A beam trapping device and neutron source system for reducing neutron backscattering background

Abstract

This invention discloses a beam trapping device and a neutron source system for reducing neutron backscattering background. The device comprises, from the inside out, an inner high-density polyethylene layer, an outer lead layer, another outer high-density polyethylene layer, and an outer steel layer. The inner high-density polyethylene layer is hollow. A first through-hole is provided on the sidewall of the outer steel layer, a second through-hole is provided on the sidewall of the outer high-density polyethylene layer, and a third and fourth through-hole are provided on the top of the outer lead layer. The first, second, and third through-holes, along with the central through-hole of the inner high-density polyethylene layer, are sequentially connected to form a beam channel. A B4C absorption layer is provided within the fourth through-hole, with the B4C absorption layer facing the beam channel. The inner lead layer is disposed on the surface of the B4C absorption layer facing the beam channel. This device and neutron source system can achieve effective shielding.

Description

Technical Field

[0001] This invention belongs to the field of beam trapping technology and relates to a beam trapping device and a neutron source system for reducing neutron backscattering background. Background Technology

[0002] In recent years, numerous neutron sources have been built worldwide to meet diverse needs in scientific research, medicine, engineering applications, and education. Ensuring high-quality neutron beams while minimizing experimental background radiation is a crucial issue. In neutron experiments, the neutron beam passes through the experimental sample and eventually stops at the back wall of the laboratory. On one hand, backscattered neutrons and gamma rays from the back wall contaminate experimental data, complicating data processing and potentially causing data invalidation; on the other hand, additional high-intensity background radiation can damage detectors and electrical equipment. One effective method to reduce backscatter background is to construct the laboratory back wall away from the detector location, but this increases construction costs. A more practical approach is to install a beam trapping device in front of the back wall to shield against backscattered neutrons and gamma rays. Although much work has been done on beam trapping device shielding design over the years, there is no universal method or structure; each specific experimental setup requires individual beam trapping device design to achieve optimal shielding adapted to the surrounding environment.

[0003] The article "Optimization of beam dump shielding for K-130cyclotron at VECC," published in the October 2017 issue of *Applied Radiation and ISOTOPES*, Volume 128, Issue 6, pp. 216-223, proposes a compact and efficient composite beam trapping device composed of lead, iron, and high-density polyethylene materials of varying thicknesses. Fluka Monte Carlo simulations and experiments verified its effectiveness in reducing the background effects of backscattered neutrons and photons during experiments. However, the proposed beam trapping device structure still has significant room for optimization in terms of geometry. Applying this beam trapping structure to the DD-110 compact neutron tube and simulating it using the MCNP Monte Carlo program revealed that adding the beam trapping device resulted in only a minimal reduction in the flux of backscattered neutrons and gamma rays at the sample location, failing to achieve an effective shielding effect. Summary of the Invention

[0004] The purpose of this invention is to overcome the shortcomings of the prior art and provide a beam trapping device and a neutron source system that reduce the neutron backscattering background, which can achieve effective shielding.

[0005] To achieve the above objectives, this invention discloses a beam trapping device for reducing neutron backscattering background, comprising, from the inside out, an inner high-density polyethylene layer, an outer lead layer, an outer high-density polyethylene layer, and an outer steel layer. The inner high-density polyethylene layer has a hollow structure. A first through-hole is provided on the sidewall of the outer steel layer, a second through-hole is provided on the sidewall of the outer high-density polyethylene layer, and a third and fourth through-hole are provided on the top of the outer lead layer. The first, second, and third through-holes and the central through-hole of the inner high-density polyethylene layer are sequentially connected to form a beam channel. A B4C absorption layer is provided inside the fourth through-hole, wherein the B4C absorption layer faces the beam channel, and the inner lead layer is provided on the surface of the B4C absorption layer facing the beam channel.

[0006] A further improvement of the beam trapping device for reducing neutron backscattering background described in this invention is as follows:

[0007] Furthermore, the beam channel has dimensions of 30cm × 30cm, an inner high-density polyethylene layer with a thickness of 5cm, an outer lead layer with a thickness of 10cm, an outer high-density polyethylene layer with a thickness of 15cm, and an outer steel layer with a thickness of 5cm.

[0008] Furthermore, the thickness of the B4C absorber layer is 15 cm, and the thickness of the inner lead layer is 1 cm.

[0009] Furthermore, the beam channel dimensions are 30cm × 30cm.

[0010] Furthermore, the outer steel layer has a cuboid structure.

