decreases to 100Pa, close the outlet valve (7), then record the internal gas pressure value of the aluminum alloy cavity (15) at a certain set time interval.

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