Device and method for measuring absolute yields of long-range alpha particles and tritium in fission nuclear tri-fission

Abstract

The invention relates to a device and a method for measuring absolute yields of long-range alpha particles and tritium in fission nuclear triple splitting, belongs to the technical field of nuclear data measurement, and solves the technical problems of low measurement efficiency and low precision of light charged particles in fission nuclear triple splitting. The measuring device comprises a screen-grid ionization chamber, a cathode, a grid electrode, an anode, a shielding electrode, an aluminum film, a four-component alpha source for scale, and a data acquisition and processing system. The aluminum film covers the sample well containing the fission target material and is used for shielding part of bipartite fission fragments and decay alpha particles. The measurement method comprises the following steps: measuring the dichotomous fission fragments by using the screen-grid ionization chamber under the conditions of no aluminum film and low-pressure working gas, simulating the measurement process of the dichotomous fission fragments, measuring the light charged particles in the three-split transformation by using the screen-grid ionization chamber under the conditions of aluminum film and high-pressure working gas, simulating the measurement process of the light charged particles in the three-split transformation, and simulating the measurement process of the light charged particles in the three-split transformation. And obtaining the absolute yield of long-range alpha particles in the tri-split transformer, and obtaining the absolute yield of tritium in the tri-split transformer.

Description

Technical Field

[0001] The present invention belongs to the technical field of nuclear data measurement, and in particular relates to a device and method for measuring the absolute yield of long-range alpha particles and tritium in the fission of a fission nucleus. Background Art

[0002] The ternary fission phenomenon plays a unique role as a probe in studying the characteristics of the breakpoint in the fission process, because the third split charged particle is emitted simultaneously with the other two binary fission fragments at the breakpoint, and its absolute yield data helps to further understand the fission process.

[0003] In common ternary fission, the measurement method of light charged particles is based on the detector telescope method or the low-pressure ionization chamber method. However, due to the low detection efficiency or lack of particle resolution capability of existing measurement methods, it is impossible to obtain experimental data on the absolute yield of light charged particles (long-range alpha particles and tritium), which are the most common in the ternary fission of fast neutron-induced fission nuclei with a fission velocity above 1MeV. Summary of the Invention

[0004] In order to overcome the shortcomings of low efficiency and low precision in measuring light charged particles in fission nuclei ternary fission, the present invention proposes a device and method for measuring the absolute yield of long-range alpha particles and tritium in fission nuclei ternary fission.

[0005] The technical solution adopted by the present invention to solve the technical problem is:

[0006] A device for measuring the absolute yield of long-range alpha particles and tritium in fission nuclei, comprising a screen grid ionization chamber, a cathode, a grid, an anode, a shielding electrode, an aluminum film, a four-component alpha source for calibration, and a data acquisition and processing system.

[0007] The screen grid ionization chamber is in a closed cylindrical shape, is provided with a sealed door for installing and removing the fission target material, and is filled with working gas, which is a mixed gas of argon and methane.

[0008] The cathode, grid, anode and shield are all rectangular flat plates, the cathode is one piece, the grid, anode and shield are two pieces, the grid is symmetrically distributed relative to the cathode, the anode is symmetrically distributed relative to the cathode, and the shield is symmetrically distributed relative to the cathode. From the inside to the outside, they are the cathode, grid, anode and shield, and the cathode, grid, anode and shield are parallel to each other and installed in the screen ionization chamber.

[0009] The cathode is a rectangular flat plate installed on the center line of the screen ionization chamber. A sample well is set, and the fission target material is placed in the sample well. The aluminum film and the four-component α source for scale are respectively located on both sides of the fission target material.

[0010] The data acquisition and processing system is used to measure a two-dimensional spectrum of cathode signal amplitude vs. anode signal amplitude, and a two-dimensional spectrum of anode signal amplitude vs. anode signal rise time.

[0011] In the above-mentioned measuring device, the aluminum film is located on the cathode plate plane, covering the sample well containing the fission target material, and is used to shield part of the binary fission fragments and decay alpha particles.

[0012] In the above-mentioned measuring device, the thickness of the aluminum film is 30 μm, or 10 μm.