[0011] This invention discloses a neutron source system, including a neutron source shield, a collimator, and a beam trapping device. The neutron source shield, collimator, and beam trapping device are arranged sequentially. The beam trapping device includes, from the inside out, an inner high-density polyethylene layer, an outer lead layer, an outer high-density polyethylene layer, and an outer steel layer. The inner high-density polyethylene layer has a hollow structure. A first through-hole is provided on the sidewall of the outer steel layer, a second through-hole is provided on the sidewall of the outer high-density polyethylene layer, and a third and fourth through-hole are provided on the top of the outer lead layer. The first, second, and third through-holes, along with the central through-hole of the inner high-density polyethylene layer, are sequentially connected to form a beam channel. A B4C absorption layer is provided within the fourth through-hole, with the B4C absorption layer facing the beam channel. An inner lead layer is disposed on the surface of the B4C absorption layer facing the beam channel.

[0012] A further improvement of the neutron source system described in this invention is that:

[0013] Furthermore, the neutron source shielding includes a source shielding graphite layer, an inner boron-containing polyethylene layer, an inner lead layer, an outer boron-containing polyethylene layer, and an outer lead layer, wherein the source shielding graphite layer, the inner boron-containing polyethylene layer, the inner lead layer, the outer boron-containing polyethylene layer, and the outer lead layer are distributed sequentially from the inside to the outside.

[0014] Furthermore, the collimator includes a source shield beam extraction channel, a collimator boron-containing polyethylene layer, and a collimator lead layer. One end of the source shield beam extraction channel is equipped with a sample position detector. The other end of the source shield beam extraction channel passes through the collimator axially and then through the side wall of the outer lead layer of the source shield, the side wall of the outer boron-containing polyethylene layer of the source shield, the side wall of the inner lead layer of the source shield, the side wall of the inner boron-containing polyethylene layer of the source shield, and the side wall of the graphite layer of the source shield. After being inserted into the graphite layer of the source shield, a source shield polyethylene neutron moderator is placed therein.

[0015] Furthermore, a DD neutron source is disposed within the graphite layer of the source shield.

[0016] Furthermore, the beam channel dimensions are 30cm × 30cm, the inner high-density polyethylene layer thickness is 5cm, the outer lead layer thickness is 10cm, the outer high-density polyethylene layer thickness is 15cm, the outer steel layer thickness is 5cm, the B4C absorption layer thickness is 15cm, the inner lead layer thickness is 1cm, and the beam channel dimensions are 30cm × 30cm.

[0017] The present invention has the following beneficial effects:

[0018] The beam trapping device and neutron source system for reducing neutron backscattering background described in this invention, in specific operation, include an inner high-density polyethylene layer, an outer lead layer, an outer high-density polyethylene layer, and an outer steel layer arranged sequentially from the inside out. The inner high-density polyethylene layer has a hollow structure. A first through-hole is provided on the side wall of the outer steel layer, a second through-hole is provided on the side wall of the outer high-density polyethylene layer, and a third and fourth through-hole are provided on the top of the outer lead layer. The first, second, and third through-holes and the central through-hole of the inner high-density polyethylene layer are sequentially connected to form a beam channel. A B4C absorption layer is provided inside the fourth through-hole, and the inner lead layer is provided on the B4C absorption layer. The beam trapping device significantly reduces the neutron backscattering background in the experimental environment, especially at the experimental sample location, and further reduces the backscattered gamma ray background. The structure is simple, easy to implement, and can meet the requirement of reducing the neutron backscattering background in experiments. It should also be noted that by absorbing gamma rays in the beam through the internal lead layer and slowing down fast neutrons in the beam, B4C has a better thermal neutron absorption effect. By absorbing thermal neutrons from the beam and generated by the internal lead layer through the B4C absorption layer, shielding can be effectively achieved. Attached Figure Description

[0019] The accompanying drawings, which form part of this specification, are used to provide a further understanding of the invention. The illustrative embodiments of the invention and their descriptions are used to explain the invention and do not constitute an undue limitation of the invention. In the drawings:

[0020] Figure 1 This is a 3D structural schematic diagram of the beam trapping device in this invention;

[0021] Figure 2 This is a top cross-sectional view of the beam trapping device in this invention;

[0022] Figure 3 This is a schematic diagram of the neutron source system in this invention;

[0023] Figure 4 Structural diagrams of the comparison samples;

[0024] Figure 5 This is a simulation result of the spatial distribution of backscattered neutron fluence in the simulation experiment;

[0025] Figure 6 The figure shows the simulation results of the backscattered neutron fluence distribution curves at the sample location cross section using the present invention, the original beam trapping device, and without a beam trapping device.

