A method for constructing an isotopic neutron source shielding benchmark experimental condition

Abstract

The present application relates to a kind of isotopic neutron source shielding benchmark experimental condition construction method, the method includes the following steps: calibration neutron source source term parameter and the response parameter of detection system;Based on calibration result and verification target, design the geometry and material parameters of series macroscopic sample, and its component, size and uniformity are detected;Design and arrange modular shadow cone device to deduct scattering background;Low scattering support and accurate positioning device are configured;The effectiveness of the experimental conditions constructed is verified.Through the whole standardization process from source term calibration, macroscopic sample design, shadow cone design to positioning, the high consistency of experimental conditions is ensured.Through systematic and standardized experimental condition construction and verification, the defects of traditional shielding benchmark experimental method, such as relying on experience and poor reproducibility, are overcome, the accuracy and consistency of shielding benchmark experimental conditions are guaranteed from the source, and experimental failure and resource waste caused by improper condition setting are avoided.

Description

Technical Field

[0001] This invention relates to the field of radiation protection technology, and in particular to a method for constructing reference experimental conditions for isotope neutron source shielding. Background Technology

[0002] In the process of conducting shielded benchmark experiments using isotopic neutron sources, there are obvious defects in the methods for constructing experimental conditions, which greatly reduces the quality and value of experimental data.

[0003] First, at the experimental design level, existing methods rely excessively on the personal experience of operators. This leads to significant arbitrariness in key aspects such as the geometric parameters of macroscopic samples, the selection of the image cone / detector, and the overall spatial arrangement, making it difficult to reproduce and compare experimental conditions between different research teams and even different batches. Furthermore, after selecting macroscopic samples and detectors based on personal experience, there is a lack of a process to systematically verify whether their performance meets the experimental objectives. This introduces systematic errors that are difficult to quantify and trace from the outset, resulting in poor reproducibility and comparability of the final experimental data, and making it difficult to form an effectively integrated and shared benchmark database.

[0004] Furthermore, in the preliminary research phase of experimental design, experiments are often conducted using a trial-and-error approach. This can easily lead to significant measurement errors due to issues such as improper detector placement, unreasonable design or placement of macroscopic samples and shadow cones, and failure to verify the rationality of the placement, thus affecting the reliability of subsequent measurement data. This problem not only reduces experimental efficiency but also wastes valuable time and funds allocated to the neutron source.

[0005] The above problems urgently need to be addressed. Summary of the Invention

[0006] This invention discloses a method for constructing the experimental conditions for shielding isotopic neutron sources, aiming to solve the technical problems existing in the prior art.

[0007] This invention employs the following technical solution, including: calibrating the source term parameters of a neutron source and the response parameters of a detector, wherein the source term parameters of the neutron source include source activity, source intensity, and a source term definition spectrum; based on the calibrated source term parameters, the detector response parameters, and the verification target, setting geometric and material parameters for a series of macroscopic samples, wherein the verification target is used to indicate the neutron reaction cross section of the sample material, used to determine the macroscopic sample material based on the neutron reaction cross section, the macroscopic sample is used to indicate the blocky experimental medium that interacts with neutrons emitted from the neutron source, and the parameters of the macroscopic sample include nuclide composition, geometric dimensions, roughness, and density; for the... The macroscopic sample is subjected to tests for nuclide composition, geometric dimensions, and density uniformity. If the test results do not meet the preset standards, the macroscopic sample is reset or adjusted. If the test results meet the preset standards, the macroscopic sample is placed between the neutron source and the detector, and the central axes of the three are collinear using a positioning device. A shadow cone is placed between the macroscopic sample and the detector, wherein the distance between the detector and the shadow cone should be greater than the length of the shadow cone, the solid angle of the shadow cone corresponding to the shadow region should be greater than the solid angle of the detector and less than twice the solid angle of the detector, and the length of the shadow cone should be sufficient to attenuate the flux of the neutron source. The above steps involve validating the experimental conditions for constructing the neutron source, the macroscopic sample, the shadow cone, and the detector. If the verification is successful, the experimental conditions are constructed.

[0008] Optionally, the source term parameters of the neutron source are calibrated, including: obtaining the manufacturing time and manufacturing activity of the neutron source through the neutron source's identification card; calculating the current activity of the neutron source based on the half-life and manufacturing activity of the neutron source; calculating the source intensity of the neutron source based on the current activity; measuring the neutron count rate emitted by the neutron source at a preset location using a long counter to obtain the neutron radiation field intensity information at the preset location; and using the neutron energy spectrum of the isotopic neutron source published in accordance with international standards as the source term definition in the Monte Carlo simulation or as a preset spectrum in the multi-sphere neutron spectrometer's spectral interpretation program.

[0009] Optionally, based on the half-life of the neutron source and its initial activity, the current activity of the neutron source is calculated, including: the current activity is calculated as follows: in, For current activity level, The activity level at the factory outlet. The half-life is denoted by t, which is the time interval between the neutron source's manufacturing date and the current time.

[0010] Optionally, based on the calibrated source term parameters, detector parameters, and verification targets, a series of geometric and material parameters for macroscopic samples are set, including: determining the mean free path of the neutrons emitted from the neutron source in the macroscopic sample material; determining the geometric volume length of the macroscopic sample based on the neutron mean free path, wherein the geometric volume length of the macroscopic sample reaches 1 to 7 neutron mean free paths; determining the surface roughness of the macroscopic sample, wherein the roughness is less than 3.2 micrometers; and determining the nuclide composition of the macroscopic sample, wherein the total mass percentage of the measured major nuclide composition should be greater than 99.99%, and the major nuclide composition is used to indicate the composition of the verification targets contained in the macroscopic sample.

