Method for measuring (n, alpha) reaction angle differential section

Abstract

The invention discloses a method for measuring a (n, alpha) reaction angle differential cross section, and belongs to the technical field of nuclear data measurement. Anode pulse rising time and anode amplitude are obtained through measurement of a screen grid ionization chamber and a gas sample, the projection length, parallel to the neutron incidence direction, of a nuclear reaction event track is obtained through the anode pulse rising time, and one projection length corresponds to two alpha particle emergence angles; the events with the same projection length and different alpha particle emergent angles can be distinguished according to different anode amplitudes, so that according to the anode amplitude-anode pulse rise time two-dimensional spectrum, the events with different alpha particle emergent angles are divided through the V-shaped event area on the two-dimensional spectrum to obtain the number of events; and the to-be-measured reaction angle differential cross section can be obtained by combining the to-be-measured reaction nuclear number and the corresponding neutron flux. The device can be used for measuring the angle differential cross section of (n, alpha) reaction, and has the characteristics that the number of nucleuses of a sample to be measured is large, the detection efficiency is high, and the device is not limited by the placement angle of a detector.

Description

Technical Field

[0001] The present invention belongs to the technical field of nuclear data measurement, and particularly relates to a method for measuring ( n , α ) The method of reaction angle differential cross section. Background Art

[0002] Angular differential cross sections are one of the most important types of nuclear data. The detailed information on nuclear reaction mechanisms they provide will help in the evaluation of nuclear data and the study of nuclear reaction theory. n , α ) reaction is one of the important types of neutron nuclear reactions. In the field of nuclear energy applications, ( n , α ) reaction is a neutron absorption reaction, and the accuracy of the cross-sectional data will directly affect the accuracy of the reactor core physical design. α Particles can also cause helium embrittlement of materials. n , α ) The method for measuring the reaction angle differential cross section is to place a detector at the angle to be measured to detect the emitted charged particles. However, this method has low detection efficiency and can only obtain the results at the angle where the detector is located. Summary of the invention

[0003] In order to overcome the existing n , α ) reaction angle differential cross section measurement has low detection efficiency, small solid angle coverage, and small number of nuclei to be measured. The present invention proposes a method for measuring ( n , α ) The method of reaction angle differential cross section.

[0004] The basic principle of the method proposed in the present invention is that the anode pulse rise time and anode amplitude can be measured by using a screen grid ionization chamber in the experiment, wherein the anode pulse rise time can be used to obtain the projection length of the nuclear reaction event track parallel to the neutron incident direction, and one projection length corresponds to two α The particle emission angle; the difference in anode amplitude can distinguish α The particle emission angle is different, so the anode pulse rise time and anode amplitude can be uniquely determined. α Particle emission angle. After determining the number of reaction nuclei to be measured and the corresponding neutron flux, the angular differential cross section of the reaction can be obtained.

[0005] The details are as follows: When conducting experiments with gas samples, the charged particles emitted from nuclear reactions and the residual nuclei will deposit their energies in the sensitive volume of the gridded ionization chamber, thus contributing to the signal amplitude. However, due to the existence of the PHD (Pulse Height Defect) effect, the energy of the heavily charged particles with a higher ionization density cannot be fully detected. Therefore, the amplitude of the anode signal reflects the total energy of the two, but at the same time, this undetected part needs to be deducted, as shown in Equation (1): (1) In Equation (1), A a is the anode amplitude, G a is a constant related to electronics, E α is the energy of the α particles emitted from the nuclear reaction, E recoil is the energy of the residual nucleus emitted from the nuclear reaction, Δ E PHD is the energy that cannot be detected due to the PHD effect. As the α particle emission angle varies, the energy of the residual nucleus is different, and the undetected energy is also different. The basic rule is that the greater the energy of the residual nucleus, the greater the undetected energy, and the lower the anode amplitude of this event.

[0006] For events with different α particle emission angles, in addition to the different anode amplitudes, there are also significant differences in their track lengths. When processing the original waveform, the rise time of the anode pulse can be extracted. The rise time of the anode pulse reflects the projection length of the event track in the direction parallel to the neutron incident direction. The rise time of the anode pulse is determined by Equation (2): (2) In Equation (2), T r is the rise time of the anode pulse, l e is the projection length of the electron group in the direction parallel to the electric field (generated by the ionization of charged particles), v g is the electron drift rate when the electron passes through the grid, t ga is the drift time of the electron between the grid and the anode.

