A transient gamma radiation shielding method

Abstract

The present invention relates to a radiation protection method, and in particular to a transient gamma radiation shielding method. The method fills the gap in the current lack of radiation shielding safety protection methods suitable for transient high-current electron accelerators. The shielding method of the present invention comprises the following steps: 1) determining the annual exposure dose constraint value of workers and the public, and the dose rate management constraint value of test equipment and workers; 2) obtaining the radiation source term estimate; 3) obtaining three distribution functions of electron landing point, incident angle and energy spectrum; 4) establishing a calculation model; 5) obtaining the outgoing gamma ray distribution diagram and energy spectrum on the reference sphere; 6) replacing the bremsstrahlung target and electron beam with a radiation point source, and simulating to obtain the radiation source term simulation value; 7) judging whether the radiation point source meets the requirements; 8) preliminarily giving the material and thickness of the shielding wall; 9) obtaining the shielding calculation model; 10) optimizing the material and thickness of the shielding wall; 11) obtaining the restricted area requirements and the height limit requirements of surrounding buildings.

Description

Technical Field

[0001] The present invention relates to a radiation protection method, in particular to a transient gamma radiation shielding method suitable for a transient high-current electron accelerator. Background Art

[0002] Radiation shielding safety design is a critical component of accelerator and reactor design. Ensuring safe and reasonable radiation shielding requires finding a solution that meets national regulations, including small size, low cost, and environmental friendliness. This is a complex engineering optimization problem.

[0003] Radiation shielding design often relies on empirical formulas or Monte Carlo methods. These methods (including lookup tables) are fast but tend to be less accurate. To ensure safety, they often produce overly conservative results, increasing project costs. They are suitable for rough estimates in the early stages and verification later in the process.

[0004] The Monte Carlo method's outstanding advantage is its suitability for calculating and handling particle transport problems in complex geometries. To meet engineering design requirements, the Radiation Shielding Center at the Oak Ridge Laboratory in the United States has developed general-purpose Monte Carlo programs such as MCNP. GEANT4, a free Monte Carlo program developed by CERN, the European Organization for Nuclear Research, offers a comprehensive range of physical processes and a large number of complete and optional models. It has been widely used in high-energy physics and radiation effects research.

[0005] Based on the Monte Carlo program, researchers and engineers have developed various radiation shielding safety designs, enabling computer-aided design and visualization of radiation fields and shielding effects. However, the long calculation cycle has always been a bottleneck, which is very unfavorable for the calculation of large-scale complex spaces and the iterative optimization of shielding schemes.

[0006] Reference literature includes, for example, Li Zhanpeng of Soochow University's 2020 master's thesis, "Design and Multi-Objective Optimization of Radiation Protection Shielding for Nondestructive Testing Accelerators." This thesis, focusing on nondestructive testing accelerators, used the accelerator's engineering CAD model and Monte Carlo software to accurately model and simulate the accelerator, using this as the basis for multi-objective optimization design. He then organically combined the GA-BP neural network with the NSGA-II multi-objective genetic algorithm to establish a multi-objective optimization method for accelerator shielding design.

[0007] In their 2022 paper, "Development and Validation of a Shipbuilding Reactor Radiation Shielding Optimization Design Platform," published in the Journal of Nuclear Power Engineering, Li Yuehang and others from the Nuclear Power Research and Design Institute of China developed a multi-objective optimization platform for shipbuilding reactor radiation shielding based on the open-source SALOME framework, integrating "geometry modeling, material modeling, shielding optimization, and result visualization." This platform enables 3D CAD solid modeling of shielding structures, genetic algorithm-based multi-objective optimization of radiation shielding, and 3D visualization of shielding calculation results and dose fields.

[0008] Wang Sheng from Xi'an Jiaotong University disclosed a radiation shielding design method based on radiation particle transport simulation in his Chinese patent publication number CN111859804A, "A Multi-Objective Radiation Shielding Design Method."

