Beam Target and Beam Target System

Abstract

The present invention comprises a beam target for generating nuclear reaction products by irradiating a beam obtained from a beam source, a cone having a tapered inner surface with a diameter reduced by a tip, and a supply means for supplying liquid metal to the inner surface of the cone and forming a liquid film of the liquid metal on the inner surface. Since a liquid film of liquid metal is formed on the surface of the cone, the irradiation area of ​​the beam can be increased, and at the same time, a target material such as LLFP can be placed around the cone, thereby allowing for efficient utilization of nuclear reaction products (e.g., neutrons) generated in the beam of the liquid metal.

Description

Technology Field

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

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

[0003] As the intensity of the beam being irradiated increases, the thermal load on the beam target becomes a problem. Patent Document 1 proposes removing the heat generated by circulating liquid metal within a container. However, in this method, since the beam is irradiated through the beam window (solid) of the container, there is a problem that the beam window is damaged.

[0004] In this regard, Non-Patent Literature 1 proposes flowing liquid metal along a curved plate to create a liquid film by free surface flow and irradiating a beam directly onto it. Since the flow path of the liquid metal is curved, the pressure of the liquid increases due to centrifugal force, making it possible to prevent boiling within the liquid metal film. In addition, it is also proposed to tilt the liquid film with respect to the beam irradiation direction in order to increase the irradiation area. Prior art literature

[0005] Patent Document 1: Japanese Published Patent Application No. 2018-72211

[0006] Non-patent Document 1: Kondo, H., et al. “IFMIF / EVEDA lithium test loop: design and fabrication technology of target assembly as a key component.” Nuclear Fusion 51.12 (2011): 123008. The problem to be solved

[0007] When using nuclear reaction products (e.g., neutrons) generated by colliding a beam with a target, it is important to be able to efficiently place the target of the nuclear reaction product (e.g., LLFP or examination / treatment site) near the target. In the method of Non-Patent Literature 1, the target of the nuclear reaction product can only be placed behind a curved plate, which is inefficient. Even when using a liquid film at an angle, the space for placing the target is limited, which is inefficient.

[0008] In consideration of such challenges, the present invention aims to provide a beam target capable of accommodating a high-intensity beam and a beam target system capable of efficiently utilizing the generated nuclear reaction products. means of solving the problem

[0009] One embodiment of the present invention is a beam target for generating nuclear reaction products by irradiating a beam obtained from a beam source,

[0010] A cone having a tapered inner surface whose diameter decreases by the tip, and

[0011] It is characterized by having a supply means for supplying liquid metal to the inner surface of the above-mentioned cone and forming a liquid film by said liquid metal on said inner surface.

[0012] A liquid film is formed by the liquid metal supplied by a supply means flowing in a spiral shape along the inner surface (inner wall) of the cone. It is preferable that the surface of the formed liquid film be conical. For this reason, the cone has a tapered inner surface with the end further from the beam receiving side as the tip, and the diameter decreases by the tip portion. The inner surface of the cone is approximately in the shape of a truncated cone, but more strictly speaking, the taper angle does not need to be constant; it may be a tapered shape where the taper angle gradually becomes gentle or a tapered shape where the taper angle gradually becomes steep. The inner surface of the cone may be cylindrical at its foremost end. Furthermore, while the overall shape of the cone is not particularly limited, it is preferable to form it thinly so as not to block neutrons when neutrons generated by beam irradiation of the liquid metal are utilized externally.

[0013] According to the beam target of the present embodiment, a liquid metal film is formed on the surface of a cone having an inner surface having a tapered shape or a truncated cone shape, so the surface area of ​​the liquid film irradiated by the beam (hereinafter, irradiation area) can be increased while maintaining the length of the beam target short. Meanwhile, the irradiation area of ​​the beam can be increased even if liquid metal is flowed on a tilted plate, but the overall length of the target becomes longer. The beam target according to the present embodiment can increase the irradiation area of ​​the beam while keeping the overall length short.

