Self-repairing lithium target for generating neutron radiation field and preparation method and self-repairing method thereof

Abstract

The invention provides a self-repairing lithium target for generating a neutron radiation field and a preparation method and a self-repairing method thereof, the lithium target comprises a target material shell and lithium poured into the target material shell, the target material shell is not completely filled with the lithium poured into the target material shell, and a reserved gap is formed between the lithium poured into the target material shell and the target material shell. The target material bombarded by the proton beam is heated until lithium in the target material shell is in a molten state, bubbles generated by bombardment of the proton beam can be separated out of the lithium to the reserved gap, and lithium target self-repairing can be completed after the lithium in the target material shell is cooled and solidified. The self-repairing lithium target is simple in structure and easy to prepare, air holes left in the lithium target after proton beam bombardment can be easily removed only by heating the target material, self-repairing of the lithium target is achieved, frequent replacement of the target material is avoided, the service life of the lithium target is prolonged, and the working efficiency of an accelerator neutron source system is improved.

Description

Technical Field

[0001] The present invention belongs to the technical field of accelerator neutron radiation fields, and in particular relates to a self-repairing lithium target for generating a neutron radiation field and a preparation method thereof. Background Art

[0002] Among accelerator-based neutron generation methods, proton beam bombardment of lithium targets is the most commonly used. The advantage of lithium targets lies in their high neutron yield at relatively low proton energies. However, lithium has a low melting point, less than 180°C. During neutron beam firing, 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 energy, causing the lithium target to melt and generate bubbles, thereby shortening its service life.

[0003] The existing solution is to add a target cooling system, using cooling water to remove heat deposited in the lithium target. However, this requires frequent target replacement to ensure radiation field stability. Another solution is to adopt a rotating target design. By rotating the lithium target, the fixed point is bombarded by the proton beam for a shorter period of time, thereby eliminating the heat removal issue and extending the life of the lithium target. For existing solutions, see patents CN113347776A, CN116156729A, and FR2555853B1.

[0004] Two current solutions—adding a target cooling system and designing a rotating target—can somewhat address the low melting point and short lifespan of lithium targets. However, both the target cooling system and the rotating target structure make the target system extremely complex and bulky. Furthermore, as the beam bombardment time increases, the lithium target will develop irreparable damage such as bubbles, necessitating frequent target replacement. Furthermore, both the addition of a target cooling system and the use of a rotating target design greatly complicate the target replacement process, thus impacting work efficiency. Frequent lithium target replacement, particularly in the medical industry, can delay patient treatment and is unacceptable. Summary of the Invention

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

[0006] To achieve the above object, the technical solution of the present invention is achieved as follows:

[0007] In a first aspect, the present invention provides a self-repairing lithium target for generating a neutron radiation field, wherein the lithium target includes a target shell and lithium poured into the target shell; the lithium poured into the target shell does not completely fill the target shell, and a reserved gap exists between the lithium poured into the target shell and the target shell.

[0008] Preferably, the target shell is made of a metal material with a melting point higher than lithium. Optionally, the target shell can be made of metal aluminum or copper.

[0009] Preferably, the height of the reserved gap is not less than 1 / 10 of the diameter of the lithium target.

[0010] In a second aspect, the present invention also provides a method for preparing a self-repairing lithium target for generating a neutron radiation field. The method comprises the following steps: selecting a metal material as the target shell, heating lithium until molten, and then pouring it into the target shell; controlling the amount of lithium poured so that the lithium poured into the target shell does not completely fill the target shell, and a gap is reserved between the lithium poured into the target shell and the target shell. After the pouring is completed, the target shell is sealed.

[0011] Preferably, the target shell is made of a metal material with a melting point higher than lithium. Optionally, the target shell can be made of metal aluminum or copper.

[0012] Preferably, the target shell has a thickness of 50 to 500 μm. The optimal thickness of the target shell can be calculated using Monte Carlo simulation. On the one hand, the target shell cannot be too thin, as 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 fall below the reaction threshold, reducing the neutron yield. For low-energy proton bombardment (3–5 MeV), 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 of the lithium reaction is greater than 2 MeV. For medium- to high-energy proton bombardment (5–10 MeV), 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.

[0013] Preferably, the height of the reserved gap is not less than 1 / 10 of the diameter of the lithium target.

[0014] Preferably, the heating temperature of the lithium during the infusion process is higher than 180°C.