[0009] Existing radiation protection standards and the work cited above are both targeted at conventional accelerators and reactors. However, transient high-current electron accelerators (TIEs) have operating times of 10-100 nanoseconds, peak electron beam currents of 10 kJ to 10 mA, electron energies of 0.3 to 50 MeV, and transient dose rates of 1 to 30 GGy / s, all significantly different from conventional accelerators and reactors. Therefore, a safe and reliable radiation shielding method suitable for TIEs is urgently needed. Summary of the Invention

[0010] The purpose of the present invention is to solve the current lack of radiation shielding safety protection methods suitable for transient high-current electron accelerators and to provide a transient gamma radiation shielding method.

[0011] The technical solution of the present invention is:

[0012] A transient gamma radiation shielding method is characterized in that it comprises the following steps:

[0013] 1) Based on the operating parameter characteristics of the transient high-current electron accelerator and relevant national standards, determine the annual exposure dose constraints for workers and the public, and the dose rate management constraints for test equipment and workers;

[0014] 2) Obtain an estimated value of the radiation source term based on the electron energy and beam intensity of the transient high-current electron accelerator;

[0015] 3) Input the electrical parameters of the transient high-current electron accelerator and the diode geometric parameters into the electron beam emission and electromagnetic field coupling calculation software to calculate and obtain the electron landing point distribution function, incident angle distribution function, and energy spectrum distribution function generated by the electron beam bombarding the bremsstrahlung target;

[0016] 4) Inputting the electron landing point distribution function, the incident angle distribution function, and the energy spectrum distribution function into the particle transport process simulation software to establish a computational model for the generation of gamma energy band X-ray radiation by electron beam bombardment of the bremsstrahlung target; the gamma energy band X-ray radiation characteristics are consistent with those of gamma rays;

[0017] 5) Using the computational model, with the center of the bremsstrahlung target as the center of the sphere, setting the radius of the reference sphere according to the radius of the bremsstrahlung target to obtain the reference sphere, and calculating the outgoing gamma-ray distribution map and energy spectrum on the reference sphere;

[0018] 6) replacing the bremsstrahlung target and the electron beam with a radiation point source having a directional distribution and an energy spectrum distribution, ensuring that the directional distribution diagram and the energy spectrum of the radiation point source on the reference sphere are identical to the outgoing gamma ray distribution diagram and energy spectrum in step 5); simulating to obtain a radiation source term simulation value of the radiation point source;

[0019] 7) Comparing the estimated radiation source value in step 2) with the simulated radiation source value in step 6) to determine whether they meet the requirements; if so, proceeding to step 8); if not, returning to step 5) and adjusting the radius of the reference sphere according to the actual result deviation until a radiation point source meeting the requirements is obtained;

[0020] 8) Preliminary determination of the material and thickness of the shielding wall;

[0021] 9) Establishing a three-dimensional model of the laboratory and its surrounding environment, and substituting the three-dimensional model and the radiation point source obtained in step 7) into particle transport process simulation software to obtain a shielding calculation model;

[0022] 10) The material and thickness of the shielding wall in step 8) are fed into a shielding calculation model, and the optimized material and thickness of the shielding wall are obtained through iterative calculation;

[0023] 11) All annual exposure dose constraint values ​​and dose rate management constraint values ​​obtained in step 1), as well as the optimized shielding wall material and thickness obtained in step 10), are fed into the shielding calculation model of step 9) to calculate the requirements for test equipment and personnel restricted areas, public restricted areas, and height restrictions for surrounding buildings during operation of the transient high-current electron accelerator.

[0024] Furthermore, step 1) includes the following steps:

[0025] 1.1) With reference to conventional accelerators and reactors, in accordance with the Basic Standards for Ionizing Radiation Protection and Radiation Source Safety and the Regulations on Radiation Protection of Particle Accelerators, and taking into account the laboratory's surrounding environment, determine the annual dose constraints for workers and the public;

[0026] The surrounding environment includes people who live in close proximity and the distribution of surrounding radiation sources;

[0027] 1.2) Determine the dose rate management constraint value of the test equipment based on the experimental experience of gamma ray transient ionizing radiation effects;

[0028] The dose rate management constraint value of the test equipment is 10 kGy / s;

[0029] 1.3) Divide the annual worker exposure dose constraint value obtained in step 1.1) by the accelerator radiation output time to obtain the worker dose rate management constraint value.