[0014] In addition, in the beam target according to the present embodiment, since the liquid metal flows inside the cone, other objects can be placed at any location outside the cone. For use in irradiating a material outside the beam target with nuclear reaction products (e.g., neutrons) generated from beam irradiation of the liquid metal, the target object can be placed around the entire periphery of the cone, thereby increasing the efficiency of utilizing the nuclear reaction products. For example, in the case of nuclear transmuting LLFP, etc. by neutrons generated by beam irradiation of the liquid metal, the material to be nuclear transmuted by neutron irradiation (e.g., LLFP) can be held around the cone.

[0015] The liquid metal (target material) may be appropriately selected according to the application, and examples include liquid lithium, liquid bismuth, liquid sodium, liquid mercury, and liquid lead bismuth. In addition, multiple supply means may be installed to facilitate the formation of a liquid film by the liquid metal over the entire inner surface of the cone.

[0016] In addition, since the liquid metal flows in a spiral shape, the internal pressure of the liquid metal film increases due to centrifugal force, which can prevent boiling associated with beam irradiation. Because it is a spiral flow, a greater centrifugal force can be obtained than when flowing the liquid metal through a curved plate, so the effect of preventing boiling is also higher.

[0017] In addition, in this embodiment, the conical body is a nuclear transmutation target material (e.g., 93It may be composed of Zr). Here, being composed of a nuclear transmutation target material means that the nuclear transmutation target material is included in the material constituting the cone body, and does not exclude the inclusion of other materials. Furthermore, in this embodiment, the liquid metal supplied by the supply means may contain a powder of the nuclear transmutation target material. Since neutrons are generated by beam irradiation of the liquid metal, by placing the nuclear transmutation target material within the liquid metal or within the cone body, the location of nuclear transmutation target material and neutron generation can be made very close, thereby increasing the efficiency of nuclear transmutation.

[0018] In addition, in this embodiment, a spiral-shaped groove may be provided on the inner surface of the cone. The flow of the liquid metal can be stabilized by the spiral-shaped groove.

[0019] Another embodiment of the present invention is a beam target system,

[0020] The above beam target and,

[0021] It is characterized by having an irradiation means for irradiating the liquid film with a beam obtained from a beam source.

[0022] The investigation means is configured to include, for example, a beam window (e.g., a plasma curtain, a liquid metal window), a deflection means for deflecting a beam obtained from an accelerator that is a beam source and guiding it to a beam target, or an adjustment means for adjusting the beam diameter.

[0023] In addition, in this embodiment, a holding portion may be further provided around the cone body to hold a target material (e.g., LLFP) that undergoes nuclear transformation by neutrons generated by beam irradiation on liquid metal. As described above, since the target material for nuclear transformation can be placed around the cone body, the efficiency of neutron utilization can be increased. For example, by covering the entire cone body with the target material for nuclear transformation, neutrons generated from the beam target can be utilized more efficiently.

[0024] The beam target system in this embodiment may be equipped with an output means that outputs neutrons generated by beam irradiation on liquid metal in a direction orthogonal to the beam irradiation direction. In addition, multiple such output means may be provided. When the generated neutrons are used for non-destructive testing or BNCT applications, the flexibility of installing the target object is increased, and it is also possible to irradiate neutrons to multiple targets simultaneously. Effects of the invention

[0025] According to the present invention, a beam target capable of accommodating a high-intensity beam and a beam target system capable of efficiently utilizing the generated nuclear reaction products can be provided. Brief explanation of the drawing

[0026] FIG. 1 is a diagram showing the overall configuration of a beam target system (first embodiment) used for nuclear transmutation of LLFP. FIGS. 2(a) to FIGS. 2(c) are drawings illustrating the shape of the cone and the supply of liquid metal to the cone. Figure 3 is a drawing illustrating a method for designing the shape of the inner surface of a cone. FIGS. 4(a) to FIGS. 4(c) are drawings illustrating that the beam irradiation area for a target can be increased in an embodiment. FIGS. 5(a) to FIGS. 5(d) are drawings showing simulation results for determining the track of the deuteron beam and the neutrons generated in the first embodiment, and the amount of heat generated during beam irradiation. FIGS. 6(a) and FIGS. 6(b) are drawings illustrating a simulation for evaluating the nuclear transmutation efficiency of LLFP in the first embodiment. FIG. 7 is a diagram showing the overall configuration of a beam target system (second embodiment) used in a multi-patient BNCT treatment system. FIG. 8 is a diagram showing the overall configuration of a beam target system (third embodiment) used in a mass production system of astatin-211. Specific details for implementing the invention

[0027] Hereinafter, embodiments for carrying out the present invention are described with reference to the drawings, but the present invention is not limited thereto. The components of each embodiment described below can be appropriately combined.

