Radionuclide production system

Abstract

To provide a radionuclide production system capable of producing a target radionuclide with high purity by suppressing incidence of unnecessary neutrons to a raw material target when producing the target radionuclide by a nuclear reaction by irradiating the raw material target with radiation.SOLUTION: A radionuclide production system includes an accelerator that accelerates charged particles, and a source target that generates radionuclides by a nuclear reaction by irradiation of a charged particle beam accelerated by the accelerator or radioactive rays generated by the charged particle beam, wherein a neutron absorber T202 that absorbs neutrons generated by irradiation of the charged particle beam or the radioactive rays is provided between the source target T201 and at least one of a shielding body T204 that surrounds the source target T201 and a radioactive ray generation target A103 that generates radioactive rays by irradiation of the charged particle beam.SELECTED DRAWING: Figure 2

Description

[Technical Field]

[0001] The present invention relates to a radionuclide production system that produces radionuclides through a nuclear reaction by irradiation with radiation. [Background technology]

[0002] One type of cancer treatment known is RI internal therapy using radioisotopes (RI). RI internal therapy involves administering a drug incorporating a radionuclide, allowing it to accumulate in the affected tissue, and then directly irradiating the affected tissue with the radiation emitted by the radionuclide. The radionuclide is incorporated, for example, into an antibody that selectively binds to cancer cells. The radiation is irradiated directly from nearby targeted cancer cells.

[0003] Radiation that can be used in RI internal therapy includes gamma rays (photons), beta rays (electrons), and alpha rays (helium nuclei). Alpha rays, in particular, have a short range and large linear energy transfer, allowing for selective concentration of the dose only on cancer cells without significantly damaging surrounding normal cells. For this reason, RI internal therapy is expected to be a highly effective treatment with few side effects, and its clinical application is being promoted.

[0004] Alpha-ray emitting nuclides for therapeutic use include radium-223 (Ra-223), astatine-211 (At-211), and actinium-225 (Ac-225). Actinium-225 has a half-life of approximately 10 days and undergoes four alpha decays and two beta decays before becoming a stable nuclide. All of the nuclides that make up the decay series are effective for treatment, and because radioactivity decreases quickly after treatment, it is attracting attention as a nuclide with high therapeutic effectiveness and safety.

[0005] Actinium-225 is a nuclide that rarely occurs in nature. Traditionally, actinium-225 has been produced by the nuclear decay of thorium-229 (Th-229), which in turn has been produced by the nuclear decay of uranium-233 (U-233). After being produced in thorium-229 by nuclear decay, actinium-225 is recovered by chemical separation methods.

[0006] Traditionally, thorium-229 has been produced in nuclear facilities, but in recent years, production volumes have been limited due to considerations of nuclear material protection. There are concerns that the supply of therapeutic actinium-225 will be insufficient in the future. Therefore, in recent years, development of technology to produce actinium-225 using accelerators has been progressing. The following (1) to (3) are known methods for producing actinium-225 using accelerators.

[0007] (1) By irradiating radium-226 (Ra-226) with a proton beam 226 Ra(p,2n) 225 A method that utilizes the proton-neutron reaction represented by Ac. (2) by irradiating thorium-232 (Th-232) with a proton beam 232 Th(p,spall) 225 A method that utilizes the nuclear spallation reaction represented by Ac. (3) Radium-226 (Ra-226) is irradiated with high-energy photons. 226 Ra(X,n) 225 This method utilizes the photonuclear reaction (photon-neutron reaction) represented by Ra and the conversion of Ra-225 to Ac-225 through beta decay.

[0008] Methods (1) and (2) have the problem of producing impurity nuclides that are difficult to separate from actinium-225. Impurity nuclides include actinium-226 and actinium-227. Actinium-226 has a half-life of approximately 29 hours. Actinium-227 has a half-life of approximately 21.8 years. Impurity nuclides with long half-lives pose safety concerns because they cause unnecessary exposure to normal cells. Furthermore, even if it is possible to separate impurity nuclides from the target nuclide, it is best to avoid producing them as much as possible in order to reduce the amount of radioactive waste generated during separation. Additionally, methods (1) and (2) have the problem of requiring large systems because they use proton accelerators.

[0009] In contrast, method (3) uses a photonuclear reaction, which is a photon-neutron reaction, and therefore has the advantage that impurity nuclides are less likely to be produced. However, photon-neutron reactions have a smaller cross section for nuclear transmutation than proton-neutron reactions or spallation reactions. In order to increase the amount of radioactive nuclides produced by photonuclear reactions, it is necessary to increase the accelerator power and increase the bremsstrahlung dose to the source nuclides.

[0010] Actinium-225 is a radionuclide with a relatively short half-life. Radionuclides with short half-lives cannot be stockpiled until needed. Therefore, a radionuclide production system is required to have the production capacity to supply the required amount of radionuclides without delay in response to demand. In any of the methods (1) to (3), it is required to increase the production amount of the radionuclide to be produced while suppressing the production amount of impurity nuclides.

