Beam capturing device for reducing neutron back scattering background and neutron source system

Abstract

The invention discloses a beam capturing device for reducing neutron back scattering background and a neutron source system.The beam capturing device comprises an internal high-density polyethylene layer, an external lead layer, an external high-density polyethylene layer and an external steel layer which are sequentially arranged from inside to outside, and the internal high-density polyethylene layer is of a hollow structure; a first through hole is formed in the side wall of the outer steel layer, a second through hole is formed in the side wall of the outer high-density polyethylene layer, a third through hole and a fourth through hole are formed in the top of the outer lead layer, and the first through hole, the second through hole, the third through hole and a center through hole of the inner high-density polyethylene layer are sequentially communicated to form a beam channel. A B4C absorption layer is arranged in the fourth through hole, the B4C absorption layer directly faces the beam channel, an internal lead layer is arranged on the face, directly facing the beam channel, of the B4C absorption layer, and effective shielding can be achieved through the device and the neutron source system.

Description

Technical Field

[0001] The invention belongs to the technical field of beam capture, and relates to a beam capture device for reducing neutron backscattering background and a neutron source system. Background Art

[0002] In recent years, many neutron sources have been built around the world to meet different needs such as scientific research, medical treatment, engineering applications and education. How to ensure high-quality neutron beams and reduce the experimental background as much as possible is an important issue. In neutron experiments, the neutron beam passes through the experimental sample and finally stops at the back wall of the laboratory. On the one hand, the backscattered neutron and gamma-ray background from the back wall of the laboratory will contaminate the experimental data, making data processing more complicated and even causing experimental data invalidation; on the other hand, the additional high-intensity background irradiation may damage the detector and electrical equipment. An effective way to reduce the backscatter background is to build the back wall of the laboratory away from the detector location, but this will increase the cost of building the laboratory. A more practical measure is to set up a beam capture device in front of the back wall of the laboratory to shield backscattered neutrons and gamma rays. Although there have been many related works on the shielding design of beam capture devices over the years, there is no universal method and structure. It is necessary to design a separate beam capture device for each specific experimental device to obtain the optimal shielding effect adapted to the surrounding environment.

[0003] In the article "Optimization of beam dump shielding for K-130cyclotron at VECC" published in Volume 128, Issue 6, Pages 216-223 of "APPLIED RADIATION AND ISOTOPES" published in October 2017, a compact and efficient composite beam capture device composed of lead, iron and high-density polyethylene materials of different thicknesses was proposed. Through FLUKA Monte Carlo simulation and experimental verification, it was found that it can effectively reduce the influence of backscattered neutron and photon background in the experiment, but the geometric dimensions of the proposed beam capture device structure still have a lot of room for optimization. The beam capture device structure was applied to the DD-110 compact neutron tube and simulated using the MCNP Monte Carlo program. The results show that after adding the beam capture device, the flux of neutrons and gamma rays from backscattering at the sample position is only slightly reduced, and no effective shielding effect is achieved. Summary of the invention

[0004] The purpose of the present invention is to overcome the shortcomings of the prior art and provide a beam capture device and a neutron source system for reducing neutron backscattering background. The device and the neutron source system can achieve effective shielding.

[0005] To achieve the above-mentioned object, the present invention discloses a beam capture device for reducing neutron backscattering background, comprising an inner high-density polyethylene layer, an outer lead layer, an outer high-density polyethylene layer and an outer steel layer arranged in sequence from the inside to the outside, wherein the inner high-density polyethylene layer is a hollow structure, a first through hole is arranged on the side wall of the outer steel layer, a second through hole is arranged on the side wall of the outer high-density polyethylene layer, a third through hole and a fourth through hole are arranged on the top of the outer lead layer, the first through hole, the second through hole, the third through hole and the central through hole of the inner high-density polyethylene layer are connected in sequence to form a beam channel, and a B is arranged in the fourth through hole. 4 C absorption layer, where B 4 C absorption layer is facing the beam channel, B 4 An inner lead layer is arranged on the surface of the C absorption layer facing the beam channel.

[0006] The further improvement of the beam capture device for reducing neutron backscattering background of the present invention is:

[0007] Furthermore, the size of the beam channel is 30 cm×30 cm, the thickness of the inner high-density polyethylene layer is 5 cm, the thickness of the outer lead layer is 10 cm, the thickness of the outer high-density polyethylene layer is 15 cm, and the thickness of the outer steel layer is 5 cm.

