Composite shielding collimator suitable for complex mixed radiation field

Abstract

The invention discloses a composite shielding collimator suitable for a complex mixed radiation field, belongs to the technical field of radiation shielding and measurement, and mainly solves the problems of low signal-to-noise ratio, high space background and mixed energy spectrum caused by the mixed radiation field of high-energy neutrons, gamma rays and the like in a fusion device and the problem that traditional equipment is heavy and difficult to flexibly adjust. The composite shielding collimator adopts a cylindrical shielding structure formed by aluminum oxide, boron-containing polyethylene, boron carbide and lead from outside to inside, and background interference and secondary radiation are remarkably inhibited by moderating and absorbing neutrons step by step and effectively shielding gamma rays; the neutron and gamma ray detector is integrally integrated on a rotatable supporting mechanism, unification of excellent radiation shielding performance and detection flexibility is achieved, and the neutron and gamma ray detector is mainly used for high-precision neutron and gamma ray diagnosis in complex radiation environments such as a magnetic confinement fusion device.

Description

Technical Field

[0001] This invention belongs to the field of radiation shielding and measurement technology, specifically relating to a composite shielding collimator suitable for complex mixed radiation fields. Background Technology

[0002] Magnetic confinement fusion energy is considered a crucial strategic direction for addressing future clean and sustainable energy needs, with its core objective being the realization of a controllable deuterium-tritium fusion reaction. Currently, the International Thermonuclear Experimental Reactor (ITER) project and fusion devices developed independently by various countries are working to translate this scientific concept into engineering reality. In fusion reactor plasma physics experiments, high-energy neutrons (14.1 MeV) and gamma rays, as the main products and byproducts of the fusion reaction, carry crucial information reflecting the core physical parameters of the plasma. Therefore, the neutron-gamma diagnostic system is figuratively called the "eyes" of the fusion device, and is an indispensable technological cornerstone for achieving real-time monitoring of high-parameter plasmas, deepening the study of physical mechanisms, and ensuring the safe and efficient operation of future fusion reactors.

[0003] However, the interior of a fusion device constitutes an extremely harsh and complex radiation environment. When the diagnostic system receives signals through a specific line of sight (LOS), it inevitably faces the following severe interferences: 1. Space background interference: The structural materials such as the first wall, cladding, and shielding layer will generate a large number of gamma-ray and neutron scattering signals in non-target areas under neutron irradiation; 2. Mixed energy spectrum: The signal received by the detector is an integral response of various reactions in the entire space direction, which causes the energies of neutrons and gamma rays produced at different locations and by different mechanisms to be superimposed, resulting in broadening and distortion of the energy spectrum, making it difficult to distinguish the characteristic signals of specific physical processes originating from the plasma core (such as fusion rate, fast ion behavior, impurity transport, etc.). 3. Instantaneous flux overload: Under high-power discharge conditions, without effective shielding measures, the particle flux directly reaching the detector may far exceed its dynamic range, causing signal saturation, a surge in dead time, or even permanent device damage.

[0004] Faced with these severe challenges, the collimator, as a key front-end component connecting the plasma radiation source and the detector, directly affects the authenticity, reliability, and accuracy of diagnostic data. Traditional simple hole or pipe-type shielding structures are no longer sufficient to meet the extremely high requirements of next-generation fusion devices for diagnostic systems in terms of accuracy, signal-to-noise ratio, and resolution. Therefore, the innovative design and development of collimators specifically for neutron-gamma diagnostics in advanced fusion devices has become an urgent and strategically significant issue in the field of fusion engineering technology.

[0005] In summary, the main problems with current neutron detection are: 1. Current mainstream collimator designs are unable to adequately handle 14 MeV high-energy neutrons in the complex mixed radiation fields of fusion reactors, typically requiring very large spaces and concrete walls for shielding. This results in low effective signal counts, causing significant difficulties in measurement. 2. Current mainstream collimators have significant bottlenecks in signal-to-noise ratio improvement, radiation suppression (suppressing radiation leakage outside the field of view), compact integration, and resistance to radiation damage / activation. They typically have low signal-to-noise ratios, poor shielding capabilities against induced gamma rays, high noise levels within the collimator itself, and poor resistance to activation. 3. Current collimators are all fixedly installed, making it impossible to measure rays within other fields of view, and their ability to measure rays under different profiles is insufficient. Summary of the Invention

[0006] This invention provides a composite shielding collimator suitable for complex mixed radiation fields. It achieves stepwise shielding and collimation of high-energy neutrons, thermal neutrons, medium-energy neutrons, and gamma rays, significantly improving the signal-to-noise ratio and energy spectrum resolution of the detected signal. This makes it suitable for accurate diagnosis in complex radiation environments such as fusion devices. The composite shielding collimator combines a multi-layered cylindrical shielding structure with a rotatable support mechanism, possessing excellent radiation shielding performance, mechanical stability, and operational flexibility. It effectively suppresses background interference, energy spectrum mixing, and instantaneous flux overload, ensuring the accuracy and reliability of diagnostic data.