[0011] Patent Document 1 describes a neutron capture therapy system equipped with a beam shaper that shapes a neutron beam. The beam shaper is composed of a reflector that reflects neutrons, a moderator that reduces the energy of neutrons, a thermal neutron absorber that absorbs thermal neutrons, etc. The beam shaper is used to adjust the beam quality of the neutron beam generated by a neutron generator. [Prior art documents] [Patent documents]

[0012] [Patent Document 1] Patent Publication No. 2021-528213 Summary of the Invention [Problem to be solved by the invention]

[0013] When producing a target radionuclide by a nuclear reaction of a source nuclide, a source target holding the source material containing the source nuclide is irradiated with radiation such as a charged particle beam or bremsstrahlung radiation having an energy equal to or greater than the threshold for the nuclear reaction. For example, when an electron beam accelerated by an accelerator is irradiated onto a bremsstrahlung target made of a heavy metal, bremsstrahlung occurs as a primary reaction, and bremsstrahlung is emitted. When the source target is irradiated with bremsstrahlung radiation, the target radionuclide can be produced by the nuclear reaction of the source nuclide.

[0014] However, when the source target is irradiated with radiation to initiate a nuclear reaction, radiation such as charged particle beams and bremsstrahlung may also be incident on the material surrounding the source target. When high-energy radiation is incident on the material surrounding the source target, the surrounding material may undergo a nuclear reaction and emit neutrons. If the source target captures the neutrons emitted by the surrounding material, impurity nuclides may be generated in the source target.

[0015] For example, when a raw target containing radium-226 is irradiated with bremsstrahlung radiation to produce actinium-225, 226 Ra(n,X) 227 A neutron capture reaction represented by Ra occurs, and actinium-227 may be produced as an impurity nuclide by beta decay of radium-227. Materials surrounding the source target that produce impurity nuclides include materials that make up the shield that isolates the source target from the outside, the target for generating bremsstrahlung radiation, the support that supports the source target, and the cooling mechanism that removes heat from the source target. In addition, the source material itself and the source container that contains the source material can also emit unwanted neutrons.

[0016] When the impurity nuclide generated in the source target is an isotope of the target radionuclide to be produced, chemical separation of the nuclides becomes difficult. When the half-life of the impurity nuclide is longer than that of the target radionuclide, such as when actinium-227, with a half-life of approximately 21.8 years, is mixed with actinium-225, with a half-life of 9.9 days, there is a concern that unnecessary exposure of normal cells may occur during treatment. When producing radionuclides, unlike the system described in Patent Document 1, measures to prevent unintentional neutrons from entering the source target are desirable from the perspective of radiopharmaceutical safety.

[0017] Therefore, an object of the present invention is to provide a radionuclide production system that can produce a target radionuclide with high purity by suppressing the incidence of unnecessary neutrons on a raw material target when irradiating the raw material target with radiation to produce the target radionuclide through a nuclear reaction. [Means for solving the problem]

[0018] In order to solve the above problems, the radionuclide production system of the present invention is a radionuclide production system comprising: an accelerator that accelerates charged particles; and a raw material target that generates radionuclides through a nuclear reaction by irradiating the raw material target with a charged particle beam accelerated by the accelerator or with radiation generated by the charged particle beam, and a neutron absorbing material that absorbs neutrons generated by irradiating the raw material target with the charged particle beam or the radiation is provided between the raw material target and at least one of a shield that surrounds the raw material target and a radiation generation target that generates the radiation by irradiating the charged particle beam. [Effects of the Invention]

[0019] According to the present invention, it is possible to provide a radionuclide production system that can produce a target radionuclide with high purity by suppressing the incidence of unnecessary neutrons on the source target when irradiating the source target with radiation to produce the target radionuclide through a nuclear reaction. [Brief explanation of the drawings]

[0020] [Figure 1] 1 is a diagram illustrating an example of a radionuclide production system according to an embodiment of the present invention. [Figure 2] FIG. 1 is a diagram showing a configuration example of a main part of a radionuclide production system. [Figure 3] FIG. 1 is a diagram showing a configuration example of a main part of a radionuclide production system. [Figure 4] FIG. 1 is a diagram showing the relationship between the energy of incident neutrons and the absorption cross section of a neutron absorber. [Figure 5] FIG. 1 is a diagram showing an example of the arrangement of neutron absorbing materials in a radionuclide production system. [Figure 6] FIG. 1 is a diagram showing an example of the arrangement of neutron absorbing materials in a radionuclide production system. [Figure 7] FIG. 1 is a diagram showing an example of the arrangement of neutron absorbing materials in a radionuclide production system. [Figure 8] FIG. 1 is a diagram showing an example of the arrangement of neutron absorbing materials in a radionuclide production system. [Figure 9] FIG. 1 is a diagram showing an example of the arrangement of neutron absorbing materials in a radionuclide production system. [Figure 10] FIG. 1 is a diagram showing an example of the arrangement of neutron absorbing materials in a radionuclide production system. [Figure 11] FIG. 1 is a diagram showing an example of the arrangement of neutron absorbing materials in a radionuclide production system. DETAILED DESCRIPTION OF THE INVENTION

[0021] A radionuclide production system according to one embodiment of the present invention will be described below with reference to the drawings. In the following drawings, common components are designated by the same reference numerals, and duplicated explanations will be omitted. In this specification, when describing nuclear reactions, high-energy photon rays such as gamma rays and X-rays are represented by "X" regardless of their wavelength or generation mechanism.

