Beam Targets and Beam Target Systems

Abstract

A beam target for generating nuclear reaction products by irradiating a beam obtained from a beam generating source, comprising: a cone having an inner surface of a cone shape whose diameter decreases toward the front end; and a supply unit for supplying liquid metal to the inner surface of the cone to form a liquid film of the liquid metal on the inner surface. The liquid film of the liquid metal can be formed on the surface of the cone to increase the irradiation area of ​​the beam, and target materials such as LLFP can be arranged around the cone, so that the nuclear reaction products (such as neutrons) generated by irradiating the liquid metal with the beam can be efficiently used.

Description

Technical Field

[0001] The present invention relates to a beam target and a beam target system. Background Art

[0002] The beam target system is used, for example, to generate neutrons by irradiating a target metal or the like with a high-intensity charged particle beam. The generated neutrons are used for nuclear transmutation of long-lived fission products (LLFP), evaluation of nuclear fusion reactor materials, boron neutron capture therapy (BNCT), non-destructive inspection, etc. In addition, the beam target system is also used to generate nuclear reaction products such as astatine-211, which is expected to be used as RI (radioactive isotope) for alpha-ray internal therapy, by irradiation with a charged particle beam.

[0003] When the intensity of the irradiated beam increases, the heat load on the beam target becomes a problem. Patent Document 1 proposes circulating liquid metal in a container to remove the generated heat. However, in this method, the beam is irradiated through the beam window (solid) of the container, so there is a problem of damage to the beam window.

[0004] In this regard, in non-patent document 1, it is proposed to make liquid metal flow along a curved plate, generate a liquid film generated by free surface flow, and directly irradiate the beam there. Since the flow path of the liquid metal is curved, the pressure of the liquid increases due to centrifugal force, which can prevent boiling inside the liquid metal film. In addition, in order to increase the irradiation area, it is also proposed to tilt the liquid film relative to the beam irradiation direction.

[0005] Prior art literature

[0006] Patent Literature

[0007] Patent Document 1: Japanese Patent Application Publication No. 2018-72211

[0008] Non-patent literature

[0009] Non-patent literature 1: Kondo, H., et al. "IFMIF / EVEDA lithium test loop: design and fabrication technology of target assembly as a key component." Nuclear Fusion51.12(2011):123008. Summary of the invention

[0010] Problems to be solved by the invention

[0011] When using a nuclear reaction product (e.g., neutron) generated by causing a beam to hit a target, it is important to efficiently arrange an irradiation object (e.g., LLFP, inspection / treatment site) of the nuclear reaction product near the target. In the method of non-patent document 1, the irradiation object of the nuclear reaction product can only be arranged behind the curved plate, which is not efficient. When the liquid film is used with an inclination, the space for arranging the irradiation object is also limited, which is not efficient.

[0012] In view of such problems, an object of the present invention is to provide a beam target capable of withstanding a high-intensity beam and a beam target system capable of efficiently utilizing generated nuclear reaction products.

[0013] Solutions for solving problems

[0014] One embodiment of the present invention is a beam target for generating a nuclear reaction product by irradiating a beam obtained from a beam generating source, characterized by comprising:

[0015] A cone having an inner surface of a tapered shape whose diameter decreases toward the front end; and

[0016] The supply unit supplies liquid metal to the inner side surface of the cone to form a liquid film of the liquid metal on the inner side surface.

[0017] The liquid film is formed by the liquid metal supplied by the supply unit flowing in a spiral shape on the inner side (inner wall) of the cone. The surface of the formed liquid film is preferably set to be conical. Therefore, the cone has a front end on the side far from the beam receiving side, and has a tapered inner side whose diameter decreases toward the front end. The inner side of the cone is roughly in the shape of a truncated cone, but more strictly speaking, the cone angle may not be fixed, and may be a cone shape with a gradually decreasing cone angle or a cone shape with a gradually increasing cone angle. The inner side of the cone may also be cylindrical at the front end. In addition, the overall shape of the cone is not particularly limited, but in the case of using neutrons generated by beam irradiation of the liquid metal externally, it is preferably formed to be thinner so as not to block the neutrons.