[0011] Optionally, the macroscopic sample is subjected to tests for nuclide composition, geometric dimensions, and density uniformity. Determining whether the density uniformity of the macroscopic sample meets the usage standards includes: randomly presetting multiple different sampling points around the macroscopic sample; obtaining the photon attenuation factor at the multiple different sampling points; calculating the relative deviation of the attenuation factor at the multiple different sampling points; if the relative deviation is greater than ±0.5%, determining that the performance of the macroscopic sample does not meet the usage standards; if the discrete deviation is less than or equal to ±0.5%, determining that the performance of the macroscopic sample meets the usage standards.

[0012] Optionally, obtaining the photon attenuation factor at multiple different sampling points includes: simulating the measurement of the first photon dose rate at multiple different sampling points without the macroscopic sample; simulating the measurement of the second photon dose rate at multiple different sampling points with the macroscopic sample placed, wherein the multiple different sampling points of the first photon dose rate and the multiple different sampling points of the second photon dose rate must be the same; the photon attenuation factor is calculated as follows: Where K is the photon attenuation factor, The first photon dose rate, This represents the second photon dose rate.

[0013] Optionally, placing a shadow cone between the macroscopic sample and the detector includes: determining the geometric placement orientation of the shadow cone, wherein the shadow cone has a frustum-shaped structure, the axis of the shadow cone is aligned with the central axis of the solid angle opened by the detector relative to the front end of the shadow cone, the smaller diameter end of the shadow cone points towards the vertex of the solid angle of the detector, and the larger diameter end of the shadow cone points towards the opening direction of the solid angle of the detector; determining the size of the solid angle of the shadow cone, wherein the solid angle of the shadow cone is greater than the solid angle of the detector and less than twice the solid angle of the detector, the solid angle of the shadow cone is used to indicate the spatial cone angle formed by extending backward from the detector direction to the front end of the shadow cone, the area within the solid angle range of the detector is the effective field of view of the detector, and the shadow cone is used to shield scattered neutrons outside the solid angle range of the detector, subtracting the background; determining a first distance between the shadow cone and the detector, wherein the distance between the shadow cone and the detector needs to be greater than the cone length of the shadow cone; and determining the position of the shadow cone based on the geometric placement orientation, the size of the solid angle, and the first distance, and placing the shadow cone between the macroscopic sample and the detector.

[0014] Optionally, the effectiveness of the experimental conditions for constructing the neutron source, the macroscopic sample, the shadow cone, and the detector is verified, including: First, a shielding benchmark example conforming to international standards is selected. Experimental conditions are constructed and measurements are performed to complete the first validity verification. If the measurement results are consistent with the reference values ​​of the shielding benchmark example within the uncertainty range of both parties, the verification is passed. Second, a standard spherical polyethylene sample with a single composition and accurate nuclear data is selected as the macroscopic sample. Experimental conditions are constructed and measurements are performed to complete the second validity verification. The measurement results are compared with high-precision simulation calculations based on an international standard evaluation nuclear database. If the deviation is within a preset tolerance range, the verification is passed. Third, multiple homogeneous macroscopic samples with different thicknesses are used. Comparative experimental conditions are constructed and measurements are performed to complete the third validity verification. Experimental data on the change in transmittance with thickness are measured. The experimental data is fitted with theoretical data. If the goodness of fit is greater than a preset goodness of fit value, and the macroscopic cross-section obtained by the fitting matches the theoretical expected value, the verification is passed. If at least two of the first, second, and third validity verification methods are arbitrarily selected, and the verification results of the selected methods are all valid, the experimental conditions are determined to be valid.

[0015] Optionally, an experiment is conducted using a neutron source under the stated experimental conditions to obtain a set of experimental data on penetration rate and thickness. The experimental data is then fitted with theoretical data, including: conducting an experiment using a neutron source under the stated experimental conditions, changing the thickness of the macroscopic sample, and measuring the neutron experimental penetration rate; calculating the theoretical penetration rate based on the thickness of the penetrating material using the penetration rate formula; fitting the experimental penetration rate with the theoretical penetration rate to obtain the goodness of fit, thus completing the third validity verification.

[0016] Optionally, based on the thickness of the penetrating object, the theoretical penetration rate is calculated using a penetration rate formula, including: the penetration rate formula is: Where T is the theoretical transmittance, d is the thickness of the penetrator, ∑ is the macroscopic neutron separation cross section of the penetrator, and A is a constant.

