Induced radioactivity assessment method suitable for mobile accelerator component

Abstract

The invention relates to the technical field of accelerator radiation protection, in particular to an induced radioactivity assessment method suitable for a mobile accelerator component. Monte Carlo simulation software is adopted to calculate radionuclide activity concentrations in different areas of an acceleration component before movement, then radionuclides serve as radiation source items, and three-dimensional space dose rate distribution of the component and the periphery when the position of the accelerator component changes is obtained through calculation. And rapid evaluation of the received dose of the staff during maintenance and rapid formulation of a maintenance scheme are realized. The method effectively promotes the application of the Monte Carlo method in the field of radiation protection of the accelerator, provides reference for radiation hazards to workers, and provides technical support for radiation protection and operation maintenance of the accelerator.

Description

Technical Field

[0001] The present invention relates to the technical field of accelerator radiation protection, in particular to an induced radioactivity assessment method applicable to mobile accelerator components. Technical Background

[0002] Currently, when evaluating induced radioactivity in accelerator components, only fixed accelerator components, that is, induced radioactivity when the position of the accelerator components does not change after irradiation, can be evaluated. It is not possible to evaluate the induced radioactivity in mobile accelerator components, that is, induced radioactivity when the position of the accelerator components changes after irradiation.

[0003] In order to solve the above problems, the present invention provides an induced radioactivity assessment method suitable for mobile accelerator components. This method takes into account the operating conditions of the accelerator components, uses Monte Carlo simulation software to calculate the activity concentration of radionuclides in different areas of the accelerator components before movement, and then uses radionuclides as radiation source items to calculate the three-dimensional spatial dose rate distribution of the components and their surroundings when the position of the accelerator components changes, thereby achieving a rapid assessment of the dose received by the staff during maintenance and a rapid formulation of maintenance plans. This solves the problem that the existing technology cannot assess the induced radioactivity of mobile accelerator components, that is, after the position of the accelerator components changes after irradiation. This method effectively promotes the application of the Monte Carlo method in the field of accelerator radiation protection, provides a reference for the radiation hazards received by the staff, and provides technical support for the radiation protection and operation and maintenance of accelerators. Summary of the Invention

[0004] To address the shortcomings of the existing technology, the present invention provides a method for assessing induced radioactivity in mobile accelerator components. This method considers the operating conditions of the accelerator components and uses Monte Carlo simulation software to calculate the activity concentration of radionuclides in different areas of the accelerator component before movement. Using the radionuclides as radiation source terms, the dose rate at the accelerator component's focal point after movement is then calculated, thereby enabling an assessment of the induced radioactivity of the mobile accelerator component. This method effectively promotes the application of Monte Carlo methods in the field of accelerator radiation protection, providing a reference for assessing radiation hazards to workers.

[0005] The technical solution adopted by the present invention is as follows: a method for evaluating induced radioactivity of mobile accelerator components, comprising the following steps:

[0006] S1. Determine the operating conditions of the accelerator components: The accelerator operating conditions include beam adjustment, beam supply, and maintenance. To meet the requirements of different operating conditions, the accelerator components can be designed to be mobile. For mobile accelerator components, the position of the mobile accelerator components is different under different operating conditions.

[0007] S2. Constructing a geometric model and inputting parameters: Using Monte Carlo simulation software to construct a geometric model, inputting radiation source terms, run time, and cooling time, the three-dimensional radionuclide activity concentration distribution is calculated.

[0008] S3. Select important areas: Based on the distribution of radionuclide activity concentration in each area, select important areas. The areas that determine the induced radioactivity are those with higher radionuclide activity concentration and larger volume.

[0009] S4. Reconstruct the geometric model of important areas: Based on the distribution of radionuclide activity concentration, the geometric model of important areas is divided into zones, and areas with similar activity concentrations are considered as one zone.

[0010] S5. Calculate radionuclide activity concentration: Calculate the radionuclide activity in each region of the new geometric model to obtain the radionuclide activity concentration in each region;

[0011] S6. Selection of important radionuclides: Important radionuclides are those whose activity accounts for a relatively high proportion of the total radionuclide activity. Considering that some individual radionuclides have short half-lives and decay rapidly, their contribution to the total radionuclide activity will soon disappear.