[0008] Furthermore, B 4 The thickness of the C absorption layer is 15cm and the thickness of the inner lead layer is 1cm.

[0009] Furthermore, the size of the beam channel is 30 cm×30 cm.

[0010] Furthermore, the outer steel layer is a rectangular parallelepiped structure.

[0011] The present invention discloses a neutron source system, comprising a neutron source shielding body, a collimator and a beam capture device, wherein the neutron source shielding body, the collimator and the beam capture device are arranged in sequence, the beam capture device comprises an inner high-density polyethylene layer, an outer lead layer, an outer high-density polyethylene layer and an outer steel layer arranged in sequence from the inside to the outside, the inner high-density polyethylene layer is a hollow structure, a first through hole is arranged on the side wall of the outer steel layer, a second through hole is arranged on the side wall of the outer high-density polyethylene layer, a third through hole and a fourth through hole are arranged on the top of the outer lead layer, the first through hole, the second through hole, the third through hole and the central through hole of the inner high-density polyethylene layer are connected in sequence to form a beam channel, a B is arranged in the fourth through hole 4 C absorption layer, where B 4 C absorption layer is facing the beam channel, B 4 An inner lead layer is arranged on the surface of the C absorption layer facing the beam channel.

[0012] The further improvement of the neutron source system of the present invention is:

[0013] Further, the neutron source shielding body comprises a source shielding body graphite layer, a boron-containing polyethylene layer inside the source shielding body, a lead layer inside the source shielding body, a boron-containing polyethylene layer outside the source shielding body and a lead layer outside the source shielding body, wherein the source shielding body graphite layer, the boron-containing polyethylene layer inside the source shielding body, the lead layer inside the source shielding body, the boron-containing polyethylene layer outside the source shielding body and the lead layer outside the source shielding body are distributed in sequence from inside to outside.

[0014] Furthermore, the collimator comprises a source shielding body beam extraction channel, a collimator boron-containing polyethylene layer and a collimator lead layer, wherein a sample position detector is arranged at one end of the source shielding body beam extraction channel, and the other end of the source shielding body beam extraction channel passes through the collimator axially and then passes through the side wall of the lead layer outside the source shielding body, the side wall of the boron-containing polyethylene layer outside the source shielding body, the side wall of the lead layer inside the source shielding body, the side wall of the boron-containing polyethylene layer inside the source shielding body and the side wall of the graphite layer of the source shielding body, and is inserted into the graphite layer of the source shielding body, and then a source shielding body polyethylene neutron moderator is arranged.

[0015] Furthermore, a DD neutron source is arranged in the graphite layer of the source shielding body.

[0016] Furthermore, the size of the beam channel is 30 cm × 30 cm, the thickness of the inner high-density polyethylene layer is 5 cm, the thickness of the outer lead layer is 10 cm, the thickness of the outer high-density polyethylene layer is 15 cm, the thickness of the outer steel layer is 5 cm, and the B 4 The thickness of the C absorption layer is 15 cm, the thickness of the internal lead layer is 1 cm, and the size of the beam channel is 30 cm × 30 cm.

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

[0018] The beam capture device and neutron source system for reducing neutron backscattering background of the present invention include, during specific operation, an inner high-density polyethylene layer, an outer lead layer, an outer high-density polyethylene layer and an outer steel layer, which are arranged in sequence from the inside to the outside. The inner high-density polyethylene layer is a hollow structure. A first through hole is arranged on the side wall of the outer steel layer, a second through hole is arranged on the side wall of the outer high-density polyethylene layer, a third through hole and a fourth through hole are arranged on the top of the outer lead layer, the first through hole, the second through hole, the third through hole and the central through hole of the inner high-density polyethylene layer are connected in sequence to form a beam channel, and a B is arranged in the fourth through hole. 4 C absorption layer, where B 4An internal lead layer is arranged on the C absorption layer, and the beam capture device can significantly reduce the neutron backscattering background in the experimental environment, especially the neutron backscattering background at the position of the experimental sample, and further reduce the backscattered gamma ray background. The structure is simple and easy to implement, and can meet the requirements of reducing the neutron backscattering background in the experiment. At the same time, it should be noted that the internal lead layer absorbs the gamma rays in the beam and slows down the fast neutrons in the beam, B 4 C has better thermal neutron absorption effect, through B 4 The C absorption layer absorbs thermal neutrons from the beam and those produced by slowing down in the internal lead layer, thus achieving effective shielding. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] The accompanying drawings constituting a part of the present invention are used to provide a further understanding of the present invention. The exemplary embodiments of the present invention and their descriptions are used to explain the present invention and do not constitute an improper limitation of the present invention. In the accompanying drawings:

[0020] Figure 1 It is a schematic diagram of the 3D structure of the beam capture device in the present invention;

[0021] Figure 2 is a top cross-sectional view of the beam capture device of the present invention;

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

[0023] Figure 4 This is the structural diagram of the comparison sample;

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

[0025] Figure 6 It is a diagram of the simulation results of the backscattered neutron flux distribution curve of the cross section where the sample is located when using the present invention, the original structure beam capture device, and no beam capture device.

[0026] Among them, 1 is the inner lead layer, 2 is B 4 C is the 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 source shielding graphite layer, 202 is the inner boron-containing polyethylene layer of the source shielding, 203 is the inner lead layer of the source shielding, 204 is the outer boron-containing polyethylene layer of the source shielding, 205 is the outer lead layer of the source shielding, 206 is the polyethylene neutron moderator of the source shielding, 207 is the source shielding beam extraction channel, 208 is the collimator boron-containing polyethylene layer, 209 is the collimator lead layer, 210 is the concrete wall, and 211 is the detector at the sample position. DETAILED DESCRIPTION

[0027] The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only a part rather than all of the embodiments of the present invention. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts shall fall within the protection scope of the present invention.

[0028] In the description of the present invention, it should be understood that the terms "include" and "comprise" indicate the presence of the described features, wholes, steps, operations, elements and / or components, but do not exclude the presence or addition of one or more other features, wholes, steps, operations, elements, components and / or their combinations.

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

[0030] It should be further understood that the term " / and" as used in the specification of the present invention and the appended claims refers to any combination and all possible combinations of one or more of the associated listed items, and includes these combinations. For example, A and / or B can represent three cases: A exists alone, A and B exist simultaneously, and B exists alone. In addition, the character " / " in the present invention generally represents an "or" relationship between the contextually related objects.

[0031] It should be understood that although the terms first, second, third, etc. may be used in the embodiments of the present invention to describe preset ranges, etc., these preset ranges should not be limited to these terms. These terms are only used to distinguish the preset ranges from each other. 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 herein can be interpreted as "when" or "while" or "in response to determining" or "in response to detecting". Similarly, depending on the context, the phrase "if determined" or "if detecting (stated condition or event)" can be interpreted as "when determined" or "in response to determining" or "when detecting (stated condition or event)" or "in response to detecting (stated condition or event)".

[0033] In order to make the purpose, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are part of the embodiments of the present invention, rather than all of the embodiments. The components of the embodiments of the present invention described and shown in the drawings here can usually be arranged and designed in various different configurations. Therefore, the following detailed description of the embodiments of the present invention provided in the drawings is not intended to limit the scope of the claimed invention, but merely represents selected embodiments of the present invention. Based on the embodiments in the present invention, all other embodiments obtained by ordinary technicians in this field without making creative work are within the scope of protection of the present invention.

[0034] Various structural schematic diagrams of the embodiments disclosed in the present invention are shown in the accompanying drawings. These figures are not drawn to scale, and some details are magnified and some details may be omitted for the purpose of clear expression. The shapes of various regions and layers shown in the figures and the relative sizes and positional relationships therebetween are only exemplary, and may deviate in practice due to manufacturing tolerances or technical limitations, and those skilled in the art may additionally design regions / layers with different shapes, sizes, and relative positions according to actual needs.

