Epithermal neutron measurement system for boron neutron capture therapy

Abstract

The invention relates to an epithermal neutron measurement system for boron neutron capture therapy, and belongs to the technical field of epithermal neutron measurement, and the system comprises a collimation shielding body which is used for shielding and collimating an incident neutron beam to be measured; the thermal neutron absorber is used for absorbing thermal neutron components of the neutron beam passing through the collimation shielding body; the epithermal neutron regulation and control body is used for regulating and controlling the proportion and energy distribution of epithermal neutron beams passing through the thermal neutron absorber; the alpha particle shielding body is used for shielding alpha particles of the detector or the surrounding environment; the detector is used for detecting the total number of alpha particles generated by nuclear reaction between the target epithermal neutron beam passing through the epithermal neutron regulation and control body and elements in a detector material based on the set detection efficiency; and the data acquisition system is used for acquiring the measurement signal information, and calculating the number of epithermal neutrons of the neutron beam to be measured based on the measurement signal information, the detector counting rule and the detection efficiency. According to the invention, accurate and real-time monitoring of the number of epithermal neutrons is realized.

Description

Technical Field

[0001] The present invention relates to the technical field of epithermal neutron measurement, and in particular to an epithermal neutron measurement system for boron neutron capture therapy. Background Art

[0002] In boron neutron capture therapy, the nuclide 10 B reacts with thermal neutrons to 10 B(n, α) 7 Li reaction to release high-energy rays to kill cancer cells in human tissues. Since human tissues are mainly composed of elements such as hydrogen, nitrogen, and oxygen, neutrons will be moderated after elastic collisions with H elements when they reach the human body. Therefore, boron neutron capture therapy mainly uses a neutron source to emit epithermal neutrons after beam shaping. These epithermal neutrons are moderated into thermal neutrons after passing through human tissues to achieve boron neutron capture therapy. Thus, the measurement of the number of epithermal neutrons after beam shaping is an important monitoring content in boron neutron capture therapy. Compared with reactor neutron sources, the energy distribution of epithermal neutrons generated by accelerator neutron sources is more ideal and more suitable for deep tumors in the human body. It is the ideal neutron source for boron neutron capture therapy at present. As Figure 1 shown, the fast neutrons generated by accelerator target bombardment pass through a moderator, thermal neutron filtration, gamma filtration, and collimation and then reach the beam outlet, becoming a mixed neutron beam mainly composed of epithermal neutrons for patient treatment. According to the definition of the International Atomic Energy Agency (IAEA) for boron neutron capture therapy, the energy ranges of thermal neutrons, epithermal neutrons, and fast neutrons are <0.5 eV, 0.5 eV - 10 keV, and >10 keV, respectively. The neutrons at the beam outlet of an accelerator-based boron neutron capture therapy device are mixed neutrons mainly composed of epithermal neutrons.

[0003] Currently, the methods for epithermal neutron measurement mainly include the activation method, Bonner sphere method, etc. Among them, the activation method mainly places activation foils, such as Au, Mn, or Cu, etc., at the measurement position for irradiation, then uses a gamma spectrometer such as high-purity germanium to read the activity of the activation foil, and then obtains the epithermal neutron flux at the measurement position through the theoretically calculated average cross-section. This method is an off-line measurement method and requires a lot of time and effort. The Bonner sphere method mainly uses polyethylene spheres wrapped with detectors such as 3He, Li, or Ga. The neutrons are moderated and absorbed by polyethylene spheres with different radii, making the detectors sensitive to epithermal neutrons, and the epithermal neutrons can be monitored online. However, since the responses of these detectors are related to the energy of epithermal neutrons, the measurement results are greatly affected by the energy distribution of epithermal neutrons, so the number of epithermal neutrons cannot be accurately measured. Summary of the Invention

[0004] The technical problem to be solved by the present invention is to provide an epithermal neutron measurement system for boron neutron capture therapy, aiming to solve at least one of the above technical problems.