[0022] Fig. 1 is a diagram showing an example of a radionuclide production system according to an embodiment of the present invention. Fig. 1 shows a radionuclide production system equipped with an accelerator. As shown in Fig. 1, the radionuclide production system A100 according to this embodiment includes an accelerator A101 that accelerates charged particles and an irradiation chamber T200 that irradiates a target with the accelerated charged particles.

[0023] The radionuclide production system A100 is an apparatus that irradiates a source target containing a source nuclide with radiation and transmutes the source nuclide through a nuclear reaction to produce a predetermined radionuclide. The radionuclide production system A100 is configured to irradiate the source target with bremsstrahlung radiation. A photonuclear reaction caused by irradiation with bremsstrahlung radiation is used as the nuclear reaction that transmutes the source nuclide. The bremsstrahlung radiation is generated by irradiating a bremsstrahlung generation target A103, which is a radiation generation target, with charged particles accelerated by an accelerator A101.

[0024] A source target T201 containing source nuclides is placed in the irradiation chamber T200. The source target T201 holds source material containing source nuclides. The accelerator A101 accelerates charged particles in an electric field and emits a high-energy charged particle beam R301. The charged particle beam R301 accelerated by the accelerator A101 passes through the inside of the beam pipe A102 and is irradiated onto a bremsstrahlung target A103 placed in the irradiation chamber T200.

[0025] The bremsstrahlung radiation generation target A103 generates bremsstrahlung radiation when the charged particle beam R301 is incident on it, generating bremsstrahlung radiation R302 equivalent to the energy lost by the charged particle beam R301 due to collisions, etc. The bremsstrahlung radiation R302 is irradiated onto the raw material target T201 containing the source nuclide. When the source nuclide is irradiated with bremsstrahlung radiation R302 having energy equal to or greater than the threshold for nuclear reaction, a predetermined nuclear reaction occurs and the source nuclide is nuclear-transformed into the target radioactive nuclide.

[0026] The accelerator A101 generates charged particles such as electrons, accelerates the charged particles to a predetermined energy band, and emits them toward the irradiation chamber T200. When a photonuclear reaction due to bremsstrahlung is used as the nuclear reaction for nuclear transmuting the source nuclide, an electron accelerator that accelerates electrons is used as the accelerator A101. The bremsstrahlung generation target A103 can generate bremsstrahlung by irradiating it with an electron beam accelerated by the accelerator A101. As the electron accelerator, it is preferable to use an electron linear accelerator that accelerates electrons in a linear electric field.

[0027] The accelerator A101 includes a charged particle source A111 that generates charged particles, an acceleration tube A114 that accelerates the charged particles to generate a focused charged particle beam R301, a vacuum pumping device A115 that evacuates the transport path of the charged particle beam R301, a focusing electromagnet system A116 that converges or diverges the charged particle beam R301, a bending electromagnet system A119 that deflects the charged particle beam R301, and a steering electromagnet system A122 that finely adjusts the irradiation position of the charged particle beam R301.

[0028] The charged particle source A111 can be composed of a three-electrode thermionic emission electron gun equipped with a cathode, an anode, and a control electrode, or an ion source that extracts ions from plasma generated in a high-frequency electric field. The charged particles generated by the charged particle source A111 are transported toward the acceleration tube A114. Appropriate types of charged particles can be used depending on the type of radioactive nuclide to be produced, the type of nuclear reaction to be used for nuclear transmutation, etc.

[0029] Solenoids A112 and A113 can be installed in the charged particle source A111 and the acceleration structure A114. In Fig. 1, the upstream solenoid A112 is installed on the exit side of the charged particle source A111. The downstream solenoid A113 is installed on the entrance side of the acceleration structure A114. The magnetic fields generated by the solenoids A112 and A113 can focus the charged particles generated by the charged particle source A111.

[0030] The accelerating structure A114 forms an electric field acting on the charged particles, accelerating the charged particles generated by the charged particle source A111. The accelerating structure A114 may accelerate the charged particles by applying a DC voltage or an AC voltage. The accelerating structure A114 may be a traveling wave type that matches the velocity of the charged particles with the velocity of the microwave inside, or a standing wave type that generates a standing wave inside.

[0031] The vacuum pumping device A115 is a device for evacuating the accelerating structure A114 and the transport path of the charged particle beam R301. The vacuum pumping device A115 suppresses diffusion and loss of the charged particle beam R301 in the transport path. In Fig. 1, the vacuum pumping device A115 is installed downstream of the accelerating structure A114, but any number of vacuum pumping devices A115 can be installed at any suitable location on the accelerating structure A114 or the transport path of the charged particle beam R301.