[0007] To achieve these objectives and other advantages of the present invention, the present invention provides a composite shielded collimator suitable for complex mixed radiation fields, comprising: A cylindrical shielding structure, wherein a aligning hole is provided through it along the axial direction, and the cylindrical shielding structure specifically comprises, from the outside to the inside: The first shielding layer, made of aluminum oxide, is located at the foremost neutron incident end and is cylindrical in shape. It is used to reduce the neutron energy by inelastic scattering with high-energy neutrons. The second shielding layer, made of 10% boron polyethylene, is located immediately after the first shielding layer and is cylindrical in shape, in order to slow down and absorb the neutrons that have passed through the first shielding layer as thermal neutrons and fast neutrons. The third shielding layer, made of boron carbide, is nested inside the second shielding layer and is used to slow down and absorb thermal neutrons and medium-energy neutrons, and suppress the generation of secondary gamma rays. The fourth shielding layer, made of lead, is nested inside the third shielding layer and is used to shield ambient gamma rays and activated gamma rays. The fourth shielding layer contains a detector mounting cavity for accommodating the detector. The collimation hole passes through the first shielding layer, the second shielding layer, the third shielding layer, and the fourth shielding layer in sequence, and leads to the detector mounting cavity.

[0008] Preferably, the third shielding layer includes a cylindrical portion and a hemispherical portion, the hemispherical portion being disposed at the front end of the cylindrical portion; the fourth shielding layer is cylindrical and nested inside the cylindrical portion of the third shielding layer.

[0009] Preferably, the first shielding layer has an axial thickness of 10cm and a radius of 25cm; the second shielding layer has a minimum front thickness of 30cm and a minimum circumferential side thickness of 15cm; the third shielding layer has a hemispherical portion with a radius of 20cm and a circumferential side thickness of 5cm; and the fourth shielding layer has a front, rear, and circumferential thickness of 10cm.

[0010] Preferably, the collimation aperture has a diameter of 2.5cm-3.5cm and a length of 70cm to limit the non-axial neutron flux.

[0011] Preferably, the cylindrical shielding structure is further provided with a stainless steel shell, which is wrapped around the outer surface of the second shielding layer, and the cylindrical shielding structure is rotatably mounted on a support platform.

[0012] Preferably, the cylindrical shielding structure is rotatably mounted on the support platform, specifically as follows: A bearing is provided on the upper surface of the support platform, and a main shaft is fixedly provided below the cylindrical shielding structure, with the main shaft disposed inside the bearing. An arc-shaped guide rail is also provided on the upper surface of the support platform. The center of curvature of the arc-shaped guide rail coincides with the axis of the main shaft. A slider adapted to the arc-shaped guide rail is fixedly provided below the cylindrical shielding structure.

[0013] Preferably, a support component is also provided for supporting the cylindrical shielding structure, the support component specifically... The setup method is as follows: The upper base plate is horizontally positioned, and the main shaft and the slider are fixedly mounted on the bottom surface; The housing, which is cuboid in shape, is fixedly mounted on the upper surface of the upper base plate, and the cylindrical shielding structure is disposed inside the housing; wherein, a first circular hole is provided through the front vertical plate, and a cylindrical first shielding layer passes through the first circular hole; a circular support plate is provided on the outer side of the rear vertical plate; the circular support plate, the rear vertical plate, and the rear end face of the cylindrical shielding structure are fixedly connected by bolts. The lower base plate is fixedly mounted on the support platform, and the lower base plate has holes for bearings to pass through, and the arc-shaped guide rail is mounted on the lower base plate.

[0014] Preferably, a circular dial and a pointer matching the arc-shaped guide rail are respectively provided on the lower base plate and the upper base plate, and the cylindrical shielding structure rotates at an angle of ±30°.

[0015] The present invention has at least the following beneficial effects: First, the cylindrical shielding structure designed in this invention employs a gradient structure, using a combination of four layers of different materials: an alumina layer, a boron-containing polyethylene layer, a boron carbide layer, and a lead layer. This achieves stepwise shielding and collimation of various particles in complex mixed radiation fields. The alumina layer primarily undergoes inelastic scattering with high-energy neutrons, thereby reducing neutron energy and effectively shielding 14 MeV high-energy neutrons. The boron-containing polyethylene layer further slows down and absorbs the neutrons after the alumina layer's action, classifying them as thermal and fast neutrons, reducing (n,γ) reactions. The boron carbide layer slows down and absorbs low-energy and medium-energy neutrons, suppressing secondary gamma rays. The lead layer effectively shields ambient gamma rays and activated gamma rays. This structure significantly improves the signal-to-noise ratio and energy spectral resolution of the detection signal, making it suitable for precise diagnosis in high-radiation environments such as fusion devices.

[0016] The second and third shielding layers, namely the boron carbide layers, adopt an integrated design with a hemispherical front end and a cylindrical rear end. The hemispherical dome structure is used to more uniformly cope with radiation incident from the front, while the cylindrical part is used to wrap and accommodate the fourth shielding layer. The fourth shielding layer is completely embedded in the cylindrical cavity of the third shielding layer, forming a nested layout, thereby suppressing secondary gamma rays generated by neutron activation to the greatest extent.

[0017] Third, by precisely setting the thickness and radius of each shielding layer, this invention ensures optimal shielding performance while controlling the overall size and weight of the device, making it easier to integrate into existing fusion diagnostic systems. This balances performance and practicality, providing a reliable structural foundation for engineering applications. The specific dimensions of the collimating aperture effectively limit the entry of non-axial neutrons, improving the selectivity of the detection direction and the spatial resolution of the signal, while ensuring sufficient flux for subsequent signal processing and analysis, thus enhancing the accuracy and reliability of diagnostic data.