[0030] Furthermore, in step 2), the method for obtaining the estimated value of the radiation source term is: according to the electron energy of the transient high-current electron accelerator, the corresponding X-ray emission constant is found in the X-ray emission constant diagram, and the X-ray emission constant is multiplied by the beam intensity of the transient high-current electron accelerator to obtain the estimated value of the dose rate 1 meter directly in front of the transient high-current electron accelerator.

[0031] Furthermore, the judgment method in step 7) is: compare the estimated value of the radiation source term with the simulated value of the radiation source term. If the deviation does not exceed 10%, it meets the requirements; if the deviation exceeds 10%, it does not meet the requirements.

[0032] Furthermore, in step 8), the method for preliminarily determining the material and thickness of the shielding wall is: obtaining the material and thickness according to the calculation method provided in NCRP-155 based on the electron peak energy of the transient high-current electron accelerator.

[0033] The beneficial effects of the present invention are:

[0034] 1. The present invention provides a transient gamma radiation shielding method for transient high-current electron accelerators. This method comprehensively considers the cumulative ionizing radiation effect (dose management constraint value) and transient ionizing radiation effect (dose rate management constraint value) of gamma radiation, applies electron beam emission and electromagnetic field coupling calculation software, particle transport process simulation software, and three-dimensional numerical simulation to establish a high-precision calculation model and a shielding calculation model. This method conforms to the radiation characteristics of transient high-current electron accelerators and can effectively perform radiation shielding safety design for transient high-current electron accelerators, thus making up for the current lack of a safe and reliable radiation shielding method suitable for transient high-current electron accelerators.

[0035] 2. The present invention provides a transient gamma radiation shielding method. Through a high-precision shielding calculation model, the restricted area requirements and the height limit requirements of surrounding buildings are obtained. At the same time, the shielding material and thickness are determined. A radiation point source is used instead of a bremsstrahlung target for point source fitting, which improves the calculation efficiency by 2-4 orders of magnitude.

[0036] 3. The present invention provides a transient gamma radiation shielding method, which uses particle transport process simulation software to establish a three-dimensional calculation model and optimize the material and thickness of the shielding wall, thereby reducing the redundant thickness of the rear shielding wall. The simulation effect is accurate and efficient, avoiding unnecessary waste.

[0037] 4. The present invention provides a transient gamma radiation shielding method, which determines the dose rate management constraint value of the test equipment to be 10 kGy / s, and proposes an annual exposure dose constraint value for workers and the public.

[0038] 5. In the transient gamma radiation shielding method of the present invention, the deviation between the radiation source term estimation value and the radiation source term simulation value does not exceed 10%, ensuring the accuracy and reliability of the radiation point source. BRIEF DESCRIPTION OF THE DRAWINGS

[0039] Figure 1 is a flow chart of a transient gamma radiation shielding method of the present invention;

[0040] Figure 2 is the X-ray emission constant diagram (contained in NCRP-51);

[0041] Figure 3 is the electron landing point distribution diagram obtained in an embodiment of the present invention;

[0042] Figure 4 is a probability distribution diagram of electron incident angles obtained in an embodiment of the present invention;

[0043] Figure 5 is the electron spectrum obtained in the embodiment of the present invention;

[0044] Figure 6 is a directional distribution diagram of a radiation point source in an embodiment of the present invention (the reference spherical radius is 2.5 m);

[0045] Figure 7 is the energy spectrum of the radiation point source in the embodiment of the present invention (the reference sphere radius is 2.5m);

[0046] Figure 8 is a shielding layout diagram in an embodiment of the present invention;

[0047] Figure 9 Optimized design diagram of the shielding wall in an embodiment of the present invention.