[0012] S7, constructing a geometric model of the accelerator component after it moves: constructing a geometric model of the accelerator component after it moves according to the operating conditions of the accelerator component;

[0013] S8. Calculate the three-dimensional spatial dose rate distribution: Take the radioactive nuclides in a single area as the radiation source term and calculate the three-dimensional spatial dose rate distribution;

[0014] S9. Calculate the three-dimensional total dose rate distribution: add the dose rates produced by each radionuclide in each area to calculate the three-dimensional total dose rate distribution;

[0015] S10. Develop a maintenance plan: Based on the three-dimensional total dose rate distribution, evaluate the dose received by workers when maintaining the Faraday cage and its shielding surface, and develop a maintenance plan.

[0016] Preferably, in step S1, a Faraday cage is used to measure the accelerator beam intensity. The accelerator operating conditions include beam adjustment, beam supply and maintenance. During beam adjustment, the accelerator components are located at the beamline height. During beam supply, the accelerator components are lowered below the beamline.

[0017] Preferably, in step S2, the geometric model is a Faraday cage and its shield, a vacuum box, a magnet upstream of the Faraday cage, and a superconducting cavity downstream of the Faraday cage, which are constructed using Monte Carlo simulation software.

[0018] Preferably, in step S2, the Monte Carlo simulation software is at least one of MCNPX or FLUKA, and the radiation source term includes the type, energy, number, direction and position information of beam loss particles.

[0019] Preferably, in step S3 , the important regions in the Faraday cage and its shield are the graphite region, the copper region, the tungsten region and the lead region.

[0020] Preferably, in step S4, the shape of the region is generally a cylinder, a torus cylinder, or a cuboid.

[0021] Preferably, in step S5, the radionuclide activities in a total of 31 areas of the Faraday cage and its shielding are calculated.

[0022] Preferably, in step S6, nuclides that contribute more than 0.5% to the total nuclide concentration and have a half-life greater than 20 seconds are selected as important radionuclides.

[0023] Preferably, in step S7, the Faraday cage is moved to a position 15 cm below the beam line, and the Faraday cage shield, upstream magnet, vacuum box and downstream part of the superconducting cavity remain in place.

[0024] Preferably, in step S10, it is considered that the worker performs maintenance at a distance of 30 cm from the lead shielding surface above the Faraday cage. It can be obtained that the worker receives a dose rate of 0.6 mSv / h. According to the requirements of the China Spallation Neutron Source for dose control during maintenance of radioactive workers, the quarterly dose does not exceed 2.5 mSv, and the annual dose does not exceed 10 mSv. It can be obtained that the maintenance time of the worker does not exceed 4.2 hours per quarter, and does not exceed 16.8 hours per year.

[0025] The present invention provides a significant method for assessing induced radioactivity in mobile accelerator components. Monte Carlo simulation software is used to calculate the activity concentration of radionuclides in different areas of the accelerator component before movement. The radionuclides are then used as radiation source terms to calculate the three-dimensional spatial dose rate distribution of the component and its surroundings when the accelerator component position changes. This allows for rapid assessment of the dose received by workers during maintenance and the rapid development of maintenance plans. This method effectively promotes the application of Monte Carlo methods in the field of accelerator radiation protection, provides a reference for assessing radiation hazards to workers, and offers technical support for radiation protection and operational maintenance of accelerators. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1 It is a logic principle diagram of the present invention;

[0027] Figure 2 It is a geometric model diagram constructed using Monte Carlo simulation software in the present invention;

[0028] Figure 3 The Faraday cup and its shielding nuclide activity concentration distribution diagram in the present invention (unit: Bq / cm3);

[0029] Figure 4 It is a geometric model diagram of the important area reconstructed in the present invention;

[0030] Figure 5 It is a geometric model diagram of the accelerator components after movement in the present invention;

[0031] Figure 6 The Faraday cup and its shielding dose rate distribution diagram in the present invention (unit: mSv / h);

[0032] Figure 7 1 is a diagram of the total dose rate distribution of the Faraday cage and its shielding (unit: mSv / h) of the present invention. DETAILED DESCRIPTION

[0033] The following describes a method for evaluating induced radioactivity of a mobile accelerator component according to the present invention by means of specific embodiments and accompanying drawings, and includes the following steps:

[0034] S1. Determine the operating conditions of the accelerator components: The accelerator operating conditions include beam adjustment, beam supply, and maintenance. To meet the requirements of different operating conditions, the accelerator components can be designed to be mobile. For mobile accelerator components, the position of the mobile accelerator components is different under different operating conditions.