[0028] <First Embodiment>

[0029] The present embodiment is a beam target system (100) used for nuclear transmutation of long-life fission products (LLFP). The beam target system (100) generates neutrons by irradiating liquid lithium with a deuteron beam (e.g., about 100 MeV per nucleon) accelerated by an accelerator, and neutralizes LLFP by nuclear transmutation using the generated neutrons.

[0030] [composition]

[0031] FIG. 1 is a drawing showing the overall configuration of a beam target system (100). As shown in the drawing, the beam target system (100) is equipped with 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).

[0032] 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 or a liquid metal window.

[0033] The deflection electromagnet (102) changes the direction of travel of the deuterium beam. In this embodiment, the horizontal deuterium beam is changed to a downward direction. The beam diameter adjustment electromagnet (103) adjusts the beam diameter of the deuterium beam to a desired size. In this embodiment, the beam diameter is set to 40 cm.

[0034] The inner surface of the cone (104) is approximately a truncated cone shape with a diameter decreasing in the direction of beam travel, and the leading edge is cylindrical. Meanwhile, the inner surface of the cone (104) is not strictly a truncated cone shape, but a tapered shape with a taper angle becoming gentler at the leading edge. Details regarding the shape of the inner surface of the cone (104) will be explained in detail later using FIG. 3.

[0035] The material of the cone (104) can be any material that has strength and does not chemically react with the liquid metal (target material), for example, stainless steel (SUS) can be used.

[0036] A liquid metal supply unit (105) (hereinafter also referred to simply as the supply unit (105)) supplies liquid metal (liquid lithium in this embodiment) from the upper side of the cone (104) so ​​that a tangential velocity remains along the inner surface of the cone (104). Since the supply of liquid metal is such that a tangential velocity remains, the supply unit (105) may be described as spraying liquid metal. The liquid lithium generates a spiral flow along the inner surface of the cone (104) to form a thin liquid film (110) on the inner surface. In FIG. 1, the liquid film (target) of liquid metal formed on the inner surface of the cone (104) is depicted by being painted black.

[0037] In order to stabilize the spiral flow of the liquid metal, a groove along the spiral flow path may be provided on the inner surface of the cone (104).

[0038] At the bottom side of the cone body (104), there is an outlet (109) for discharging liquid metal, and the liquid metal is discharged to the outside of the cone target from the liquid metal outlet (107). The discharged liquid metal is circulated by a circulation system (120) (see (c) in FIG. 2) consisting of a heat exchanger (121), an impurity removal device (122), a circulation pump (123), etc., and is supplied again from the fluid inlet (108) at the top side of the cone body (104).

[0039] The holding portion (106) holds LLFP, which is a target material to be nuclear-transformed by generated neutrons. An example of LLFP is palladium-107 ( 107 Pd), Cesium-135 ( 135 Cs), Zirconium-93( 93 Zr), Selen-79 ( 79 Examples include Se). The LLFP held by the holding part (106) comes into contact with the outer surface of the cone (104).

[0040] FIG. 2(a) shows the vertical cross-sectional shape of the cone (104), and FIG. 2(b) shows the top view of the cone (104). The inner surface of the cone (104) has a truncated cone shape and a cylindrical shape as described above. In addition, the cone (104) is formed as thin as possible so as not to hinder neutrons generated by beam irradiation on the liquid metal from reaching the LLFP held in the holding part (106). Meanwhile, reinforcing rings may be installed in several places to increase the strength and stability of the cone (104). The supply part (105) is installed near the top of the cone (104). In FIG. 2(b), an example is shown in which four supply units (105) are installed at 90-degree intervals, but as long as a liquid film can be formed over the entire inner surface of the cone (104), the number of supply units (105) does not matter.