[0005] The technical solution of the present invention to solve the above technical problems is as follows:

[0006] The present application provides a epithermal neutron measurement system for boron neutron capture therapy, adopting the following technical solution:

[0007] An epithermal neutron measurement system for boron neutron capture therapy, comprising:

[0008] A collimating shield for shielding and collimating the incident neutron beam to be measured to obtain a neutron beam with a specific direction and energy range;

[0009] A thermal neutron absorber for absorbing the thermal neutron component of the neutron beam passing through the collimating shield to obtain an epithermal neutron beam;

[0010] An epithermal neutron regulator for regulating the proportion and energy distribution of the epithermal neutron beam passing through the thermal neutron absorber to obtain a target epithermal neutron beam;

[0011] An α-particle shield for shielding α-particles in the detector or the surrounding environment of the detector to reduce the interference of the α-particles in the detector or the surrounding environment of the detector on the measurement of the target epithermal neutron beam;

[0012] A detector for detecting the total number of α-particles generated by the nuclear reaction between the target epithermal neutron beam passing through the epithermal neutron regulator and the elements in the detector material based on the set detection efficiency, and generating measurement signal information;

[0013] A data acquisition system for acquiring the measurement signal information of the detector, and calculating the number of epithermal neutrons in the neutron beam to be measured based on the measurement signal information, the detector counting rule and the detection efficiency.

[0014] The beneficial effects of the present invention are as follows: The measurement system can effectively shield and collimate the incident neutron beam to be measured, ensuring that a neutron beam with a specific direction and energy range is obtained. The thermal neutron absorber absorbs the thermal neutron component in the neutron beam passing through the collimating shield, making the epithermal neutrons the main component. The epithermal neutron regulator further adjusts the proportion and energy distribution of the epithermal neutron beam to meet the target requirements. The α-particle shield reduces the interference of α-particles in the detector and its surrounding environment, improving the measurement accuracy. Finally, the detector detects the total number of α-particles generated by the nuclear reaction between the epithermal neutrons and 10 the

[0015] Based on the above technical solution, the present invention can also be improved as follows.

[0016] Furthermore, the thermal neutron absorber is made of cadmium material, the thickness of the thermal neutron absorber is 0.5 mm, the thermal neutron absorber is located on one side of the epithermal neutron beam, and the cross-sectional area of the thermal neutron absorber is the same as that of the detector.

[0017] The beneficial effects of adopting the above further solution are as follows: It can effectively absorb thermal neutrons and reduce the interference of thermal neutrons on subsequent epithermal neutron measurements. Specifically, using 0.5 mm thick cadmium material as the thermal neutron regulator can efficiently absorb thermal neutrons. At the same time, since the reaction cross-section of cadmium with epithermal neutrons is small, it will not significantly affect the flux of epithermal neutrons. In addition, the cross-sectional area of the thermal neutron absorber is the same as that of the detector, ensuring the effective absorption of thermal neutrons and improving the measurement accuracy and stability of the system.

[0018] Furthermore, the collimating shield is made of the same material as the epithermal neutron regulator.

[0019] The beneficial effects of adopting the above further solution are as follows: The collimating shield is made of the same material as the epithermal neutron regulator, which can effectively shield and collimate the incident neutron beam to be measured, ensuring that the neutrons entering the subsequent components have a specific direction and energy range. This not only improves the measurement accuracy and reliability of the system, but also reduces the interference of background noise, making the detection results more accurate and reliable.

[0020] Furthermore, both the collimating shield and the epithermal neutron regulator are made of 10 B material.

[0021] The beneficial effects of adopting the above further solution are as follows: The epithermal neutron regulator made of 10 B material can effectively absorb and adjust the ratio and energy distribution of the epithermal neutron beam. 10 B material has a high epithermal neutron nuclear reaction cross-section and can efficiently react with epithermal neutrons within a specific energy range to 10 B(n,α) 7 Li reaction to generate high-energy α particles. This design not only improves the measurement accuracy of the system, but also ensures that the detection efficiency of the detector for epithermal neutrons in different energy intervals remains constant, thus achieving accurate measurement of the number of epithermal neutrons. At the same time, 10 the selection of B material also reduces background interference and improves the stability and reliability of the system.

[0022] Furthermore, the epithermal neutron regulator includes a plurality of sub-regulators with different thicknesses and cross-sectional areas, and the ratio of the thickness to the cross-sectional area of each sub-regulator is a constant value.

[0023] The beneficial effects of adopting the above further scheme are as follows: It ensures that the detection efficiency of the epithermal neutron moderator for epithermal neutrons in each energy group is close to constant. By optimizing the ratio of the thickness to the cross-sectional area of each sub-moderator, the detector can uniformly and effectively respond to epithermal neutrons in different energy intervals, thus achieving accurate measurement of the number of epithermal neutrons. This design not only improves the reliability and accuracy of the measurement system, but also reduces the measurement error caused by the difference in neutron energy distribution, making the measurement results more stable and precise.