[0035] S2. Constructing a geometric model and inputting parameters: Using Monte Carlo simulation software to construct a geometric model, inputting radiation source terms, run time, and cooling time, the three-dimensional radionuclide activity concentration distribution is calculated.

[0036] S3. Select important areas: Based on the distribution of radionuclide activity concentration in each area, select important areas. The areas that determine the induced radioactivity are those with higher radionuclide activity concentration and larger volume.

[0037] S4. Reconstruct the geometric model of important areas: Based on the distribution of radionuclide activity concentration, the geometric model of important areas is divided into zones, and areas with similar activity concentrations are considered as one zone.

[0038] S5. Calculate radionuclide activity concentration: Calculate the radionuclide activity in each region of the new geometric model to obtain the radionuclide activity concentration in each region;

[0039] S6. Selection of important radionuclides: Important radionuclides are those whose activity accounts for a relatively high proportion of the total radionuclide activity. Considering that some individual radionuclides have short half-lives and decay rapidly, their contribution to the total radionuclide activity will soon disappear.

[0040] S7, constructing a geometric model of the accelerator component after it moves: constructing a geometric model of the accelerator component after it moves according to the operating conditions of the accelerator component;

[0041] S8. Calculate the three-dimensional spatial dose rate distribution: Take the radioactive nuclides in a single area as the radiation source term and calculate the three-dimensional spatial dose rate distribution;

[0042] S9. Calculate the three-dimensional total dose rate distribution: add the dose rates produced by each radionuclide in each area to calculate the three-dimensional total dose rate distribution;

[0043] S10. Develop a maintenance plan: Based on the three-dimensional total dose rate distribution, evaluate the dose received by workers when maintaining the Faraday cage and its shielding surface, and develop a maintenance plan.

[0044] Preferably, in step S1, a Faraday cage is used to measure the accelerator beam intensity. The accelerator operating conditions include beam adjustment, beam supply and maintenance. During beam adjustment, the accelerator components are located at the beamline height. During beam supply, the accelerator components are lowered below the beamline.

[0045] Preferably, in step S2, the geometric model is a Faraday cage and its shield, a vacuum box, a magnet upstream of the Faraday cage, and a superconducting cavity downstream of the Faraday cage, which are constructed using Monte Carlo simulation software.

[0046] Preferably, in step S2, the Monte Carlo simulation software is at least one of MCNPX or FLUKA, and the radiation source term includes the type, energy, number, direction and position information of beam loss particles.

[0047] Preferably, in step S3 , the important regions in the Faraday cage and its shield are the graphite region, the copper region, the tungsten region and the lead region.

[0048] Preferably, in step S4, the shape of the region is generally a cylinder, a torus cylinder, or a cuboid.

[0049] Preferably, in step S5, the radionuclide activities in a total of 31 areas of the Faraday cage and its shielding are calculated.

[0050] Preferably, in step S6, nuclides that contribute more than 0.5% to the total nuclide concentration and have a half-life greater than 20 seconds are selected as important radionuclides.

[0051] Preferably, in step S7, the Faraday cage is moved to a position 15 cm below the beam line, and the Faraday cage shield, upstream magnet, vacuum box and downstream part of the superconducting cavity remain in place.

[0052] Preferably, in step S8, a radiation source position sampling model is established, considering that the activity concentration of radionuclides in a single area is uniformly distributed;

[0053] For a cylinder, the position sampling model is as follows:

[0054]

[0055] x=R·cos(2πε3)

[0056] y=R·sin(2πε3)

[0057] z=z1+(z2-z1)·ε4

[0058] Among them, the z direction is the axis of the cylinder, (x, y, z) is the coordinate of the particle sampling position, R0 is the radius of the cylinder, z1 and z2 are the maximum z-axis coordinate and minimum z-axis coordinate of the particle sampling, ε1, ε2, ε3, ε4 are random numbers;

[0059] For a donut cylinder, the position sampling model is as follows:

[0060]

[0061] x=R·cos(2πε4)