[0017] The technical solution adopted in this invention can achieve at least one of the following beneficial effects: In this embodiment of the invention, the trial-and-error method relying on personal experience is abandoned. A standardized process, from source term calibration, macroscopic sample design, shadow cone design to positioning, ensures a high degree of consistency in experimental conditions. This allows any laboratory to reproduce the experiment using this method, effectively solving the data silo problem in existing technologies and laying the foundation for building a high-quality, shareable benchmark database. Verification of macroscopic samples ensures they meet standards, reducing the possibility of poor sample functionality due to reliance on personal experience, thereby improving experimental accuracy. Validation of experimental conditions, conducted from multiple angles before the formal experiment, allows for the early detection and correction of potential problems, avoiding experimental failures and resource waste due to improper condition settings, thus saving valuable neutron source time and experimental costs. Attached Figure Description

[0018] To more clearly illustrate the technical solutions of the embodiments of the present invention, the accompanying drawings used in the description of the embodiments will be briefly introduced below, forming part of the present invention. The illustrative embodiments of the present invention and their descriptions explain the present invention and do not constitute an improper limitation of the present invention. In the accompanying drawings: Figure 1 This is a flowchart of the steps in constructing the experimental conditions for shielding an isotopic neutron source according to the present invention. Figure 2 This is a simplified flowchart of a method for constructing the experimental conditions for shielding an isotopic neutron source according to the present invention. Figure 3 This is a distribution diagram of macroscopic sample homogeneity test sampling points in the method for constructing isotopic neutron source shielding reference experimental conditions of the present invention; Figure 4This is a diagram of the shadow cone support in the method for constructing the shielding reference experimental conditions of an isotopic neutron source according to the present invention; Figure 5 This is a diagram of a spherical macroscopic sample support frame in the method for constructing shielded reference experimental conditions for an isotopic neutron source according to the present invention; Figure 6 This is a diagram of a plate-shaped macroscopic sample support frame in the method for constructing shielded reference experimental conditions for an isotopic neutron source according to the present invention; Figure 7 This is a structural diagram of the experimental positioning device in the method for constructing the shielding reference experimental conditions of an isotopic neutron source according to the present invention. Detailed Implementation

[0019] To make the objectives, technical solutions, and advantages of this invention clearer, the technical solutions of this invention will be clearly and completely described below in conjunction with specific embodiments and corresponding drawings. In the description of this invention, it should be noted that the term "or" is generally used to include the meaning of "and / or," unless otherwise expressly indicated.

[0020] In the description of this invention, it should be noted that, unless otherwise explicitly specified and limited, the terms "installation," "connection," and "linking" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral connection; they can refer to a mechanical connection or a magnetic connection; they can refer to a direct connection or an indirect connection through an intermediate medium; and they can refer to the internal communication between two components. Those skilled in the art can understand the specific meaning of the above terms in this invention based on the specific circumstances. Furthermore, in the description of this application, the terms "first," "second," etc., are used only for distinguishing descriptions and should not be construed as indicating or implying relative importance. In the description of this invention, "a plurality of" means at least two, such as two, three, or more, unless otherwise explicitly specified.

[0021] Obviously, the described embodiments are only some, not all, of the embodiments of the present invention. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without inventive effort are within the scope of protection of the present invention.

[0022] First, to facilitate understanding of the embodiments of the present invention, some terms or nouns involved in the present invention will be explained below: Source activity, which characterizes the rate at which the atomic nuclei of a radioactive substance undergo spontaneous decay, is a fundamental physical quantity describing the decay capability of a radioactive source.

[0023] Source strength is an engineering / application concept without a unified and strict physical definition. Its core characteristic is the intensity / flux of radiation emitted by a radiation source. It is a derivative quantity of activity combined with radiation characteristics.

[0024] A source term is a comprehensive description of the characteristics and parameters of the radiation / hazardous substances released by a radiation source (radioactive / non-radioactive); it is a set of integrated parameters.

[0025] To address the problems existing in related technologies, this application provides a method for constructing isotopic neutron source shielding reference experimental conditions.

[0026] This embodiment provides a method for constructing the experimental conditions for shielding isotopic neutron sources, such as... Figure 1 and Figure 2 As shown, Figure 1 This is a flowchart illustrating the steps of a method for constructing a shielding reference experimental condition for an isotopic neutron source according to the present invention. Figure 2 This is a simplified flowchart of a method for constructing shielding reference experimental conditions for an isotopic neutron source according to the present invention. The method includes: Step S102: Calibrate the source term parameters of the neutron source and the response parameters of the detector, wherein the source terms of the neutron source include source activity, source intensity, and source term definition spectrum. In some preferred embodiments, calibrating the source terms of the neutron source includes: obtaining the manufacturing time and manufacturing activity of the neutron source through the neutron source's identification card; calculating the current activity of the neutron source based on its half-life and manufacturing activity; calculating the source intensity of the neutron source based on the current activity; measuring the neutron count rate emitted by the neutron source at a preset location using a long counter to obtain neutron radiation field intensity information at the preset location; and using the neutron energy spectrum of the isotopic neutron source published in accordance with international standards as the source term definition in the Monte Carlo simulation or as a preset spectrum for the multi-sphere neutron spectrometer's spectral interpretation program.

[0027] Optionally, the manufacturing time and activity information can be obtained through the neutron source's identification card. The core of the neutron source's "identity card" is the radioactive source coding card (commonly known as the radioactive source ID card), which is a unique 12-bit coding identification carrier assigned to each neutron source (including isotopic neutron sources such as Am-Be and Cf-252) in accordance with the national "Radioactive Source Coding Rules" (Huanfa

[2004] No. 118). It is also accompanied by a manufacturing certificate / label for tracing key information such as manufacturing time and activity.

[0028] Optionally, the source term parameters of the neutron source include source activity, source intensity, and source term definition spectrum; the detector response parameters include detector type, sensitive volume size, sensitive medium material and pressure, detector shell size and material, operating parameters, and response characteristic parameters; the parameters of the macroscopic sample include nuclide composition, geometric dimensions, roughness, and density.