[0048] Figure numerals: 1-restricted area for test equipment and staff, 2-front shielding wall, 3-public restricted area, 4-side front shielding wall, 5-test equipment area, 6-transient high-current electron accelerator, 7-side rear shielding wall, 8-rear shielding wall, 9-radiation source of accelerator, 10-additional shielding wall. DETAILED DESCRIPTION

[0049] The present invention is described in detail below with reference to the accompanying drawings and specific embodiments.

[0050] like Figure 1 As shown, the present invention provides a transient gamma radiation shielding method, which addresses the radiation protection problem of a transient high-current electron accelerator, and includes the following steps:

[0051] 1) Based on the operating parameter characteristics of the transient high-current electron accelerator and relevant national standards, determine the annual exposure dose constraint values ​​for workers and the public, and the dose rate management constraint values ​​for test equipment and workers. The annual exposure dose constraint values ​​correspond to the cumulative ionizing radiation effects, and the dose rate management constraint values ​​correspond to the transient ionizing radiation effects.

[0052] 1.1) With reference to conventional accelerators and reactors, in accordance with the relevant national standards GB18871-2002-B1 "Basic Standard for Ionizing Radiation Protection and Radiation Source Safety" and GB5172-85 "Regulations on Radiation Protection of Particle Accelerators", and taking into account the laboratory's surrounding environment (including close-range permanent personnel, distribution of surrounding radiation sources, etc.), determine the annual exposure dose constraints for workers and the public.

[0053] 1.2) Determine the dose rate management constraints of the test equipment;

[0054] According to the experimental experience of gamma-ray transient ionizing radiation effects, when the dose rate is lower than 10 kGy / s, the transient ionizing radiation effects can be ignored for the test equipment in power-on operation. Therefore, 10 kGy / s is used as the dose rate management constraint value for the test equipment.

[0055] 1.3) Divide the annual worker dose constraint obtained in step 1.1) by the accelerator radiation output time to obtain the worker dose rate management constraint. The public dose rate management constraint is too small and can be ignored.

[0056] 2) Obtain an estimated value of the radiation source term based on the electron energy and beam intensity of the transient high-current electron accelerator;

[0057] The method for obtaining the estimated value of the radiation source term is as follows: based on the electron energy of the transient high-current electron accelerator, find the corresponding X-ray emission constant in the X-ray emission constant chart, multiply the X-ray emission constant by the beam intensity of the transient high-current electron accelerator, and obtain the estimated value of the dose rate at 1 meter directly in front of the transient high-current electron accelerator;

[0058] The X-ray emission constant diagram and the method for obtaining the estimated value of the radiation source term both adopt the X-ray emission constant diagram and the method for obtaining the estimated value of the radiation source term provided in NCRP-51 (National Council on Radiation Protection and Measurements Report No. 51, "Radiation Protection Design Guidelines For 0.1-100MeV Particle Accelerator Facilities").

[0059] 3) Input the electrical parameters of the transient high-current electron accelerator and the diode geometric parameters into the electron beam emission and electromagnetic field coupling calculation software to calculate and obtain the electron landing point distribution function, incident angle distribution function, and energy spectrum distribution function generated by the electron beam bombarding the bremsstrahlung target;

[0060] 4) The electron landing point distribution function, incident angle distribution function, and energy spectrum distribution function are input into the particle transport process simulation software to establish a computational model for the generation of gamma energy band X-ray radiation by electron beam bombardment of the bremsstrahlung target; the radiation characteristics of gamma energy band X-rays are consistent with those of gamma rays.

[0061] 5) Using the computational model, with the center of the bremsstrahlung target as the center of the sphere, setting the radius of the reference sphere according to the radius of the bremsstrahlung target to obtain the reference sphere, and calculating and obtaining the outgoing gamma-ray distribution map and energy spectrum on the reference sphere;

[0062] 6) Replace the bremsstrahlung target and electron beam with a radiation point source having a directional distribution and an energy spectrum distribution, ensuring that the directional distribution diagram and the energy spectrum of the radiation point source on the reference sphere are identical to the outgoing gamma-ray distribution diagram and energy spectrum in step 5); this step is the process of fitting the gamma source to a radiation point source; and simulate to obtain a radiation source term simulation value of the radiation point source, which is the dose rate simulation value 1 meter directly in front of the transient high-current electron accelerator.