[0007] From Equation (2), it can be seen that on the premise of knowing v g and t ga , it is possible to pass Tr Calculated l e . Therefore, when the electron diffusion effect of the working gas is weak, the projection length of the electron cluster parallel to the electric field direction l e is equal to the projection length of the nuclear reaction event track parallel to the electric field direction l . In formula (2), l e and the relationship between α the emission angle of the particle in the nuclear reaction event is as shown in Figure 2 (a). Among them, l α is the range of the emitted α particle, θ α is the emission angle of the emitted α particle, l recoil is the range of the emitted residual nucleus, θ recoil is the recoil angle of the emitted residual nucleus. When the neutron energy is determined, for any one θ α , can be uniquely calculated through nuclear reaction kinematics θ recoil and the energies of the emitted α particle and the residual nucleus, and can be calculated through the energy loss law of charged particles in the gas l α and l recoil .

[0008] Figure 2 (b) shows the θ α of nuclear reaction events with different l e . It can be seen that as θ α increases, l e shows a trend of first decreasing and then increasing, and for a certain range of l e there will be two θ α corresponding to it. Therefore, in order to uniquely determine θ α , it is necessary to distinguish different l e under the same θ αnuclear reaction events. They can be distinguished by the anode amplitude. With the rise time of the anode pulse as the ordinate and the anode amplitude as the abscissa, a two-dimensional spectrum of anode amplitude-anode pulse rise time can be made. Figure 3 This is a typical two-dimensional spectrum of anode amplitude-anode pulse rise time. The V-shaped event area is framed by red lines, and the Figure 2 5 different θ α The position of the nuclear reaction event on the two-dimensional spectrum. Figure 3 It can be seen that the anode pulse rise time provides different l e The ability to distinguish nuclear reaction events, while the difference in anode amplitude can distinguish l e Same but θ α Different events (e.g. Figure 2 Using this information, we can infer the nuclear reaction events ② and ④ in the equation (3). α Particle emission angle: (3) Next, we will explain how to determine v g and t ga . v g and t ga For an experiment, it is almost unchanged, so in order to determine v g and t ga , you can select Figure 3 There are two special positions in the V-shape, namely the upper left corner α Particles 180° out and upper right corner α The particle's 0° exit position (corresponding to Figure 2 The nuclear reaction events ① and ⑤ in these two locations T r Available from Figure 3 obtained in l e It can be obtained based on the energy loss law of charged particles in the gas and the kinematics of nuclear reactions. According to formula (2), the equations of the two positions can be solved together to obtain v g and t ga .

[0009] Finally, the systematic errors caused by the range straggling of charged particles and the diffusion during the electron drift process are discussed. Range straggling occurs because charged particles move in a gas medium and are eventually stopped. Therefore, charged particles may change their directions violently due to elastic collisions with gas atoms. However, this form of interaction generally occurs at the end of the track, so the interference caused is relatively small. This interference can be calculated using the Geant4 program package or SRIM software. The diffusion during the electron drift process needs to be considered because electron clusters are generated on the track of charged particles and need to drift to the grid to generate an anode signal. The diffusion in different gases is different, so a gas with a smaller diffusion effect needs to be selected. The influence of the diffusion effect can be obtained using the Garfield++ program package.

[0010] Based on the above principles, a method for measuring the n , α ) reaction angle differential cross section proposed by the present invention includes the following steps: 1) Determine the nuclear reaction to be measured, select a gas sample containing the nucleus to be measured, and design a working gas containing the gas sample. It is required that the working gas has a certain PHD effect during the experiment in the screen-grid ionization chamber, so that the event region of the nuclear reaction event to be measured presents a V shape in the two-dimensional spectrum of anode amplitude - anode pulse rise time.

[0011] 2) Fill the working gas containing the gas sample to be measured in the screen-grid ionization chamber for an in-beam experiment, and collect the cathode signal, anode signal, and fission signal of the screen-grid ionization chamber.

[0012] 3) Analyze the collected anode signals to obtain the pulse rise time and anode amplitude of each anode signal, and make a two-dimensional spectrum of anode amplitude - anode pulse rise time.