[0029] Optionally, the current activity of the neutron source can be calculated by combining the half-life of the neutron source and its initial activity. The calculation formula is as follows: in, Let N(t) be the initial activity of the source, and N(t) be the current activity. The value is the half-life, and t is the time elapsed from the date of source activity calibration to the start of the experiment.

[0030] Optionally, a long counter can be used to measure the neutron count rate at a specified location to obtain neutron radiation field intensity information at that specific location during the experiment. The neutron energy spectrum of the isotopic neutron source published by the IAEA is used as the source term definition spectrum for Monte Carlo simulation calculations and the preset spectrum for the multi-sphere neutron spectrometer interpretation software to minimize simulation calculation errors and interpretation errors caused by the preset spectrum.

[0031] Optionally, before conducting the experiment, the detector used in the benchmark experiment needs to be tested and calibrated. Specifically, the detector is placed in a Cs-137 standard gamma radiation field (which must be consistent with the neutron source used to avoid energy response errors caused by nuclide differences), and 3 to 5 known standard dose rate points are set; the indicated dose rate of the instrument at each standard point is recorded, compared with the standard true dose rate, and a correction factor is obtained. Based on the product of the correction factor and the example dose rate, the true photon dose rate is obtained, and the photon dose rate of the detector is determined.

[0032] In some preferred embodiments, the current activity of the neutron source is calculated based on the half-life of the neutron source and its initial activity, including: the current activity is calculated as follows: in, For current activity level, The activity level at the factory outlet. The half-life is denoted by t, which is the time interval between the neutron source's manufacturing date and the current time.

[0033] Step S104: Based on the calibrated source term parameters, detector response parameters and verification targets, set the geometric and material parameters of a series of macroscopic samples. The verification targets are used to indicate the neutron reaction cross section of the sample material and to determine the macroscopic sample material based on the neutron reaction cross section. The macroscopic samples are used to indicate the blocky experimental medium that interacts with the neutrons emitted from the neutron source. The parameters of the macroscopic samples include nuclide composition, geometric dimensions, roughness and density. The verification target is either the neutron reaction cross section of a certain material or the reliability of the Monte Carlo calculation software. The preparation of macroscopic samples is determined based on the specific verification target: when the verification target is the neutron reaction cross section data of a specific material, macroscopic samples are prepared using that material; when the verification target is the reliability of the Monte Carlo calculation program in shielding calculations for a specific material, macroscopic samples are also prepared using that material.

[0034] In some preferred embodiments, based on the calibrated source term parameters, detector parameters, and verification targets, a series of geometric and material parameters for macroscopic samples are set, including: determining the mean free path of neutrons emitted from the neutron source in the macroscopic sample material; determining the geometric volume length of the macroscopic sample based on the neutron mean free path, wherein the geometric volume length of the macroscopic sample reaches 1 to 7 neutron mean free paths; determining the surface roughness of the macroscopic sample, wherein the roughness is less than 3.2 micrometers; and determining the nuclide composition of the macroscopic sample, wherein the total mass percentage of the measured major nuclide composition should be greater than 99.99%, and the major nuclide composition is used to indicate the composition of the verification targets contained in the macroscopic sample.

[0035] Optionally, to better verify nuclear databases and shielding calculation programs, the number of interactions between neutrons and the material medium should be sufficiently high, highlighting the nuclide being tested. Therefore, the design of macroscopic samples for benchmark experiments must meet the following requirements: The macroscopic sample should be large enough, with a volume length equal to 1–7 neutron mean free paths. Its geometry should be a regular shape, such as spherical or plate-like, facilitating theoretical calculations. The composition of the macroscopic sample should highlight the nuclide being tested. The surface of the macroscopic sample should be as smooth and flat as possible, with a roughness ≤3.2 μm. The macroscopic sample should have good density homogeneity.

[0036] Optionally, regarding the placement of macroscopic samples, for spherical macroscopic samples, the neutron source should be located at the center of the sphere. For plate-shaped macroscopic samples, simulation calculations are needed to determine the size range of the macroscopic sample, following the principles of coaxiality, perpendicular incidence, full beam coverage, and controllable spacing. Plate-shaped macroscopic samples are planar two-dimensional structures, and the neutron beam must be incident perpendicularly to the plane of the macroscopic sample (to avoid changes in effective penetration thickness and increased beam reflection / scattering due to oblique incidence). Furthermore, the macroscopic sample must completely cover the neutron beam cross section (without any beam leakage). At the same time, the sample, neutron source, shadow cone, and detector must be strictly coaxial (the axis is the direction of neutron beam propagation). This is the basis for ensuring the reproducibility of experimental data.

[0037] Optionally, the main nuclide component here refers to the components contained in the material. For example, polyethylene material should contain C and H, and the remaining nuclides are impurities.

[0038] Step S106: The macroscopic sample is tested for nuclide composition, geometric size and density uniformity. If the test results do not meet the preset standards, the macroscopic sample is reset or adjusted. If the test results meet the preset standards, the macroscopic sample is placed between the neutron source and the detector, and the central axes of the three are collinear using a positioning device. In some preferred embodiments, the macroscopic sample is tested for radionuclide composition, geometric dimensions, and density uniformity. Determining whether the density uniformity of the macroscopic sample meets the usage standard includes: randomly setting multiple different sampling points around the macroscopic sample; obtaining the photon attenuation factor at the multiple different sampling points; calculating the relative deviation of the attenuation factor at the multiple different sampling points; if the relative deviation is greater than ±0.5%, the performance of the macroscopic sample is determined to not meet the usage standard; if the discrete deviation is less than or equal to ±0.5%, the performance of the macroscopic sample is determined to meet the usage standard.