[0024] Furthermore, the target epithermal neutron beam includes multiple neutron energy groups, and the constant value of the ratio of the thickness to the cross-sectional area of each sub-moderator satisfies the target condition. The target condition is that when multiple neutron energy groups pass through each sub-moderator and reach the detector, the detection efficiency of all neutron energy groups on the detector is within the target detection efficiency range. The target detection efficiency range is that the fluctuation range relative to the average value of the detection efficiency of all neutron energy groups remains within ±5%.

[0025] The beneficial effects of adopting the above further scheme are as follows: Since the geometric parameters of each sub-moderator are carefully designed and adjusted, the stability of the entire measurement system is significantly improved. This helps to reduce the measurement error caused by system instability and improve the success rate and safety of treatment.

[0026] Furthermore, the detection efficiency of the detector for neutrons is:

[0027] where ε j is the detection efficiency, S i is the cross-sectional area of the i-th sub-moderator, D i is the thickness of the i-th sub-moderator, η is the detection efficiency of the detector for the α particles generated by the 10 B and neutrons in the probe coating 10 B(n,α) 7 Li nuclear reaction, and N B-10 is the nucleon density of 10 B in the epithermal neutron moderator.

[0028] The beneficial effects of adopting the above further scheme are as follows: It can ensure that the detector has a constant detection efficiency for epithermal neutrons in each energy interval.

[0029] Furthermore, the detector uses a diamond detector with a surface coated with 10 B material, and the cross-sectional shape of the diamond detector is the same as the cross-sectional shape of the epithermal neutron moderator.

[0030] The beneficial effects of adopting the above further scheme are as follows: Selecting a surface coated with 10The diamond detector made of Material B has high radiation tolerance and good anti-gamma interference ability, ensuring stable operation in a high-dose rate environment. The cross-sectional shape of the diamond detector is the same as that of the epithermal neutron moderator, ensuring that the detector can fully capture the epithermal neutrons passing through the moderator, improving the reliability and accuracy of the measurement. Since the surface of the detector is coated with 10 Material B, when an epithermal neutron reacts with 10 B, 10 B(n,α) 7 Li reaction occurs, α particles with energies of 1.77 MeV and 1.47 MeV are generated. These α particles are effectively detected by the detector, and thus the number of epithermal neutrons can be accurately calculated.

[0031] Furthermore, the α particle shield is located between the epithermal neutron moderator and the detector. The α particle shield is made of aluminum material, and the thickness of the α particle shield is 1 mm.

[0032] The beneficial effect of adopting the above further solution is that the α particle shield effectively shields the α particles emitted from the epithermal neutron moderator, reducing the interference of these α particles on the measurement results of the detector and improving the accuracy and reliability of the measurement of the number of epithermal neutrons. At the same time, the 1-mm-thick aluminum material not only ensures sufficient shielding effect but also does not reduce the number of epithermal neutrons reaching the detector.

[0033] Furthermore, the data acquisition system is specifically used for:

[0034] Obtaining the measurement signal information of the detector, where the measurement signal information includes the measurement signal generated by the number of α particles with an energy of 1.77 MeV and the measurement signal generated by the number of α particles with an energy of 1.47 MeV;

[0035] Based on the neutron detection efficiency of the detector, the detector counting rule, and the measurement signal generated by the number of α particles with an energy of 1.77 MeV and the measurement signal generated by the number of α particles with an energy of 1.47 MeV, calculating the number of epithermal neutrons in the neutron beam to be measured;

[0036] Among them, the detector counting rule is:

[0037]

[0038] Among them, is the total number of α particles with energies of 1.77 MeV and 1.47 MeV detected by the data acquisition system on the detector, N B-10 is the nucleon density of 10 B in the moderator, and η is the detection efficiency of the detector for 10 B in the detector probe coating reacting with neutrons 10The detection efficiency of α particles produced by the B(n,α)7Li nuclear reaction is a fixed value of the ratio of the thickness to the cross-sectional area of the i-th sub-regulator of the epithermal neutron regulator.