[0032] The focusing electromagnet system A116 is composed of electromagnets that focus the charged particle beam R301 accelerated by the accelerator A101 toward the central axis. The focusing electromagnet system A116 is formed by a combination of multiple quadrupole electromagnets A117 and A118. The quadrupole electromagnets A117 and A118 generate magnetic fields that cancel out beam position deviations in two axial directions perpendicular to the direction of travel of the charged particle beam R301. A quadrupole electromagnet that focuses the beam in a certain direction diverges the beam in a direction perpendicular to that direction. By arranging such quadrupole electromagnets with their polarities alternately reversed, the charged particle beam R301 can be focused in both directions.

[0033] The bending electromagnet system A119 is composed of electromagnets that deflect the trajectory of the charged particle beam R301. The bending electromagnet system A119 is formed by combining a plurality of bending electromagnets A120. It is preferable that the bending electromagnet system A119 is combined with a quadrupole electromagnet A121. The quadrupole electromagnet A121 can adjust the convergence or divergence of the deflected charged particle beam R301. The bending electromagnet system A119 does not need to be installed if it is not necessary to deflect the trajectory of the charged particle beam R301.

[0034] The steering electromagnet system A122 is composed of electromagnets that deflect the trajectory of the charged particle beam R301. The steering electromagnet system A122 is formed by a combination of multiple steering electromagnets A123 and A124. The steering electromagnets A123 and A124 are dipole electromagnets that generate a weak magnetic field in a direction perpendicular to the traveling direction of the charged particle beam R301, allowing for fine adjustment of the traveling direction of the charged particle beam R301. A quadrupole electromagnet may be combined with the steering electromagnet system A122. The quadrupole electromagnets allow for adjustment of the convergence or divergence of the deflected charged particle beam R301.

[0035] The irradiation chamber T200 is a space for irradiating a target with a charged particle beam R301 accelerated by an accelerator A101. In Fig. 1, the irradiation chamber T200 is equipped with a beam monitor A126, a bremsstrahlung target A103, a raw material target T201, and a beam dump T212. The irradiation chamber T200 is isolated from the outside by a shield T204 that forms the outer periphery of the space.

[0036] The shielding T204 shields against radiation such as the charged particle beam R301 and bremsstrahlung radiation R302, and prevents leakage of radiation from the inside to the outside of the irradiation chamber T200. The shielding T204 protects equipment outside the irradiation chamber T200, such as the accelerator A101, from the charged particle beam R301 accelerated by the accelerator A101, the bremsstrahlung radiation R302 emitted from the bremsstrahlung generation target A103, and secondary radiation emitted by activated materials.

[0037] The shielding body T204 is made of a material with high shielding ability against charged particle beams, X-rays, and neutron beams, such as iron, lead, antimony, bismuth, tungsten, aluminum, resins such as polyethylene, boron-containing polyethylene, polypropylene, and polypropylene carbonate, concrete, water, graphite, lead glass, and sintered iron oxide.

[0038] The beam monitor A126 is a device for measuring the profile of the charged particle beam R301. The beam monitor A126 measures the position of the beam axis of the charged particle beam R301, the shape of the charged particle beam R301, the intensity of the charged particle beam R301, etc. In Fig. 1, the beam monitor A126 is installed at the rear end of the transport path of the charged particle beam R301. However, any number of beam monitors A126 can be installed at any suitable location on the acceleration structure A114 or the transport path of the charged particle beam R301.

[0039] The beam monitor A126 can be a screen monitor, a beam current monitor, a beam position monitor, or the like. A screen monitor is a device that irradiates charged particles onto a fluorescent screen, photographs the fluorescent light distribution produced on the fluorescent screen with a CCD camera, or the like, and analyzes the position of the beam axis and the beam shape. A beam current monitor is a device that uses a current transformer to measure the current of the beam that has passed inside the magnetic core. A beam position monitor is a device that uses a button-type electrode or the like placed inside the beam pipe to determine the image charge when the beam passes, and measures the position of the beam axis, etc.

[0040] The bremsstrahlung target A103 is a target for generating bremsstrahlung radiation R302 to be irradiated onto the raw material target T201. The bremsstrahlung target A103 is installed behind the beam outlet in the traveling direction of the charged particle beam R301. The beam outlet is installed at the rear end of the transport path of the charged particle beam R301. When the bremsstrahlung target A103 is irradiated with the charged particle beam R301 accelerated by the accelerator A101, it causes bremsstrahlung and generates bremsstrahlung radiation R302.

[0041] The bremsstrahlung target A103 can be made of a heavy metal with a high atomic number, high density, and high heat resistance, such as gold (Au), mercury (Hg), platinum (Pt), tungsten (W), tantalum (Ta), lead (Pb), or bismuth (Bi).

[0042] The source target T201 is a target that produces predetermined radionuclides through a nuclear reaction caused by irradiation with radiation. The source target T201 is composed of a source material containing a source nuclide that undergoes a nuclear reaction when irradiated with radiation and is nuclear-transformed into a predetermined radionuclide, or of such a source material and a source container or source substrate that holds the source material. The source container may be a glass tube, a metal tube, a capsule, a dish, or the like. The source target T201 is placed behind the bremsstrahlung generation target A103 in the traveling direction of the charged particle beam R301.