[0035] Embodiment 1

[0036] refer to Figure 1 and Figure 2 The beam capture device of the present invention 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 which are arranged in sequence from the inside to the outside. The inner high-density polyethylene layer 3 is a hollow structure. A first through hole is arranged on the side wall of the outer steel layer 6, a second through hole is arranged on the side wall of the outer high-density polyethylene layer 5, and a third through hole and a fourth through hole are arranged 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 connected in sequence to form a beam channel 7. A B is arranged in the fourth through hole. 4 C absorption layer 2, wherein B 4 C absorption layer 2 faces the beam channel 7, and B 4 An inner lead layer 1 is arranged on the surface of the C 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. As the innermost layer of the device, it is mainly used to slow down neutrons and absorb gamma rays. 4 C absorption layer 2, using 10B has a higher thermal neutron absorption cross section, which effectively absorbs thermal neutrons from the beam and those generated by slowing down 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 covered with the external lead layer 4 and the external high-density polyethylene layer 5 in sequence, further improving the shielding effect of neutrons and gamma rays; the external steel layer 6 wraps 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 size of the beam channel 7 is 30 cm×30 cm, the thickness of the internal high-density polyethylene layer 3 is 5 cm, and the thickness of the internal lead layer 1 is 1 cm, which is used for absorbing gamma rays and slowing down neutrons; B 4 The thickness of the absorption layer 2 is 15 cm, 4 C in the absorbing layer 2 10 B has a good thermal neutron absorption cross section and does not produce high-energy secondary rays after reacting with thermal neutrons. It is used to absorb thermal neutrons from the beam and generated by slowing down the internal lead layer 1; the outside of the internal high-density polyethylene layer 3 is covered with an external lead layer 4 and an external high-density polyethylene layer 5 in sequence. The thickness of the external lead layer 4 and the external high-density polyethylene layer 5 are 10 cm and 15 cm respectively, which are used 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 to further reduce the impact of radiation generated by the beam capture device during use on the surrounding environment, and plays a structural support role to ensure the mechanical stability and durability of the entire beam capture device.

[0039] Embodiment 2

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

[0041] The beam capture device comprises an inner high-density polyethylene layer 3, an outer lead layer 4, an outer high-density polyethylene layer 5, an outer steel layer 6, 4 C absorption layer 2 and internal lead layer 1, the specific connection structure is as shown in Example 1.

[0042] The neutron source shielding body comprises a source shielding body graphite layer 201, a boron-containing polyethylene layer 202 inside the source shielding body, a lead layer 203 inside the source shielding body, a boron-containing polyethylene layer 204 outside the source shielding body and a lead layer 205 outside the source shielding body, wherein the source shielding body graphite layer 201, the boron-containing polyethylene layer 202 inside the source shielding body, the lead layer 203 inside the source shielding body, the boron-containing polyethylene layer 204 outside the source shielding body and the lead layer 205 outside the source shielding body are sequentially distributed from inside to outside.

[0043] The collimator comprises a source shielding beam extraction channel 207, a collimator boron-containing polyethylene layer 208 and a collimator lead layer 209, wherein a detector 211 at a sample position is arranged at one end of the source shielding beam extraction channel 207, and the other end of the source shielding beam extraction channel 207 passes through the collimator axially and then passes through the side wall of the lead layer 205 outside the source shielding, the side wall of the boron-containing polyethylene layer 204 outside the source shielding, the side wall of the lead layer 203 inside the source shielding, the side wall of the boron-containing polyethylene layer 202 inside the source shielding and the side wall of the graphite layer 201 of the source shielding, and is inserted into the graphite layer 201 of the source shielding. An active shielding polyethylene neutron moderator 206 is arranged inside and behind, and a DD neutron source is located in the source shielding graphite layer 201, wherein the fast neutrons generated by the DD neutron source are reduced in energy by the source shielding polyethylene neutron moderator 206 to obtain more thermal neutrons, and the neutron beam is collimated by a collimator composed of a collimator boron-containing polyethylene layer 208 and a collimator lead layer 209, and then passes through a detector 211 at the sample position, and finally enters a beam capture device, where the neutrons and gamma rays are absorbed and shielded by the multi-layer composite shielding structure of the beam capture device, 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 the fast neutrons in the beam. 4 C has better thermal neutron absorption effect, through B 4 The C absorption layer 2 absorbs thermal neutrons from the beam and produced by slowing down of the inner lead layer 1.

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

[0046] Confirmatory test

[0047] Two comparative samples were set in this experiment. In the first comparative sample, compared with the beam capture device of the present invention, the inner lead layer 1 was removed and B 4 C absorbent layer 2 is replaced with a high-density polyethylene absorbent layer, refer to Figure 4 ; The second comparison sample does not have a beam capture device, and the test results are as follows Figure 5 andFigure 6 shown.