[0018] Fourth, a stainless steel shell is installed on the outer surface of the cylindrical shielding structure. This shell not only enhances the mechanical strength and corrosion resistance of the equipment but also provides an additional barrier against radiation. The rotatable support structure allows the collimator to flexibly adjust its detection direction, adapting to varying working environments and greatly improving the equipment's applicability and ease of operation. The dual guiding mechanism of the spindle-bearing and slider-guide rail ensures the stability and accuracy of the collimator during rotation, avoiding measurement errors caused by structural swaying or offset, and improving the reliability and repeatability of angle control. The design of the support assembly enhances the rigidity and stability of the overall structure. Bolt connections and hole fittings enable quick installation and disassembly, facilitating maintenance and replacement, while ensuring a secure connection between the collimator and the support platform, suitable for long-term high-load operating environments. The circular dial allows operators to intuitively and accurately control the rotation angle. The ±30° rotation range meets most practical measurement needs while avoiding mechanical interference or cable failures caused by excessive rotation, improving the equipment's safety and operability.

[0019] Other advantages, objectives and features of the present invention will become apparent in part from the following description, and in part from those skilled in the art through study and practice of the invention. Attached Figure Description

[0020] Figure 1 This is a schematic cross-sectional view of the structural relationship of multiple composite layers in the composite shielding collimator applicable to complex mixed radiation fields of the present invention. Figure 2 A schematic diagram of the cylindrical shielding structure in a composite shielding collimator suitable for complex mixed radiation fields; Figure 3 The shielding capability of lead of different thicknesses against neutrons is presented. Figure 4 The moderation spectra of lead of different thicknesses for 14 MeV neutrons are presented. Figure 5 The gamma-ray shielding ability of lead of different thicknesses; Figure 6 The moderating energy spectra of 17 MeV gamma rays by lead of different thicknesses; Figure 7 The neutron shielding capabilities of alumina with different thicknesses are presented. Figure 8 The moderation spectra of 14 MeV neutrons for alumina of different thicknesses are presented. Figure 9 The neutron shielding capabilities of polyethylene of different thicknesses are presented. Figure 10 The moderation spectra of polyethylene with different thicknesses for 14 MeV neutrons are presented. Figure 11The neutron shielding capability of graphite of different thicknesses is presented. Figure 12 The moderation spectra of 14 MeV neutrons for graphite of different thicknesses are presented. Figure 13 The neutron shielding capabilities of boron carbide with different thicknesses are presented. Figure 14 The moderation spectra of boron carbide with different thicknesses for 14 MeV neutrons are presented. Figure 15 The neutron shielding capability of boron-containing polyethylene of different thicknesses is presented. Figure 16 The moderation spectra of boron-containing polyethylene of different thicknesses for 14 MeV neutrons are presented. Figure 17 The neutron shielding capabilities of the front and side composite plates are presented. Figure 18 The moderation spectra of 14 MeV neutrons for the front and side composite plates are presented. Figure 19 The change in the penetration ratio of neutrons as they pass through the shielding material is given; Figure 20 The energy spectrum changes of neutrons passing through the shielding material layer by layer are given; Figure 21 The collimator calculation model based on a simple loop source is presented in the paper; Figure 22 The signal and background of 2.5 MeV neutrons under different apertures are presented; Figure 23 The signal and background of 14MeV neutrons under different apertures are presented; Figure 24 The collimator provides the signal, background, and activated gamma spectrum of a 2.5 MeV neutron source; Figure 25 The collimator provides the signal, background, and activated gamma spectrum of a 14MeV neutron source. Figure 26 The energy spectrum of a 1 MeV gamma-ray source after collimation is given. Figure 27 The energy spectrum of a 3MeV gamma-ray source after collimation is given. Figure 28 The energy spectrum of a 5MeV gamma-ray source after collimation is given. Figure 29 The energy spectrum of a 17MeV gamma-ray source after collimation is given. Figure 30 This is a schematic diagram of the overall structure of the composite shielded collimator of the present invention applicable to complex mixed radiation fields; Figure 31This is an enlarged schematic diagram of the bearing component of the present invention; Figure 32 This is a top view of the composite shielding collimator of the present invention, applicable to complex mixed radiation fields. Detailed Implementation

[0021] The present invention will now be described in further detail so that those skilled in the art can implement it based on the description.

[0022] It should be understood that terms such as “having,” “comprising,” and “including” as used herein do not exclude the presence or addition of one or more other elements or combinations thereof.

[0023] like Figures 1-2 As shown, the present invention provides a composite shielded collimator suitable for complex mixed radiation fields, comprising: A cylindrical shielding structure, wherein a aligning hole 6 is provided through it along the axial direction, and the cylindrical shielding structure specifically includes, from the outside to the inside: The first shielding layer 1, made of aluminum oxide, is located at the foremost neutron incident end and is cylindrical in shape. It is used to reduce the neutron energy by inelastic scattering with high-energy neutrons. The second shielding layer 2, which is made of polyethylene containing 10% boron, is immediately following the first shielding layer and is cylindrical in shape, so as to slow down and absorb the neutrons that have passed through the first shielding layer as thermal neutrons and fast neutrons. The third shielding layer 3, made of boron carbide, is nested inside the second shielding layer and is used to slow down and absorb thermal neutrons and medium-energy neutrons, and suppress the generation of secondary gamma rays. The fourth shielding layer 4, made of lead, is nested inside the third shielding layer and is used to shield ambient gamma rays and activated gamma rays. The fourth shielding layer 4 has a detector mounting cavity inside to accommodate the detector 5. The collimation hole 6 passes through the first shielding layer 1, the second shielding layer 2, the third shielding layer 3 and the fourth shielding layer 4 in sequence, and leads to the detector mounting cavity.