[0039] The beneficial effects of adopting the above further scheme are as follows: The data acquisition system can accurately read the measurement signals generated by the detector, and calculate the specific number of epithermal neutrons in the neutron beam to be measured according to the preset detection efficiency and counting rules. The real-time monitoring of the number of epithermal neutrons in different energy ranges is realized, and the problem that the traditional measurement method cannot directly measure the number of epithermal neutrons is effectively solved. Description of the Drawings

[0040] Figure 1 Schematic diagram of the structure of a typical beam shaping assembly of the accelerator-based boron neutron capture therapy device provided by the present invention

[0041] Figure 2 Schematic diagram of the principle of the epithermal neutron measurement system for boron neutron capture therapy provided by the present invention

[0042] Figure 3 Schematic diagram of the neutron energy spectrum emitted by a typical neutron therapy device provided by the present invention

[0043] Figure 4 For the neutrons provided by the present invention and 10 B to occur 10 B(n,α) 7 L reaction microscopic cross-section diagram

[0044] Figure 5 For the neutrons provided by the present invention and 10 B to occur 10 B(n,γ) 11 B reaction microscopic cross-section diagram

[0045] Figure 6 For the neutrons provided by the present invention and 10 B to occur 10 B(n,el) 10 B reaction microscopic cross-section

[0046] Figure 7 For the neutrons provided by the present invention and 10 B to occur 10 B(n,T) 8 B reaction microscopic cross-section

[0047] Figure 8 When the areas S of the respective sub-regulators are the same in the present invention, for different regulator thicknesses D i corresponding detection efficiency ε i,j with the epithermal neutron energy E jSchematic diagram of changes;

[0048] Figure 9 For each sub-regulator area S provided by the present invention i and thickness D i When the ratio is constant, the detection efficiency ε i,j varies with the epithermal neutron energy E j Schematic diagram of changes.

[0049] Reference numerals: 1, neutron beam to be measured; 2, collimating shield; 3, thermal neutron absorber; 4, epithermal neutron regulator; 5, alpha particle shield; 6, detector; 7, signal transmission; 8, data acquisition system. Detailed implementation manners

[0050] To make the objectives, technical solutions, and advantages of the embodiments of the present application clearer, the technical solutions in the embodiments of the present application will be clearly and completely described below with reference to the accompanying drawings from Figure 1 to Figure 9 . It is obvious that the described embodiments are some, but not all, of the embodiments of the present application. All other embodiments obtained by those of ordinary skill in the art based on the embodiments in the present application without creative efforts shall fall within the protection scope of the present application.

[0051] In addition, the term "and / or" in this article is only a description of the association relationship of associated objects, indicating that there can be three relationships. For example, A and / or B can represent: A exists alone, A and B exist simultaneously, and B exists alone. In addition, the character " / " in this article generally represents an "or" relationship between the associated objects before and after unless otherwise specified.

[0052] As Figure 2 shown, an epithermal neutron measurement system for boron neutron capture therapy provided by an embodiment of the present application includes:

[0053] A collimating shield 2 for shielding and collimating the incident neutron beam 1 to be measured to obtain a neutron beam with a specific direction and energy range;

[0054] A thermal neutron absorber 3 for absorbing the thermal neutron component of the neutron beam passing through the collimating shield 2 to obtain an epithermal neutron beam;

[0055] An epithermal neutron regulator 4 for regulating the ratio and energy distribution of the epithermal neutron beam passing through the thermal neutron absorber 3 to obtain a target epithermal neutron beam;

[0056] An alpha particle shield 5 for shielding alpha particles in the detector 6 or the surrounding environment of the detector 6 to reduce the interference of alpha particles in the detector 6 or the surrounding environment of the detector 6 on the measurement of the target epithermal neutron beam;

[0057] A detector 6, configured to detect the total number of α particles generated by the nuclear reaction between the target epithermal neutron beam after passing through the epithermal neutron moderator 4 and the elements in the detector 6 material based on a set detection efficiency, and generate measurement signal information, and send the measurement signal information to the data acquisition system 8 through signal transmission 7;

[0058] A data acquisition system 8, configured to obtain the measurement signal information of the detector 6, and calculate the number of epithermal neutrons in the to-be-measured neutron beam 1 based on the measurement signal information, the counting rule of the detector 6, and the detection efficiency.

[0059] In the embodiment of the present application, as Figure 3 shown, the neutrons emitted by the boron neutron capture therapy device are mainly epithermal neutrons, with only a small amount of thermal neutrons and fast neutrons. The incident to-be-measured neutron beam 1 passes through the collimating shield 2 and then vertically enters the thermal neutron absorber 3, the epithermal neutron moderator 4, and the detector 6.

[0060] In the embodiment of the present application, the collimating shield 2 is made of the same material as the epithermal neutron moderator 4. The collimating shield 2 is made of 10 B material with a relatively large nuclear reaction cross section for epithermal neutrons and thermal neutrons. Its function is to shield and collimate the incident to-be-measured neutron beam 1 to obtain a neutron beam with a specific direction and energy range. Specifically, the collimating shield 2 can be in a cylindrical or cuboid shape, with a moderate thickness, and the length and width can be adjusted according to actual needs.