[0039] Optionally, to ensure the authenticity and reliability of experimental data and the reproducibility of experimental results, the nuclide composition, geometric dimensions (including tolerances), roughness, and density uniformity of the macroscopic samples used need to be tested and evaluated. A uniformity testing and verification experiment of plate-shaped macroscopic samples was conducted based on a portable Cs-137 photon source and a photon dose rate meter. By comparing the photon attenuation factors at different sampling points, a quantitative evaluation of the composition and density uniformity of various plate materials was achieved.

[0040] Specifically, for each type of sample material with different thicknesses, seven sampling points can be selected as sample uniformity test points to conduct photon transmittance tests, such as... Figure 3 As shown. For different sampling points, it is necessary to ensure that the distance between the test source and the sample, the distance between the detector and the macroscopic sample, and the relative position between the detector and the test source remain unchanged.

[0041] Optionally, meticulous pre-design and verification significantly improve the reliability and authority of experimental data. Rigorous testing of macroscopic samples systematically reduces systematic errors and background interference in the experiments.

[0042] In some preferred embodiments, obtaining the photon attenuation factor at multiple different sampling points includes: simulating the measurement of the first photon dose rate at multiple different sampling points without a macroscopic sample; simulating the measurement of the second photon dose rate at multiple different sampling points with a macroscopic sample, wherein the multiple different sampling points for the first photon dose rate and the multiple different sampling points for the second photon dose rate must be the same; the photon attenuation factor is calculated as follows: Where K is the photon attenuation factor, The first photon dose rate, This represents the second photon dose rate.

[0043] Step S108: Place a shadow cone between the macroscopic sample and the detector. The distance between the detector and the shadow cone should be greater than the length of the shadow cone. The solid angle of the shadow cone corresponding to the shadow region should be greater than the solid angle of the detector but less than twice the solid angle of the detector. The length of the shadow cone should be sufficient to attenuate the flux of the neutron source. above; In some preferred embodiments, placing a shadow cone between the macroscopic sample and the detector includes: determining the geometric orientation of the shadow cone, wherein the shadow cone has a frustum-shaped structure, the axis of the shadow cone is aligned with the central axis of the solid angle opened by the detector to the front end of the shadow cone, the smaller diameter end of the shadow cone points towards the vertex of the solid angle of the detector, and the larger diameter end of the shadow cone points towards the opening direction of the solid angle of the detector; determining the size of the solid angle of the shadow cone, wherein the solid angle of the shadow cone is greater than the solid angle of the detector and less than twice the solid angle of the detector, the solid angle of the shadow cone is used to indicate the spatial cone angle formed by extending backward from the detector direction to the front end of the shadow cone, the area within the solid angle range of the detector is the effective field of view of the detector, and the shadow cone is used to shield scattered neutrons outside the solid angle range of the detector, subtracting the background; determining a first distance between the shadow cone and the detector, wherein the distance between the shadow cone and the detector must be greater than the cone length of the shadow cone; and determining the position of the shadow cone based on the geometric orientation, the size of the solid angle, and the first distance, and placing the shadow cone between the macroscopic sample and the detector.

[0044] Optionally, the neutrons within the detector's solid angle are direct neutrons, which are the neutrons ultimately measured; those outside the solid angle are scattered neutrons, which interfere with the measurement results of direct neutrons. Without the shadow cone, the detector measures S1 = "scattered neutrons + direct neutrons". The shadow cone's function is to shield the neutrons within the detector's solid angle, that is, to shield the direct neutrons, so that with the shadow cone, the detector can only measure S2 = "scattered neutrons" outside the solid angle. Thus, by subtracting S2 from S1, the desired direct neutron measurement result is obtained.

[0045] Optionally, the primary function of the shadow cone is to accurately measure and subtract scattered particles, thereby greatly reducing the influence of background on experimental measurement results and improving the reliability and usability of measured reference data. Referring to GB / T 14055.2-2012 / ISO 8529-2:2000, the overall design of the shadow cone should meet the following requirements: the shadow cone should be sufficiently long in the neutron incident direction of the source term (to attenuate the direct neutron flux). The above measures are taken to ensure the shadow cone design has good background subtraction. The width of the shadow cone in the direction perpendicular to the incident neutron from the source ensures that the solid angle of the shadow cone is greater than the solid angle of the detector, but less than twice the solid angle of the detector. The shape and position of the shadow cone need to be optimized. The core is to ensure that it can effectively block neutrons directly incident from the source (or macroscopic sample) to the detector, while minimizing the obstruction of neutrons scattered from the experimental environment to the detector, and minimizing the additional scattering introduced by the shadow cone itself. Specifically, its position and size should ensure that the shadow cone body is not within the direct field of view of the detector and collimation channel to ensure that the shadow cone can completely block direct neutrons; and the solid angle of the shadow cone should not exceed the solid angle of the detector by too much to avoid blocking too much environmental scattering. The shadow cone should be positioned appropriately from the neutron source. Proximity to the neutron source can prevent neutrons in the front hemisphere from entering the detector, but may increase back-end scattering. The relative position of the shadow cone to the detector should be appropriate, and the distance from the back end of the shadow cone to the detector should not be less than the length of the cone body.