[0024] The above technical solution employs a multi-layered cylindrical shielding structure. This cylindrical shielding structure has a through-hole along its axial direction for guiding and filtering radiation signals. The entire structure comprises four shielding layers with different functions from the outside in. Each layer shields and processes specific types or energies of particles in the mixed radiation field, ultimately achieving comprehensive shielding and collimation of high-energy neutrons, thermal neutrons, medium-energy neutrons, and gamma rays, significantly improving the quality of the signals received by the detector.

[0025] The first shielding layer, the alumina layer, is located at the outermost layer of the entire structure, i.e., the radiation incident end, and is cylindrical in shape. Alumina, as a common ceramic material, has a high melting point and good radiation stability, making it particularly suitable for inelastic scattering of high-energy neutrons. When a high-energy neutron (such as a 14 MeV neutron) is incident, the atomic nuclei in the alumina undergo inelastic collisions with it. The neutron loses some energy and changes its direction of motion, thus achieving initial slowing down and energy reduction of the high-energy neutron. This layer not only acts as a physical barrier but also, through its material properties, converts some of the neutron energy into secondary gamma rays or thermal energy, creating more favorable conditions for subsequent shielding layers.

[0026] Following the first shielding layer is the second shielding layer, a 10% boron-containing polyethylene layer, also in a cylindrical structure. Polyethylene contains a large number of hydrogen atoms, which can further reduce neutron energy through elastic scattering with neutrons, making it particularly suitable for moderating thermal and fast neutrons. The added boron element provides a high thermal neutron absorption cross-section. 10 The B(n,α) cross section (3837 barns) effectively captures moderated thermal neutrons and converts them into alpha particles and lithium nuclei through the (n,α) reaction, thus preventing further neutron penetration or the initiation of secondary gamma radiation. This second shielding layer is tightly connected to the first shielding layer, forming a moderated path with progressively decreasing energy, significantly reducing the probability of neutron penetration. Therefore, 10% boron-containing polyethylene, compared to polyethylene, can be used for the direct moderated and absorbed neutron fields in complex environments, such as fusion device neutron fields, which contain a large number of scattered neutrons with energy covering the thermal neutron energy region. Boron can directly absorb thermal neutrons in the environment to a greater extent, thus reducing the capture of gamma rays.

[0027] The third shielding layer, a boron carbide layer, is nested within the second shielding layer. Boron carbide not only possesses excellent neutron absorption capabilities but also effectively suppresses the generation of secondary gamma rays. This layer primarily absorbs thermal neutrons moderated by the first two layers, as well as some medium-energy neutrons. Simultaneously, its high boron content provides excellent gamma-ray suppression performance, preventing neutron capture reactions from generating new gamma radiation. Its structure can be designed as a combination of a hemispherical front end and a cylindrical rear end to more uniformly handle radiation incident from different directions, improving the overall shielding uniformity and efficiency.

[0028] The innermost layer is the fourth shielding layer, the lead layer, nested inside the third shielding layer. Lead, as a high-density, high-atomic-number material, has an extremely strong shielding ability against gamma rays, effectively absorbing gamma rays from the external environment as well as secondary gamma rays generated by neutron activation. This layer forms a sealed cavity structure, within which a detector mounting cavity is located for housing the radiation detector. The collimating aperture penetrates all four shielding layers sequentially from the outside in, ultimately leading to the detector mounting cavity. This ensures that only axially incident radiation signals, filtered by each layer, reach the detector, greatly improving signal directionality and signal-to-noise ratio.

[0029] By combining and spatially arranging the aforementioned four layers of materials, this composite shielding collimator achieves stepwise processing and shielding of multiple particles in complex mixed radiation fields. This not only significantly reduces background interference and signal clutter but also further enhances the spatial resolution and signal purity of the detection through the geometric constraints of the collimating aperture. This structure is particularly suitable for the joint diagnosis of neutrons and gamma rays in high-radiation environments such as fusion devices, and has significant engineering application value.

[0030] It should be noted that the mixed radiation field of neutrons and gamma rays requires addressing the generation of secondary gamma rays and material compatibility. If only gamma rays are shielded, a lead sandwich design is suitable, with the outer lead layer attenuating high-energy gamma rays and the inner lead layer handling residual photons. However, a large number of high-energy neutrons exist in the mixed neutron-gamma field. Directly using a high-Z material for the outer layer would easily generate a large number of transient gamma rays and form a large amount of activation products, causing environmental pollution. Therefore, only an inner lead layer is used to shield gamma rays.

[0031] In one technical solution, the third shielding layer includes a cylindrical portion and a hemispherical portion, the hemispherical portion being disposed at the front end of the cylindrical portion; the fourth shielding layer is cylindrical and nested inside the cylindrical portion of the third shielding layer.

[0032] In the above technical solution, the third shielding layer consists of two parts: a cylindrical portion and a hemispherical portion located at the front end of the cylinder. The hemispherical structure is located at the front end in the radiation incident direction, and its curved surface design can more evenly disperse and receive the radiation flow from the front, reducing the possibility of excessively high local radiation flux, thereby improving the uniformity and overall durability of the shielding. The cylindrical portion extends from the rear end of the hemispherical shape, forming a continuous internal cavity to accommodate the fourth shielding layer. The third shielding layer is entirely made of boron carbide, a material with excellent thermal neutron absorption capacity and certain mechanical strength. Its structural design ensures that the layer not only has sufficient shielding thickness in the axial direction but also provides continuous and consistent coverage in the radial direction, further suppressing the leakage of neutrons and gamma rays.