[0018] According to the beam target of this embodiment, a liquid metal film is formed on the surface of a cone having a conical or truncated cone-shaped inner surface, so that the surface area of ​​the liquid film irradiated by the beam (hereinafter referred to as the irradiation area) can be increased while keeping the length of the beam target short. It should be noted that even if the liquid metal is made to flow on an inclined flat plate, the irradiation area of ​​the beam can be increased, but the total length of the target becomes longer. The beam target of this embodiment can increase the irradiation area of ​​the beam while keeping the total length short.

[0019] In addition, in the beam target of the present embodiment, liquid metal flows inside the cone, so other objects can be arranged at any position outside the cone. In the use of irradiating the material outside the beam target with the nuclear reaction product (e.g., neutrons) generated by beam irradiation of the liquid metal, the object can be arranged around the cone as a whole, so the utilization efficiency of the nuclear reaction product can be improved. For example, in the case of performing nuclear transmutation on LLFP or the like using neutrons generated by beam irradiation of the liquid metal, the object material (e.g., LLFP) to be irradiated with neutrons for nuclear transmutation can be kept around the cone.

[0020] The liquid metal (target material) can be appropriately selected according to the application, and examples thereof include liquid lithium, liquid bismuth, liquid sodium, liquid mercury, and liquid lead bismuth. In addition, in order to easily form a liquid film of the liquid metal on the entire inner side surface of the cone, a plurality of supply units may be provided.

[0021] In addition, the liquid metal flows in a spiral shape, so the pressure inside the liquid metal film increases due to centrifugal force, and boiling accompanying beam irradiation can be prevented. Since it is a spiral flow, a greater centrifugal force can be obtained compared to making the liquid metal flow on a curved plate, and the effect of preventing boiling is also better.

[0022] In addition, in this embodiment, the cone may also be formed by a nuclear transmutation target substance (e.g., 93 Here, the so-called "composed of the nuclear transmutation object material" means that the nuclear transmutation object material is contained in the material constituting the cone, and other materials are not excluded. In addition, in this scheme, the liquid metal supplied by the supply unit may also contain powder of the nuclear transmutation object material. Neutrons are generated by irradiating the liquid metal with a beam. Therefore, by arranging the nuclear transmutation object material in the liquid metal or in the cone, the nuclear transmutation object material can be very close to the generation position of the neutrons, which can improve the efficiency of nuclear transmutation.

[0023] In addition, in this embodiment, a spiral groove may be provided on the inner side surface of the cone. The spiral groove can stabilize the flow of the liquid metal.

[0024] Another embodiment of the present invention is a beam target system, characterized by comprising:

[0025] The beam target as described above;

[0026] The irradiation unit irradiates the liquid film with a beam obtained from a beam generation source.

[0027] The irradiation unit is configured to include, for example: a beam window (eg, plasma curtain, liquid metal window); a deflection unit that deflects a beam obtained from an accelerator as a beam generation source and guides the beam to a beam target; and an adjustment unit that adjusts the beam diameter.

[0028] In addition, in this embodiment, there may be provided a holding portion for holding a substance (e.g., LLFP) to be subjected to nuclear transmutation using neutrons generated by irradiating a beam of liquid metal around the cone. As described above, the nuclear transmutation target substance can be arranged around the cone, thereby improving the utilization efficiency of neutrons. For example, by covering the entire cone with the nuclear transmutation target substance, the neutrons generated in the beam target can be more efficiently utilized.

[0029] The beam target system in this embodiment may also include: an output unit that outputs neutrons generated by irradiating the liquid metal with a beam in a direction orthogonal to the irradiation direction of the beam. In addition, a plurality of such output units may be provided. When the generated neutrons are used for non-destructive inspection or BNCT, the flexibility of object setting can be improved, and neutrons can be irradiated to multiple objects at the same time.

[0030] Effects of the Invention

[0031] According to the present invention, a beam target capable of withstanding a high-intensity beam and a beam target system capable of efficiently utilizing generated nuclear reaction products can be provided. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] Figure 1 This is a diagram showing the overall configuration of a beam target system (first embodiment) for nuclear transmutation of LLFP.

[0033] Figure 2 A- Figure 2 C is a diagram illustrating the shape of a cone and the supply of liquid metal to the cone.

[0034] Figure 3 This is a diagram for explaining a method for designing the inner surface shape of a cone.