[0043] When the source target T201 is irradiated with bremsstrahlung radiation R302, it generates a predetermined radionuclide in the source material. The radionuclide generated in the source material is recovered by chemical separation methods such as extraction chromatography or precipitation separation. The radionuclide finally produced may be the radionuclide generated in the source material by irradiation with radiation, or it may be a progeny nuclide generated by nuclear decay of that radionuclide.

[0044] The source material constituting the source target T201 may be in any suitable physical state or chemical form, including solids such as powder, powder aggregates, powder compacts, and bulk masses, liquids such as pure liquids, solutions, and suspensions, and semi-liquids, as well as gases.

[0045] The beam dump T212 is a device that receives radiation and attenuates its intensity. The beam dump T212 is installed behind the raw material target T201 in the traveling direction of the charged particle beam R301. The charged particle beam R301 and other particles that have passed through the raw material target T201 are incident on and absorbed by the beam dump T212. The beam dump T212 prevents radiation from leaking outside the irradiation chamber T200. It is preferable to install the beam dump T212 at least when the output of the accelerator A101 is large.

[0046] The beam dump T212 is made of a material with high shielding ability against radiation such as charged particle beams. The beam dump T212 is preferably made of a light element, since it is less likely to become activated. Examples of materials for the beam dump T212 include carbon (C), aluminum (Al), titanium (Ti), hydrogen (H), oxygen (O), nitrogen (N), and helium (He). The beam dump T212 can be made of simple elements such as these, compounds containing these elements, alloys containing these elements, or mixtures or composites of these simple elements, compounds, or alloys.

[0047] The raw material target T201 and the beam dump T212 may be equipped with a cooling mechanism to remove the heat load caused by the charged particle beam R301, etc. Examples of cooling mechanisms that can be used include a heat exchange mechanism that circulates a coolant through a coolant flow path to perform heat exchange, a conduction cooling mechanism that uses a heat sink or a refrigerator to perform cooling by thermal conduction, an air cooling mechanism that uses a cooling fan to perform forced air cooling, and an immersion cooling mechanism that cools the object to be cooled by immersing it in a coolant. Examples of coolants that can be used include water such as light water or heavy water, gases such as carbon dioxide or an inert gas, and fluid neutron absorbers.

[0048] In the radionuclide production system A100, a photonuclear reaction due to bremsstrahlung is used as the nuclear reaction for nuclear transmutation of the source nuclide, but other nuclear reactions such as a proton-neutron reaction can also be used as the nuclear reaction for nuclear transmutation of the source nuclide, depending on the type of radionuclide to be produced, etc. As the radiation to be irradiated onto the source target T201, a charged particle beam R301 accelerated by an accelerator A101 can also be used, depending on the type of radionuclide to be produced, the type of nuclear reaction used for nuclear transmutation, etc.

[0049] The source nuclide can be selected from a variety of sources depending on the type of radionuclide to be produced. Specific examples of source nuclides include radium-226 (Ra-226), molybdenum-100 (Mo-100), zinc-68 (Zn-68), germanium-70 (Ge-70), hafnium-178 (Hf-178), osmium-189 (Os-189), and palladium-106 (Pd-106). The source target T201 can be formed from simple elements of these elements, compounds containing these elements, pure metals or alloys containing these elements, or mixtures of these simple elements, compounds, or alloys.

[0050] As the nuclear reaction for nuclear transmuting the source nuclide, an appropriate nuclear reaction can be used depending on the type of radioactive nuclide to be produced, the type of source nuclide, the required energy, etc., such as photonuclear reactions caused by bremsstrahlung radiation (X,n), (X,p), (X,2n), (X,pn), etc., or nuclear reactions caused by charged particle beams such as protons or particle beams such as heavy particle beams.

[0051] In Fig. 1, the radionuclide production system A100 is configured to irradiate a raw material target T201 with bremsstrahlung radiation R302 and includes a bremsstrahlung generation target A103. However, if the raw material nuclide is irradiated with radiation other than bremsstrahlung, the bremsstrahlung generation target A103 need not be provided. Any radiation generation target that generates radiation by irradiation with a charged particle beam can be provided behind the beam outlet. The raw material target T201 can be a target that produces a predetermined radionuclide by a nuclear reaction caused by irradiation with radiation generated by the charged particle beam R301.

[0052] Alternatively, when a proton-neutron reaction or a spallation reaction caused by irradiation with a charged particle beam is used as the nuclear reaction for transmuting the source nuclides, it is not necessary to install a radiation generation target behind the beam outlet at the rear end of the transport path of the charged particle beam R301. The source target T201 can also be directly irradiated with the charged particle beam R301 extracted from the beam outlet. The source target T201 can be a target that generates a predetermined radioactive nuclide through a nuclear reaction caused by irradiation with the charged particle beam R301 accelerated by the accelerator A101.