[0015] In a third aspect, the present invention also provides a self-repair method for the above-mentioned self-repairing lithium target for generating a neutron radiation field, the method comprising the following steps: heating the target material bombarded by a proton beam until the lithium inside the target shell becomes molten, keeping the target material warm, and stopping heating the target material after the bubbles generated by the proton beam bombardment precipitate from the lithium into the reserved gap; and completing the self-repair after the lithium inside the target shell cools and solidifies.

[0016] Preferably, the heating temperature is higher than 180° C. and lower than the melting point of the metal material of the target shell.

[0017] Preferably, the heat preservation and heating time is greater than 30 minutes.

[0018] The present invention creatively proposes a lithium target that can effectively meet the neutron yield and achieve self-repair. By using a metal with a higher melting point as the target shell of the lithium target, liquid lithium is poured into the target shell in a high-temperature environment. When pouring lithium, the target shell is not completely filled, but a certain gap is left. After the proton beam bombards the lithium target for a period of time, the lithium target is heated, thereby converting the solid lithium into liquid lithium. The bubbles generated in the lithium target by the proton beam bombardment will precipitate from the lithium and run into the reserved gaps. After the lithium target cools down and solidifies, the self-repair of the lithium target is completed. After the above self-repair treatment, the lithium target can be restored to its original state. There are no pores in the metallic lithium inside the lithium target, and it can continue to be used.

[0019] Compared with the prior art, the self-repairing lithium target and its preparation method proposed in the present invention have the following advantages:

[0020] The self-repairing lithium target of the present invention has a simple structure and is easy to prepare. The lithium target obtained by the preparation method of the present invention overcomes the problem of short service life of the lithium target caused by the low melting point of metallic lithium. After the lithium target is bombarded by a proton beam, only a simple heating treatment of the target material is required to easily remove the pores remaining in the lithium target after the proton beam bombardment, thereby realizing self-repair 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 use cost of the accelerator neutron source system, but also improves the working efficiency of the accelerator neutron source system. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] The accompanying drawings, which constitute part of the present invention, are provided to provide a further understanding of the present invention. The exemplary embodiments of the present invention and their descriptions are provided to explain the present invention and do not constitute an undue limitation of the present invention. In the accompanying drawings:

[0022] Figure 1 This is a schematic structural diagram of the self-repairing lithium target of the present invention;

[0023] Figure 2 Schematic diagram of the repair process of the self-repairing lithium target of the present invention;

[0024] Figure 3 This is the SEM fracture morphology of lithium metal after proton beam bombardment of the self-repairing lithium target of the present invention (the target shell is Al);

[0025] Figure 4 This is the SEM fracture morphology of lithium metal after the self-repairing treatment of the self-repairing lithium target (the target shell is Al) of the present invention;

[0026] Figure 5This is the SEM fracture morphology of lithium metal after proton beam bombardment of the self-repairing lithium target of the present invention (the target shell is Al, and the height of the reserved gap is 1 / 9 of the lithium target diameter);

[0027] Figure 6 This is the SEM fracture morphology of lithium metal after self-repair treatment of the self-repairing lithium target of the present invention (the target shell is Al, and the height of the reserved gap is 1 / 9 of the lithium target diameter);

[0028] Figure 7 This is the SEM fracture morphology of lithium metal after proton beam bombardment of the self-repairing lithium target (target shell is Cu) of the present invention;

[0029] Figure 8 This is the SEM fracture morphology of lithium metal after the self-repairing lithium target (the target shell is Cu) of the present invention has undergone self-repairing treatment.

[0030] Explanation of the accompanying symbols: 1. target shell; 2. reserved gap; 3. lithium poured into the target shell; 4. pore. DETAILED DESCRIPTION

[0031] In order to make the purpose, technical solutions and advantages of the present invention more clear, 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. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not used to limit the present invention. The described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of 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.

[0032] In the description of the present invention, it should be noted that the terms "upper," "lower," "vertical," and "horizontal," etc., indicating orientations or positional relationships, are based on the orientations or positional relationships shown in the accompanying drawings and are intended solely to facilitate and simplify the description of the present invention. They are not intended to indicate or imply that the devices or components referred to must have, be constructed, or operate in a specific orientation, and therefore should not be construed as limitations on the present invention. Furthermore, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance.

[0033] In addition, many specific details of the present invention are described below, such as device structure, materials, dimensions, processing techniques, and technologies, to facilitate a clearer understanding of the present invention. However, as will be appreciated by those skilled in the art, the present invention may be practiced without following these specific details. Unless otherwise noted below, various components of the device may be constructed from materials known to those skilled in the art, or materials with similar functions developed in the future.