[0062] y=R·sin(2πε4)

[0063] z=z1+(z2-z1)·ε5

[0064] Among them, the z direction is the axis of the cylinder, (x, y, z) is the coordinate of the particle sampling position, R0 is the inner radius of the ring cylinder, R1 is the outer radius of the ring cylinder, z1 and z2 are the maximum z-axis coordinate and minimum z-axis coordinate of the particle sampling, ε1, ε2, ε3, ε4, ε5 are random numbers;

[0065] For a cuboid, the position sampling model is as follows:

[0066] x=x1+(x2-x1)·ε1

[0067] y=y1+(y2-y1)·ε2

[0068] z=z1+(z2-z1)·ε3

[0069] Where (x, y, z) is the particle sampling position coordinate, x1 and x2 are the maximum x-axis coordinate and minimum x-axis coordinate of the particle sampling, y1 and y2 are the maximum y-axis coordinate and minimum y-axis coordinate of the particle sampling, z1 and z2 are the maximum z-axis coordinate and minimum z-axis coordinate of the particle sampling, ε1, ε2, ε3 are random numbers;

[0070] When radioactive nuclides decay, the contribution of low-energy gamma rays and beta rays to the dose can be ignored compared to high-energy gamma rays. At the same time, the contribution of gamma rays with a lower emission probability to the dose can also be ignored. The energy sampling model of the radiation source term can be obtained as follows:

[0071]

[0072] Among them, P1, P2...P n-1 、P n , E1, E2...E n-1 、E n are the probability and energy of high energy and high probability gamma rays emitted when radioactive nuclides decay, respectively, and ε is a random number;

[0073] The emitted gamma rays are evenly distributed in a 4π solid angle, and the radiation source direction sampling model can be obtained as follows:

[0074] u=sin(2πε1)·cos(2πε2)

[0075] v=sin(2πε1)·sin(2πε2)

[0076] w=cos(2πε1)

[0077] Among them, (u, v, w) are the cosine vectors of the particle emission direction, ε1, ε2 are random numbers;

[0078] The three-dimensional spatial dose rate distribution is obtained by dividing the accelerator components and their surroundings into i*j*k cubic grids at fixed intervals along the x-axis, y-axis, and z-axis. The dose rate in each cubic grid is calculated, where the x-axis is divided into i intervals, the y-axis is divided into j intervals, and the z-axis is divided into k intervals.

[0079] Preferably, in step S9, the dose rates generated by the radionuclides in the respective regions are added together to calculate the total dose rate distribution in the three-dimensional space:

[0080] D i,j,k =D1 i,j,k +D2 i,j,k +...+Dn i,j,k

[0081] Among them, D i,j,kis the total dose rate produced by each radionuclide in each region at the cubic grid (i, j, k), D1 i,j,k is the dose rate produced by each radionuclide in region 1 at the cubic grid (i, j, k), Dn i,j,k is the dose rate produced by each radionuclide in region n at the cubic grid (i, j, k), where n is the number of regions;

[0082] Preferably, in step S10, it is considered that the worker performs maintenance at a distance of 30 cm from the lead shielding surface above the Faraday cage. It can be obtained that the worker receives a dose rate of 0.6 mSv / h. According to the requirements of the China Spallation Neutron Source for dose control during maintenance of radioactive workers, the quarterly dose does not exceed 2.5 mSv, and the annual dose does not exceed 10 mSv. It can be obtained that the maintenance time of the worker does not exceed 4.2 hours per quarter, and does not exceed 16.8 hours per year.

[0083] Example:

[0084] like Figure 1-7 As shown, the implementation of an induced radioactivity assessment method applicable to a mobile accelerator component involved in this embodiment specifically includes:

[0085] S1. Determine the operating conditions of the accelerator components: The accelerator operating conditions include beam adjustment, beam supply, and maintenance. To meet the requirements of different operating conditions, the accelerator components can be designed to be mobile. For mobile accelerator components, the Faraday cage is located at the beamline height during beam adjustment. During beam supply and maintenance, the Faraday cage is lowered to 15 cm below the beamline.