[0035] Figure 4 A- Figure 4 C is a diagram for explaining that the beam irradiation area on the target can be increased in the embodiment.

[0036] Figure 5 A- Figure 5 D is a diagram showing simulation results for obtaining the flight trajectory of the deuteron beam and the generated neutrons, and the amount of heat accompanying the beam irradiation in the first embodiment.

[0037] Figure 6 A. Figure 6 B is a diagram illustrating a simulation for evaluating the nuclear transmutation efficiency of the LLFP in the first embodiment.

[0038] Figure 7 This is a diagram showing the overall configuration of a beam target system (second embodiment) used in a multi-patient BNCT treatment system.

[0039] Figure 8 This is a diagram showing the overall configuration of a beam target system (third embodiment) used in a mass production system of astatine-211. DETAILED DESCRIPTION

[0040] Hereinafter, specific embodiments of the present invention will be described with reference to the drawings, but the present invention is not limited thereto. The constituent elements of each embodiment described below can be combined as appropriate.

[0041] <First embodiment>

[0042] This embodiment is a beam target system 100 for nuclear transmutation of long-lived fission products (LLFP). The beam target system 100 generates neutrons by irradiating liquid lithium with a deuterium nuclear beam (e.g., about 100 MeV per nucleon) accelerated by an accelerator, and uses the generated neutrons to perform nuclear transmutation on LLFP and render it harmless.

[0043]

structure

[0044] Figure 1 1 is a diagram showing the overall configuration of the beam target system 100. As shown in the figure, the beam target system 100 includes a beam window 101, a deflection electromagnet 102, a beam diameter adjustment electromagnet 103, a cone 104, a liquid metal supply unit 105, and an LLFP holding unit 106.

[0045] The beam window 101 is a device that separates the high vacuum on the accelerator side from the beam target system side, and is composed of a plasma curtain and a liquid metal window.

[0046] The deflection electromagnet 102 changes the traveling direction of the deuteron beam. In this embodiment, the horizontal deuteron beam is directed downward. The beam diameter adjustment electromagnet 103 adjusts the beam diameter of the deuteron beam to a desired size. In this embodiment, the beam diameter is set to 40 cm.

[0047] The inner side of the cone 104 is generally in the shape of a truncated cone whose diameter decreases as it moves toward the beam traveling direction, and the front end is cylindrical. It should be noted that the inner side of the cone 104 is not strictly a truncated cone, but a cone whose taper angle becomes gentler as it moves toward the front end. The details of the inner side of the cone 104 will be described later. Figure 3 Provide detailed explanation.

[0048] The material of the cone 104 may be any material as long as it does not chemically react with the liquid metal (target material) and has strength. For example, stainless steel (SUS) may be used.

[0049] The liquid metal supply unit 105 (hereinafter also referred to as the supply unit 105) supplies liquid metal (liquid lithium in this embodiment) from the upper side of the cone 104 along the inner side surface of the cone 104 in a manner that maintains the velocity in the tangential direction. Since the liquid metal is supplied while maintaining the velocity in the tangential direction, it can also be expressed as the supply unit 105 spraying the liquid metal. The liquid lithium generates a spiral flow along the inner side surface of the cone 104, forming a thin liquid film 110 on the inner side surface. Figure 1 In the figure, the liquid metal film (target) formed on the inner surface of the cone 104 is expressed in black.

[0050] In order to stabilize the spiral flow of the liquid metal, grooves along the spiral flow path may be provided on the inner surface of the cone 104 .

[0051] The lower end of the cone 104 has a discharge port 109 for discharging liquid metal. The liquid metal is discharged to the outside of the cone target from the liquid metal outlet 107. The discharged liquid metal passes through a circulation system 120 (see Figure 2 C) is circulated and supplied again from the liquid metal inlet 108 on the upper end side of the cone 104.

[0052] The storage unit 106 stores LLFP, which is a substance to be subjected to nuclear transmutation using the generated neutrons. Examples of LLFP include palladium-107 ( 107 Pd), cesium-135( 135 Cs), zirconium-93( 93 Zr), selenium-79 ( 79 Se), etc. The LLFP held by the holding portion 106 is in contact with the outer side surface of the cone 104.