[0034] Figure 1 Schematic diagram of the structure of the self-repairing lithium target of the present invention. Figure 1 As shown, the present invention discloses a self-repairing lithium target for generating a neutron radiation field, comprising a target shell 1 and lithium 3 poured into the interior of the target shell 1. The lithium 3 poured into the interior of the target shell does not completely fill the target shell 1, and a reserved gap 2 is provided between the lithium poured into the interior of the target shell and the target shell. The target shell 2 is made of a metal material with a higher melting point than lithium. Optionally, the target shell can be made of a metal material such as aluminum or copper. The height of the reserved gap 3 is not less than 1 / 10 of the diameter of the lithium target. The thickness of the target shell is generally 50μm to 500μm, and the optimal thickness of the target shell can be calculated through Monte Carlo simulation. On the one hand, the target shell cannot be too thin, considering the mechanical strength and heat dissipation of the shell; on the other hand, it cannot be too thick, as excessive thickness will cause the energy of the incident protons to fall below the reaction threshold, reducing the neutron yield. For low-energy proton (3–5MeV) bombardment: the thickness of the aluminum shell is generally preferably 50–200μm, and the thickness of the copper shell is generally preferably 50–100μm, to ensure that the proton energy of the lithium reaction is >2MeV; for medium- and high-energy proton (5–10MeV) bombardment: the thickness of the aluminum shell is generally preferably 200–500μm, and the thickness of the copper shell is generally preferably 100–300μm, to balance energy loss and heat dissipation.

[0035] To prepare this self-healing lithium target for generating a neutron radiation field, a metal material with a higher melting point than lithium, such as aluminum or copper, is used as the target shell 1. Lithium is heated until molten and then poured into the target shell 1. The amount of lithium poured is controlled so that the lithium does not completely fill the target shell 1. After solidification, a gap 2 is left between the lithium 3 poured into the target shell 1 and the target shell 1. The height of this gap is no less than 1 / 10 of the lithium target diameter. During the pouring process, the lithium should be heated to a temperature above 180°C to ensure that the lithium remains molten. After pouring, the target shell is sealed. The target shell thickness is generally 50 to 500 μm. For low-energy proton bombardment (3–5 MeV), the thickness of the aluminum shell is preferably 50–200 μm, and the thickness of the copper shell is preferably 50–100 μm. For medium-to-high energy proton bombardment (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.

[0036] Figure 2 Schematic diagram of the repair process of the self-repairing lithium target of the present invention. Figure 2As shown, in the initial state of a lithium target that has not been bombarded by a proton beam, the metallic lithium structure is uniform and there are no pores. When a high-energy proton beam is incident on a lithium target, most of the protons will be retained in the target material to form thermal deposits. The high heat load on the surface of the lithium target is difficult to effectively remove. Since the melting point of metallic lithium in the target material is low, the metallic lithium is easily melted when the proton beam bombards the lithium target. After the metallic lithium cools and solidifies again, pores 4 will be formed in it. By adopting the lithium target self-repair method of the present invention, the target material that has been bombarded by a proton beam is heated until the lithium inside the target shell becomes molten. The heat preservation and heating are continued. The pores 4 generated by the proton beam bombardment will precipitate as bubbles during the remelting process of the metallic lithium and be discharged into the reserved gap. After all the bubbles are precipitated, the target material is stopped from being heated; after the lithium inside the target shell cools and solidifies, the self-repair process is completed. After the self-repair treatment, the crystal phase structure of the metallic lithium in the lithium target is still uniform and stable, without the presence of pores. The above-mentioned heat preservation and heating temperature should be higher than 180°C and lower than the melting point of the metal material of the target shell. The heat preservation and heating time can be adjusted according to the size of the target. Generally, heat preservation and heating for more than 30 minutes can achieve self-repair of the lithium target.

[0037] Example 1

[0038] This embodiment provides a self-healing lithium target for generating a neutron radiation field. The target comprises a circular target shell and lithium infused within the target shell. The lithium infused within the target shell does not completely fill the target shell, and a gap is reserved between the lithium infused within the target shell and the target shell. The target shell is made of aluminum and has a thickness of 500 μm. The lithium target has a diameter of 3 cm, and the height of the reserved gap is 1 / 10 of the lithium target diameter.