[0013] 4) On the two-dimensional spectrum of anode amplitude - anode pulse rise time, the event region to be measured presents as a V-shaped region. This V-shaped region is all the event regions to be measured because α the emission angles of the particles θ α are different, resulting in different events at different positions in the V-shaped region. Therefore, at this time, different θ α events need to be distinguished on this V-shaped region, that is, determine the angle binning method, divide the V-shaped region into multiple bins, and a certain bin is the event region corresponding to a certain angle interval.

[0014] 5) After determining the angle binning method, calculate the anode pulse rise times corresponding to the upper and lower boundaries of each bin using Equation (2) T r , thereby completing the binning.

[0015] 6) Count the number of events in each bin, correct for the interference caused by background and / or low-energy neutrons according to the actual experimental conditions, and calculate α the detection efficiency of the particles.

[0016] 7) Determine the neutron flux and the number of nuclei in the experiment. The method can be the method for determining the neutron flux and the number of nuclei in a gas sample established in the reference (Y. Hu, Y. Gledenov, Z. Cui, et al. Eur. Phys. J. A, 60, 51(2024)), and calculate the angular differential cross section.

[0017] Furthermore, the working gas described in step 1) above is mainly composed of an inert gas with little interference to the nuclear reaction to be measured, plus the gas sample containing the nucleus to be measured. For example, in an embodiment of the present invention, the nuclear reaction to be measured is 16 O( n , α ) 13 C reaction. The gas sample containing the nucleus to be measured is selected as CO2, and the working gas is 3 atm 96% Kr + 4% CO2.

[0018] After the working gas is filled into the screen grid ionization chamber, evaluate whether the electron drift rate and the PHD effect meet the requirements. Generally, it is required that the electron drift rate is in an appropriate range. In the embodiments of the present invention, it is preferably 0.6~0.8 cm / μs, neither too slow to avoid electron recombination during drift, nor too fast so that the anode pulse rise time is too short. It is necessary to have a certain PHD effect, which can make the event region of the nuclear reaction event to be measured present a V-shaped region in the two-dimensional spectrum of anode amplitude - anode pulse rise time. Generally speaking, having some electronegative gases (such as carbon dioxide, tetrafluoromethane, etc.) in the working gas can make the working gas have a PHD effect.

[0019] As the α emission angle θ α of the emitted T r particles increases from 0° to 180°, the anode pulse rise time T r will first decrease and then increase. For the V-shaped event region on the two-dimensional spectrum of anode amplitude - anode pulse rise time, it is from the upper right to the middle and then to the upper left. Preferably, in step 4), use θ α binning in the V-shaped event region, starting from the upper right corner T rSmaller positions are grouped into a bin, such as Figure 3 shown.

[0020] In step 5), as described above, use the upper left corner of the V-shaped area α Particles 180° out and upper right corner α The two positions where the particle exits at 0° are solved by solving the equations together. v g and t ga .because v g and t ga For an experiment, it is almost unchanged, so the anode pulse rise time T r It reflects the projection length of the event track parallel to the neutron incident direction.

[0021] Getting parameters v g and t ga Then, for each event in the V-shaped area, according to formula (2), T r Calculate the corresponding l e , and then according to the anode amplitude and formula (3), the emission of the event can be inferred α Particle emission angle θ α Since a bin is the event area corresponding to a certain angle interval, the T r It can be inferred that θ α , so that according to the event T r Divide it into the corresponding bins.

[0022] Furthermore, the interference caused by the background in step 6) can be obtained by the following method: using a trapezoid to frame the V-shaped area, and obtaining the ratio of the background events in the trapezoidal area to the total events in the trapezoidal area through simulation; obtaining the background events per unit area in the trapezoidal area by counting the total number of events in the trapezoidal area multiplied by the ratio and divided by the area of the trapezoidal area; and then multiplying the background events per unit area by the area of each bin to calculate the number of background events in each bin. At the same time, a liquid scintillator detector is used to monitor the neutron energy spectrum, and the interference of low-energy neutrons is determined through simulation, and the low-energy neutron interference is corrected in combination with the neutron energy spectrum.

[0023] Further, in step 7), using the start time difference between the anode signal and the cathode signal, the distance range from the end of the nuclear reaction event track to the grid is determined, and the ratio of the events occurring in this distance range to all the events occurring in the main reaction area is determined by simulation, and this ratio is used as α the detection efficiency of the particle.