[0053] Figure 2 A represents the vertical cross-sectional shape of the cone 104, Figure 2 B represents a top view of the cone 104. As described above, the inner side surface of the cone 104 has a truncated cone-shaped portion and a cylindrical portion. In addition, the cone 104 is formed as thin as possible so as not to prevent neutrons generated by beam irradiation to the liquid metal from reaching the LLFP held in the holding portion 106. It should be noted that in order to increase the strength and stability of the cone 104, reinforcement rings may be provided at several locations. The supply portion 105 is provided near the upper end of the cone 104. Figure 2FIG. 1B shows an example in which four supply units 105 are provided at intervals of 90 degrees. However, as long as a liquid film can be formed on the entire inner surface of the cone 104, the number of supply units 105 may be any number.

[0054] Figure 2 C is a diagram for explaining a circulation system 120 for circulating liquid metal. The liquid metal discharged to the outside through the discharge port 109 of the cone 104 and the liquid metal outlet 107 is supplied again to the liquid metal inlet 108 by the circulation pump 123. During the circulation, the liquid metal is cooled by the heat exchanger 121, and impurities are removed by the impurity removal device 122.

[0055] Figure 3 This is a diagram for explaining a method for designing the inner surface shape of the cone 104 . Figure 3 The vertical cross-sectional shape 310 of the cone 104 and the horizontal cross-sectional views 321, 322, and 333 at the upper end, the middle part, and the lower end are shown. 301 indicates the inner side surface of the cone 104, and 302 indicates the surface of the liquid metal film. 纵i represents the velocity of the fluid along the longitudinal direction, V 横i represents the velocity of the fluid along the lateral direction, S i Represents the area of ​​the fluid at each cross section.

[0056] The shape of the inner side surface of the cone 104 is designed so that the surface of the liquid metal film formed by the supply unit 105 becomes a conical shape. Therefore, first, the shape of the liquid metal film surface, more specifically, its inclination angle is obtained. This is determined by the intensity of the introduced beam and the properties of the liquid metal, so that the irradiation intensity of the beam per unit area of ​​the liquid film becomes an irradiation intensity that does not cause boiling of the liquid metal.

[0057] Next, make the V 纵 The shape (inclination angle) of the inner wall of the cone 104 is determined by making S equal. Figure 3 As shown in FIG. 1 , the inclination of the inner side surface of the cone 104 is gentler than the inclination of the target (liquid film). In addition, strictly speaking, the inner side surface 301 of the cone 104 is a cone shape whose diameter decreases toward the front end (lower side), but its cone angle becomes gentler toward the front end. It should be noted that the V at each cross section is set to be ignoring the influence of friction and gravity. 纵 However, strictly speaking, it is better to design the shape based on the flow rate taking these effects into consideration.

[0058] It should be noted that the liquid metal film surface is set to a cone shape when the distribution (profile) of the beam intensity is constant regardless of the distance from the center. In the case where the beam intensity has a distribution that becomes weaker as it is farther from the center, in order to make the beam intensity per unit area of ​​the liquid film constant, a cone shape in which the inclination angle of the surface of the liquid film gradually becomes steeper can also be adopted. Accordingly, the shape of the inner side surface of the cone 104 is also appropriately determined.

[0059]

Effect

[0060] Hereinafter, advantageous effects of the beam target system of the present embodiment will be described.

[0061] Figure 4 A~ Figure 4 C is a diagram for explaining that the irradiation area of ​​the beam to the target can be increased in this embodiment. Figure 4 A is the situation where liquid metal falls freely. Figure 4 B is the case where the liquid metal flows along an inclined plate. Figure 4 C is the case where the liquid metal flows in a spiral shape along the inner surface of the cone 104 as in the present embodiment. If the diameter of the irradiated beam is d, then Figure 4 The irradiation area in case of A is π(d / 2) 2 .on the other hand, Figure 4 B. Figure 4 The irradiation area in the case of C is π(d / 2) 2 / sinθ. Here, θ is the inclination angle of the inclined plate and the cone.

[0062] In the case of using an inclined plate ( Figure 4 B) and the present embodiment ( Figure 4 In C), the irradiation area is the same, but the length of the target is d / sinθ in the former and d / (2×sinθ) in the latter. This embodiment has the advantage of being able to achieve miniaturization of the device.