[0046] Optionally, to facilitate experiments, the shadow cone is usually designed in a modular fashion, such as... Figure 4 As shown. For the Cf-252 neutron source, the shadow cone can be designed as 20 cm iron + 30 cm boron-containing polyethylene or boron-containing paraffin (boron mass percentage not less than 5 wt%). Depending on the energy of the neutron source, it can be replaced with other material combinations with good neutron moderation and absorption capabilities, or a combination of fast neutron moderators such as tungsten and copper with boron-containing hydrogen-rich materials can be used.

[0047] Optionally, a standardized process, from source term calibration, sample design, and image cone design to positioning device, ensures a high degree of consistency in experimental conditions. This allows any laboratory to reproduce the experiment using this method, laying the foundation for building a high-quality, shareable benchmark database. The systematization and standardization of experimental conditions significantly improves the reproducibility and comparability of the data.

[0048] Step S110: Verify the validity of the experimental conditions for constructing the neutron source, macroscopic sample, shadow cone, and detector. If the verification is qualified, complete the construction of the experimental conditions.

[0049] Optionally, a support frame can be set up for the macroscopic samples before constructing the experimental conditions. Macroscopic samples include plate-shaped and spherical macroscopic samples. The macroscopic samples used in the shielded reference experiment are relatively large, requiring a support frame to hold the spherical, plate-shaped, and shadow cone samples. The experimental support frame must be safe and reliable, have minimal impact on the experimental results, and facilitate experimental operation. The support frame is designed as an aluminum basket-like structure to ensure support while minimizing the generation of scattered neutrons. The design of the support frame needs to be adjusted according to the specific requirements of the shielded reference experiment and the laboratory layout. The structure can be as follows: Figure 5 and Figure 6 As shown.

[0050] Optionally, during the placement of macroscopic samples, neutron sources, and detectors, distance and position determination is required. A positioning device can be set up to accurately locate the radiation source, experimental sample, shadow cone, detector, etc. This has a crucial impact on the rationality, reliability, and reproducibility of the final measurement results of the shielded reference experiment. The positional parameters of each structure are also key to constructing the simulation calculation model. When constructing experimental conditions, the positioning device needs to be designed in conjunction with the actual measurement environment. The positioning device consists of a support rod, a scale, and a bevel gauge, where the scale and bevel gauge must be standard measuring instruments. The structure can be as follows: Figure 7 As shown. Meanwhile, to ensure the plate-shaped sample is placed vertically and to avoid thickness variations due to tilting, a three-point plane determination method is required. This involves taking three symmetrical positions on the macroscopic sample plate surface and measuring the distances between each point and the source term. If the distances are consistent, the sample plate is placed vertically.

[0051] In some preferred embodiments, the validity of the experimental conditions for constructing the neutron source, macroscopic sample, shadow cone, and detector is verified, including: selecting a shielding reference example conforming to international standards, executing the constructed experimental conditions and performing measurements to complete the first validity verification, wherein the verification is passed if the measurement results are consistent with the reference values ​​of the shielding reference example within the uncertainty range of both parties; selecting a polyethylene standard spherical sample with a single composition and accurate nuclear data as the macroscopic sample, executing the constructed experimental conditions and performing measurements to complete the second validity verification, wherein the measurement results are compared with the high-precision simulation calculation results based on the international standard evaluation nuclear database, and the deviation is passed within the preset tolerance range; using multiple homogeneous macroscopic samples with different thicknesses, executing the constructed comparative experimental conditions and performing measurements to complete the third validity verification, wherein experimental data on the transmission rate as a function of thickness are measured and obtained, and the experimental data are fitted with theoretical data, and the verification is passed if the goodness of fit is greater than the preset goodness of fit value and the macroscopic separation cross section obtained by the fitting matches the theoretical expected value; and determining that the experimental conditions are valid if at least two of the first, second, and third validity verification methods are arbitrarily selected and the verification results of the selected methods are all valid.

[0052] Optionally, after the shielded reference experimental conditions are established, the reliability and effectiveness of the experimental measurement conditions need to be verified. The main verification methods include the following three: The first method is to use a typical benchmark example for verification. A generally recognized and reliable typical benchmark example is selected, and experimental conditions consistent with the example are constructed to conduct a control experiment. The experimental measurement results (mainly the leakage neutron spectrum) are compared with the reference experimental values ​​or high-confidence simulation values ​​provided in the example. The absolute value of the relative deviation between the measured value and the reference value should not exceed 10%.

[0053] The second method involves standard sample verification, using standard spherical polyethylene samples to test the accuracy and validity of the experimental conditions. Polyethylene is primarily composed of H and C elements; neutrons react with H nuclei through only one pathway, namely elastic scattering, ensuring measurement accuracy. The experimental results are compared with theoretical predictions calculated using high-precision Monte Carlo simulations based on evaluation kernel databases (such as ENDF and JEFF). The relative deviation between the experimental and theoretical predictions should not exceed 10%, and the measurement uncertainty should cover the theoretical prediction.

[0054] The third method is theoretical verification, where the penetrability of neutrons / photons through matter is expressed as follows: Where T is the transmittance; d is the thickness of the penetrated material; ∑ is the macroscopic neutron / photon separation cross section of the material; and A is a constant.

[0055] Experiments were conducted using a series of samples from the same batch to obtain a set of data on transmittance T versus thickness d. Substituting the experimental data into the formula for fitting yielded a high goodness of fit (R²). 2 If the value is greater than 0.95, it proves that the experimental data conforms to the exponential decay law and the physical process is clear. This formula can be used to conduct a preliminary evaluation and verification of the accuracy and rationality of the currently constructed shielding benchmark experimental conditions; it can also be used to correct the experimental measurement results to a certain extent.