[0053] In the radionuclide production system A100, a neutron absorber that absorbs neutrons is installed inside the irradiation chamber T200. The neutron absorber is provided to absorb neutrons generated by irradiation with the charged particle beam R301 or radiation generated by the charged particle beam R301 that are not required for producing radionuclides. The neutron absorber is provided between the raw material target T201 and at least one of the shielding T204 that surrounds the raw material target T201 and the radiation generation target that generates radiation by irradiation with the charged particle beam R301.

[0054] Fig. 2 is a diagram showing an example of the configuration of the main parts of a radionuclide production system according to an embodiment of the present invention. Fig. 2 shows the configuration around the raw material target T201 inside the irradiation chamber T200 of the radionuclide production system A100. As shown in Fig. 2, the neutron absorber T202 can be installed between the raw material target T201 and a shielding body T204 surrounding the raw material target T201.

[0055] The raw material target T201 is placed in the irradiation chamber T200 and is surrounded by a shield T204. The accelerator A101 accelerates charged particles in an electric field and emits a high-energy charged particle beam R301. The charged particle beam R301 accelerated by the accelerator A101 passes through the inside of the beam pipe A102 and is irradiated onto a bremsstrahlung target A103 placed in the irradiation chamber T200.

[0056] The bremsstrahlung radiation generation target A103 generates bremsstrahlung radiation when the charged particle beam R301 is incident on it, and emits bremsstrahlung radiation R302 equivalent to the energy lost by the charged particle beam R301 due to collisions, etc. The bremsstrahlung radiation R302 is irradiated onto the raw material target T201 containing the source nuclide. When the source nuclide is irradiated with bremsstrahlung radiation R302 having energy equal to or greater than the threshold for nuclear reaction, a predetermined nuclear reaction occurs and the source nuclide is nuclear-transformed into the target radioactive nuclide.

[0057] A part of the charged particle beam R301 and bremsstrahlung radiation R302 incident on the raw material target T201 may pass through the raw material target T201 and be incident on the material around the raw material target T201. After passing through the raw material target T201, the charged particle beam R301 and bremsstrahlung radiation R302 are gradually attenuated and diffused by collisions, scattering, absorption, etc., and are incident on the material around the raw material target T201.

[0058] When the charged particle beam R301 accelerated by the accelerator A101 or the bremsstrahlung radiation R302 emitted by the bremsstrahlung radiation generating target A103 is incident on the material surrounding the raw material target T201, it may undergo a neutron emission reaction, a photonuclear reaction, etc., thereby emitting a small amount of neutrons. In addition, when the charged particle beam R301 or the bremsstrahlung radiation R302 is incident on the raw material material itself constituting the raw material target T201, or the container or substrate holding the raw material, it may also undergo a neutron emission reaction, a photonuclear reaction, etc., thereby emitting a small amount of neutrons.

[0059] When such unintentionally generated neutrons are incident on the raw target T201, a neutron capture reaction represented by (n, X) occurs, which may result in the production of impurity nuclides in the raw target T201. The production of impurity nuclides in the raw target T201 poses a problem of reduced purity and quality of the target radioactive material being produced. If the impurity nuclides are isotopes of the target radioactive nuclide being produced, chemical separation of the nuclides is difficult. Therefore, measures to prevent unintentionally generated neutrons from being incident on the raw target T201 are desirable.

[0060] In the radionuclide production system A100, neutrons not required for the production of such radionuclides are absorbed by the neutron absorber T202 installed inside the irradiation chamber T200. The neutron absorber T202 is installed around the source target T201 between the neutron source and the source target T201. With this arrangement, unnecessary neutrons are absorbed before they enter the source target T201, suppressing the generation of impurity nuclides in the source target T201.

[0061] Neutron generating sources around the raw material target T201 include the shielding T204, the bremsstrahlung target A103, the beam dump T212, supports such as an arm or stand that supports the raw material target T201, structural materials and working fluids that form a cooling mechanism that removes heat from the raw material target T201, etc. Also, neutron generating sources include the raw material target T201 itself, the raw material material containing the raw material nuclide, a container that contains the raw material material, a substrate that supports the raw material material, etc.

[0062] The raw material target T201 can be provided with a small volume and mass, so the neutron generation source that generates neutrons not required for radionuclide production is dominated by the shielding body T204, the bremsstrahlung target A103, the beam dump T212, the support for the raw material target T201, and the cooling mechanism for removing heat from the raw material target T201, etc.

[0063] The amount of unwanted neutrons generated depends on the type of nuclide constituting the neutron source, the density of the material constituting the neutron source, the shape of the neutron source, etc. Therefore, the main neutron source in the radionuclide production system A100 differs depending on the configuration of the system. However, since the shielding body T204 and the bremsstrahlung generation target A103 are positioned so that the charged particle beam R301 and the bremsstrahlung radiation R302 can easily enter them, they serve as neutron sources in any configuration.