[0063] In addition, Figure 4 In the method B, the LLFP can be arranged only behind the inclined plate. In contrast, in the present embodiment, the LLFP can be arranged around the entire periphery of the cone 104, so the generated neutrons can be efficiently utilized and the LLFP can be efficiently subjected to nuclear transmutation.

[0064] Furthermore, the pressure in the liquid metal increases due to the centrifugal force accompanying the spiral flow, so the boiling point increases, which can prevent the boiling of the liquid metal caused by beam irradiation. As shown in the prior art, making the liquid metal flow along the curved plate also generates centrifugal force, but the spiral flow as in this embodiment can obtain a greater centrifugal force, and the boiling suppression effect is better.

[0065] Figure 5 A~ Figure 5 D is a diagram for explaining the evaluation of target heating caused by a deuteron beam (100 MeV / u) using radiation simulation. Figure 5 A is a diagram showing a target system, 501 is a liquid lithium target, and 502 is a cone. Figure 5 B represents the flight trajectory (flow rate) of the deuteron beam, Figure 5 C represents the flight trajectory (flow rate) of neutrons. Figure 5 As shown in B, the deuteron beam is almost completely stopped by the liquid lithium target. Figure 5 As shown in C, it can be seen that sufficient neutrons are also released from the side of the cone.

[0066] Figure 5 D is a diagram showing the heat generation distribution of the target. For the cases of a conical target and a cylindrical target as in the present embodiment, the heat generation was evaluated by simulation for beam intensities of 100MeV / u and 40MeV / u. Graphs 511 and 512 show the heat generation when a 100MeV beam is irradiated on a conical target and a cylindrical target. In addition, graphs 521 and 522 show the heat generation when a 40MeV beam is irradiated on a conical target and a cylindrical target. The horizontal axis represents the depth [cm] from the surface of liquid lithium, and the vertical axis represents the heat generation [kW / cc]. It can be seen that regardless of the beam intensity, the present embodiment can reduce the local heat generation at the end of the beam range (z = about 37cm and z = about 8cm) compared to the case of a cylindrical target as a comparative example. That is, it can be seen that the present embodiment can suppress the generation of gas caused by the boiling of liquid lithium.

[0067] Figure 6 A. Figure 6 B is a diagram illustrating the evaluation of the nuclear transmutation efficiency of LLFP based on simulation. Figure 6 A is a diagram showing the configuration of liquid metal 601, cone 602 and LLFP 603. LLFP uses palladium ( 105 Pd, 107 As shown in the figure, LLFP 603 is arranged around cone 602, and uses high-intensity neutrons generated in the liquid metal target to perform nuclear transmutation. Figure 6 B represents the energy distribution of neutrons released outside the liquid metal target. It can be seen that each 100 MeV / u deuterium nucleus will produce about one neutron.

[0068] In addition, when irradiating a 1A deuterium beam, the number of nuclear transmutations per deuterium nucleus is calculated to be about 0.7, and the nuclear transmutation amount is 25 kg per year. In this way, 25 kg of palladium can be nuclear transmuted (detoxified) per year through one accelerator, which is very efficient.

[0069] [Modifications]

[0070] In the present embodiment, LLFP powder may be mixed in the liquid metal supplied by the supply unit 105. By locating the LLFP at a position closest to the generation position of neutrons by beam irradiation, nuclear transmutation of the LLFP can be efficiently performed.

[0071] In addition, in this embodiment, LLFP (for example 93 The cone 104 is made of Zr. The cone 104 is also located close to the neutron generation position, and the nuclear transmutation of LLFP can be performed efficiently.

[0072] Furthermore, in the present embodiment, neutrons generated by beam irradiation of liquid metal are used for nuclear transmutation of LLFP, but the substance to be subjected to nuclear transmutation by neutrons is not limited to LLFP, and may be any substance.

[0073] <Second embodiment>

[0074] The present embodiment is a beam target system used in a multi-patient BNCT treatment system capable of performing boron neutron capture therapy (BNCT) on a plurality of patients. Figure 7 The overall structure of the beam target system 700 of this embodiment is shown. It should be noted that Figure 7 The description of the circulation system of liquid metal is omitted.