[0061] Since the microscopic cross section of the reaction between thermal neutrons and 10 B is higher than that of epithermal neutrons, a thermal neutron absorber 3 is provided in front of the detector 6 to absorb thermal neutrons. Since cadmium has a very large reaction cross section with thermal neutrons and can be used to absorb thermal neutrons, while the reaction cross section of cadmium with epithermal neutrons is relatively small, a 0.5 mm thick spacer is commonly used in neutron physics experiments to separate epithermal neutrons.

[0062] In the embodiment of the present application, the material and thickness of the thermal neutron absorber 3 are fixed. The thermal neutron absorber 3 is made of cadmium material with a thickness of 0.5 mm. The thermal neutron absorber 3 is located on one side of the epithermal neutron beam, and the cross-sectional area of the thermal neutron absorber 3 is the same as the cross-sectional area of the detector 6. The thermal neutron absorber 3 is used to absorb the thermal neutron component in the neutron beam passing through the collimating shield 2, so that the remaining neutron beam is mainly epithermal neutrons.

[0063] In the embodiment of the present application, the epithermal neutron moderator 4 is made of 10 B material. The epithermal neutron moderator 4 includes a plurality of sub-moderators with different thicknesses and cross-sectional areas, and the ratio of the thickness to the cross-sectional area of each sub-moderator is a constant value.

[0064] Further, the target epithermal neutron beam includes multiple neutron energy groups, and the constant value of the ratio of the thickness to the cross-sectional area of each sub-regulator satisfies the target condition; the target condition is that when multiple neutron energy groups pass through each sub-regulator and reach the detector 6, the detection efficiencies of all neutron energy groups on the detector 6 are within the target detection efficiency range, and the target detection efficiency range is that the fluctuation range relative to the average value of the detection efficiencies of all neutron energy groups remains within ±5%.

[0065] A method for determining the ratio of the thickness to the cross-sectional area of the epithermal neutron regulator 4 includes:

[0066] First step, establish a calculation model of the thermal neutron shield, the epithermal neutron regulator 4, the alpha particle shield 5, and the detector 6 using a Monte Carlo particle transport calculation program;

[0067] Second step, in the calculation model, set the neutron source direction to be vertically incident, and sequentially pass through the collimation shield 2, the thermal neutron absorber 3, the epithermal neutron regulator 4, the alpha particle shield 5, and the detector 6 models.

[0068] Third step, set the neutron source energy range to be 10 keV - 0.5 eV. In the calculation model, set each neutron energy group to be [10 keV, 1 keV), [1 keV, 100 eV), [100 eV, 10 eV), [10 eV, 0.5 eV);

[0069] Fourth step, according to the 4 energy segments, set 4 different thicknesses D of the sub-regulators i to be 10 cm, 1 cm, 0.1 cm, 0.01 cm respectively;

[0070] Fifth step, set to be 1 cm, then the cross-sectional area S corresponding to each sub-regulator i is 10 cm 2 、1 cm 2 、0.1 cm 2 、0.01 cm 2 .

[0071] Sixth step, based on the Monte Carlo transport calculation program, calculate the detection efficiency when each neutron energy group is used as the source term.

[0072] Seventh step, compare the detection efficiencies of each neutron energy group. If the fluctuation range of the detection efficiencies corresponding to these 4 energy groups exceeds ±5% relative to their average value, then change the ratio, and execute the fifth step to the seventh step until the detection efficiency fluctuation range is within ±5%, and obtain the ratio of the thickness to the cross-sectional area of each sub-regulator.

[0073] Since neutrons interact with 10The microscopic cross-section of the reaction of B shows an exponential decay law of 10 with respect to neutron energy, that is, the fast neutron energy is higher than the epithermal neutron energy, and the fast neutrons at the beam outlet of the boron neutron capture therapy device are fewer than the epithermal neutrons. Therefore, the nuclear reaction of fast neutrons with B in the epithermal neutron moderator 4 can be ignored. 10 By optimizing the thickness and corresponding area of the epithermal neutron moderator (containing B), the detection efficiency of the detector 6 for epithermal neutrons in different energy ranges is a constant. 10 B)

[0074] In the embodiment of the present application, the detection efficiency of the detector for neutrons is:

[0075] Among them, ε j is the detection efficiency, S i is the cross-sectional area of the i-th sub-moderator, D i is the thickness of the i-th sub-moderator, η is the detection efficiency of the detector for the α particles generated by the nuclear reaction of B with neutrons in the probe coating 10 B 10 B(n, α) 7 Li, N B-10 is the nucleon density of B in the epithermal neutron moderator. 10 B

[0076] Optionally, the detector 6 uses a diamond detector with a surface coated with B material, and the cross-sectional shape of the diamond detector is the same as the cross-sectional shape of the epithermal neutron moderator 4. 10 B

[0077] Select a diamond detector with a surface coated with B material. This detector 6 has high radiation resistance and good anti-gamma interference ability, ensuring stable operation in a high-dose rate environment. The cross-sectional shape of the diamond detector is the same as the cross-sectional shape of the epithermal neutron moderator 4, ensuring that the detector can fully capture the epithermal neutrons passing through the moderator, improving the reliability and accuracy of the measurement. Since the surface of the detector 6 is coated with 10 B material, when epithermal neutrons react with 10 B 10 B 10 B(n, α) 7 Li reaction, α particles with energies of 1.77 MeV and 1.47 MeV will be generated, and these α particles are effectively detected by the detector 6, so as to accurately calculate the number of epithermal neutrons.

[0078] In the embodiment of the present application, the α-particle shield 5 is located between the epithermal neutron moderator 4 and the detector 6. The α-particle shield 5 is made of aluminum material, and the thickness of the α-particle shield 5 is 1 mm. The α-particle shield 5 effectively shields the α-particles emitted from the epithermal neutron moderator 4, reduces the interference of these α-particles on the measurement results of the detector 6, and improves the accuracy and reliability of the measurement of the number of epithermal neutrons. At the same time, the 1-mm-thick aluminum material not only ensures sufficient shielding effect but also does not significantly increase the complexity and cost of the system.

[0079] In the embodiment of the present application, the data acquisition system 8 is specifically used for:

[0080] Obtaining the measurement signal information of the detector 6, where the measurement signal information includes the measurement signal generated by the number of α-particles with an energy of 1.77 MeV and the measurement signal generated by the number of α-particles with an energy of 1.47 MeV;

[0081] Based on the detection efficiency of the detector 6 for neutrons, the counting rule of the detector 6, and the measurement signal generated by the number of α-particles with an energy of 1.77 MeV and the measurement signal generated by the number of α-particles with an energy of 1.47 MeV, calculating the number of epithermal neutrons in the to-be-measured neutron beam 1; where the detector counting rule is:

[0082]

[0083] Where is the total number of α-particles with energies of 1.77 MeV and 1.47 MeV collected by the data acquisition system 8 on the detector 6, N B-10 is the nucleon density of 10 B in the epithermal neutron moderator 4, η is the detection efficiency of the detector 6 for the 10 B in the probe coating to generate α-particles through the 10 B(n, α) 7 Li nuclear reaction with neutrons, is the fixed value of the ratio of the thickness of the i-th sub-moderator of the epithermal neutron moderator 4 to its cross-sectional area.

[0084] In the above embodiment, the number of epithermal neutrons measured by the detector 6 can be expressed as:

[0085]

[0086] In the formula, N Epi is the measured number of epithermal neutrons; M j is the energy of E jAfter the epithermal neutron beam passes through the regulator, the number of α particles with energies of 1.77 MeV and 1.47 MeV on the detector 6 collected by the data acquisition system 8; n is the total number of sub-regulators of the epithermal neutron regulator 4; i is the number of the i-th epithermal neutron sub-regulator; m is the total number of epithermal neutron energy group divisions. The epithermal neutrons are divided into several energy intervals [E0, E1), [E1, E2), …, [E j-1 , E j ), …, [E m-1 , E m ), and the energy interval [E j-1 , E j ) is abbreviated as E j ; ε j is the detection efficiency of the detector 6 for the epithermal neutron beam with energy E j after it passes through the regulator; ε j,i is the detection efficiency of the detector 6 for the epithermal neutron beam with energy E j after it passes through the i-th sub-regulator; D i is the thickness of the i-th sub-regulator of the epithermal neutron regulator 4; ∑ j is the macroscopic cross-section of the nuclear reaction of 10 B with neutrons with energy E j ; σ j is the microscopic cross-section of the nuclear reaction of 10 B with neutrons with energy E j to occur 10 B(n, α) 7 Li; η is the efficiency of the detector 6 for 10 B in the probe coating to generate α particles in the nuclear reaction of 10 B(n, α) 7 Li; S i is the cross-sectional area of the i-th sub-regulator of the epithermal neutron regulator 4.