[0064] Therefore, it is preferable that the neutron absorber T202 be provided between the raw material target T201 and at least one of the shielding surrounding the raw material target T201 and the bremsstrahlung generation target A103, which generates bremsstrahlung radiation R302 by irradiation with a charged particle beam R301 accelerated by the accelerator A101.

[0065] The neutron absorber T202 is made of a material with a large neutron absorption cross section. The neutron absorber T202 can be made of a substance in an appropriate physical state or chemical form. The neutron absorber T202 may be in a solid form such as a powder, a powder aggregate, a powder compact, or a bulk mass, or in a liquid or semi-fluid form such as a pure substance liquid, solution, or suspension, or in a gaseous form. It is preferably made of a substance with a large neutron absorption cross section in the kinetic energy range of 5 to 500 meV.

[0066] Examples of materials for the neutron absorber T202 include boron (B), lithium (Li), beryllium (Be), cadmium (Cd), xenon (Xe), hafnium (Hf), samarium (Sm), gadolinium (Gd), etc. The neutron absorber T202 can be formed from simple elements of these elements, compounds containing these elements, alloys containing these elements, or mixtures or composites of these simple elements, compounds, or alloys.

[0067] Boron is a material commonly used as a neutron absorber. Boron has a mass number of 10, boron-10( 10 B) and boron-11 ( 11 B) There are two stable isotopes of boron. 10 B(n,α) 7 It undergoes a neutron capture reaction represented by Li, and exhibits a neutron absorption cross section of approximately 3800 barns for thermal neutrons.

[0068] Lithium is a material that is commonly used as a neutron absorber by vitrifying it or by compounding it with polyethylene. Lithium contains lithium 6( 6 Li) and lithium 7( 7 There are two stable isotopes of lithium: 6 Li(n,α) 3 It undergoes a neutron capture reaction represented by H and exhibits a neutron absorption cross section of approximately 940 barns for thermal neutrons.

[0069] Beryllium, cadmium, xenon, hafnium, samarium, and gadolinium undergo neutron capture reactions represented by (n,X) and have high neutron shielding capabilities. In particular, cadmium exhibits a neutron absorption cross section of approximately 3,000 barns for thermal neutrons. Gadolinium exhibits a neutron absorption cross section of approximately 42,000 barns for thermal neutrons.

[0070] The neutron absorber T202 is chemically stable, flexible, highly processable, and resistant to dissipation due to volatilization, and is preferably used in a form that ensures high strength when used in structural materials. For example, the neutron absorber T202 can be installed by being supported on a structural material, by being mixed into a structural material or fluid, or by being housed in a container or housing. The fluid can be water, such as light water or heavy water, or oil, such as paraffinic oil, naphthenic oil, or aromatic oil.

[0071] In Figure 2, the neutron absorber T202 is installed so as to surround the raw material target T201 from the rear, sides, and front in the direction of travel of the charged particle beam R301, and is installed between the raw material target T201 and the shielding T204 behind the raw material target T201, between the raw material target T201 and the shielding T204 to the side of the raw material target T201, and between the bremsstrahlung generation target A103 in front of the raw material target T201 and the raw material target T201.

[0072] With this arrangement, neutrons R303 emitted from the neutron generation sources around the raw material target T201 can be prevented from entering the raw material target T201 in all directions. Even if neutrons R303 are emitted from the shielding T204 behind the raw material target T201, which is the main neutron generation source, or from the shielding T204 in its vicinity, or from the bremsstrahlung generation target A103, the neutrons R303 scattered by scattering can be reliably prevented from entering the raw material target T201.

[0073] However, the neutron absorber T202 can be installed at any location between the neutron generation source around the raw material target T201 and the raw material target T201. The neutron absorber T202 can be installed between the raw material target T201 and at least one of the shielding T204 surrounding the raw material target T201 and the bremsstrahlung target A103. The neutron absorber T202 may be installed only between the raw material target T201 and the shielding T204 behind the raw material target T201 in the traveling direction of the charged particle beam R301, or only between the shielding T204 on the side of the raw material target T201 and the raw material target T201, or only between the bremsstrahlung target A103 and the raw material target T201, or at multiple locations among these.

[0074] According to this radionuclide production system A100, the neutron absorber T202 is provided between the source material surrounding the source target T201 and the source target T201, thereby preventing unwanted neutrons emitted by the neutron source surrounding the source target T201 from being incident on the source target T201. The source nuclides contained in the source target T201 are prevented from undergoing unintended nuclear reactions and being transmuted into unwanted impurity nuclides. This reduces the amount of impurity nuclides produced in the source target T201, allowing for the production of highly pure target radionuclides. Furthermore, the separation and purification process for separating the target radionuclides from the impurity nuclides is reduced, thereby reducing the cost of separation and purification and the amount of radioactive waste generated during the separation and purification process. Furthermore, because the source nuclides are less likely to be consumed by unintended nuclear reactions, the production of the target radionuclides can be increased.