[0026] Among them, 1 is the inner lead layer, 2 is the B4C absorption layer, 3 is the inner high-density polyethylene layer, 4 is the outer lead layer, 5 is the outer high-density polyethylene layer, 6 is the outer steel layer, 7 is the beam channel, 201 is the graphite layer of the source shield, 202 is the inner boron-containing polyethylene layer of the source shield, 203 is the inner lead layer of the source shield, 204 is the outer boron-containing polyethylene layer of the source shield, 205 is the outer lead layer of the source shield, 206 is the polyethylene neutron moderator of the source shield, 207 is the beam extraction channel of the source shield, 208 is the boron-containing polyethylene layer of the collimator, 209 is the lead layer of the collimator, 210 is the concrete wall, and 211 is the detector at the sample location. Detailed Implementation

[0027] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some, not all, of the embodiments of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0028] In the description of this invention, it should be understood that the terms "comprising" and "including" indicate the presence of the described features, integrals, steps, operations, elements and / or components, but do not exclude the presence or addition of one or more other features, integrals, steps, operations, elements, components and / or collections thereof.

[0029] It should also be understood that the terminology used in this specification is for the purpose of describing particular embodiments only and is not intended to limit the invention. As used in this specification and the appended claims, the singular forms “a,” “an,” and “the” are intended to include the plural forms unless the context clearly indicates otherwise.

[0030] It should also be further understood that the term "and / or" as used in this specification and the appended claims refers to any combination and all possible combinations of one or more of the associated listed items, and includes such combinations. For example, A and / or B can represent three cases: A alone, A and B simultaneously, and B alone. Additionally, the character " / " in this invention generally indicates that the preceding and following objects have an "or" relationship.

[0031] It should be understood that although terms such as first, second, third, etc., may be used in the embodiments of the present invention to describe the preset range, these preset ranges should not be limited to these terms. These terms are only used to distinguish the preset ranges from one another. For example, without departing from the scope of the embodiments of the present invention, the first preset range may also be referred to as the second preset range, and similarly, the second preset range may also be referred to as the first preset range.

[0032] Depending on the context, the word "if" as used here can be interpreted as "when," "when," "in response to determination," or "in response to detection." Similarly, depending on the context, the phrase "if determination" or "if detection (of the stated condition or event)" can be interpreted as "when determination," "in response to determination," "when detection (of the stated condition or event)," or "in response to detection (of the stated condition or event)."

[0033] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some, not all, of the embodiments of the present invention. The components of the embodiments of the present invention described and shown in the accompanying drawings can generally be arranged and designed in various different configurations. Therefore, the following detailed description of the embodiments of the present invention provided in the accompanying drawings is not intended to limit the scope of the claimed invention, but merely to illustrate selected embodiments of the invention. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without inventive effort are within the scope of protection of the present invention.

[0034] The accompanying drawings illustrate various structural schematic diagrams according to embodiments disclosed in this invention. These drawings are not to scale, and some details have been enlarged for clarity, and some details may have been omitted. The shapes of the various regions and layers shown in the drawings, as well as their relative sizes and positional relationships, are merely exemplary and may deviate from reality due to manufacturing tolerances or technical limitations. Furthermore, those skilled in the art can design regions / layers with different shapes, sizes, and relative positions as needed.

[0035] Example 1

[0036] refer to Figure 1 and Figure 2 The beam capture device of the present invention includes an inner high-density polyethylene layer 3, an outer lead layer 4, an outer high-density polyethylene layer 5, and an outer steel layer 6 arranged sequentially from the inside to the outside. The inner high-density polyethylene layer 3 has a hollow structure. A first through hole is provided on the side wall of the outer steel layer 6. A second through hole is provided on the side wall of the outer high-density polyethylene layer 5. A third through hole and a fourth through hole are provided on the top of the outer lead layer 4. The first through hole, the second through hole, the third through hole, and the central through hole of the inner high-density polyethylene layer 3 are sequentially connected to form a beam channel 7. A B4C absorption layer 2 is provided in the fourth through hole. The B4C absorption layer 2 faces the beam channel 7, and an inner lead layer 1 is provided on the surface of the B4C absorption layer 2 facing the beam channel 7.