[0041] FIG. 2(c) is a diagram illustrating a circulation system (120) for circulating liquid metal. Liquid metal discharged to the outside through the discharge port (109) and liquid metal outlet (107) of the cone (104) is supplied back to the liquid metal inlet (108) by a circulation pump (123). During circulation, the liquid metal is cooled by a heat exchanger (121) and impurities are removed by an impurity removal device (122).

[0042] FIG. 3 is a drawing illustrating a design method for the inner surface shape of a cone (104). FIG. 3 shows the vertical cross-sectional shape (310) of the cone (104) and horizontal cross-sectional views (321, 322, 333) at the upper, middle, and lower parts. 301 represents the inner surface of the cone (104), and 302 represents the surface of the liquid metal film. Also, V 縱i represents the fluid velocity along the longitudinal direction, and V 橫i represents the fluid velocity along the transverse direction, and S i represents the fluid area at each cross-section.

[0043] The inner surface shape of the cone (104) is designed such that the liquid metal film surface formed by the supply unit (105) has a conical shape. Accordingly, first, the shape of the liquid metal film surface, more specifically, its angle of inclination, is determined. This is determined by the intensity of the beam introduced and the properties of the liquid metal so that the beam irradiation intensity per unit area of ​​the liquid film becomes an irradiation intensity that does not cause boiling of the liquid metal.

[0044] Next, V at each cross-section 縱 This is made identical, and the shape (angle of inclination) of the inner wall of the cone (104) is determined so that S becomes identical. As shown in FIG. 3, the inclination of the inner surface of the cone (104) becomes gentler than the inclination of the target (liquid film). Also, strictly speaking, the inner surface (301) of the cone (104) has a tapered shape in which the diameter becomes smaller by the tip (lower side), and the taper angle becomes gentler by the tip. Meanwhile, here, the effects of friction or gravity are ignored, and V at each cross-section 縱 While calculations are being performed based on this identical basis, it is more rigorous to design the shape based on the flow velocity that also takes these influences into account.

[0045] Meanwhile, the surface of the liquid metal film is shaped like a cone when the beam strength profile is constant regardless of the distance from the center. In the case where the beam strength has a profile that weakens as it moves away from the center, the angle of inclination of the surface of the liquid film may be made tapered so that it gradually becomes steeper in order to keep the beam strength per unit area of ​​the liquid film constant. Accordingly, the shape of the inner surface of the cone (104) is also appropriately determined.

[0046] [effect]

[0047] The advantageous effects of the beam target system according to the present embodiment are described below.

[0048] FIGS. 4(a) to FIGS. 4(c) are drawings illustrating that, in the present embodiment, the irradiation area of ​​the beam toward the target can be increased. FIG. 4(a) shows the case where liquid metal is dropped in free fall, FIG. 4(b) shows the case where liquid metal is flowed along an inclined plate, and FIG. 4(c) shows the case where liquid metal is flowed in a spiral shape along the inner surface of the cone (104) as in the present embodiment. If the diameter of the irradiating beam is d, the irradiation area in the case of FIG. 4(a) is π(d / 2). 2 is. Meanwhile, the survey area in the cases of Fig. 4(b) and Fig. 4(c) is π(d / 2) 2 / sinθ. Here, θ is the angle of inclination of the inclined plate and the cone.

[0049] In the case where an inclined plate is used (Fig. 4 (b)) and in the present embodiment (Fig. 4 (c)), the irradiation area is the same, but the length of the target is d / sinθ for the former and d / (2×sinθ) for the latter, and the present embodiment has the advantage that the device can be made smaller.

[0050] In addition, while the method of FIG. 4 (b) allows LLFP to be placed only behind the inclined plate, in this embodiment, LLFP can be placed around the entire periphery of the cone (104), and thus, the generated neutrons can be utilized efficiently, allowing LLFP to be efficiently nuclear-transformed.