[0086] S2, such as Figure 2-3 As shown, the geometric model and input parameters are constructed: the geometric model is constructed using Monte Carlo simulation software (one of FLUKA, MCNPX, etc.), and the radiation source term, running time and cooling time are input to calculate the radionuclide activity concentration distribution in three-dimensional space: the geometric model includes the Faraday cage and its shielding, the vacuum box, the magnet upstream of the Faraday cage and the superconducting cavity downstream of the Faraday cage; the running time is 16 hours and the cooling time is 1 hour; the constructed geometric model is as shown Figure 2 As shown; the activity concentration distribution of the Faraday cage and its shielding nuclides is shown as Figure 3 As shown, the Faraday cage and its shield are divided into 180*160*160 cubic grids; wherein, the x-axis direction is divided into 180 intervals, the y-axis direction is divided into 160 intervals, and the z-axis direction is divided into 160 intervals;

[0087] S3. Select important areas: Based on the distribution of radionuclide activity concentrations in each area, select important areas. Areas with higher radionuclide activity concentrations and larger volumes determine the induced radioactivity. Important areas in the Faraday cage and its shielding are the graphite area, copper area, tungsten area, and lead area.

[0088] S4, such as Figure 4 As shown in the figure, the geometric model of the important areas is reconstructed: according to the distribution of radionuclide activity concentration, the geometric model of the important areas is divided into zones, and areas with similar activity concentration are considered as one zone. The shapes of the zones are generally cylinders, torus and cuboids; the graphite area is divided into 4 zones, including 2 cylindrical areas and 2 torus areas; the copper area is divided into 3 zones, including 2 torus areas and 1 cylindrical area; the tungsten area is divided into 4 zones, including 2 torus areas and 2 cylindrical areas; the lead area is divided into 20 zones, including 20 cuboid areas;

[0089] S5. Calculate radionuclide activity concentration: Calculate the radionuclide activity in each region of the new geometric model to obtain the radionuclide activity concentration in each region. Calculate the radionuclide activity in a total of 31 regions, including the Faraday cage and its shielding.

[0090] S6. Select important radionuclides: Important radionuclides are those with a relatively high activity percentage in the total radionuclide concentration. Select nuclides that contribute more than 0.5% to the total radionuclide concentration and have a half-life greater than 20 seconds as important radionuclides. Taking the graphite 1 area as an example, the important radionuclide activities are shown in Table 1.

[0091] Table 1 Radionuclide activity in region 1 of the graphite layer

[0092]

[0093]

[0094] S7, such as Figure 5 As shown in the figure, the geometric model of the accelerator components after movement is constructed: According to the operating conditions of the accelerator components, the geometric model of the accelerator components after movement is constructed, considering that the Faraday cage is moved to a position 15 cm below the beam line, and the Faraday cage shield, upstream magnet, vacuum box and downstream part of the superconducting cavity are fixed;

[0095] S8. Calculate the three-dimensional spatial dose rate distribution: Take the radioactive nuclides in a single area as the radiation source item, calculate the three-dimensional spatial dose rate distribution, divide the Faraday cage and its shield into 45*40*40 cubes, where the x-axis direction is divided into 45 intervals, the y-axis direction is divided into 40 intervals, and the z-axis direction is divided into 40 intervals; take the graphite 1 area as the 11C as an example, the Faraday cage and its shielding dose rate distribution are calculated as follows Figure 6 As shown;

[0096] S9, such as Figure 7 As shown, the three-dimensional total dose rate distribution is calculated: the dose rate produced by each radionuclide in 31 areas is added together to calculate the dose rate distribution of the Faraday cup and its shielding;

[0097] S10. Develop a maintenance plan: Based on the three-dimensional total dose rate distribution, evaluate the dose received by workers when maintaining the Faraday cage and its shielding surface, and develop a maintenance plan. Considering that workers perform maintenance at a distance of 30 cm from the lead shielding surface above the Faraday cage, it can be obtained that the dose rate received by workers is 0.6 mSv / h. Based on the dose control requirements of the China Spallation Neutron Source for radioactive workers during maintenance: at a distance of 30 cm from the equipment surface, the dose rate is 0.1 to 1 mSv / h, and manual maintenance requires time control; the quarterly dose does not exceed 2.5 mSv, and the annual dose does not exceed 10 mSv. It can be obtained that the maintenance time of workers does not exceed 4.2 hours per quarter and 16.8 hours per year.

