A self-repairing lithium target for generating a neutron radiation field and a method for producing and repairing the same

Abstract

The application provides a self-repairing lithium target for generating a neutron radiation field, a preparation method and a self-repairing method. The lithium target comprises a target material shell and lithium filled in the target material shell. The lithium filled in the target material shell does not completely fill the target material shell, and a reserved gap is formed between the lithium and the target material shell. By heating the target material after being bombarded by a proton beam until the lithium in the target material shell becomes a molten state, the gas bubbles generated by the proton beam bombardment can be separated from the lithium and enter the reserved gap. After the lithium in the target material shell cools and solidifies, the self-repairing of the lithium target is completed. The self-repairing lithium target of the application has a simple structure and is easy to prepare. By only heating the target material, the pores remaining in the lithium target after the proton beam bombardment can be easily removed, the self-repairing of the lithium target is realized, the target material is avoided from being frequently replaced, the service life of the lithium target is prolonged, and the working efficiency of the accelerator neutron source system is improved.

Description

Technical Field

[0001] This invention belongs to the field of accelerator neutron radiation field technology, and particularly relates to a self-healing lithium target for generating neutron radiation fields and its preparation method. Background Technology

[0002] Among accelerator-based neutron generation methods, proton beam bombardment of a lithium target is the most common. The advantage of a lithium target lies in its high neutron yield at relatively low proton energies; however, lithium has a low melting point, less than 180°C. During neutron generation via beam bombardment, the beam intensity is typically quite high, reaching hundreds of μA or even tens of mA. The power deposited by the proton beam on the lithium target is converted into heat, causing the lithium target to melt and generate bubbles, thus shortening the target's lifespan.

[0003] Existing solutions involve adding a target cooling system to remove heat deposited in the lithium target using cooling water. However, this requires frequent replacement of the lithium target to ensure the stability of the radiation field. Another solution is to adopt a rotating target design. By rotating the lithium target, the time the fixed point is bombarded by the proton beam is shortened, thus solving the problem of lithium target thermal removal and extending its service life. Existing solutions can be found in patent documents CN113347776A, CN116156729A, and FR2555853B1.

[0004] The two current solutions—adding a target cooling system and designing a rotating target—can address the issues of low melting point and short lifespan of lithium targets to some extent. However, both target cooling systems and rotating target structures significantly increase the complexity and size of the target system. Furthermore, with increasing beam bombardment time, the lithium target will develop irreparable damage such as bubbles, making frequent target replacements inevitable. Moreover, adding a target cooling system or adopting a rotating target design makes the target replacement process extremely complex, thus affecting work efficiency. Especially in the medical industry, frequent lithium target replacements would delay patient treatment, which is unacceptable. Summary of the Invention

[0005] In view of this, the present invention aims to propose a self-healing lithium target for generating neutron radiation fields, a lithium target preparation method, and a lithium target self-healing method, so as to solve the problems of short service life of lithium targets and the need for frequent target material replacement in the prior art.

[0006] To achieve the above objectives, the technical solution of the present invention is implemented as follows: In a first aspect, the present invention provides a self-healing lithium target for generating a neutron radiation field, the lithium target comprising a target shell and lithium injected into the target shell; the lithium injected into the target shell does not completely fill the target shell, and there is a reserved gap between the lithium injected into the target shell and the target shell.

[0007] Preferably, the target shell is made of a metal material with a melting point higher than that of lithium. Optionally, the target shell can be made of aluminum or copper.

[0008] Preferably, the height of the reserved gap is not less than 1 / 10 of the diameter of the lithium target.

[0009] Secondly, the present invention also provides a method for preparing a self-healing lithium target for generating a neutron radiation field. The method includes the following steps: selecting a metallic material as the target shell; heating lithium to molten state and then injecting it into the target shell; controlling the amount of lithium injected so that the lithium injected into the target shell does not completely fill the target shell, leaving a pre-reserved gap between the lithium injected into the target shell and the target shell; and encapsulating the target shell after injection.

[0010] Preferably, the target shell is made of a metal material with a melting point higher than that of lithium. Alternatively, the target shell can be made of aluminum or copper.

[0011] Preferably, the thickness of the target shell is generally between 50 μm and 500 μm, where the optimal thickness can be calculated using Monte Carlo simulations. On the one hand, the target shell cannot be too thin, as mechanical strength and heat dissipation must be considered; on the other hand, it cannot be too thick, as excessive thickness would cause the incident proton energy to fall below the reaction threshold, reducing neutron yield. For low-energy proton (3–5 MeV) bombardment: the aluminum shell thickness is preferably 50–200 μm, and the copper shell thickness is preferably 50–100 μm, to ensure that the proton energy for lithium reaction is >2 MeV; for medium-to-high-energy proton (5–10 MeV) bombardment: the aluminum shell thickness is preferably 200–500 μm, and the copper shell thickness is preferably 100–300 μm, to balance energy loss and heat dissipation.