[0033] The fourth shielding layer is a cylindrical structure, completely nested within the cylindrical portion of the third shielding layer, forming a tight spatial containment. Made of lead, the fourth shielding layer's primary function is to absorb gamma rays, especially secondary gamma radiation generated by neutron activation or the external environment. By fully embedding it within the third shielding layer, it fully utilizes the neutron moderation and absorption effects of the boron carbide layer while leveraging the high density of the lead layer to achieve highly efficient gamma-ray shielding.

[0034] In one technical solution, the axial thickness of the first shielding layer is 10cm and the radius is 25cm; the minimum thickness of the front part of the second shielding layer is 30cm and the minimum thickness of the circumferential side is 15cm; the radius of the hemispherical part of the third shielding layer is 20cm and the thickness of the circumferential side is 5cm; and the front, rear and circumferential thicknesses of the fourth shielding layer are 10cm.

[0035] In the above technical solution, the specific dimensional parameters of each shielding layer are further defined. These parameters collectively ensure the optimized configuration of the shielding body in terms of geometric space and radiation protection performance. The first shielding layer is designed with aluminum oxide material and an axial thickness of 10cm. In practical applications, this thickness can be adjusted within the range of 8cm to 12cm according to neutron energy distribution and shielding requirements. The radius is set at 25cm, but can also be selected between 20cm and 30cm to adapt to different installation spaces and radiation field ranges. This dimension ensures that the layer has sufficient volume to undergo inelastic scattering of high-energy neutrons, effectively reducing neutron energy. Simultaneously, its cylindrical shape and selected radius help maintain the mechanical balance of the overall structure and the coverage of the radiation incident surface. The second shielding layer has a minimum front thickness of 30cm and a minimum side thickness of 15cm. In practical designs, the front thickness can be between 25cm and 35cm, and the side thickness can vary between 10cm and 20cm to address the attenuation requirements of radiation flux in different directions. The boron-containing polyethylene material in this first layer further slows down neutrons through elastic scattering and absorbs thermal neutrons with the help of the boron component. The thickness variations in different directions reflect the higher protection requirements for frontal radiation intensity. The hemispherical portion of the third shielding layer has a radius of 20 cm, selectable between 15 cm and 25 cm, and a side thickness of 5 cm, which can also be slightly adjusted, for example, between 3 cm and 7 cm. Boron carbide material, with these dimensions, forms effective shielding layers in both the radial and axial directions. The hemispherical structure improves the uniformity of radiation incident response, while the cylindrical portion covers and protects the internal lead layer.

[0036] The fourth shielding layer is made of lead, with a thickness of 10 cm on the front, back, and circumference. In practice, a thickness between 8 cm and 12 cm can be selected. This thickness effectively absorbs gamma rays and suppresses activation radiation in most radiation scenarios. The uniform thickness design in all directions avoids the appearance of localized weak points and ensures a tighter fit with the internal cavity of the third shielding layer. During assembly, the lead layer is prefabricated in a cylindrical form and then embedded within the boron carbide layer. The dimensional tolerances between the two must be strictly controlled, typically achieved through machining or filling with composite materials to achieve a seamless connection, thereby eliminating radiation leakage paths.

[0037] The cylindrical shielding structure configured with the above parameters has a total mass of 1009.6 kg, and the alumina layer has a density of 3.97 g / cm³. 3It weighs 77.95 kg; contains a 10% boron polyethylene layer, and has a density of 1 g / cm³. 3 The mass is 388.9 kg; the boron carbide layer has a density of 2.52 g / cm³. 3 The mass is 134.3 kg; the lead layer has a density of 11.35 g / cm³. 3 The weight is 408.45 kg.

[0038] In one of the technical solutions, the collimation aperture has a diameter of 2.5cm-3.5cm and a length of 70cm to limit the non-axial neutron flux.

[0039] In the above technical solution, the aperture is limited to between 2.5 cm and 3.5 cm. In practical design and application, this aperture value can be selected and fine-tuned within the range of 2 cm to 4 cm, depending on the size of the detector's sensitive surface and the required spatial resolution. The physical principle of this aperture is that it determines the solid angle at which the radiated signal enters the detector; a smaller aperture can more strictly restrict the direction of incident radiation, effectively blocking neutrons and gamma rays that deviate significantly from the axis, thereby significantly reducing the spatial background noise, but also resulting in a corresponding decrease in signal flux. Conversely, a larger aperture allows more particles to pass through, which is beneficial for increasing the count rate, but sacrifices some directional selectivity. Therefore, this range is an engineering balance point sought between flux and resolution. The collimation aperture length is 70 cm, but in practical design, it can be adjusted within the range of 60 cm to 80 cm according to the axial dimensions of the overall shield and the required collimation effect. The length of the channel and the aperture together determine the aspect ratio of the collimator, and this ratio directly affects its collimation performance. The combination of a 2.5-3.5 cm aperture and a 70 cm length constitutes a collimation system with a specific aspect ratio. The system operates based on rectilinear propagation and geometric blocking. Non-axial neutrons, due to the angle between their path and the axis, have a higher probability of interacting with the aperture wall and being absorbed in the long aperture, thus greatly limiting their flux.