[0024] Figure 4 is a typical experimental device of the present invention. It is marked with 238 the U3O8 sample for determining the neutron flux. This sample is placed on the shielding electrode on the side of the screen grid ionization chamber close to the neutron source because 238 the reaction cross section of U( n , f ) is the standard cross section at 0.5 MeV - 200 MeV, so the neutron flux is measured through 238 the U( n , f ) reaction. Figure 4 It also marks the main reaction area. The number of nuclei in the experiment is calculated by monitoring the pressure and temperature of the gas during the experiment and combining with the volume of the main reaction area. Thus, the angular differential cross section of the reaction to be measured can be obtained, as shown in Equation (4).

[0025] (4) In Equation (4), is the angular differential cross section, θ is the middle value of the angular range of this bin, N event ( θ ) is the number of events in this bin, Φ MRV is the average neutron flux in the main reaction area. The method can refer to the literature (Y. Hu, Y. Gledenov, Z. Cui, et al. Eur. Phys. J. A, 60, 51(2024)), N sample is the number of nuclei, and ΔΩ is the solid angle size subtended by the angular range of this bin.

[0026] The present invention uses a screen grid ionization chamber and a gas sample to measure the anode pulse rise time and anode amplitude of the ( n , α ) reaction. The projection length of the nuclear reaction event track parallel to the neutron incident direction is obtained through the anode pulse rise time. One projection length corresponds to two α particle emission angles; and the difference in anode amplitude can distinguish events with the same projection length but α different particle emission angles. Therefore, according to the anode pulse rise time and anode amplitude, αParticle emission angle. By dividing events with different particle emission angles in the V-shaped event region of the two-dimensional spectrum of anode amplitude - anode pulse rise time, the number of events is obtained. Combining the number of reaction nuclei to be measured and the corresponding neutron flux, the differential cross-section of the reaction angle to be measured is obtained. The method of the present invention can be used to measure the differential cross-section of the reaction of ( α , n , α ) with the characteristics of a large number of sample nuclei to be measured, high detection efficiency, and no limitation on the placement angle of the detector. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1 is the anode signal waveform measured by the typical screen-grid ionization chamber of the present invention, where the anode pulse rise time is marked T r and the start time of the signal.

[0028] Figure 2 In (a), it shows the projection length of the nuclear reaction event track parallel to the electric field direction l e and α the emission angle of the particle θ α between; (b) shows the projection length of the nuclear reaction event track parallel to the electric field direction corresponding to the emission angles of different α particles.

[0029] Figure 3 is the typical two-dimensional spectrum of anode amplitude - anode pulse rise time, where the positions of the nuclear reaction events of 5 different Figure 2 in (b) α particle emission angles θ α on this two-dimensional spectrum are marked.

[0030] Figure 4 is the structural schematic diagram of the experimental device of the present invention.

[0031] Figure 5 is the fission cathode spectrum of the 10.45 MeV energy point experiment measured in the embodiment of the present invention and the simulated fission cathode spectrum.

[0032] Figure 6 is the neutron energy spectrum measured by using the EJ-309 liquid scintillation detector in the embodiment of the present invention.

[0033] Figure 7 is the differential cross-section of the 10.45 MeV energy point measured in the embodiment of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0034] The technical solutions of the present invention will be further described in detail below in conjunction with the drawings and specific embodiments.

[0035] Oxygen is the most abundant element in the earth's crust and also the most abundant element in the human body. Accurately knowing 16 O( n , α ) 13 C reaction cross-section information is of great significance in the field of nuclear engineering. Contemporary power reactors generally use uranium dioxide as nuclear fuel. Accurate 16 O( n , α ) 13 C reaction cross-section will be beneficial for core physics design and evaluating α the damage caused by particles to materials. This reaction also has important applications in the fields of radiobiology, astrophysics, etc. Since it is relatively difficult to carry out nuclear reaction experiments and there is less experimental data, theoretical calculations and data evaluation for neutron nuclear reactions are particularly important. For 16 light nuclei such as O, R-matrix analysis is mostly used theoretically at present, and R-matrix analysis is highly dependent on high-quality experimental data, especially angular differential cross-section data.