[0012] Preferably, the height of the reserved gap is not less than 1 / 10 of the diameter of the lithium target.

[0013] Preferably, the heating temperature of lithium during the filling process is higher than 180°C.

[0014] Thirdly, the present invention also provides a self-healing method for the self-healing lithium target used to generate a neutron radiation field, the method comprising the following steps: heating the target material after being bombarded by a proton beam until the lithium inside the target material shell becomes molten, maintaining the temperature and heating until bubbles generated by the proton beam bombardment precipitate from the lithium into the reserved gap, and then stopping the heating of the target material; and completing the self-healing after the lithium inside the target material shell cools and solidifies.

[0015] Preferably, the heating temperature is higher than 180°C and lower than the melting point of the target shell metal material.

[0016] Preferably, the heat preservation and heating time is greater than 30 minutes.

[0017] This invention creatively proposes a lithium target that can effectively meet neutron yield requirements and achieve self-repair. It uses a high-melting-point metal as the target shell, and liquid lithium is injected into the shell at high temperature. During lithium injection, the target shell is not completely filled, leaving some gaps. After the lithium target is bombarded by a proton beam for a period of time, it is heated, thereby turning solid lithium into liquid lithium. Bubbles generated by the proton beam bombardment precipitate from the lithium and escape into the reserved gaps. After the lithium target cools and solidifies, the self-repair process is completed. Through this self-repair process, the lithium target can be restored to its original state; the metallic lithium inside the target has no pores and can continue to be used.

[0018] Compared with existing technologies, the self-healing lithium target and its preparation method proposed in this invention have the following advantages: The self-healing lithium target of this invention has a simple structure and is easy to prepare. The lithium target prepared by the method of this invention overcomes the problem of short service life of lithium targets caused by the low melting point of metallic lithium. After being bombarded by a proton beam, the pores remaining in the lithium target after proton beam bombardment can be easily removed by simply heating the target material, thus realizing the self-healing of the lithium target and avoiding frequent replacement of the target material, thereby extending the service life of the lithium target. This not only reduces the operating cost of the accelerator neutron source system, but also improves the working efficiency of the accelerator neutron source system. Attached Figure Description

[0019] The accompanying drawings, which form part of this invention, 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: Figure 1 This is a schematic diagram of the structure of the self-healing lithium target of the present invention; Figure 2 This is a schematic diagram of the repair process of the self-healing lithium target of the present invention; Figure 3 This is a SEM image of the fracture surface of lithium metal after the self-healing lithium target (target shell is Al) of the present invention has been bombarded by a proton beam. Figure 4 This is a SEM image of the fracture surface morphology of lithium metal after the self-healing lithium target (target shell is Al) of the present invention has undergone self-healing treatment. Figure 5 This is a SEM image of the fracture surface of lithium metal after the self-healing lithium target (the target shell is made of Al, and the height of the reserved gap is 1 / 9 of the diameter of the lithium target) is bombarded by a proton beam. Figure 6 This is a SEM image of the fracture surface of lithium metal after the self-healing lithium target (the target shell is made of Al, and the height of the reserved gap is 1 / 9 of the diameter of the lithium target) has undergone self-healing treatment according to the present invention. Figure 7 This is a SEM image of the fracture surface of lithium metal after the self-healing lithium target (target shell is Cu) of the present invention has been bombarded by a proton beam. Figure 8 This is a SEM image of the fracture surface of lithium metal after the self-healing lithium target (target shell is Cu) of the present invention has undergone self-healing treatment.

[0020] Explanation of reference numerals in the attached diagram: 1. Target shell; 2. Reserved gap; 3. Lithium injected into the target shell; 4. Pore. Detailed Implementation

[0021] To make the objectives, technical solutions, and advantages of this invention clearer, the technical solutions in the embodiments of this invention will be clearly and completely described below with reference to the accompanying drawings. It should be understood that the specific embodiments described herein are only for explaining this invention and are not intended to limit this invention. The described embodiments are only some embodiments of this invention, not all embodiments. Based on the embodiments of this invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this invention.

[0022] In the description of this invention, it should be noted that the terms "upper," "lower," "vertical," and "horizontal," etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are used only for the convenience of describing the invention and for simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on the invention. Furthermore, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance.

[0023] Furthermore, many specific details of the invention, such as the structure, materials, dimensions, processing techniques, and methods of the device, are described below to provide a clearer understanding of the invention. However, as will be understood by those skilled in the art, the invention may be implemented without adhering to these specific details. Unless specifically indicated below, various parts of the device may be made of materials known to those skilled in the art, or may employ materials with similar functionality developed in the future.