[0040] It should be noted that the radius of the cylinder can be increased to increase the aperture, enabling simultaneous measurement of multiple neutrons and gamma rays; the size of the boron-containing polyethylene can be increased to further improve the collimation effect, but the weight will increase sharply accordingly; the thickness of the lead can be appropriately increased to improve the signal-to-noise ratio during gamma measurement, but the weight will also increase; the aperture size can be appropriately changed to adapt to different measurement distances and improvements in signal-to-noise ratio.

[0041] In one of the technical solutions, such as Figures 30-32As shown, the cylindrical shielding structure also includes a stainless steel outer shell, which wraps around the outer surface of the second shielding layer. The cylindrical shielding structure is rotatably mounted on a support platform 7. The specific mounting method of the cylindrical shielding structure on the support platform 7 is as follows: A bearing 13 is provided on the upper surface of the support platform 7, and a main shaft 14 is fixedly provided below the cylindrical shielding structure. The main shaft 14 is located inside the bearing 13. An arc-shaped guide rail 11 is also provided on the upper surface of the support platform 7. The curvature center of the arc-shaped guide rail 11 coincides with the axis of the main shaft 14. A slider 12 adapted to the arc-shaped guide rail 11 is fixedly provided below the cylindrical shielding structure.

[0042] In the above technical solution, the cylindrical shielding structure is externally fitted with a stainless steel shell. This shell tightly wraps around the outer surface of the second shielding layer, serving to provide mechanical protection, environmental sealing, and auxiliary electromagnetic shielding. The stainless steel material is typically 304 or 316 grade, and its thickness can be selected from 1 to 3 mm depending on actual mechanical strength and weight requirements; preferably, it is set to 2 mm. This shell is fixed to the inner shielding layer by welding or bolting, forming an integral cylindrical structure.

[0043] The cylindrical shielding structure is mounted on a support platform via a rotating mechanism, enabling limited-angle rotation within the horizontal plane. This rotating mechanism includes a bearing fixed to the upper surface of the support platform and a main shaft rigidly connected to the bottom of the cylindrical shielding structure. The lower end of the main shaft is inserted into the inner ring of the bearing. This combination allows the operator to easily rotate the cylinder around the main shaft axis manually or via a motor. Specifically, a groove is provided on the support platform, and the bearing is placed within the groove.

[0044] To further enhance the stability and load-bearing capacity during rotation, an arc-shaped guide rail is installed on the support platform, with its center of curvature coinciding with the axis of the main shaft. A slider matching the guide rail is installed at a corresponding position at the bottom of the cylindrical shielding structure. The clearance between the guide rail and the slider is adjustable to ensure that the cylinder rotates without wobbling or jamming.

[0045] In one technical solution, a support component is also provided, which is used to support the cylindrical shielding structure. The specific configuration method for the support component is as follows: The upper base plate 9 is horizontally set, and the main shaft 14 and the slider 12 are fixedly set on the bottom surface; The housing 8 is rectangular and is fixedly mounted on the upper surface of the upper base plate 9. The cylindrical shielding structure is disposed inside the housing 8. A first circular hole is provided through the front vertical plate, and a cylindrical first shielding layer passes through the first circular hole. A circular support plate is provided on the outer side of the rear vertical plate. The circular support plate, the rear vertical plate, and the rear end face of the cylindrical shielding structure are fixedly connected by bolts. The lower base plate 10 is fixedly mounted on the support platform 7, and the lower base plate 10 has holes for the bearing to pass through.

[0046] The lower base plate 10 and the upper base plate 9 are respectively provided with a circular dial 16 and a pointer 15 that match the arc-shaped guide rail 11, and the cylindrical shielding structure rotates at an angle of ±30°.

[0047] In the above technical solution, the upper base plate serves as a horizontally positioned support platform. A spindle and a slider are fixedly mounted on its bottom surface. The spindle is inserted into a bearing on the support platform to enable the rotation of the entire assembly, while the slider engages with an arc-shaped guide rail on the support platform to provide additional lateral support and guidance. During actual assembly, the spindle must be welded or bolted to the bottom surface of the upper base plate and kept perpendicular to it to ensure the consistency of the rotation axis and smooth operation.

[0048] The shell is fixed to the upper surface of the base plate by welding or bolting, forming a rigid frame. A cylindrical shielding structure is positioned between the front and rear vertical plates. The front vertical plate has a first circular hole at its center, with a diameter slightly larger than the outer diameter of the first shielding layer, allowing the cylindrical shielding layer to pass through for axial positioning and partial load-bearing. A circular support plate is also provided on the outer side of the rear vertical plate. This circular support plate is detachably connected to the rear vertical plate and the rear end face of the cylindrical shielding structure by multiple bolts. The number of bolts can be selected according to the actual structural strength requirements, for example, three bolts, evenly distributed to ensure the connection's strength and sealing. The lower base plate is fixedly installed on the support platform, typically permanently connected by anchor bolts or welding. It has a central hole for the bearing to pass through, with a diameter slightly larger than the bearing's outer diameter. A circular dial 15 matching the arc-shaped guide rail 11 is also provided on the lower base plate, and a pointer 15 matching the circular dial is provided on the upper base plate for easy determination of the rotation angle.

[0049] In summary, the composite shielding collimator designed in this invention, suitable for complex mixed radiation fields, exhibits good collimation performance for 14 MeV fast neutrons in DT fusion, good shielding capability for accompanying gamma rays, and a signal-to-noise ratio exceeding 100 for 2.5 MeV neutron measurements in DD fusion reactions. This invention can also be used for collimation of 17 MeV high-energy gamma rays. The collimator designed in this invention has good shielding capability for ambient sub-gamma rays and performs well in complex mixed radiation fields.