[0036] According to the method for measuring the angular differential cross-section of the ( n , α ) reaction proposed by the present invention, in this embodiment, a multi-wire proportional chamber and a gas sample are used to measure the 16 O( n , α 0) 13 C reaction angular differential cross-section at a neutron energy of 10.45 MeV. The specific steps are as follows: 1) Determine that the nuclear reaction to be measured is 16 O( n , α 0) 13 C reaction. The gas sample containing the nucleus to be measured is selected as CO2, and the working gas is 3 atm 96% Kr + 4% CO2, which meets the requirement of the electron drift rate in an appropriate range. At the same time, CO2 itself has a certain PHD effect, so that the event region of the nuclear reaction event to be measured shows a V shape in the two-dimensional spectrum of anode amplitude - anode pulse rise time.

[0037] 2) Fill the above working gas in the multi-wire proportional chamber for in-beam experiments. The experiment is carried out on the HI-13 tandem accelerator. The experimental device is as Figure 4 shown. The cathode signal, anode signal and fission signal of the multi-wire proportional chamber are obtained in the experiment and collected.

[0038] 3) Analyze the collected anode signals to obtain the pulse rise time and anode amplitude of each anode signal, and make a two-dimensional spectrum of anode amplitude - anode pulse rise time, as Figure 3as shown

[0039] 4) On the two-dimensional spectrum of anode amplitude - anode pulse rise time as shown Figure 3 shown, the event area to be measured presents a V shape, and this V shape has been outlined with a red frame line. All the events to be measured are included in the V-shaped area because α the emission angle of the particles θ α is different, resulting in different events at different positions in the V-shaped area. Therefore, at this time, different θ α events need to be distinguished on this V-shaped area, that is, to determine the binning method of the angle. Figure 3 shows the schematic of the event area corresponding to a certain angle range (i.e., a certain bin). This bin is bounded by two black lines above and below as the upper and lower boundaries, and the red line outlining the "V-shaped" event area to be measured is used as the left and right boundaries.

[0040] 5) After determining the binning method of the angle, use Equation (2) to calculate the anode pulse rise time corresponding to the upper and lower boundaries of each bin T r . Among them l e , v g and t ga are determined using the method described after Equation (3).

[0041] As the emission α the emission angle of the particles θ α increases from 0° to 180°, T r it will first decrease and then increase. For the V-shaped event area, it is from the upper right to the middle and then to the upper left. Using T r to bin on the V-shaped event area, starting from the position in the upper right corner θ α with an angle of 0° and binning in the order from the upper right to the middle and then to the upper left. The position in the middle of the V-shaped event area T r with a relatively small value is assigned to one bin. Figure 3 shows the schematic of the event area corresponding to a certain angle range (i.e., a certain bin), and the bins for the remaining angle ranges are given according to this method.

[0042] 6) Count the number of events in each bin and correct for the background and interference caused by low-energy neutrons according to the actual experimental conditions. After binning, the number of events in each bin can be obtained. Next, correct for the background according to the actual experimental conditions. In this embodiment, the main interference to the events to be measured is the ( n , α ) events of Kr (referred to as background events). First, give a trapezoidal region that includes this V-shaped region, as shown by the region outlined by the dark green line in Figure 3 . First, obtain the proportion of the ( n , α ) events of Kr in this trapezoidal region through simulation. The simulation method can be found in the literature (Y. Hu, H. Jiang, Z. Cui et al. Nucl. Sci. Tech. 32(8), 062001(2021), Y.Hu, Y. Gledenov, Z. Cui, et al. Eur. Phys. J. A, 60,51(2024)). The number of background events in the trapezoidal region can be obtained by counting the total number of events in the trapezoidal region and multiplying by the above proportion. Since the background events are almost uniform in this trapezoidal region, the number of background events per unit area in this trapezoidal region can be obtained by counting the number of background events in this trapezoidal region and dividing by the area of this trapezoidal region. Next, multiply the number of background events per unit area of this trapezoidal region by the area of each bin in the two-dimensional spectrum of anode amplitude - anode pulse rise time to calculate the number of background events in each bin. In the experiment, an EJ-309 liquid scintillator detector is used to monitor the neutron energy spectrum, and the interference of low-energy neutrons is corrected in combination with the neutron energy spectrum. The interference of low-energy neutrons is also determined by simulation. The method can be found in the literature (Y. Hu, H.Jiang, Z. Cui et al. Nucl. Sci. Tech. 32(8), 062001(2021), Y. Hu, Y. Gledenov,Z. Cui, et al. Eur. Phys. J. A, 60,51(2024)). In this example, the interference of low-energy neutrons is extremely small. For simplicity, the interference of low-energy neutrons in each bin is considered uniformly.