[0087] In the formula, if the number of epithermal neutrons is to be measured, the measured value must be independent of the epithermal neutron energy. That is to say, for must be a constant independent of the energy E j . The following analysis is carried out:

[0088] 1) The detector 6 uses 10 B coating. Considering the use of 10 B as the material of the epithermal neutron regulator 4 and the detector 6, this material has a j nuclear reaction of 10 B(n, α) 7The microscopic cross-section of Li's nuclear reaction is more than two orders of magnitude larger than other microscopic cross-sections of nuclear reactions, such as (n,γ), (n,el), (n,T), etc. The microscopic cross-sections are as follows Figure 4 , Figure 5 , Figure 6 and Figure 7 shown. Therefore, it is approximately considered that only the 10 B in the regulator only undergoes the 10 B(n,α) 7 Li nuclear reaction with epithermal neutrons, that is, ∑ j =σ j ×N B-10 , N B-10 is the nucleon density of 10 B in the regulator.

[0089] Therefore,

[0090] 2) By taking the differential of σ j in ε j , that is,

[0091] 3) When D i ×σ j ×N B-10 <1, that is , that is, ε j,i decreases as σ j decreases. When D i ×σ j ×N B-10 <0.01, that is, ε j,i ≈σ j ×η×S i , that is, the regulator with thickness D i has basically no influence on the microscopic cross-section of epithermal neutrons.

[0092] 4) When D i ×σ j ×N B-10 >1, that is, ε j,i decreases as σ j increases, and shows an exponential decay.

[0093] 5) When D i ×σ j ×N B-10 =1, that is , it reaches the maximum value.

[0094] It can be seen from the above analysis that

[0095] As shown Figure 8 for a specific thickness D i the regulator, when keeping S i = S as a constant value, has a specific detection efficiency range for the neutron energy E j Considering for a specific D i when ε j,i has a maximum value

[0096] As shown Figure 9 for a specific thickness D i the regulator, when σ j takes a specific range, by optimizing the regulator area S i is proportional to D i it is possible to make the detection efficiency of the neutron energy E j approximate to a constant value i.e., independent of σ j and considered independent of the neutron energy E j At this time is a constant value.

[0097] According to the definition of boron neutron capture therapy by the IAEA, the measurement accuracy of epithermal neutrons should be controlled within ±5%. Therefore, the detection efficiency j of the epithermal neutron beam after passing through the i-th sub-regulator by the detector 6 has a fluctuation range within ±5%.

[0098] To sum up, the number of epithermal neutrons measured by the detector 6 can be expressed as where is the total number of α particles with energies of 1.77 MeV and 1.47 MeV collected by the data acquisition system 8 on the detector 6, is a constant value.

[0099] This measurement system can effectively shield and collimate the incident neutron beam 1 to be measured, ensuring that a neutron beam with a specific direction and energy range is obtained. The thermal neutron absorber 3 absorbs the thermal neutron component in the neutron beam passing through the collimating shield 2, making the epithermal neutrons the main component. The epithermal neutron regulator 4 further adjusts the proportion and energy distribution of the epithermal neutron beam to meet the target requirements. The α particle shield 5 reduces the interference of α particles in the detector 6 and its surrounding environment, improving the measurement accuracy. Finally, the detector 6 detects epithermal neutrons based on the set detection efficiency and 10The total number of α particles generated by the nuclear reaction of Material B, and generate measurement signal information. The data acquisition system 8 then calculates the number of epithermal neutrons of the neutron beam 1 to be measured based on this information, achieving accurate and real-time monitoring of the number of epithermal neutrons. Ensure the safety and effectiveness of boron neutron capture therapy.

[0100] The above description is only a preferred embodiment of the present application and an explanation of the applied technical principles. Those skilled in the art should understand that the scope of the application involved in the present application is not limited to the technical solutions formed by the specific combination of the above technical features, and should also cover other technical solutions formed by any combination of the above technical features or their equivalent features without departing from the foregoing application concept. For example, the technical solutions formed by mutually replacing the above features with the technical features (but not limited to) having similar functions applied in the present application.