[0063] 7) Compare the estimated radiation source value from step 2) with the simulated radiation source value from step 6) to determine whether they meet the requirements. If so, proceed to step 8). If not, return to step 5) and adjust the radius of the reference sphere according to the actual result deviation. Each time the radius is returned, a small increase is made based on the previous radius size until a radiation point source that meets the requirements is obtained.

[0064] The judgment method is: compare the estimated value of the radiation source item with the simulated value of the radiation source item, that is, compare the estimated value of the dose rate 1 meter directly in front of the transient high-current electron accelerator with the simulated value of the dose rate 1 meter directly in front of the transient high-current electron accelerator. If the deviation does not exceed 10%, it meets the requirements; if the deviation exceeds 10%, it does not meet the requirements.

[0065] 8) Preliminary determination of the material and thickness of the shielding wall;

[0066] Based on the peak electron energy of the transient high-current electron accelerator and the calculation method provided in NCRP-155 (National Council on Radiation Protection and Measurements Report No. 155, "Structural Shielding Design And Evaluation For Megavoltage X-And Gamma-Ray Radiotherapy Facilities"), the material and thickness of the shielding wall are given.

[0067] 9) Establishing a three-dimensional model of the laboratory and its surrounding environment, and substituting the three-dimensional model and the radiation point source obtained in step 7) into particle transport process simulation software to obtain a shielding calculation model;

[0068] 10) The material and thickness of the shielding wall in step 8) are fed into a shielding calculation model, and the optimized material and thickness of the shielding wall are obtained through iterative calculation;

[0069] 11) All annual exposure dose constraint values ​​and dose rate management constraint values ​​obtained in step 1), as well as the optimized shielding wall material and thickness obtained in step 10), are fed into the shielding calculation model of step 9) to calculate and obtain the restricted area requirements for test equipment and personnel, the public restricted area requirements, and the height limit requirements for surrounding buildings when the transient high-current electron accelerator is in operation.

[0070] This is further explained using a laboratory as an example.

[0071] For example, a laboratory has a radiation source located 100 meters from a residential building, with multiple sources within a 200-meter radius. Based on these considerations, the annual dose constraint for workers is 5 mSv, a quarter of the annual effective dose limit for occupational exposure. The annual dose constraint for the public is 0.1 mSv, a tenth of the annual effective dose limit for the public. The radiation output duration is 50 nanoseconds. Dividing the annual dose constraints for both workers and the public by the accelerator's output duration yields the dose rate management constraint for workers. The public does not need to consider the dose rate because it is too low. The dose rate management constraint for the test equipment is 10 kGy / s.

[0072] 2) The electron energy of the transient high-current electron accelerator is 20 MeV, and the beam current intensity is 72 kA. Using the method in NCRP-51, based on the electron energy of 20 MeV, the corresponding X-ray emission constant is found to be 1570 Gy·mA from the X-ray emission constant diagram (contained in NCRP-51). -1 min -1 , multiplying the X-ray emission constant by the beam intensity 72kA, we get the dose rate of 1.884Gy / s at 1 meter in front of the transient high-current electron accelerator. Figure 2shown.

[0073] 3) Input the electrical parameters of the transient high-current electron accelerator and the geometric parameters of the diode into the electron beam emission and electromagnetic field coupling calculation software for calculation, and obtain the electron landing point distribution function, incident angle distribution function and energy spectrum distribution function generated by the electron beam bombarding the bremsstrahlung target. The electron landing point distribution function, incident angle distribution function and energy spectrum distribution function, the electron landing point distribution diagram, the electron incident angle probability distribution diagram and the electron energy spectrum are shown as follows: Figure 3 、 Figure 4 and Figure 5 shown.

[0074] 4) The electron landing point distribution function, incident angle distribution function, and energy spectrum distribution function are input into the particle transport process simulation software to establish a computational model for the generation of gamma energy band X-ray radiation by electron beam bombardment of the bremsstrahlung target. The radiation characteristics of gamma energy band X-rays are consistent with those of gamma rays.