[0024] Figure 1 This is a schematic diagram of the structure of the self-healing lithium target of the present invention. Figure 1As shown, this invention discloses a self-healing lithium target for generating a neutron radiation field, comprising a target shell 1 and lithium 3 infused inside the target shell 1. The lithium 3 infused inside the target shell 1 does not completely fill the target shell 1, and there is a reserved gap 2 between the lithium infused inside the target shell and the target shell. The target shell 1 is made of a metal material with a melting point higher than that of lithium; optionally, the target shell can be made of a metal material such as aluminum or copper. The height of the reserved gap 2 is not less than 1 / 10 of the diameter of the lithium target. The thickness of the target shell is generally 50 μm to 500 μm, and the optimal thickness of the target shell can be obtained through Monte Carlo simulation calculations. On the one hand, the target shell cannot be too thin, and the mechanical strength and heat dissipation of the shell must be considered; on the other hand, it cannot be too thick, as excessive thickness will cause the incident proton energy to be lower than the reaction threshold, reducing the neutron yield. For low-energy proton (3–5 MeV) bombardment: the thickness of the aluminum shell is generally preferred to be 50–200 μm, and the thickness of the copper shell is generally preferred to be 50–100 μm, to ensure that the proton energy for lithium reaction is >2 MeV; for medium-high energy proton (5–10 MeV) bombardment: the thickness of the aluminum shell is generally preferred to be 200–500 μm, and the thickness of the copper shell is generally preferred to be 100–300 μm, to balance energy loss and heat dissipation.

[0025] In preparing the self-healing lithium target for generating a neutron radiation field, aluminum, copper, or other metals with melting points higher than lithium are selected as the target shell 1. Lithium is heated to molten and then poured into the target shell 1. During pouring, the amount of lithium poured must be controlled so that the lithium poured into the target shell 1 does not completely fill it. After the lithium 3 poured into the target shell 1 solidifies, there is a certain reserved gap 2 between it and the target shell 1. The height of this reserved gap is not less than 1 / 10 of the lithium target diameter. The heating temperature of lithium during the pouring process should be higher than 180℃ to ensure that the lithium remains in a molten state throughout the pouring process. After pouring, the target shell is encapsulated. The thickness of the target shell is generally 50μm to 500μm. For low-energy proton (3–5 MeV) bombardment: the thickness of the aluminum shell is preferably 50–200μm, and the thickness of the copper shell is preferably 50–100μm. For bombardment by medium- to high-energy protons (5–10 MeV): the thickness of the aluminum shell is preferably 200–500 μm, and the thickness of the copper shell is preferably 100–300 μm.

[0026] Figure 2 This is a schematic diagram illustrating the repair process of the self-healing lithium target of the present invention. For example... Figure 2As shown, in its initial state, a lithium target that has not been bombarded by a proton beam has a uniform lithium metal structure without pores. When a high-energy proton beam is incident on the lithium target, most of the protons remain in the target material, forming thermal deposits. The high heat load on the surface of the lithium target is difficult to remove effectively. Due to the low melting point of lithium metal in the target material, it is easy for the lithium metal to melt when bombarded by the proton beam. After the lithium metal cools and solidifies again, pores 4 will be formed in it. By using the self-healing method of the lithium target of the present invention, the target material bombarded by the proton beam is heated until the lithium inside the target shell becomes molten. The heating is continued, and the pores 4 generated by the proton beam bombardment will precipitate as bubbles during the remelting of the lithium metal and be discharged into the reserved gaps. After all the bubbles have precipitated, the heating of the target material is stopped. After the lithium inside the target shell cools and solidifies, the self-healing process is completed. After the lithium target has undergone self-healing treatment, the crystal phase structure of the lithium metal remains uniform and stable, without the presence of pores. The aforementioned heat preservation and heating temperature should be higher than 180℃ and lower than the melting point of the target's outer metal material. The heat preservation and heating time can be adjusted according to the target size; typically, heat preservation and heating for more than 30 minutes can achieve self-repair of the lithium target.

[0027] Example 1 This embodiment provides a self-healing lithium target for generating a neutron radiation field, comprising a disc-shaped target shell and lithium injected into the target shell; the lithium injected into the target shell does not completely fill the target shell, and there is a reserved gap between the lithium injected into the target shell and the target shell. The target shell is made of aluminum and has a thickness of 500 μm. The diameter of the lithium target is 3 cm, and the height of the reserved gap is 1 / 10 of the diameter of the lithium target.

[0028] After the lithium target is bombarded by a proton beam, as Figure 3 As shown, numerous pores appear within the metallic lithium inside the lithium target. The lithium target, after being bombarded by a proton beam, was heated to 182°C. After 1 hour of heating, the lithium inside the target shell became molten. Heating was continued for another 2 hours, after which the heating was stopped. The target was then air-cooled to room temperature, completing the self-healing process. The metallographic structure of the metallic lithium inside the self-healed lithium target was observed, as shown... Figure 4 As shown, the metallic lithium has a uniform structure and clear grain boundaries, with only a very small number of pores present, which proves that the pores generated by the proton beam bombardment have been deposited from the lithium.