[0051] Furthermore, since the pressure within the liquid metal increases due to the centrifugal force accompanying the spiral flow, the boiling point is raised, thereby preventing the liquid metal from boiling due to beam irradiation. As shown in the prior art, centrifugal force is generated even when the liquid metal is flowed along a curved plate; however, a larger centrifugal force is obtained with the spiral flow as in the present embodiment, resulting in a higher effect of suppressing boiling.

[0052] FIGS. 5(a) to FIGS. 5(d) illustrate the evaluation of target heating by a deuteron beam (100 MeV / u) using radiation simulation. FIG. 5(a) is a diagram showing the target system, where 501 is a liquid lithium target and 502 is a cone. FIG. 5(b) shows the track (flow rate) of the deuteron beam, and FIG. 5(c) shows the track (flow rate) of the neutron. As shown in FIG. 5(b), the deuteron beam is almost completely stopped by the liquid lithium target. In addition, as shown in FIG. 5(c), it can be seen that a sufficient amount of neutrons are emitted from the side of the cone.

[0053] FIG. 5(d) is a diagram showing the heat distribution of the target. For each case of a cone-shaped target and a cylindrical target as in the present embodiment, the amount of heat generated was evaluated by simulation for beam intensities of 100 MeV / u and 40 MeV / u. Graphs 511 and 512 show the amount of heat generated when a 100 MeV beam is irradiated onto the cone-shaped target and the cylindrical target. In addition, graphs 521 and 522 show the amount of heat generated when a 40 MeV beam is irradiated onto the cone-shaped target and the cylindrical target. The horizontal axis represents the depth [cm] from the surface of the liquid lithium, and the vertical axis represents the amount of heat generated [kW / cc]. For any beam intensity, it can be seen that the present embodiment can reduce local heat generation at the beam range end (z = approximately 37 cm and z = approximately 8 cm) compared to the case of the cylindrical target, which is a comparative example. In other words, it can be seen that in this embodiment, gas generation caused by the boiling of liquid lithium can be suppressed.

[0054] FIGS. 6(a) and FIGS. 6(b) are diagrams illustrating the evaluation of the nuclear transmutation efficiency of LLFP by simulation. FIGS. 6(a) is a diagram showing the arrangement of liquid metal (601), a cone (602), and LLFP (603). LLFP is a palladium separated into even and odd numbers ( 105 Pd, 107 Pd) was used. As shown, the LLFP (603) is placed around the cone (602) and is nuclear-transformed by high-intensity neutrons generated from the liquid metal target. FIG. 6 (b) shows the neutron energy distribution emitted outside the liquid metal target. It can be seen that for every 100 MeV / u deuteron, about 1 neutron is generated.

[0055] In addition, when irradiated with the 1A deuteron beam, the number of nuclear transmutations per deuteron is approximately 0.7, and the amount of nuclear transmutation is calculated to be 25 kg per year. As such, 25 kg of palladium can be nuclear transmuted (neutralized) in one year by one accelerator, which is efficient.

[0056] [Variation Example]

[0057] In this embodiment, powder of LLFP may be mixed into the liquid metal supplied by the supply unit (105). Since LLFP is located closest to the location where neutrons are generated by beam irradiation, nuclear transmutation of LLFP can be performed efficiently.

[0058] In addition, in this embodiment, the cone (104) is an LLFP (e.g., 93 It may be written as Zr). The cone (104) is also a location close to the neutron generation location, and can efficiently perform nuclear transmutation of LLFP.

[0059] In addition, in this embodiment, neutrons generated from beam irradiation of liquid metal are used for nuclear transmutation of LLFP, but the material subject to nuclear transmutation by neutrons is not limited to LLFP and can be any material.

[0060] <Second Embodiment>

[0061] This embodiment is a beam targeting system used in a multi-patient BNCT treatment system that enables boron neutron capture therapy (BNCT) for multiple patients. FIG. 7 shows the overall configuration of the beam targeting system (700) according to this embodiment. Meanwhile, the description of the liquid metal circulation system in FIG. 7 is omitted.