[0013] In the above-mentioned measuring device, the working gas pressure is 0.5 atmospheres, or exceeds 6 atmospheres.

[0014] In the above-mentioned measuring device, the working gas is a 90% Ar+10% CH4 mixed gas at 0.5 atm, or a 90% Ar+10% CH4 mixed gas at 7.0 atm, or a 90% Ar+10% CH4 mixed gas at 7.5 atm.

[0015] The above-mentioned measuring device, the fission target material is 252 Cf, or 235 U, or 239 Pu fissile material.

[0016] A method for measuring the absolute yield of long-range alpha particles and tritium in fission of a fission nucleus comprises the following steps:

[0017] Step 1: Measure binary fission fragments using a screened ionization chamber without an aluminum film and using low-pressure working gas.

[0018] The fission target material is placed in a sample well of a device for measuring the absolute yield of long-range alpha particles and tritium in fission nuclei without placing an aluminum film. The pressure of the working gas is 0.5 atmospheres.

[0019] When the fission target material undergoes binary fission spontaneously or neutron-induced, a data acquisition and processing system is used to collect the anode signal amplitude spectrum when the screen grid ionization chamber measures binary fission fragments.

[0020] Step 2: Simulate the measurement process of binary fission fragments

[0021] The Monte Carlo method was used to simulate the measurement of binary fission fragments emitted by fission nuclei within a screened ionization chamber. The mass, independent yield, and total energy released by the binary fission fragments were calculated using GEF 2020 / 1.1 software. The energy of the binary fission fragments was then calculated based on the conservation of momentum and energy. The anode signal amplitude spectrum of the binary fission fragments measured in a screened ionization chamber was simulated by taking into account the mass, independent yield, energy, and emission angle of the binary fission fragments obtained by discrete sampling of the energy of the binary fission fragments, as well as sample thickness, sample inhomogeneity, and PHD effects.

[0022] The simulated anode signal amplitude spectrum is compared with the anode signal amplitude spectrum measured in step 1. If the two are consistent with each other, the detection efficiency of the screen grid ionization chamber for binary fission fragments can be determined, the subthreshold fraction of binary fission can be corrected, and the total binary fission count rate can be obtained.

[0023] Step 3: Using a screen grid ionization chamber to measure light charged particles in tri-fission under conditions of aluminum film and high-pressure working gas

[0024] Aluminum films of different thicknesses were placed separately, and the pressure of the working gas was adjusted to be over 6 atmospheres.

[0025] When the fission target material undergoes spontaneous or neutron-induced ternary fission, a data acquisition and processing system is used to collect the cathode signal amplitude vs. anode signal amplitude two-dimensional spectrum, the anode signal amplitude vs. anode signal rise time two-dimensional spectrum, and the anode signal amplitude spectrum when the screen grid ionization chamber measures lightly charged particles in the ternary fission.

[0026] Step 4: Simulate the measurement process of light charged particles in tri-fission

[0027] The Monte Carlo method is used to simulate the measurement process of light charged particles in the fission triad of fission nuclei in a screen-grid ionization chamber. The charge number, mass number, energy distribution and exit angle of the light charged particles in the triad fission are sampled. Considering the influence of sample thickness, sample non-uniformity and aluminum film, the deposition energy of these charged particles in the screen-grid ionization chamber is calculated, and the track length, exit angle and deposition energy information of the charged particles are obtained. Based on the above information, the corresponding two-dimensional spectrum of cathode signal amplitude vs. anode signal amplitude, the two-dimensional spectrum of anode signal amplitude vs. anode signal rise time, and the anode signal amplitude spectrum are obtained.

[0028] Step 5: Obtain the absolute yield of long-range alpha particles in tri-fission

[0029] For long-range alpha particles in ternary fission, the event region of the long-range alpha particles is delineated in the two-dimensional spectra of cathode signal amplitude vs. anode signal amplitude obtained by measurement in step 3 and simulation calculation in step 4, respectively, to obtain the corresponding experimentally measured and simulated anode signal amplitude spectra. The two are consistent with each other to determine the detection efficiency of the screen ionization chamber for long-range alpha particles in ternary fission, correct the subthreshold fraction of long-range alpha particles, and obtain the total long-range alpha particle count rate. Divide it by the total binary fission count rate obtained in step 2 to obtain the absolute yield of long-range alpha particles in ternary fission.