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

[0049] It should be understood that the present invention is not limited to the exact construction that has been described above and shown in the drawings and that various modifications and changes may be made without departing from the scope thereof. The scope of the present invention is limited only by the appended claims.

[0050] The above description is only a preferred embodiment of the present invention and does not limit the present invention in any way. Any simple modification, change and equivalent structural change made to the above embodiment based on the technical essence of the present invention still falls within the protection scope of the technical solution of the present invention.

Claims

1. A beam capture device for reducing neutron backscattering background, characterized in that: The invention 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) which are arranged in sequence from the inside to the outside, wherein the inner high-density polyethylene layer (3) is a hollow structure, a first through hole is arranged on the side wall of the outer steel layer (6), a second through hole is arranged on the side wall of the outer high-density polyethylene layer (5), a third through hole and a fourth through hole are arranged 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 connected in sequence to form a beam channel (7), a B4C absorption layer (2) is arranged in the fourth through hole, wherein the B4C absorption layer (2) is opposite to the beam channel (7), and an inner lead layer (1) is arranged on the surface of the B4C absorption layer (2) opposite to the beam channel (7).

2. The beam capture device for reducing neutron backscattering background according to claim 1, characterized in that: The size of the beam channel (7) is 30cm×30cm, the thickness of the inner high-density polyethylene layer (3) is 5cm, the thickness of the outer lead layer (4) is 10cm, the thickness of the outer high-density polyethylene layer (5) is 15cm, and the thickness of the outer steel layer (6) is 5cm.

3. The beam capture device for reducing neutron backscattering background according to claim 1, characterized in that: The thickness of the B4C absorption layer (2) is 15 cm and the thickness of the inner lead layer (1) is 1 cm.

4. The beam capture device for reducing neutron backscattering background according to claim 1, characterized in that: The size of the beam channel (7) is 30 cm×30 cm.

5. The beam capture device for reducing neutron backscattering background according to claim 1, characterized in that: The outer steel layer (6) is a rectangular parallelepiped structure.

6. A neutron source system, characterized in that: It comprises a neutron source shielding body, a collimator and the beam capture device according to claim 1, wherein the neutron source shielding body, the collimator and the beam capture device are distributed in sequence.

7. The neutron source system according to claim 6, characterized in that: The neutron source shielding body comprises a source shielding body graphite layer (201), a boron-containing polyethylene layer (202) inside the source shielding body, a lead layer (203) inside the source shielding body, a boron-containing polyethylene layer (204) outside the source shielding body, and a lead layer (205) outside the source shielding body, wherein the source shielding body graphite layer (201), the boron-containing polyethylene layer (202) inside the source shielding body, the lead layer (203) inside the source shielding body, the boron-containing polyethylene layer (204) outside the source shielding body, and the lead layer (205) outside the source shielding body are sequentially distributed from inside to outside.

8. The neutron source system according to claim 6, characterized in that: The collimator comprises a source shielding beam extraction channel (207), a collimator boron-containing polyethylene layer (208) and a collimator lead layer (209), wherein a detector (211) at a sample position is arranged at one end of the source shielding beam extraction channel (207), and the other end of the source shielding beam extraction channel (207) passes through the collimator in the axial direction, passes through the side wall of the lead layer (205) outside the source shielding, the side wall of the boron-containing polyethylene layer (204) outside the source shielding, the side wall of the lead layer (203) inside the source shielding, the side wall of the boron-containing polyethylene layer (202) inside the source shielding and the side wall of the graphite layer (201) of the source shielding, and is inserted into the graphite layer (201) of the source shielding, and then a source shielding polyethylene neutron moderator (206) is arranged.

9. The neutron source system according to claim 6, characterized in that: A DD neutron source is arranged in the graphite layer (201) of the source shielding body.

10. The neutron source system according to claim 6, characterized in that: The size of the beam channel (7) is 30cm×30cm, the thickness of the inner high-density polyethylene layer (3) is 5cm, the thickness of the outer lead layer (4) is 10cm, the thickness of the outer high-density polyethylene layer (5) is 15cm, the thickness of the outer steel layer (6) is 5cm, the thickness of the B4C absorption layer (2) is 15cm, the thickness of the inner lead layer (1) is 1cm, and the size of the beam channel (7) is 30cm×30cm.

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