Claims

1. A method for evaluating induced radioactivity of mobile accelerator components, characterized by: The following steps are involved: S1. Determine the operating conditions of the accelerator components: The accelerator operating conditions include beam adjustment, beam supply, and maintenance. To meet the requirements of different operating conditions, the accelerator components can be designed to be mobile. For mobile accelerator components, the position of the mobile accelerator components is different under different operating conditions. S2. Constructing a geometric model and inputting parameters: Using Monte Carlo simulation software to construct a geometric model, inputting radiation source terms, run time, and cooling time, the three-dimensional radionuclide activity concentration distribution is calculated. S3. Select important areas: Based on the distribution of radionuclide activity concentration in each area, select important areas. The areas that determine the induced radioactivity are those with higher radionuclide activity concentration and larger volume. S4. Reconstruct the geometric model of important areas: Based on the distribution of radionuclide activity concentration, the geometric model of important areas is divided into zones, and areas with similar activity concentrations are considered as one zone. S5. Calculate radionuclide activity concentration: Calculate the radionuclide activity in each region of the new geometric model to obtain the radionuclide activity concentration in each region; S6. Select important radionuclides: The important radionuclides are nuclides whose activity accounts for a relatively high proportion of the total radionuclides; S7, constructing a geometric model of the accelerator component after it moves: constructing a geometric model of the accelerator component after it moves according to the operating conditions of the accelerator component; S8. Calculate the three-dimensional spatial dose rate distribution: Take the radioactive nuclides in a single area as the radiation source term and calculate the three-dimensional spatial dose rate distribution; S9. Calculate the three-dimensional total dose rate distribution: add the dose rates produced by each radionuclide in each area to calculate the three-dimensional total dose rate distribution; S10. Develop a maintenance plan: Based on the three-dimensional total dose rate distribution, evaluate the dose received by workers when maintaining the Faraday cage and its shielding surface, and develop a maintenance plan.

2. The method for evaluating induced radioactivity of mobile accelerator components according to claim 1, wherein: In step S1, a Faraday cage is used to measure the accelerator beam intensity. The accelerator operating conditions include beam adjustment, beam supply, and maintenance. During beam adjustment, the accelerator components are located at the beamline height. During beam supply, the accelerator components are lowered below the beamline.

3. The method for evaluating induced radioactivity of mobile accelerator components according to claim 1, wherein: In step S2, the geometric model is a Faraday cage and its shield, a vacuum box, a magnet upstream of the Faraday cage, and a superconducting cavity downstream of the Faraday cage, which are constructed using Monte Carlo simulation software.

4. The method for evaluating induced radioactivity of mobile accelerator components according to claim 1, wherein: In step S2, the Monte Carlo simulation software is at least one of MCNPX and FLUKA, and the radiation source term includes the type, energy, number, direction and position information of beam loss particles.

5. The method for evaluating induced radioactivity of mobile accelerator components according to claim 1, wherein: In step S3 , the important regions in the Faraday cage and its shield are the graphite region, the copper region, the tungsten region, and the lead region.

6. The method for evaluating induced radioactivity of mobile accelerator components according to claim 1, wherein: In step S4, the shape of the region is generally a cylinder, a torus cylinder, or a cuboid.

7. The method for evaluating induced radioactivity of mobile accelerator components according to claim 1, wherein: In step S5 , the radionuclide activities in a total of 31 areas of the Faraday cage and its shielding are calculated.

8. The method for evaluating induced radioactivity of mobile accelerator components according to claim 1, wherein: In step S6 , nuclides that contribute more than 0.5% to the total nuclide concentration and have a half-life greater than 20 seconds are selected as important radionuclides.

9. The method for evaluating induced radioactivity of mobile accelerator components according to claim 1, wherein: In step S7 , it is considered that the Faraday cage is moved to a position 15 cm below the beamline, and the Faraday cage shield, upstream magnet, vacuum box and downstream part of the superconducting cavity remain in place.

10. The method for evaluating induced radioactivity of mobile accelerator components according to claim 1, wherein: In step S10, the worker performs maintenance at a specific position away from the upper lead shielding surface of the Faraday cage, and the worker's dose rate can be obtained. Then, according to the dose control requirements during the worker's maintenance, the worker's maintenance time can be obtained.

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