[0043] 7) Next, determine the α particle detection efficiency. To reduce the impact caused by charged particles hitting the plate and being unable to deposit all their energy in the V-shaped region, only a part of the region where the main reaction area (see Figure 4 ) is far from the plate is selected for the reaction to be measured. Specifically, use the start time difference between the anode signal and the cathode signal. The so-called start time is the time when the signal starts to rise, with Figure 1Take the anode signal of as an example, the start time has been marked in the figure. The reason for their time difference is that the event occurs between the cathode and the grid, so the cathode signal is generated immediately after the event occurs, but the anode signal starts to be generated when the electron group ionized by the event drifts to the grid, so their start time difference is proportional to the distance from the end of the nuclear reaction event track to the grid. In this example, we selected events with a time difference between 1000 ns and 5000 ns, corresponding to the distance from the end of the nuclear reaction event track to the grid from 7.8 mm to 39.1 mm. The ratio of events occurring between 7.8 mm and 39.1 mm to all events occurring in the main reaction zone was determined using simulations (Y. Hu, H. Jiang, Z. Cui et al. Nucl. Sci. Tech. 32(8), 062001(2021), Y. Hu, Y. Gledenov, Z. Cui, et al. Eur. Phys. J. A, 60, 51(2024)). α Particle detection efficiency.

[0044] 8) Determine the neutron flux and nucleus number in the experiment. The method can refer to the method for determining the neutron flux and nucleus number in gas samples established in the literature (Y. Hu, Y. Gledenov, Z.Cui, et al. Eur. Phys. J. A, 60, 51(2024)). The experiment uses a shielding electrode placed on the side close to the neutron source. 238 U3O8 samples monitor neutron flux. Figure 5 Given the measured 238 U( n , f ) fission cathode spectrum and simulated fission cathode spectrum. The simulation is implemented by the Geant4 program package and uses realistic experimental conditions as input. It can be seen that the simulation results are in good agreement with the measured results, so they can be used to determine the detection efficiency and obtain the neutron flux. 16 The number of O nuclei was determined by monitoring the pressure and temperature of the gas during the experiment and combining the main reaction zone (see Figure 4 ) volume. A high-precision barometer and thermometer were used in the experiment to ensure the accuracy of the nucleus count. 16 O nuclei will also participate in the reaction, and this part of the nuclei is also taken into account. The specific proportion is given by the simulation. The main reaction area consists of the inner area of the ionization chamber collimated by the neutron collimator and the penumbra area at the edge. Most of the reactions to be measured occur in this area. Determining the neutron flux and the number of nuclei can calculate the angular differential cross section. The measured angular differential cross section of the 10.45 MeV energy point is as follows: Figure 7 shown.

[0045] The above embodiments are not intended to limit the scope of the present invention. Any person skilled in the art can make many possible changes, modifications or optimizations to the technical solution of the present invention by using the methods and technical contents disclosed above without departing from the concept of the present invention. Therefore, any simple transformation, modification and improvement made in accordance with the technical essence of the present invention still fall within the scope of protection of the technical solution of the present invention.

Claims

1. A method for measuring ( n , α ) the differential cross section of the reaction angle, characterized in that It includes the following steps: 1) Select a gas sample containing the nucleus to be measured according to the nuclear reaction to be measured, and design a working gas containing the gas sample, requiring that the working gas has a PHD effect during the experiment in the screen-grid ionization chamber; 2) Fill the working gas into the screen-grid ionization chamber for in-beam experiments, and collect the cathode signal, anode signal and fission signal of the screen-grid ionization chamber; 3) Analyze the collected anode signals, obtain the pulse rise time and anode amplitude of each anode signal, and make a two-dimensional spectrum of anode amplitude - anode pulse rise time; 4) On the two-dimensional spectrum of anode amplitude - anode pulse rise time, the area to be measured for events appears as a V-shaped region. α The emission angle of the particle θ α Differences in result in different events being at different positions in the V-shaped region. Determine the binning method for the angle, divide the V-shaped region into multiple bins, and a certain bin is the event area corresponding to a certain angle interval. 5) Calculate the anode pulse rise times corresponding to the upper and lower boundaries of each bin using Equation (2) T r , thus completing binning; （2） Among them, l e is the projection length of the electron group parallel to the electric field direction, v g is the electron drift rate when the electron passes through the grid, t ga is the drift time of the electron between the grid and the anode; 6) Count the number of events in each bin, correct for the interference caused by background and / or low-energy neutrons according to the actual experimental conditions, and calculate α the detection efficiency of the particles; 7) Determine the neutron flux and the number of nuclei in the experiment, and calculate the angular differential cross section.