[0075] 5) Using the computational model, with the center of the bremsstrahlung target as the center of the sphere, the radius of the reference sphere is set according to the radius of the bremsstrahlung target to obtain the reference sphere, and the outgoing gamma-ray distribution map and energy spectrum on the reference sphere are calculated.

[0076] 6) Replace the Bremsstrahlung target and electron beam with a radiation point source with directional distribution and energy spectrum distribution, ensuring that the directional distribution diagram and energy spectrum of the radiation point source on the reference sphere are the same as the distribution diagram and energy spectrum diagram in step 5); and simulate the radiation source term simulation value of the radiation point source, and simulate the dose rate of 1.74Gy / s at 1 meter in front of the transient high-current electron accelerator. The replacement process involved in this step is the process of fitting the gamma source to a radiation point source. The reference sphere radius is 2.5m, and the directional distribution diagram and energy spectrum distribution of the radiation point source are as follows: Figure 6 and Figure 7 As shown, in the method of the present invention, the gamma source is fitted as a radiation point source, which increases the calculation efficiency by 1000 times.

[0077] 7) Comparing the estimated radiation source term from step 2) with the simulated radiation source term from step 6), the deviation is 8.28%, which is less than 10%. This proves that the simulated radiation point source meets the requirements, and step 8) is directly executed.

[0078] 8) Based on the peak electron energy of the transient high-current electron accelerator and using the calculation method provided by NCRP-155 (National Council on Radiation Protection and Measurements Report No. 155, "Structural Shielding Design And Evaluation For Megavoltage X-And Gamma-Ray Radiotherapy Facilities"), the shielding wall material is preliminarily determined to be concrete, with a density of >1.9×103 kg·m -3 ; The positional relationship between the shielding wall and the transient high-current electron accelerator is as follows Figure 8 As shown in the figure, 1 is the restricted area for test equipment and staff; 2 is the front shielding wall with a thickness of 3m; 3 is the public restricted area, with the shortest distance from the radiation source being 30m; 4 is the side front shielding wall with a thickness of 2m; 5 is the test equipment area; 6 is the transient high-current electron accelerator; 7 is the side rear shielding wall with a thickness of 0.4m; 8 is the rear shielding wall with a thickness of 0.9m; and 9 is the radiation source of the transient high-current electron accelerator.

[0079] 9) Build a three-dimensional model of the laboratory and its surrounding environment, substitute the three-dimensional model and the obtained radiation point source into the particle transport process simulation software to complete the shielding calculation model.

[0080] 10) The material and thickness of the shielding wall in step 8) are fed into the shielding calculation model, and the material and thickness of the shielding wall are optimized through iterative calculation. The optimized results are as follows: Due to the scattering effect of the transient high-current electron accelerator, risk points appear in some areas of the side and rear shielding wall 7, so an additional shielding wall 10 with a thickness of 0.4m is added. Due to the forward nature of the radiation source and the shielding effect of the accelerator itself, the thickness of the rear shielding wall 8 is too redundant, so it is reduced to 0.6m. The overall optimized layout is as follows Figure 9 shown.

[0081] 11) All annual exposure dose constraint values ​​and dose rate management constraint values ​​obtained in step 1), as well as the optimized shielding wall material and thickness obtained in step 10), are fed into the shielding calculation model of step 9) to calculate and obtain the height limit requirements for test equipment and personnel restricted areas and surrounding buildings when the transient high-current electron accelerator is in operation. The calculation result shows that the radius of the restricted area for test equipment and personnel during accelerator operation is 7 meters, the radius of the restricted area for the public is 30 meters, and buildings within 30 meters of the surrounding area shall not be higher than 20 meters.