[0050] First, we calculate the shielding capability of each individual material, and then we perform a combined calculation of the materials to evaluate the shielding effect.

[0051] 1) Shielding calculation for a single material.

[0052] Figure 3 , Figure 4 , Figure 5 and 6 The shielding effect of lead on neutrons and gamma rays is given. Specifically: Figure 3 The shielding capability of lead of different thicknesses against neutrons is presented. Figure 4 The moderation spectra of lead of different thicknesses for 14 MeV neutrons are presented. Figure 5 The gamma-ray shielding ability of lead of different thicknesses; Figure 6 Moderation spectra of 17MeV gamma rays by lead of different thicknesses.

[0053] Figure 7 and Figure 8 The shielding effect of alumina on neutrons is given as follows: Figure 7 The neutron shielding capabilities of alumina with different thicknesses are presented. Figure 8 Moderation spectra of 14 MeV neutrons for alumina of different thicknesses are presented.

[0054] Figure 9 and Figure 10 The shielding effect of polyethylene against neutrons is given as follows: Figure 9 The neutron shielding capabilities of polyethylene of different thicknesses are presented. Figure 10 The moderation spectra of polyethylene with different thicknesses for 14 MeV neutrons are presented.

[0055] Figure 11 and Figure 12 The shielding effect of graphite on neutrons is given as follows: Figure 11 The neutron shielding capability of graphite of different thicknesses is presented. Figure 12 The moderation spectra of 14 MeV neutrons for graphite of different thicknesses are presented.

[0056] Figure 13 and Figure 14 The shielding effect of boron carbide against neutrons is given as follows: Figure 13 The neutron shielding capabilities of boron carbide with different thicknesses are presented. Figure 14 The moderation spectra of boron carbide with different thicknesses for 14 MeV neutrons are presented.

[0057] Figure 15 and Figure 16 The neutron shielding effect of boron-containing polyethylene is given, specifically: Figure 15 The neutron shielding capability of boron-containing polyethylene of different thicknesses is presented. Figure 16 The moderation spectra of boron-containing polyethylene of different thicknesses for 14 MeV neutrons are presented.

[0058] Based on the data shown in the figure above, alumina has a good moderating effect on fast neutrons, and it is designed as the outermost layer of the collimator for direct fast neutron incidence. While boron-containing polyethylene has a smaller weight difference than polyethylene and provides better neutron shielding and absorption, its effectiveness in neutron absorption is somewhat inferior to boron carbide. Therefore, using boron carbide after boron-containing polyethylene can further modulate and absorb medium-energy neutrons. Considering that placing lead in the outermost layer would cause a sudden increase in the collimator's weight and would result in an inelastic reaction with fast neutrons producing more gamma rays, and that the gamma rays generated during the slowing and absorption of fast neutrons also require further shielding, lead is placed in the innermost layer of the collimator to reduce weight while shielding gamma rays and accompanying gamma rays.

[0059] 2) The shielding effect of the designed composite material.

[0060] Figure 17 , Figure 18 , Figure 19 and Figure 20 The shielding effect of composite materials on neutrons is given in detail as follows: Figure 17 The neutron shielding capabilities of the front and side composite plates are presented. Figure 18 The moderation spectra of 14 MeV neutrons for the front and side composite plates are presented. Figure 19 The change in the penetration ratio of neutrons as they pass through the shielding material is given; Figure 20 The energy spectrum changes of neutrons passing through the shielding material layer by layer are presented.

[0061] 3) Optimization of the incident collimation aperture.

[0062] based on Figure 21 Based on a collimator calculation model with a simple ring source, the signal-to-noise ratio of neutrons at 2.5 MeV and 14 MeV was calculated with the collimator aperture set to 2.5 cm, 3 cm and 3.5 cm respectively. Figure 22 A comparison is presented between the signal detected by the liquid scintillation detector after 2.5 MeV neutrons pass through the collimator and the neutron background entering the detector from outside the collimation aperture. The signal increases with increasing aperture size, and the neutron background also increases accordingly. Figure 23 The signal and background of 14 MeV neutrons show a significant increase in neutron background when the aperture increases to 3.5 cm, while the difference in neutron background is relatively small when the aperture is 2.5 cm and 3 cm. Table 1 shows the signal-to-noise ratio (SNR) of 2.5 MeV and 14 MeV neutrons at different apertures, with the SNR being optimal at an aperture of 3 cm.

[0063] Table 1. Signal-to-noise ratio of collimator at different apertures The shielding capability estimation of the collimator designed in this invention under a simple loop source is as follows: Figure 24 and Figure 25 The collimator signal, background, and activated gamma spectrum of the neutron source are given in detail below: Figure 24 It is a 2.5 MeV neutron source; Figure 25 It is a 14MeV neutron source.