2. The method for measuring n , α ) the differential cross section of the reaction angle as claimed in claim 1, characterized in that In step 1), the working gas mainly consists of an inert gas with little interference to the nuclear reaction to be measured, plus the gas sample containing the nucleus to be measured.

3. The method for measuring n , α ) the differential cross section of the reaction angle according to claim 1, characterized in that In step 4), utilize the anode pulse rise time T r Bin on the V-shaped region, starting from the upper right corner θ α Bin in the order from the upper right to the middle and then to the upper left at the position of 0°, and place the smaller position in the middle of the V-shaped region into one bin T r into one bin 4. The method for measuring n , α ) the differential cross section of the reaction angle, characterized in that In step 5), the parameters in formula (2) v g and t ga are obtained by the following method: First, according to the two positions of the 180° emission of particle 1 at the upper left corner of the V-shaped region α and the 0° emission of particle 1 at the upper right corner α the corresponding T r is obtained. Then, according to the energy loss law of charged particles in the gas and nuclear reaction kinematics, the corresponding l e at these two positions are obtained. By solving the equations of formula (2) corresponding to these two positions simultaneously, v g and t ga are obtained; After obtaining the parameters v g and t ga for each event in the V-shaped region, according to Equation (2), through its T r calculate to obtain l e , and then based on the anode amplitude and Equation (3), inversely deduce the emission α emission angle of the particle θ α : （3） In formula (3), θ α is the emission α angle of the emitted particle, l α is the emission α range of the emitted particle, l recoil is the range of the emitted residual nucleus, θ recoil is the recoil angle of the emitted residual nucleus; Then, from each event's T r infer its θ α , and partition it into the corresponding bin.

5. The method for measuring n , α ) the differential cross section of the reaction angle as claimed in claim 1, characterized in that In step 6), the interference caused by the background is obtained by the following method: frame the V-shaped region with a trapezoid, and obtain the proportion of the background events in the trapezoid region to the total events in the trapezoid region through simulation; obtain the background events per unit area in the trapezoid region by multiplying the total number of events in the trapezoid region by this proportion and dividing by the area of the trapezoid region; then multiply the background events per unit area by the area of each bin to calculate the number of background events in each bin.

6. The method for measuring n , α ) the differential cross section of the reaction angle as claimed in claim 1, characterized in that In step 6), a liquid scintillator detector is used to monitor the neutron energy spectrum, and the interference of low-energy neutrons is determined through simulation, and the interference of low-energy neutrons is corrected in combination with the neutron energy spectrum.

7. The method for measuring n , α ) the differential cross section of the reaction angle according to claim 1, characterized in that In step 6), using the starting time difference between the anode signal and the cathode signal, determine the distance range from the end of the nuclear reaction event track to the grid, and by means of simulation, determine the ratio of the events occurring in this distance range to all the events occurring in the main reaction area, and use this ratio as α the detection efficiency of the particle.

8. The method for measuring ( n , α ) the differential cross section of the reaction angle as claimed in claim 1, wherein An U3O8 sample is arranged on the shielding electrode on the side of the screen grid ionization chamber close to the neutron source, and the neutron flux is obtained by monitoring 238 the 238 U( n , f ) reaction 9. The method for measuring n , α ) the differential cross section of the reaction angle as claimed in claim 1, wherein The number of nuclei in step 7) is calculated by monitoring the pressure and temperature of the gas during the experiment and combining with the volume of the main reaction zone.

10. The method for measuring ( n , α ) the differential cross section of the reaction angle according to claim 1, characterized in that In step 7), the angular differential cross section of the reaction to be measured is calculated using Equation (4): （4） In Equation (4), is the differential angular cross section,[[]] θ is the mid-value of the angular interval of a certain bin,[[]] N event ( θ ) is the number of events in this bin, Φ MRV is the average neutron flux in the main reaction area,[[]] N sample is the number of nuclei, and ΔΩ is the solid angle subtended by the angular interval of this bin.[[]]

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