[0037] It should be noted that the inner lead layer 1 is located at the bottom of the beam channel 7, serving as the innermost layer of the device, and is mainly used to moderate neutrons and absorb gamma rays; the inner lead layer 1 is in close contact with the B4C absorption layer 2, utilizing... 10 The high thermal neutron absorption cross section of B effectively absorbs thermal neutrons from the beam and those moderated by the internal lead layer 1, further reducing neutron backscattering; the internal high-density polyethylene layer 3 is closely attached to the side of the beam channel 7, and its outer side is successively covered by the external lead layer 4 and the external high-density polyethylene layer 5, further improving the shielding effect of neutrons and gamma rays; the external steel layer 6 encloses the entire device, further reducing the impact of radiation on the surrounding environment and ensuring the structural strength and stability of the entire device.

[0038] Preferably, the beam channel 7 has dimensions of 30cm × 30cm, with an inner high-density polyethylene layer 3 of 5cm thickness and an inner lead layer 1 of 1cm thickness, used for gamma ray absorption and neutron moderation; the B4C absorption layer 2 has a thickness of 15cm, and the B4C absorption layer 2 contains... 10 B has a good thermal neutron absorption cross section. After reacting with thermal neutrons, it does not produce high-energy secondary rays. It is used to absorb thermal neutrons from the beam and those generated by the internal lead layer 1. The internal high-density polyethylene layer 3 is covered by an external lead layer 4 and an external high-density polyethylene layer 5 in sequence. The thicknesses of the external lead layer 4 and the external high-density polyethylene layer 5 are 10 cm and 15 cm, respectively, to further shield neutrons and gamma rays. Finally, the entire device is wrapped by an external steel layer 6 with a thickness of 5 cm. The external steel layer 6 serves as a radiation shielding layer, further reducing the impact of radiation generated by the beam capture device on the surrounding environment during use, and also provides structural support to ensure the mechanical stability and durability of the entire beam capture device.

[0039] Example 2

[0040] refer to Figure 3 The neutron source system of the present invention includes a neutron source shield, a collimator, and a beam trapping device;

[0041] The beam capture device includes an inner high-density polyethylene layer 3, an outer lead layer 4, an outer high-density polyethylene layer 5, an outer steel layer 6, a B4C absorption layer 2, and an inner lead layer 1, with the specific connection structure shown in Embodiment 1.

[0042] The neutron source shield includes a source shield graphite layer 201, an inner boron-containing polyethylene layer 202, an inner lead layer 203, an outer boron-containing polyethylene layer 204, and an outer lead layer 205, wherein the source shield graphite layer 201, the inner boron-containing polyethylene layer 202, the inner lead layer 203, the outer boron-containing polyethylene layer 204, and the outer lead layer 205 are distributed sequentially from the inside to the outside.

[0043] The collimator includes a source shield beam extraction channel 207, a collimator boron-containing polyethylene layer 208, and a collimator lead layer 209. One end of the source shield beam extraction channel 207 is equipped with a sample position detector 211. The other end of the source shield beam extraction channel 207 passes axially through the collimator and then through the sidewalls of the outer lead layer 205, the outer boron-containing polyethylene layer 204, the inner lead layer 203, the inner boron-containing polyethylene layer 202, and the graphite layer 201 of the source shield, inserting into the graphite layer 201 of the source shield. An active shielding polyethylene neutron moderator 206 is installed inside the rear. The DD neutron source is located inside the graphite layer 201 of the source shielding. The fast neutrons generated by the DD neutron source have their energy reduced by the polyethylene neutron moderator 206, resulting in more thermal neutrons. The neutron beam is collimated by a collimator composed of a boron-containing polyethylene layer 208 and a lead layer 209. It then passes through the detector 211 at the sample location and finally enters the beam trapping device. The multi-layer composite shielding structure of the beam trapping device absorbs and shields neutrons and gamma rays, thereby reducing the backscattering background of neutrons and gamma rays.

[0044] It should be noted that the present invention absorbs gamma rays in the beam through the internal lead layer 1 and slows down fast neutrons in the beam. B4C has a better thermal neutron absorption effect. The B4C absorption layer 2 absorbs thermal neutrons from the beam and those generated by the slowing down of the internal lead layer 1.

[0045] In this embodiment, a concrete wall 210 is also included, which encloses an accommodating space. The inner lead layer 1, B4C absorption layer 2, inner high-density polyethylene layer 3, outer lead layer 4, outer high-density polyethylene layer 5, outer steel layer 6, beam channel 7, source shield graphite layer 201, inner boron-containing polyethylene layer 202 of the source shield, inner lead layer 203 of the source shield, outer boron-containing polyethylene layer 204 of the source shield, outer lead layer 205 of the source shield, polyethylene neutron moderator 206 of the source shield, beam extraction channel 207 of the source shield, collimator boron-containing polyethylene layer 208, collimator lead layer 209, and detector 211 at the sample position are all located within the accommodating space.