[0064] Depend on Figure 24 and Figure 25 It is evident that the collimator exhibits excellent collimation performance for 2.5 MeV neutron sources, with very low neutron background and activated gamma rays. However, at 14 MeV neutron energy, the neutron signal increases, and some neutrons outside the aperture also enter the detector. This is primarily due to the relatively thin boron-containing polyethylene layer on the sides, meaning that 14 MeV neutrons entering the collimator from the sides are not completely slowed down and shielded. Secondly, the activated gamma spectrum indicates that the liquid scintillation detector itself undergoes inelastic scattering with fast neutrons, exhibiting a 4.4 MeV gamma response for carbon nuclei and a 2.2 MeV gamma response for hydrogen nuclei. The collimator itself generates relatively little inelastic gamma while slowing down neutron absorption; the 10 cm lead layer within the collimator almost completely shields the gamma rays, resulting in a low-energy response on the detector for the portion that does enter. Figure 26 , Figure 27 , Figure 28 and Figure 29 The energy spectra of 1 MeV, 3 MeV, 5 MeV, and 17 MeV gamma sources after collimation are presented. The 1 MeV gamma has a low background and provides good collimation for gamma rays entering directly from the toroidal source. As the gamma energy increases, gamma rays that are not completely shielded appear outside the source energy, but their interference remains low.

[0065] The number of devices and processing scale described herein are for the purpose of simplifying the description of the invention. Applications, modifications, and variations of the invention will be readily apparent to those skilled in the art.

[0066] Although the embodiments of the present invention have been disclosed above, they are not limited to the applications listed in the specification and embodiments. They can be applied to various fields suitable for the present invention. For those skilled in the art, other modifications can be easily made. Therefore, without departing from the general concept defined by the claims and their equivalents, the present invention is not limited to the specific details.

Claims

1. A composite shielded collimator suitable for complex mixed radiation fields, characterized in that, include: A cylindrical shielding structure, wherein a aligning hole is provided through it along the axial direction, and the cylindrical shielding structure specifically comprises, from the outside to the inside: The first shielding layer, made of aluminum oxide, is located at the foremost neutron incident end and is cylindrical in shape. It is used to reduce the neutron energy by inelastic scattering with high-energy neutrons. The second shielding layer, made of 10% boron polyethylene, is located immediately after the first shielding layer and is cylindrical in shape, in order to slow down and absorb the neutrons that have passed through the first shielding layer as thermal neutrons and fast neutrons. The third shielding layer, made of boron carbide, is nested inside the second shielding layer and is used to slow down and absorb thermal neutrons and medium-energy neutrons, and suppress the generation of secondary gamma rays. The fourth shielding layer, made of lead, is nested inside the third shielding layer and is used to shield ambient gamma rays and activated gamma rays. The fourth shielding layer contains a detector mounting cavity for accommodating the detector. The collimation hole passes through the first shielding layer, the second shielding layer, the third shielding layer, and the fourth shielding layer in sequence, and leads to the detector mounting cavity.

2. The composite shielded collimator suitable for complex mixed radiation fields as described in claim 1, characterized in that, The third shielding layer includes a cylindrical portion and a hemispherical portion, with the hemispherical portion disposed at the front end of the cylindrical portion; the fourth shielding layer is cylindrical and nested inside the cylindrical portion of the third shielding layer.

3. The composite shielding collimator suitable for complex mixed radiation fields as described in claim 2, characterized in that, The first shielding layer has an axial thickness of 10cm and a radius of 25cm; the second shielding layer has a minimum front thickness of 30cm and a minimum circumferential side thickness of 15cm; the third shielding layer has a hemispherical portion with a radius of 20cm and a circumferential side thickness of 5cm; and the fourth shielding layer has a front, rear, and circumferential thickness of 10cm.

4. The composite shielding collimator suitable for complex mixed radiation fields as described in claim 2, characterized in that, The collimation aperture has a diameter of 2.5cm-3.5cm and a length of 70cm to limit the non-axial neutron flux.

5. The composite shielding collimator suitable for complex mixed radiation fields as described in claim 1, characterized in that, The cylindrical shielding structure is further provided with a stainless steel shell, which is wrapped around the outer surface of the second shielding layer. The cylindrical shielding structure is rotatably mounted on a support platform.

6. The composite shielding collimator suitable for complex mixed radiation fields as described in claim 5, characterized in that, The cylindrical shielding structure is rotatably mounted on the support platform, specifically as follows: A bearing is provided on the upper surface of the support platform, and a main shaft is fixedly provided below the cylindrical shielding structure, with the main shaft disposed inside the bearing. An arc-shaped guide rail is also provided on the upper surface of the support platform. The center of curvature of the arc-shaped guide rail coincides with the axis of the main shaft. A slider adapted to the arc-shaped guide rail is fixedly provided below the cylindrical shielding structure.

7. The composite shielded collimator suitable for complex mixed radiation fields as described in claim 6, characterized in that, A support assembly is also provided to support the cylindrical shielding structure. The support assembly is specifically configured as follows: The upper base plate is horizontally positioned, and the main shaft and the slider are fixedly mounted on the bottom surface; The housing, which is cuboid in shape, is fixedly mounted on the upper surface of the upper base plate, and the cylindrical shielding structure is disposed inside the housing; wherein, a first circular hole is provided through the front vertical plate, and a cylindrical first shielding layer passes through the first circular hole; a circular support plate is provided on the outer side of the rear vertical plate; the circular support plate, the rear vertical plate, and the rear end face of the cylindrical shielding structure are fixedly connected by bolts. The lower base plate is fixedly mounted on the support platform, and the lower base plate has holes for bearings to pass through, and the arc-shaped guide rail is mounted on the lower base plate.

8. The composite shielded collimator suitable for complex mixed radiation fields as described in claim 7, characterized in that, A circular dial and a pointer matching the arc-shaped guide rail are respectively provided on the lower base plate and the upper base plate, and the cylindrical shielding structure rotates at an angle of ±30°.

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