[0062] The basic configuration of the beam target system (700) according to the present embodiment is the same as that of the first embodiment, but a holding part (106) holding LLFP is not installed around the cone (104), and a plurality of neutron collimators (701) are installed. The neutron collimators (701) parallelize the neutrons generated by beam irradiation on the liquid metal and output them toward the irradiated object (patient). Since the cone (104) has a truncated cone shape, the neutron collimators (701) output neutrons in a direction perpendicular to the beam irradiation direction. In addition, a plurality of neutron collimators (701) can be installed around the cone (104) and also in the beam irradiation direction.

[0063] According to the present embodiment, neutrons can be irradiated to multiple patients. Therefore, more efficient treatment becomes possible. In addition, since the output direction of the neutrons is orthogonal to the irradiation direction of the beam, patients can be positioned away from the beam's irradiation line, thereby increasing safety.

[0064] Meanwhile, although BNCT was explained here as an example, a similar configuration as above can also be adopted in inspection systems that use generated neutron beams for non-destructive testing.

[0065] <Third Embodiment>

[0066] This embodiment is astatin-211 ( 211 It is a beam targeting system used in a system that generates large quantities of (At). Astatin-211 is a radionuclide that emits alpha rays and is used in RI therapy to directly irradiate the cancerous lesion with alpha rays by administering it orally or intravenously.

[0067] FIG. 8 is a diagram showing the overall configuration of a beam target system (800) according to the present embodiment. Astatine-211 is generated by irradiating bismuth (Bi) with a helium beam (~7.2 MeV / u) accelerated by an accelerator to induce nuclear transmutation ( 4 He+Bi→211 At+X). Therefore, in this embodiment, the supply unit (105) irradiates liquid bismuth onto the inner surface of the cone (104).

[0068] Liquid bismuth is circulated by a circulation pump (801). Astatine generated by beam irradiation is recovered along with liquid bismuth from the bottom of the cone (104). Since astatine has a lower boiling point than bismuth, only astatine can be separated and extracted as a gas by a recovery device (803).

[0069] According to the present embodiment, astatin-211 can be produced efficiently and in large quantities. Explanation of the symbols

[0070] 100: Beam Target System 101: Beam Window 102: Deflection Electromagnet 103: Beam Diameter Adjusting Electromagnet 104: Conche 105: Liquid metal supply unit 106: LLFP Holders 107: Liquid metal outlet 108: Liquid metal inlet 109: Outlet 110: Liquid metal (liquid film) 120: Circulatory System 121: Heat exchanger 122: Impurity removal device 123: Circulation pump

Claims

Claim 1 A beam target for generating nuclear reaction products by irradiating a beam obtained from a beam source, comprising a cone having a tapered inner surface with a diameter reduced by a tip, and a supply means for supplying liquid metal to the inner surface of the cone and forming a liquid film of the liquid metal on the inner surface, wherein the angle of inclination of the inner surface of the cone is determined such that the velocity of the liquid metal along the longitudinal direction of the cone becomes uniform. Claim 2 A beam target in which the cone body is formed by a target material that undergoes nuclear transmutation by neutrons generated by beam irradiation of the liquid metal in claim 1. Claim 3 A beam target according to claim 1, wherein the liquid metal supplied by the supply means includes a powder of a target material that undergoes nuclear transformation by neutrons generated by beam irradiation of the liquid metal. Claim 4 A beam target according to claim 1, wherein a spiral-shaped groove is provided on the inner surface of the cone. Claim 5 A beam target system comprising a beam target and an irradiation means for irradiating the beam target with a beam obtained from a beam source for generating nuclear reaction products, wherein the beam target comprises a cone having a tapered inner surface with a diameter reduced by a tip, and a supply means for supplying liquid metal to the inner surface of the cone and forming a liquid film by the liquid metal on the inner surface, and wherein the angle of inclination of the inner surface of the cone is determined such that the velocity of the liquid metal along the longitudinal direction of the cone becomes uniform. Claim 6 A beam target system according to claim 5, comprising a holding portion around the cone body that holds a target material that undergoes nuclear transmutation by neutrons generated by beam irradiation on the liquid metal. Claim 7 A beam target system according to claim 5, comprising an output means for outputting neutrons generated by beam irradiation on the liquid metal in a direction orthogonal to the direction in which the beam is irradiated. Claim 8 A beam target system having a plurality of the above-mentioned output means in claim 7.

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