[0046] Confirmatory test

[0047] This experiment included two control samples. The first control sample, compared to the beam trapping device described in this invention, had its internal lead layer 1 removed and the B4C absorber layer 2 replaced with a high-density polyethylene absorber layer. (Refer to...) Figure 4 The second comparative sample lacked a beam trapping device, and the test results are as follows: Figure 5 and Figure 6 As shown.

[0048] Other embodiments of the invention will readily occur to those skilled in the art upon consideration of the specification and disclosure of the invention. This application is intended to cover any variations, uses, or adaptations of the invention that follow the general principles of the invention and include common knowledge or customary techniques in the art not disclosed herein. The specification and examples are to be considered exemplary only, and the true scope and spirit of the invention are indicated by the following claims.

[0049] It should be understood that the present invention is not limited to the precise structure described above and shown in the accompanying drawings, and various modifications and changes can be made without departing from its scope. The scope of the invention is limited only by the appended claims.

[0050] The above description is merely a preferred embodiment of the present invention and does not constitute any limitation on the present invention. Any simple modifications, alterations, or equivalent structural changes made to the above embodiments based on the technical essence of the present invention shall still fall within the protection scope of the present invention.

Claims

1. A beam trapping device for reducing neutron backscattering background, characterized in that, The device comprises an inner high-density polyethylene layer (3), an outer lead layer (4), an outer high-density polyethylene layer (5), and an outer steel layer (6) arranged sequentially from the inside to the outside. The inner high-density polyethylene layer (3) is a hollow structure. The outer steel layer (6) has a first through hole on its side wall, the outer high-density polyethylene layer (5) has a second through hole on its side wall, and the outer lead layer (4) has a third through hole and a fourth through hole on its top. The first through hole, the second through hole, the third through hole, and the central through hole of the inner high-density polyethylene layer (3) are connected sequentially to form a beam channel (7). The fourth through hole contains a B4C absorption layer (2), which faces the beam channel (7). The inner lead layer (1) is arranged on the surface of the B4C absorption layer (2) facing the beam channel (7). The beam channel (7) has a size of 30cm×30cm, the inner high-density polyethylene layer (3) has a thickness of 5cm, the outer lead layer (4) has a thickness of 10cm, the outer high-density polyethylene layer (5) has a thickness of 15cm, and the outer steel layer (6) has a thickness of 5cm. The thickness of the B4C absorber layer (2) is 15cm, and the thickness of the inner lead layer (1) is 1cm. The beam channel (7) has a size of 30cm×30cm.

2. The beam trapping device for reducing neutron backscattering background according to claim 1, characterized in that, The outer steel layer (6) has a cuboid structure.

3. A neutron source system, characterized in that, It includes a neutron source shield, a collimator, and the beam trapping device as described in claim 1, wherein the neutron source shield, the collimator, and the beam trapping device are arranged sequentially.

4. The neutron source system according to claim 3, characterized in that, The neutron source shield includes a source shield graphite layer (201), an inner boron-containing polyethylene layer (202), an inner lead layer (203), an outer boron-containing polyethylene layer (204), and an outer lead layer (205), wherein the source shield graphite layer (201), the inner boron-containing polyethylene layer (202), the inner lead layer (203), the outer boron-containing polyethylene layer (204), and the outer lead layer (205) are distributed sequentially from the inside to the outside.

5. The neutron source system according to claim 3, characterized in that, The collimator includes a source shield beam extraction channel (207), a collimator boron-containing polyethylene layer (208), and a collimator lead layer (209). One end of the source shield beam extraction channel (207) is provided with a sample position detector (211). The other end of the source shield beam extraction channel (207) passes through the collimator along the axial direction and then passes through the side wall of the outer lead layer (205) of the source shield, the side wall of the outer boron-containing polyethylene layer (204) of the source shield, the side wall of the inner lead layer (203) of the source shield, the side wall of the inner boron-containing polyethylene layer (202) of the source shield, and the side wall of the graphite layer (201) of the source shield. After being inserted into the graphite layer (201) of the source shield, a source shield polyethylene neutron moderator (206) is provided.

6. The neutron source system according to claim 3, characterized in that, A DD neutron source is disposed within the graphite layer (201) of the source shield.

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