[0030] Step 6: Obtain the absolute yield of tritium in tritium fission

[0031] For tritium in ternary fission, the event region of tritium is delineated in the two-dimensional spectra of anode signal amplitude vs. anode signal rise time obtained by measurement in step 3 and simulation calculation in step 4, respectively, to obtain the corresponding experimentally measured and simulated anode signal amplitude spectra. The two are consistent with each other to determine the detection efficiency of the screen ionization chamber for tritium in ternary fission, and the total tritium counting rate is corrected for the subthreshold fraction of tritium and the influence of long-range alpha particles on it to obtain the total tritium counting rate. This is divided by the total binary fission counting rate obtained in step 2 to obtain the absolute yield of tritium in ternary fission.

[0032] The beneficial effects of the present invention are:

[0033] A device for measuring the absolute yield of long-range alpha particles and tritium in fission nuclei ternary fission is based on a screened ionization chamber with a certain particle resolution. By measuring binary fission fragments at low pressure without shielding aluminum film and long-range alpha particles and tritium in ternary fission at high pressure with shielding aluminum film, the device obtains an experimental spectrum of the screened ionization chamber's anode amplitude when measuring binary fission fragments, a two-dimensional experimental spectrum of the screened ionization chamber's cathode signal amplitude versus anode signal amplitude when measuring ternary fission particles, and a two-dimensional experimental spectrum of the anode signal amplitude versus anode signal rise time, as well as an anode signal amplitude spectrum. Combined with high-fidelity simulation, the device then provides the corresponding absolute yield data. The stopping power of alpha particles and tritium in the same working gas varies significantly. These two lightly charged particles with the same energy and angle will have different ranges in the gas, resulting in different rise times and cathode signal amplitudes. The two two-dimensional experimental spectra make it easy to distinguish long-range alpha particles from tritium.

[0034] A device for measuring the absolute yield of long-range alpha particles and tritium in fission tricons of fission nuclei uses a screen grid ionization chamber to measure the absolute yield of long-range alpha particles and tritium in fission tricons of fission nuclei. The device has high detection efficiency and can be applied to the measurement of absolute yield data of long-range alpha particles and tritium in fission tricons of fission nuclei induced by fast neutrons above 1MeV.

[0035] A method for measuring the absolute yield of long-range alpha particles and tritium in fission nuclei trion fission can significantly reduce the uncertainty of the measurement results and obtain more accurate absolute yield data under the conditions of the same fission target material and neutron source.

[0036] The invention discloses a method for measuring the absolute yield of long-range alpha particles and tritium in the fission of fission nuclei. The method uses Monte Carlo simulation to simulate the measurement process of a screen grid ionization chamber. The simulation method is simple and easy to implement. BRIEF DESCRIPTION OF THE DRAWINGS

[0037] Figure 1 It is a schematic diagram of the principle of the measuring device of the present invention;

[0038] Figure 2 It is a flow chart of the high-fidelity simulation process;

[0039] Figure 3 The screen grid ionization chamber measurement obtained by experimental measurement and simulation calculation 252 Anode signal amplitude spectrum during Cf binary fission fragmentation;

[0040] Figure 4 The screen grid ionization chamber measurement obtained by experimental measurement and simulation calculation 252 Two-dimensional spectrum of cathode signal amplitude vs. anode signal amplitude during Cf trion fission and anode signal amplitude spectrum of selected α particle event regions. Figure 4 (a) is the experimental measurement of the screen ionization chamber 252 Two-dimensional spectrum of cathode signal amplitude vs anode signal amplitude during Cf tri-fission of lightly charged particles. Figure 4 (b) is the screen grid ionization chamber measurement obtained by simulation calculation 252 Two-dimensional spectrum of cathode signal amplitude vs anode signal amplitude during Cf tri-fission of lightly charged particles. Figure 4 (c) is the anode signal amplitude spectrum of the selected α-particle event region obtained from experimental measurements and simulation calculations;