[0029] Example 2 This embodiment provides a self-healing lithium target for generating a neutron radiation field, comprising a disc-shaped target shell and lithium injected into the target shell; the lithium injected into the target shell does not completely fill the target shell, and there is a reserved gap between the lithium injected into the target shell and the target shell. The target shell is made of aluminum and has a thickness of 50 μm. The diameter of the lithium target is 4 cm, and the height of the reserved gap is 1 / 9 of the diameter of the lithium target.

[0030] After the lithium target is bombarded by a proton beam, as Figure 5 As shown, numerous pores appear within the metallic lithium inside the lithium target. The lithium target, after being bombarded by a proton beam, was heated to 200°C. After 1 hour of heating, the lithium inside the target shell became molten. Heating was continued for another hour, after which the heating was stopped. The target was then air-cooled to room temperature, completing the self-healing process. The metallographic structure of the metallic lithium inside the self-healed lithium target was observed, as shown... Figure 6 As shown, the metallic lithium has a uniform structure and clear grain boundaries, and no pores were found, which proves that the pores generated by the proton beam bombardment have been deposited from the lithium.

[0031] Example 3 This embodiment provides a self-healing lithium target for generating a neutron radiation field, comprising a disc-shaped target shell and lithium injected into the target shell; the lithium injected into the target shell does not completely fill the target shell, and there is a reserved gap between the lithium injected into the target shell and the target shell. The target shell is made of copper and has a thickness of 200 μm. The diameter of the lithium target is 5 cm, and the height of the reserved gap is 1 / 8 of the diameter of the lithium target.

[0032] After the lithium target is bombarded by a proton beam, as Figure 7 As shown, numerous pores appear within the metallic lithium inside the lithium target. The lithium target, after being bombarded by a proton beam, was heated to 300°C. After 40 minutes of heating, the lithium inside the target shell became molten. Heating was continued for another 30 minutes, after which the heating was stopped. The target was then air-cooled to room temperature, completing the self-healing process. The metallographic structure of the metallic lithium inside the self-healed lithium target was observed, as shown... Figure 8 As shown, the metallic lithium has a uniform structure, clear grain boundaries, and almost no pores, which proves that the pores generated by proton beam bombardment have been deposited from the lithium.

[0033] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A self-healing lithium target for generating a neutron radiation field, characterized in that, The self-healing lithium target includes a target shell and lithium injected into the target shell; the target shell is made of a metal material with a melting point higher than that of lithium; the lithium injected into the target shell does not completely fill the target shell, and there is a reserved gap between the lithium injected into the target shell and the target shell. The lithium target bombarded by a proton beam is heated until the lithium inside the target shell becomes molten. The heating is maintained at this temperature until bubbles generated by the proton beam bombardment precipitate from the lithium into the reserved gaps. The heating of the lithium target is then stopped. After the lithium inside the target shell cools and solidifies, the self-repair process is completed.

2. The self-healing lithium target according to claim 1, characterized in that, The thickness of the target shell is 50-500 μm.

3. The self-healing lithium target according to claim 1, characterized in that, The height of the reserved gap is not less than 1 / 10 of the diameter of the lithium target.

4. A method for preparing a self-healing lithium target for generating a neutron radiation field, characterized in that, The method for preparing the self-healing lithium target includes the following steps: selecting a metal material with a melting point higher than that of lithium as the target shell, heating lithium to molten state and then injecting it into the target shell; controlling the amount of lithium injected so that the lithium injected into the target shell does not completely fill the target shell, and there is a reserved gap between the lithium injected into the target shell and the target shell. The lithium target bombarded by a proton beam is heated until the lithium inside the target shell becomes molten. The heating is maintained at this temperature until bubbles generated by the proton beam bombardment precipitate from the lithium into the reserved gaps. The heating of the lithium target is then stopped. After the lithium inside the target shell cools and solidifies, the self-repair process is completed.

5. The method for preparing a self-healing lithium target according to claim 4, characterized in that, The thickness of the target shell is 50-500 μm.

6. The method for preparing a self-healing lithium target according to claim 4, characterized in that, The height of the reserved gap is not less than 1 / 10 of the diameter of the lithium target.

7. The method for preparing a self-healing lithium target according to claim 4, characterized in that, The lithium is heated to a temperature above 180°C during the filling process.

8. The method for preparing a self-healing lithium target according to claim 4, characterized in that, The temperature of the heat preservation heating is higher than 180°C and lower than the melting point of the target shell metal material.

9. The method for preparing a self-healing lithium target according to claim 4, characterized in that, The heat preservation and heating time is greater than 30 minutes.

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