[0056] The above three verification methods can be used individually or in combination. When the constructed experimental conditions can simultaneously meet at least two verification criteria, the platform is deemed effective and reliable, qualified to conduct formal shielding benchmark experiments, and the data it produces can be used as benchmark data for verifying the kernel database and shielding calculation software.

[0057] In some preferred embodiments, experiments are conducted using a neutron source under experimental conditions to obtain a set of experimental data on penetration rate and thickness. The experimental data is then fitted with theoretical data, including: conducting experiments using a neutron source under experimental conditions, changing the thickness of the macroscopic sample, and measuring the neutron experimental penetration rate; calculating the theoretical penetration rate based on the thickness of the penetrating material using the penetration rate formula; fitting the experimental penetration rate with the theoretical penetration rate to obtain the goodness of fit, and completing the third validity verification.

[0058] Optionally, by verifying the validity of experimental conditions, the constructed experimental conditions can be validated from multiple perspectives before the formal experiment. This can help identify and correct potential problems in advance, avoid experimental failures and resource waste caused by improper condition settings, and thus save valuable neutron source time and experimental costs.

[0059] Neutron penetration experiments were conducted using a series of standard samples, which were shielding materials of the same material but different thicknesses. The neutron penetration rate of each thickness was measured and recorded. Based on the exponential decay model, the experimental data were used to fit the model. If the goodness of fit was not less than 0.95 and the relative deviation between the macroscopic separation section obtained by fitting and the theoretical reference value was within the allowable range, the third validity verification was deemed to have passed.

[0060] In some preferred embodiments, the theoretical transmittance is calculated based on the thickness of the penetrating material using a transmittance formula, including: the transmittance formula is: Where T is the theoretical transmittance, d is the thickness of the penetrated object, ∑ is the macroscopic neutron separation cross section of the penetrated object, and A is a constant. Through steps S102 to S110, and through comprehensive quality control and prior design optimization, the traditional experience-based trial-and-error experiment is transformed into a predictable and verifiable engineering process. This method sequentially covers key aspects such as source term and detector calibration, serialized macroscopic sample design and testing, background suppression device (shadow cone) and low-scattering support design, application of precise positioning devices, and overall validity verification of experimental conditions. It comprehensively ensures the accuracy, consistency, and reliability of experimental conditions from source to output, thereby providing high-confidence benchmark verification data for the nuclear database and shielding calculation program.

[0061] The above are merely preferred embodiments of the present invention. It should be noted that those skilled in the art can make various improvements and modifications without departing from the principle of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A method for constructing the experimental conditions for shielding an isotopic neutron source, characterized in that, include: The source term parameters of the neutron source and the response parameters of the detector are calibrated, wherein the source term parameters of the neutron source include source activity, source intensity, and source term definition spectrum; Based on the calibrated source term parameters, detector response parameters, and verification targets, a series of macroscopic sample geometric and material parameters are set. The verification targets are used to indicate the neutron reaction cross section of the sample material and to determine the macroscopic sample material based on the neutron reaction cross section. The macroscopic samples are used to indicate the blocky experimental medium that interacts with the neutrons emitted from the neutron source. The parameters of the macroscopic samples include nuclide composition, geometric dimensions, roughness, and density. The macroscopic sample is tested for nuclide composition, geometric size and density uniformity. If the test results do not meet the preset standard, the macroscopic sample is reset or adjusted. If the test results meet the preset standard, the macroscopic sample is placed between the neutron source and the detector, and the central axes of the three are collinear using a positioning device. A shadow cone is placed between the macroscopic sample and the detector, wherein the distance between the detector and the shadow cone should be greater than the length of the shadow cone, the solid angle of the shadow cone corresponding to the shadow region should be greater than the solid angle of the detector and less than twice the solid angle of the detector, and the length of the shadow cone should be sufficient to attenuate the flux of the neutron source. above; The effectiveness of the experimental conditions constructed for the neutron source, the macroscopic sample, the shadow cone, and the detector is verified. If the verification is satisfactory, the construction of the experimental conditions is completed.

2. The method for constructing the experimental conditions for shielding an isotopic neutron source according to claim 1, characterized in that, The source term parameters of the neutron source are calibrated, including: The manufacturing time and activity level of the neutron source are obtained through its identification card. Calculate the current activity of the neutron source based on its half-life and initial activity. Based on the current activity, calculate the source strength of the neutron source; The neutron count rate emitted by the neutron source at the preset location is measured using a long counter to obtain the neutron radiation field intensity information at the preset location. The neutron energy spectrum of the isotopic neutron source, which conforms to international standards, is used as the source term definition in the Monte Carlo simulation or as the preset spectrum in the multi-sphere neutron spectrometer's spectral interpretation program.

3. The method for constructing the isotopic neutron source shielding reference experimental conditions according to claim 2, characterized in that, Based on the half-life of the neutron source and its initial activity, the current activity of the neutron source is calculated, including: The current activity is calculated as follows: in, For current activity level, The activity level at the factory outlet. The half-life is denoted by t, which is the time interval between the neutron source's manufacturing date and the current time.