[0041] Figure 5 The screen grid ionization chamber measurement obtained by experimental measurement and simulation calculation 252 Two-dimensional spectrum of anode signal amplitude vs. anode signal rise time during Cf trion fission and anode signal amplitude spectrum of selected tritium event region. Figure 5 (a) is the experimental measurement of the screen ionization chamber 252 Two-dimensional spectrum of anode signal amplitude vs. anode signal rise time during Cf tri-fission of lightly charged particles. Figure 5 (b) is the screen grid ionization chamber measurement obtained by simulation calculation 252 Two-dimensional spectrum of anode signal amplitude vs. anode signal rise time during Cf tri-fission of lightly charged particles. Figure 5(c) is the anode signal amplitude spectrum of the selected tritium event region obtained by experimental measurement and simulation calculation;

[0042] Figure 6 This is a comparison chart of the absolute yields of long-range alpha particles and tritium obtained from the experimental measurements in this work and the measurement results in five literatures. Figure 6 (a) is a comparison chart of the absolute yield of long-range α particles obtained by experimental measurement in this work and the measurement results of five references. Figure 6 (b) is a comparison chart of the absolute tritium yield obtained by experimental measurement in this work and the measurement results in five literatures.

[0043] Figure numerals: 1. Screen ionization chamber, 2. Fission target material, 3. Aluminum film, 4. Four-component alpha source for calibration, 5. Cathode, 6. Grid, 7. Anode, 8. Shielding electrode, 9. Working gas. DETAILED DESCRIPTION

[0044] The present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments.

[0045] Example 1

[0046] 252 Cf is the most commonly used spontaneous fission source, because it is spontaneous fission, no additional neutron source is needed, and it is convenient to carry out experiments. 252 There are many studies on the tri-fission phenomenon of Cf. 252 Experimental data on the absolute yields of long-range alpha particles and tritium in Cf tri-fission, so in this case, the object of study is the spontaneous fission source 252 Cf.

[0047] A schematic diagram of a device for measuring the absolute yield of long-range alpha particles and tritium in the fission of a fission nucleus is shown in FIG. Figure 1 shown.

[0048] A method for measuring the absolute yield of long-range alpha particles and tritium in the trifission of a fission nucleus is as follows:

[0049] Will 252 The Cf fission target is placed in the cathode sample well. The Monte Carlo method is used to simulate the measurement process of the binary fission fragments and light charged particles in the ternary fission of the fission nucleus emitted by the screen grid ionization chamber. The flow chart of the high-fidelity simulation process is shown in the figure below. Figure 2 First, without setting the shielding aluminum film and using 0.5atm 90% Ar + 10% CH4 as the working gas, the experiment obtained the screen grid ionization chamber measurement 252 The experimental spectrum of the anode signal amplitude during Cf spontaneous binary fission fragmentation is compared with the amplitude spectrum calculated above. The experimental spectrum and the simulated spectrum of the anode signal amplitude are as follows: Figure 3The two are consistent with each other to determine the detection efficiency of the screen grid ionization chamber for binary fission fragments, correct the subthreshold fraction of binary fission, and obtain the total binary fission rate. Secondly, set a 30μm shielding aluminum film and use 7atm 90% Ar + 10% CH4 as the working gas, and the experiment obtained the screen grid ionization chamber measurement efficiency. 252 The cathode signal amplitude vs. anode signal amplitude two-dimensional spectrum of Cf spontaneous tri-fission particle is obtained. The event area of ​​long-range α particle is delineated in the experimental and simulated two-dimensional spectrum, and the corresponding experimental and simulated anode signal amplitude spectrum is obtained. The experimental and simulated cathode signal amplitude vs. anode signal amplitude two-dimensional spectrum and the anode signal amplitude spectrum of the selected long-range α particle event area are shown as follows: Figure 4 (a) Figure 4 (b) Figure 4 (c) As shown. The experimental and simulated anode signal amplitude spectra are consistent with each other to determine the detection efficiency of the screen grid ionization chamber for long-range alpha particles in triadic fission, correct the subthreshold fraction of long-range alpha particles, and obtain the total long-range alpha particle count rate. Dividing it by the above total binary fission count rate, the absolute yield of long-range alpha particles in triadic fission is obtained. Finally, a 10μm shielding aluminum film is set and 7.5atm 90% Ar + 10% CH4 is used as the working gas. The experimental results show that the screen grid ionization chamber measurement efficiency is 0.01%. 252 The cathode signal amplitude vs. anode signal amplitude two-dimensional spectrum of Cf spontaneous tritium fission particles is obtained. The tritium event region is demarcated in the experimental and simulated two-dimensional spectra, and the corresponding experimental and simulated anode signal amplitude spectra are obtained. The experimental and simulated anode signal amplitude vs. anode signal rise time two-dimensional spectra and the anode signal amplitude spectrum of the selected tritium event region are shown as follows: Figure 5 (a) Figure 5 (b) Figure 5 (c) The experimental and simulated anode signal amplitude spectra are consistent with each other to determine the detection efficiency of the screen ionization chamber for tritium in tritium fission. The subthreshold fraction of tritium and the influence of long-range alpha particles on it are corrected to obtain the total tritium counting rate. Dividing it by the total binary fission counting rate obtained above, the absolute yield of tritium in tritium fission is obtained. The present invention measures 252 The data on the absolute yield of long-range alpha particles and tritium from spontaneous tritium fission of Cf are consistent with the measurement results of five references, such as Figure 6 (a) Figure 6 (b) is shown. The five papers are: [1] SW Cosper, J. Cerny and R. C. Gatti, Long-Range Particles of Z = 1 to 4 Emitted During the Spontaneous Fission of 252Cf[J].Phys.Rev,1967,154:1193-1206.[2]SLWhetstone,TDThomas,LightChargedParticles fromSpontaneousFissionof 252 Cf[J].Phys.Rev,1967,154:1174-1181.[3]GM Raisbeck,TDThomas,LightNucleiEmittedintheFissionof 252 Cf[J].Phys.Rev,1968,172:1272-1282.[4]JFWild,PABaisden,RJDouganetal.,Light-charged-particle EmissionintheSpontaneousFissionof 250 Cf, 256 Fm,and 257 Fm[J].Phys.Rev.C,1985,32:488-495.[5]S.Vermote,C.Wagemans,O.Serotetal.,TernaryParticleEmissionin SpontaneousFissionof 250 Cfand 252 CfandinNeutronInducedFissionof 249 Cfand 251 Cf[J].Nucl.Phys.A,2010,837:176-194.

[0050] The above examples illustrate the accuracy of the simulation results obtained in the present invention. 252 The absolute yields of long-range alpha particles and tritium of Cf were measured, and reliable absolute yield results were obtained, which fully demonstrated the feasibility of using this method to measure absolute yields.

[0051] Example 2

[0052] A device for measuring the absolute yield of long-range alpha particles and tritium in ternary fission of a fission nucleus mainly comprises a fission target material 2, a screen ionization chamber 1, aluminum films 3 of different thicknesses, working gases 9 of different pressures, and a data acquisition and processing system. The fission target material 2 is placed in a sample well of a cathode plate 5 of the screen ionization chamber. The fission target material 2 produces binary fission fragments, long-range alpha particles from ternary fission, and tritium from ternary fission through spontaneous fission or neutron-induced fission. The screen ionization chamber 1 is used to measure the binary fission fragments and lightly charged particles (i.e., long-range alpha particles and tritium) in ternary fission. The aluminum films 3 of different thicknesses are used to shield most of the binary fission fragments and decay alpha particles. The working gases 9 of different pressures are used to prevent long-range alpha particles and high-energy tritium from being trapped in the working gas. The data acquisition and processing system is used to measure and obtain corresponding two-dimensional spectra of cathode signal amplitude vs. anode signal amplitude and a two-dimensional spectra of anode signal amplitude vs. anode signal rise time.

[0053] The screen grid ionization chamber 1 is a closed cylindrical chamber with a sealed door for installing and removing the fission target material 2, and is filled with working gas 9.