Claims

1. An epithermal neutron measurement system for boron neutron capture therapy, characterized in that: include: A collimation shield is used to shield and collimate the incident neutron beam to be measured to obtain a neutron beam in a specific direction and energy range; A thermal neutron absorber, used for absorbing thermal neutron components of the neutron beam passing through the collimating shield to obtain an epithermal neutron beam; An epithermal neutron regulator, used to regulate the proportion and energy distribution of the epithermal neutron beam passing through the thermal neutron absorber to obtain a target epithermal neutron beam; An alpha particle shield is used to shield the detector or the environment around the detector from alpha particles; A detector, for detecting the total number of alpha particles generated by the nuclear reaction between the target epithermal neutron beam after passing through the epithermal neutron regulator and the elements in the detector material based on a set detection efficiency, and generating measurement signal information; The data acquisition system is used to obtain the measurement signal information of the detector, and calculate the number of epithermal neutrons in the neutron beam to be measured based on the measurement signal information, the detector counting rule and the detection efficiency.

2. An epithermal neutron measurement system for boron neutron capture therapy according to claim 1, characterized in that: The thermal neutron absorber is made of cadmium material and has a thickness of 0.5 mm. The thermal neutron absorber is located on a side of the epithermal neutron regulator that receives the epithermal neutron beam, and the cross-sectional area of ​​the thermal neutron absorber is the same as the cross-sectional area of ​​the detector.

3. The epithermal neutron measurement system for boron neutron capture therapy according to claim 1, characterized in that: The collimating shield is made of the same material as the epithermal neutron regulating body.

4. An epithermal neutron measurement system for boron neutron capture therapy according to claim 3, characterized in that: The collimating shield and the epithermal neutron regulating body are both 10 B material.

5. An epithermal neutron measurement system for boron neutron capture therapy according to claim 4, characterized in that: The epithermal neutron control body comprises a plurality of sub-control bodies with different thicknesses and cross-sectional areas, and the ratio of the thickness to the cross-sectional area of ​​each sub-control body is a constant value.

6. An epithermal neutron measurement system for boron neutron capture therapy according to claim 5, characterized in that: The target epithermal neutron beam includes multiple neutron energy groups, and the constant value of the ratio of the thickness to the cross-sectional area of ​​each of the sub-regulators satisfies the target condition, which is that when the multiple neutron energy groups pass through each of the sub-regulators and reach the detector, the detection efficiency of all neutron energy groups on the detector is within a target detection efficiency range, and the target detection efficiency range is a fluctuation range relative to the average value of the detection efficiency of all neutron energy groups maintained within ±5%.

7. The epithermal neutron measurement system for boron neutron capture therapy according to claim 5, wherein the detection efficiency of the detector for neutrons is: in, ε j is the detection efficiency, S i is the cross-sectional area of ​​the ith sub-regulator, D i is the thickness of the i-th sub-regulator, η is the detector's thickness in the probe coating 10 B and neutrons 10 B(n,α) 7 Detection efficiency of α particles produced by Li nuclear reactions, N B-10 For epithermal neutron regulation 10 The nuclear density of B.

8. An epithermal neutron measurement system for boron neutron capture therapy according to claim 1, characterized in that: The detector adopts surface coating 10 A diamond detector made of material B, wherein the cross-sectional shape of the diamond detector is the same as the cross-sectional shape of the epithermal neutron control body.

9. An epithermal neutron measurement system for boron neutron capture therapy according to claim 1, characterized in that: The α particle shielding body is located between the epithermal neutron control body and the detector. The α particle shielding body is made of aluminum material and has a thickness of 1 mm.

10. An epithermal neutron measurement system for boron neutron capture therapy according to claim 5, characterized in that: The data acquisition system is specifically used for: Acquiring measurement signal information of the detector, the measurement signal information including a measurement signal generated by the number of alpha particles with an energy of 1.77 MeV and a measurement signal generated by the number of alpha particles with an energy of 1.47 MeV; Calculating the number of epithermal neutrons in the neutron beam to be measured based on the detection efficiency of the detector for neutrons, the detector counting rule, and the measurement signal generated by the number of alpha particles with an energy of 1.77 MeV and the measurement signal generated by the number of alpha particles with an energy of 1.47 MeV; The detector counting rule is: in, N is the total number of alpha particles with energies of 1.77 MeV and 1.47 MeV collected by the data acquisition system on the detector. B-10 For epithermal neutron regulation 10 The nuclear density of B, η, is detected by the detector in the probe coating. 10 B and neutrons 10 B(n,α) 7 The detection efficiency of α particles produced by Li nuclear reactions, is a fixed value of the ratio of the thickness of the i-th sub-control volume of the epithermal neutron control volume to its cross-sectional area.

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