[0075] The basic structure of the beam target system 700 of this embodiment is the same as that of the first embodiment, but a plurality of neutron collimators 701 are provided instead of a holding portion 106 for holding the LLFP around the cone 104. The neutron collimators 701 collimate the neutrons generated by beam irradiation to the liquid metal and output them to the irradiated object (patient). The cone 104 has a truncated cone shape, so the neutron collimators 701 output neutrons in a direction orthogonal to the beam irradiation direction. In addition, a plurality of neutron collimators 701 may be provided in the circumferential direction of the cone 104 and in the beam irradiation direction.

[0076] According to this embodiment, multiple patients can be irradiated with neutrons. Therefore, more efficient treatment can be performed. In addition, the output direction of the neutrons is orthogonal to the irradiation direction of the beam, so the patient can be arranged away from the irradiation line of the beam, and safety is further improved.

[0077] It should be noted that although BNCT is used as an example for explanation here, the same configuration as above can be adopted even in an inspection system that uses the generated neutron rays for non-destructive inspection.

[0078] <Third Embodiment>

[0079] This embodiment is used to produce a large amount of astatine-211 ( 211 Astatine-211 is a radioactive nuclide that emits α-rays and is used for RI internal therapy that directly irradiates the cancer lesion with α-rays via oral or intravenous administration.

[0080] Figure 8 211 is a diagram showing the overall structure of the beam target system 800 of this embodiment. Astatine-211 is produced by irradiating bismuth (Bi) with a helium beam (~7.2 MeV / u) accelerated by an accelerator to undergo nuclear transmutation ( 4 He+Bi→ 211 At+X). Therefore, in this embodiment, the supply unit 105 supplies liquid bismuth to the inner side surface of the cone 104.

[0081] The liquid bismuth is circulated by the circulation pump 802. Astatine generated by the irradiation of the beam is recovered together with the liquid bismuth from the lower part of the cone 104. Since the boiling point of astatine is lower than that of bismuth, only astatine can be separated and taken out as a gas by the recovery device 803.

[0082] According to this embodiment, astatine-211 can be produced efficiently and in large quantities.

[0083] Description of reference numerals:

[0084] 100: beam target system; 101: beam window; 102: deflection electromagnet; 103: beam diameter adjustment electromagnet; 104: cone; 105: liquid metal supply unit; 106: LLFP holding unit; 107: liquid metal outlet; 108: liquid metal inlet; 109: exhaust port; 110: liquid metal (liquid film); 120: circulation system; 121: heat exchanger; 122: impurity removal device; 123: circulation pump.

Claims

1. A beam target, used for irradiating a beam obtained from a beam generating source and passing through a beam window to produce a nuclear reaction product, the beam target comprising: A cone having an inner surface of a tapered shape whose diameter decreases toward the front end; and a supply unit for supplying liquid metal to the inner side surface of the cone in a manner of maintaining a velocity in a tangential direction, so as to form a liquid film of the liquid metal on the inner side surface; The inclination angle of the inner wall of the cone is determined in such a way that the speed of the liquid metal along the height direction of the cone is equal, The beam window separates the high vacuum on the beam generation source side from the beam target side.

2. The beam target according to claim 1, wherein: The cone is composed of a material to be subjected to nuclear transmutation using neutrons generated by irradiating the liquid metal with a beam.

3. The beam target according to claim 1, wherein: The liquid metal supplied by the supply unit contains powder of a substance to be subjected to nuclear transmutation using neutrons, and the neutrons are generated by irradiating the liquid metal with a beam.

4. The beam target according to claim 1, wherein: A spiral groove is provided on the inner side surface of the cone.

5. A beam target system, comprising: The beam target of claim 1; and an irradiation unit, irradiating the liquid film with a beam obtained from a beam generation source, The irradiation unit includes a beam window that separates a high vacuum on a beam generation source side from a beam target side.

6. The beam target system according to claim 5, wherein: have: The holding unit holds a substance to be subjected to nuclear transmutation using neutrons generated by irradiating the liquid metal with the beam around the cone.

7. The beam target system according to claim 5, wherein: have: The output unit outputs neutrons generated by irradiating the liquid metal with the beam in a direction orthogonal to the irradiation direction of the beam.

8. The beam target system according to claim 7, wherein: A plurality of the output units are provided.

Images