[0054] The cathode 5, the grid 6, the anode 7 and the shielding electrode 8 are all rectangular flat plates, the cathode 5 is one piece, the grid 6, the anode 7 and the shielding electrode 8 are two pieces, the grid 6 is symmetrically distributed relative to the cathode, the anode 7 is symmetrically distributed relative to the cathode, and the shielding electrode 8 is symmetrically distributed relative to the cathode. From the inside to the outside, they are the cathode 5, the grid 6, the anode 7 and the shielding electrode 8, and the cathode 5, the grid 6, the anode 7 and the shielding electrode 8 are parallel to each other and installed in the screen ionization chamber 1;

[0055] The cathode 5 is a rectangular flat plate installed on the center line of the screen ionization chamber 1. A sample well is set, and the fission target material 2 is placed in the sample well. The aluminum film 3 and the four-component α source 4 for calibration are respectively located on both sides of the fission target material 2.

[0056] Fission target material 2 uses 252 Cf, 235 U and 239 Pu and other fissile materials.

[0057] The working gas 9 has different pressures. For binary fission rate measurement, the working gas 9 has a low pressure (about 0.5 atmospheres); for ternary fission rate measurement, the working gas 9 has a high pressure (more than 6 atmospheres).

[0058] The aluminum films 3 of different thicknesses are placed on the plane of the cathode 5 plate to cover the sample well where the fission target material 2 is placed.

[0059] A method for measuring the absolute yield of long-range alpha particles and tritium in fission of a fission nucleus comprises the following steps:

[0060] Step 1: Under the conditions of no aluminum film and low pressure (about 0.5 atmospheres) working gas, the anode signal amplitude spectrum of the screen grid ionization chamber when measuring spontaneous or neutron-induced binary fission fragments of fission nuclei is experimentally obtained.

[0061] Step 2: Use the Monte Carlo method to simulate the measurement process of binary fission fragments emitted by a screened ionization chamber. GEF 2020 / 1.1 software is used to calculate information such as the mass, independent yield, and total energy released by the binary fission fragments. The energy of the binary fission fragments is then calculated based on the conservation of momentum and energy. The energy of the binary fission fragments is discretely sampled, taking into account the mass, independent yield, energy, and emission angle of the binary fission fragments, as well as sample thickness, sample inhomogeneity, and PHD effects. The anode signal amplitude spectrum of the screened ionization chamber's binary fission fragment measurement is then obtained. By comparing this spectrum with the experimental amplitude spectrum obtained in Step 1, if the two agree, the detection efficiency of the screened ionization chamber for binary fission fragments is determined. The subthreshold fraction of binary fission is then corrected to obtain the total binary fission count rate.

[0062] Step 3. Under the conditions of placing aluminum films of different thicknesses and high-pressure (over 6 atmospheres) working gas, the experiment obtains the cathode signal amplitude vs. anode signal amplitude two-dimensional spectrum, the anode signal amplitude vs. anode signal rise time two-dimensional spectrum, and the anode signal amplitude spectrum when the screen grid ionization chamber measures light charged particles in spontaneous or neutron-induced ternary fission of fission nuclei.

[0063] Step 4: Use the Monte Carlo method to simulate the measurement process of light charged particles in the fission of fission nuclei in the screen grid ionization chamber, sample the charge number, mass number, energy distribution and emission angle of the light charged particles in the trion fission, consider the influence of sample thickness, sample non-uniformity and aluminum film, calculate the deposition energy of these charged particles in the screen grid ionization chamber, and obtain information such as the charged particle track length, emission angle and deposition energy. Based on the above information, the corresponding cathode signal amplitude vs anode signal amplitude two-dimensional spectrum, anode signal amplitude vs anode signal rise time two-dimensional spectrum and anode signal amplitude spectrum are calculated.

[0064] Step 5. For long-range alpha particles in ternary fission, the event region of the long-range alpha particles is delineated in the two-dimensional spectra of cathode signal amplitude vs. anode signal amplitude obtained by experimental measurement in step 3 and simulation calculation in step 4, respectively, to obtain the corresponding anode signal amplitude spectra obtained by experimental measurement and simulation calculation. The two spectra are consistent with each other to determine the detection efficiency of the screen ionization chamber for long-range alpha particles in ternary fission, correct the subthreshold fraction of long-range alpha particles, and obtain the total long-range alpha particle counting rate. The total long-range alpha particle counting rate is divided by the total binary fission counting rate obtained in step 2 to obtain the absolute yield of long-range alpha particles in ternary fission.