4. The method for constructing the experimental conditions for shielding an isotopic neutron source according to claim 1, characterized in that, Based on the calibrated source term parameters, detector parameters, and verification targets, the geometric and material parameters of a series of macroscopic samples are set, including: The mean free path of the neutrons emitted from the neutron source in the macroscopic sample material is determined, and the geometric volume length of the macroscopic sample is determined based on the mean free path of the neutrons, wherein the geometric volume length of the macroscopic sample reaches 1 to 7 mean free paths of the neutrons. The roughness of the macroscopic sample surface is determined, wherein the roughness is less than 3.2 micrometers; The nuclide composition of the macroscopic sample is determined, wherein the total mass percentage of the measured major nuclide composition should be greater than 99.99%, and the major nuclide composition is used to indicate the components of the verification target contained in the macroscopic sample.

5. The method for constructing the experimental conditions for shielding an isotopic neutron source according to claim 1, characterized in that, The macroscopic sample is subjected to tests for radionuclide composition, geometric dimensions, and density uniformity. Determining whether the density uniformity of the macroscopic sample meets the applicable standards includes: Multiple different sampling points are randomly preset around the macroscopic sample; Obtain the photon attenuation factor at multiple different sampling points; Calculate the relative deviation of the attenuation factor at the multiple different sampling points. If the relative deviation is greater than ±0.5%, it is determined that the performance of the macroscopic sample does not meet the usage standard; if the discrete deviation is less than or equal to ±0.5%, it is determined that the performance of the macroscopic sample meets the usage standard.

6. The method for constructing the experimental conditions for shielding an isotopic neutron source according to claim 5, characterized in that, Obtain the photon attenuation factor at multiple different sampling points, including: Simulated measurements of the first photon dose rate at multiple different sampling points without the macroscopic sample being placed; When simulating the placement of the macroscopic sample, the second photon dose rate at multiple different sampling points is measured, wherein the multiple different sampling points of the first photon dose rate and the multiple different sampling points of the second photon dose rate must be the same; The photon attenuation factor is calculated as follows: Where K is the photon attenuation factor, The first photon dose rate, This represents the second photon dose rate.

7. The method for constructing the experimental conditions for shielding an isotopic neutron source according to claim 1, characterized in that, Placing an image cone between the macroscopic sample and the detector includes: The geometric placement of the shadow cone is determined, wherein the shadow cone has a frustum-shaped structure, the axis of the shadow cone is consistent with the direction of the central axis of the solid angle opened by the front end of the shadow cone of the detector, the small diameter end of the shadow cone points to the vertex of the solid angle of the detector, and the large diameter end of the shadow cone points to the opening direction of the solid angle of the detector. The solid angle of the shadow cone is determined, wherein the solid angle of the shadow cone is greater than the solid angle of the detector and less than twice the solid angle of the detector. The solid angle of the shadow cone is used to indicate the spatial cone angle formed by extending backward from the detector direction to the front end of the shadow cone. The area within the solid angle range of the detector is the effective field of view of the detector. The shadow cone is used to shield scattered neutrons outside the solid angle range of the detector, subtracting the background. Determine a first distance between the shadow cone and the detector, wherein the distance between the shadow cone and the detector must be greater than the cone length of the shadow cone; Based on the geometric placement orientation, the solid angle size, and the first distance, the position of the shadow cone is determined, and the shadow cone is placed between the macroscopic sample and the detector.

8. The method for constructing the experimental conditions for shielding an isotopic neutron source according to claim 1, characterized in that, The effectiveness of the experimental conditions for constructing the neutron source, the macroscopic sample, the shadow cone, and the detector was verified, including: Select a shielding benchmark example that conforms to international standards, implement the experimental conditions and perform measurements to complete the first validity verification. If the measurement results are consistent with the reference values ​​of the shielding benchmark example within the uncertainty range of both parties, the verification is passed. A polyethylene standard spherical sample with a single composition and accurate nuclear data was selected as the macroscopic sample. The experimental conditions were constructed and measurements were taken to complete the second validity verification. The measurement results were compared with the high-precision simulation calculation results based on the international standard evaluation nuclear database. If the deviation was within the preset tolerance range, the verification was passed. Using multiple homogeneous macroscopic samples of different thicknesses, comparative experimental conditions were constructed and measurements were taken to complete the third validity verification. Specifically, experimental data on the change of transmittance with thickness were measured and obtained. The experimental data were then fitted with theoretical data. If the goodness of fit was greater than the preset goodness of fit value and the macroscopic cross-section obtained by fitting matched the theoretical expected value, the verification was passed. If at least two of the first, second, and third valid verification methods are selected, and the verification results of the selected methods are all valid, then the experimental conditions are determined to be valid.

9. The method for constructing the experimental conditions for shielding an isotopic neutron source according to claim 8, characterized in that, Experiments were conducted using a neutron source under the stated experimental conditions to obtain a set of experimental data on penetration rate and thickness. These experimental data were then fitted to theoretical data, including: An experiment was conducted using a neutron source under the stated experimental conditions, the thickness of the macroscopic sample was varied, and the neutron experimental penetration rate was measured. Based on the thickness of the penetrating material, the theoretical penetration rate is calculated using the penetration rate formula; The experimental penetration rate is fitted to the theoretical penetration rate to obtain the goodness of fit, thus completing the third validity verification.

10. The method for constructing the experimental conditions for shielding an isotopic neutron source according to claim 9, characterized in that, Based on the thickness of the penetrating material, the theoretical penetration rate is calculated using the penetration rate formula, including: The penetration rate formula is: Where T is the theoretical transmittance, d is the thickness of the penetrator, ∑ is the macroscopic neutron separation cross section of the penetrator, and A is a constant.

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