[0039] After the lithium target is bombarded by the proton beam, Figure 3 As shown in the figure, a large number of pores appear in the lithium metal inside the lithium target. The lithium target bombarded by the proton beam is heated at 182 ° C. After heating for 1 hour, the lithium inside the target shell becomes molten. After continuing to heat for 2 hours, the target heating is stopped. After the target is air-cooled to room temperature, the self-repair process is completed. The metallographic structure of the lithium metal inside the lithium target after self-repair is observed, as shown in the figure. Figure 4 As shown, the metallic lithium has a uniform structure, clear grain boundaries, and only a very small number of pores. This proves that the pores generated by proton beam bombardment have been precipitated from the lithium.

[0040] Example 2

[0041] This embodiment provides a self-healing lithium target for generating a neutron radiation field. The target comprises a circular target shell and lithium infused within the shell. The lithium infused within the target shell does not completely fill the shell, and a gap is left between the lithium infused within the target shell and the shell. The target shell is made of aluminum and has a thickness of 50 μm. The lithium target has a diameter of 4 cm, and the height of the gap is 1 / 9 of the target diameter.

[0042] After the lithium target is bombarded by the proton beam, Figure 5 As shown in the figure, a large number of pores appear in the lithium metal inside the lithium target. The lithium target bombarded by the proton beam is heated at 200 ° C. After heating for 1 hour, the lithium inside the target shell becomes molten. After heating for another hour, the target is stopped. After the target is air-cooled to room temperature, the self-repair process is completed. The metallographic structure of the lithium metal inside the lithium target after self-repair is observed, as shown in the figure. Figure 6 As shown, the metallic lithium structure is uniform, the grain boundaries are clear, and no pores are found, which proves that the pores generated by proton beam bombardment have been precipitated from the lithium.

[0043] Example 3

[0044] This embodiment provides a self-healing lithium target for generating a neutron radiation field. The target comprises a circular target shell and lithium infused within the shell. The lithium infused within the target shell does not completely fill the shell, and a gap is left between the lithium infused within the target shell and the shell. The target shell is made of copper and has a thickness of 200 μm. The lithium target has a diameter of 5 cm, and the height of the gap is 1 / 8 of the target diameter.

[0045] After the lithium target is bombarded by the proton beam, Figure 7 As shown in the figure, a large number of pores appear in the lithium metal inside the lithium target. The lithium target bombarded by the proton beam is heated at 300 ° C. After heating for 40 minutes, the lithium inside the target shell becomes molten. After continuing to heat for 30 minutes, the target heating is stopped. After the target is air-cooled to room temperature, the self-repair process is completed. The metallographic structure of the lithium metal inside the lithium target after self-repair is observed, as shown in the figure. 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 precipitated from the lithium.

[0046] 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 in the scope of protection of the present invention.

Claims

1. A self-repairing lithium target for generating a neutron radiation field, characterized in that: The self-repairing lithium target includes a target shell and lithium poured into the target shell; the target shell is made of a metal material with a melting point higher than lithium; the lithium poured into the target shell does not completely fill the target shell, and a gap is reserved between the lithium poured into the target shell and the target shell.

2. The self-repairing lithium target according to claim 1, characterized in that The target shell has a thickness of 50-500 μm.

3. The self-repairing 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-repairing lithium target for generating a neutron radiation field, characterized in that: The preparation method comprises the following steps: selecting a metal material with a higher melting point than lithium as a target shell, heating lithium until it is molten and then pouring it into the target shell; controlling the pouring amount of lithium so that the lithium poured into the target shell does not completely fill the target shell, and a gap is reserved between the lithium poured into the target shell and the target shell.

5. The method for preparing a self-repairing lithium target according to claim 4, wherein: The target shell has a thickness of 50-500 μm.

6. The method for preparing a self-repairing lithium target according to claim 4, wherein: 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-repairing lithium target according to claim 4, wherein: The heating temperature of lithium during the infusion process is higher than 180°C.

8. A self-repairing method for a self-repairing lithium target for generating a neutron radiation field according to any one of claims 1 to 3, characterized in that: The self-repair method includes the following steps: heating the lithium target bombarded by a proton beam until the lithium inside the target shell becomes molten, maintaining the heat, and stopping heating the lithium target after bubbles generated by the proton beam bombardment are precipitated from the lithium into the reserved gap; and completing the self-repair after the lithium inside the target shell cools and solidifies.

9. The self-repairing method according to claim 8, characterized in that: The heating temperature is higher than 180° C. and lower than the melting point of the metal material of the target shell.

10. The self-repairing method according to claim 8, characterized in that: The heat preservation and heating time is greater than 30 minutes.

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