[0065] Step 6. For tritium in ternary fission, the event region of tritium is delineated in the two-dimensional spectrum of anode signal amplitude vs. anode signal rise time obtained by experimental measurement in step 3 and simulation calculation in step 4, respectively, to obtain the corresponding experimentally measured and simulated anode signal amplitude spectra. The two spectra are consistent with each other to determine the detection efficiency of the screen ionization chamber for tritium in ternary fission, correct the subthreshold fraction of tritium and the influence of long-range alpha particles on it, and obtain the total tritium counting rate. Divide it by the total binary fission counting rate obtained in step 2 to obtain the absolute yield of tritium in ternary fission.

Claims

1. A device for measuring the absolute yield of long-range alpha particles and tritium in the fission of a fission nucleus, characterized in that: It comprises a screen grid ionization chamber (1), a cathode (5), a grid (6), an anode (7), a shielding electrode (8), an aluminum film (3), a four-component α source for calibration (4), and a data acquisition and processing system; The screen grid ionization chamber (1) is a closed cylindrical chamber, provided with a sealed door for installing and removing the fission target material (2), and is filled with a working gas (9) which is a mixed gas of argon and methane; The cathode (5), grid (6), anode (7) and shield (8) are all rectangular flat plates, the cathode (5) is one piece, the grid (6), anode (7) and shield (8) are two pieces, the grid (6) is symmetrically distributed relative to the cathode (5), the anode (7) is symmetrically distributed relative to the cathode (5), and the shield (8) is symmetrically distributed relative to the cathode (5), and the cathode (5), grid (6), anode (7) and shield (8) are arranged from the inside to the outside in order, and the cathode (5), grid (6), anode (7) and shield (8) are parallel to each other and are installed in the screen ionization chamber (1); The cathode (5) is installed on the center line of the screen grid ionization chamber (1), a sample well is provided, a fission target material (2) is placed in the sample well, and an aluminum film (3) and a four-component α source (4) for calibration are respectively located on both sides of the fission target material (2); The data acquisition and processing system is used to measure a two-dimensional spectrum of cathode signal amplitude vs. anode signal amplitude, and a two-dimensional spectrum of anode signal amplitude vs. anode signal rise time.

2. The device for measuring the absolute yield of long-range alpha particles and tritium in fission of fission nuclei according to claim 1, characterized in that: The aluminum film (3) is located on the cathode (5) plate plane, covers the sample well containing the fission target material (2), and is used to shield part of the binary fission fragments and decay alpha particles.

3. The device for measuring the absolute yield of long-range alpha particles and tritium in fission of fission nuclei according to claim 2, characterized in that: The thickness of the aluminum film (3) is 30 μm, or 10 μm.

4. The device for measuring the absolute yield of long-range alpha particles and tritium in fission of fission nuclei according to claim 1, characterized in that: The pressure of the working gas (9) is 0.5 atmospheres, or exceeds 6 atmospheres.

5. The device for measuring the absolute yield of long-range alpha particles and tritium in fission of fission nuclei according to claim 4, characterized in that: The working gas (9) is a 90% Ar+10% CH4 mixed gas at 0.5 atm, or a 90% Ar+10% CH4 mixed gas at 7.0 atm, or a 90% Ar+10% CH4 mixed gas at 7.5 atm.

6. The device for measuring the absolute yield of long-range alpha particles and tritium in fission of fission nuclei according to claim 1, characterized in that: The fission target material (2) is 252 Cf, or 235 U, or 239 Pu fissile material.