Claims

1. A transient gamma radiation shielding method, characterized in that: The following steps are involved: 1) Based on the operating parameter characteristics of the transient high-current electron accelerator and relevant national standards, determine the annual exposure dose constraints for workers and the public, and the dose rate management constraints for test equipment and workers; 1.1) With reference to conventional accelerators and reactors, in accordance with the Basic Standards for Ionizing Radiation Protection and Radiation Source Safety and the Regulations on Radiation Protection of Particle Accelerators, and taking into account the laboratory's surrounding environment, determine the annual dose constraints for workers and the public; The surrounding environment includes people who live in close proximity and the distribution of surrounding radiation sources; 1.2) Determine the dose rate management constraint value of the test equipment based on the experimental experience of gamma ray transient ionizing radiation effects; The dose rate management constraint value of the test equipment is 10 kGy / s; 1.3) Dividing the annual worker exposure dose constraint value obtained in step 1.1) by the accelerator radiation output time to obtain the worker dose rate management constraint value; 2) Obtain an estimated value of the radiation source term based on the electron energy and beam intensity of the transient high-current electron accelerator; 3) Input the electrical parameters of the transient high-current electron accelerator and the diode geometric parameters into the electron beam emission and electromagnetic field coupling calculation software to calculate and obtain the electron landing point distribution function, incident angle distribution function, and energy spectrum distribution function generated by the electron beam bombarding the bremsstrahlung target; 4) Inputting the electron landing point distribution function, the incident angle distribution function, and the energy spectrum distribution function into the particle transport process simulation software to establish a computational model for the generation of gamma energy band X-ray radiation by electron beam bombardment of the bremsstrahlung target; the gamma energy band X-ray radiation characteristics are consistent with those of gamma rays; 5) Using the computational model, with the center of the bremsstrahlung target as the center of the sphere, setting the radius of the reference sphere according to the radius of the bremsstrahlung target to obtain the reference sphere, and calculating the outgoing gamma-ray distribution map and energy spectrum on the reference sphere; 6) replacing the bremsstrahlung target and the electron beam with a radiation point source having a directional distribution and an energy spectrum distribution, ensuring that the directional distribution diagram and the energy spectrum of the radiation point source on the reference sphere are identical to the outgoing gamma ray distribution diagram and energy spectrum in step 5); simulating to obtain a radiation source term simulation value of the radiation point source; 7) Comparing the estimated radiation source value in step 2) with the simulated radiation source value in step 6) to determine whether they meet the requirements; if so, proceeding to step 8); if not, returning to step 5) and adjusting the radius of the reference sphere according to the actual result deviation until a radiation point source meeting the requirements is obtained; 8) Preliminary determination of the material and thickness of the shielding wall; 9) Establishing a three-dimensional model of the laboratory and its surrounding environment, and substituting the three-dimensional model and the radiation point source obtained in step 7) into particle transport process simulation software to obtain a shielding calculation model; 10) The material and thickness of the shielding wall in step 8) are fed into a shielding calculation model, and the optimized material and thickness of the shielding wall are obtained through iterative calculation; 11) All annual exposure dose constraint values ​​and dose rate management constraint values ​​obtained in step 1), as well as the optimized shielding wall material and thickness obtained in step 10), are fed into the shielding calculation model of step 9) to calculate the requirements for test equipment and personnel restricted areas, public restricted areas, and height restrictions for surrounding buildings during operation of the transient high-current electron accelerator.

2. A transient gamma radiation shielding method according to claim 1, characterized in that: In step 2), the method for obtaining the estimated value of the radiation source term is: based on the electron energy of the transient high-current electron accelerator, the corresponding X-ray emission constant is found in the X-ray emission constant diagram, and the X-ray emission constant is multiplied by the beam intensity of the transient high-current electron accelerator to obtain the estimated value of the dose rate 1 meter directly in front of the transient high-current electron accelerator.

3. A transient gamma radiation shielding method according to claim 2, characterized in that: The judgment method in step 7) is: compare the estimated value of the radiation source term with the simulated value of the radiation source term. If the deviation does not exceed 10%, it meets the requirements; if the deviation exceeds 10%, it does not meet the requirements.

4. A transient gamma radiation shielding method according to claim 3, characterized in that: In step 8), the material and thickness of the shielding wall are preliminarily determined by the calculation method provided in the U.S. National Radiation Protection and Measurement Council Report No. 155 based on the electron peak energy of the transient high-current electron accelerator.

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