7. A method for measuring the absolute yield of long-range alpha particles and tritium in the fission of a fission nucleus, characterized in that: The following steps are involved: Step 1: measuring binary fission fragments using a screen ionization chamber (1) without an aluminum film (3) and using a low-pressure working gas (9): The fission target material (2) is placed in a sample well of a device for measuring the absolute yield of long-range alpha particles and tritium in fission nuclei, without placing an aluminum film (3), and the pressure of the working gas (9) is 0.5 atmospheres; When the fission target material (2) undergoes binary fission spontaneously or neutron-induced, a data acquisition and processing system is used to collect an anode signal amplitude spectrum when the screen grid ionization chamber (1) measures binary fission fragments; Step 2, simulate the measurement process of binary fission fragments: The Monte Carlo method is used to simulate the measurement process of binary fission fragments emitted by fission nuclei in a screen-grid ionization chamber (1); the mass, independent yield and total energy released by the fission of the fission nucleus are calculated by GEF 2020 / 1.1 software; the energy of the binary fission fragments is then calculated based on the conservation of momentum and energy conservation, and the mass, independent yield, energy and emission angle of the binary fission fragments of the fission nucleus are taken into account by discrete sampling of the energy of the binary fission fragments, and the sample thickness, sample inhomogeneity and PHD effect are taken into account to simulate the anode signal amplitude spectrum when the screen-grid ionization chamber (1) measures the binary fission fragments; The simulated anode signal amplitude spectrum is compared with the anode signal amplitude spectrum measured in step 1. If the two agree with each other, the detection efficiency of the screen grid ionization chamber (1) for binary fission fragments is determined, the subthreshold fraction of binary fission is corrected, and the total binary fission count rate is obtained; Step 3, using the screen grid ionization chamber (1) to measure the light charged particles in the triad fission under the conditions of the aluminum film (3) and the high pressure working gas (9): Aluminum films (3) of different thicknesses are placed respectively, and the pressure of the working gas (9) is adjusted to be greater than 6 atmospheres; When the fission target material (2) undergoes spontaneous or neutron-induced triadic fission, a data acquisition and processing system is used to acquire a cathode signal amplitude vs. anode signal amplitude two-dimensional spectrum, anode signal amplitude vs. anode signal rise time two-dimensional spectrum, and anode signal amplitude spectrum when the screen grid ionization chamber (1) measures light charged particles in the triadic fission; Step 4: Simulate the measurement process of light charged particles in tri-fission: The Monte Carlo method is used to simulate the measurement process of light charged particles in the fission nucleus trion in the screen grid ionization chamber (1). The charge number, mass number, energy distribution and emission angle of the light charged particles in the trion fission are sampled. Considering the influence of sample thickness, sample non-uniformity and aluminum film, the deposition energy of these charged particles in the screen grid ionization chamber is calculated, and the track length, emission angle and deposition energy information of the charged particles are obtained. Through the calculation of the above information, the corresponding cathode signal amplitude vs anode signal amplitude two-dimensional spectrum, anode signal amplitude vs anode signal rise time two-dimensional spectrum and anode signal amplitude spectrum are obtained; Step 5: Obtain the absolute yield of long-range alpha particles in ternary fission: For long-range α particles in triadic fission, the event region of long-range α particles is delineated in the cathode signal amplitude vs. anode signal amplitude two-dimensional spectrum obtained by measurement in step 3 and simulation calculation in step 4, respectively, and the corresponding anode signal amplitude spectrum obtained by experimental measurement and simulation calculation is obtained. The two are consistent with each other to determine the detection efficiency of the screen ionization chamber (1) for long-range α particles in triadic fission, correct the subthreshold fraction of long-range α particles, and obtain the total long-range α particle counting rate. Divide it by the total binary fission counting rate obtained in step 2 to obtain the absolute yield of long-range α particles in triadic fission; Step 6, obtain the absolute yield of tritium in ternary fission: For tritium in ternary fission, the event area of ​​tritium is delineated in the two-dimensional spectrum of anode signal amplitude vs. anode signal rise time obtained by measurement in step 3 and simulation calculation in step 4, respectively, and the corresponding anode signal amplitude spectrum of experimental measurement and simulation calculation is obtained. The two are consistent with each other to determine the detection efficiency of the screen grid ionization chamber (1) for tritium in ternary fission, correct the subthreshold fraction of tritium and the influence of long-range alpha particles on it, and obtain the total tritium counting rate. Divide it by the total binary fission counting rate obtained in step 2 to obtain the absolute yield of tritium in ternary fission.

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