[0075] Fig. 3 is a diagram showing an example of the configuration of the main parts of a radionuclide production system according to an embodiment of the present invention. Fig. 3 shows the configuration around the raw material target T201 inside the irradiation chamber T200 of the radionuclide production system A100. As shown in Fig. 3, a neutron absorber T202 and a neutron moderator T203 for moderating neutrons can be installed between the neutron generation source around the raw material target T201 and the raw material target T201.

[0076] The neutrons emitted from the neutron generating source around the raw material target T201 by the incidence of the charged particle beam R301 or bremsstrahlung radiation R302 are high-energy neutrons, such as fast neutrons with a kinetic energy of 500 keV or more. High-energy neutrons are difficult to shield by absorption reactions. The neutron absorber T202 alone may not be able to sufficiently prevent unwanted neutrons from entering the raw material target T201.

[0077] In contrast, if a neutron moderator T203 is installed together with the neutron absorber T202, high-energy neutrons such as fast neutrons can be slowed down to low-energy neutrons such as thermal neutrons. The neutron moderator T203 is installed between the neutron generation source around the raw material target T201 and the raw material target T201. By slowing down the neutrons emitted by the neutron generation source around the raw material target T201, the efficiency of neutron absorption by the neutron absorber T202 is improved.

[0078] The neutron moderator T203 is made of a material with a large neutron scattering cross section. The neutron moderator T203 can be made of a substance in an appropriate physical state or chemical form. The neutron moderator T203 may be in a solid form such as a powder, a powder aggregate, a powder compact, or a bulk mass, or in a liquid or semi-fluid form such as a pure substance liquid, solution, or suspension, or in a gaseous form. The neutron moderator T203 is preferably made of a substance with a large neutron scattering cross section and a small neutron absorption cross section. Such a substance has a large moderation ratio and can efficiently moderate high-energy neutrons.

[0079] The neutron moderator T203 can be made from materials such as polyolefins such as polyethylene and polypropylene, polymethacrylates, unsaturated polyesters, esters such as dibutyl phthalate, beryllium oxide, lithium hydroxide, lithium fluoride, magnesium fluoride, calcium fluoride, light water, heavy water, concrete, paraffin, metal hydrides, graphite, aluminum, iron, hydrogen, helium, beryllium, compounds containing these elements, alloys containing these elements, and mixtures and composites of these simple substances, compounds, or alloys.

[0080] As a material for the neutron moderator T203, a substance containing hydrogen is preferable because it has a large microscopic neutron scattering cross section and a large moderation ratio. A substance with a high density is also preferable. This is because the macroscopic neutron scattering cross section is affected not only by the microscopic neutron scattering cross section but also by the atomic number density. The higher the density of a substance, the more easily neutrons are scattered and moderated. Examples of such substances include polyethylene, dibutyl phthalate, light water, heavy water, and metal hydrides.

[0081] As the material for the neutron moderator T203, high density polyethylene and metal hydrides are particularly preferred because of their high hydrogen atom number density. High density polyethylene has a density of 0.942 g / cm 3 More than 0.970g / cm 3 The following polyethylene: Metal hydrides include lithium hydride, lithium borohydride, magnesium hydride, magnesium borohydride, titanium hydride, zirconium hydride, and the like.

[0082] In Figure 3, the neutron absorber T202 is installed so as to surround the raw material target T201 from the rear, sides, and front in the direction of travel of the charged particle beam R301, and is installed between the raw material target T201 and the shielding T204 behind the raw material target T201, between the raw material target T201 and the shielding T204 to the side of the raw material target T201, and between the bremsstrahlung generation target A103 in front of the raw material target T201 and the raw material target T201.

[0083] The neutron moderator T203 is installed so as to surround the neutron absorber T202 from the rear, sides, and front in the direction of travel of the charged particle beam R301, and is installed between the shielding T204 behind the raw material target T201 and the neutron absorber T202 behind the raw material target T201, between the shielding T204 on the sides of the raw material target T201 and the neutron absorber T202 on the sides of the raw material target T201, and between the bremsstrahlung generation target A103 in front of the raw material target T201 and the neutron absorber T202 in front of the raw material target T201.

[0084] With this arrangement, it is possible to decelerate in all directions the neutrons R303 emitted from the neutron generation sources around the raw material target T201. Even if the shielding T204 behind the raw material target T201, which is the main neutron generation source, the shielding T204 in its vicinity, or the bremsstrahlung generation target A103 emits neutrons R303, the neutrons R303 are decelerated and then absorbed, so that it is possible to more reliably prevent the scattered neutrons R303 from entering the raw material target T201.

[0085] However, the neutron moderator T203 can be installed at any position between the neutron generation source around the raw material target T201 and the raw material target T201. The neutron moderator T203 can be installed between the raw material target T201 and at least one of the shielding T204 surrounding the raw material target T201 and the bremsstrahlung target A103. The neutron moderator T203 is preferably installed between the neutron absorber T202 and at least one of the shielding T204 surrounding the raw material target T201 and the bremsstrahlung target A103. The neutron moderator T203 may be installed only between the raw material target T201 and the shielding T204 behind the raw material target T201 in the direction of travel of the charged particle beam R301, or only between the raw material target T201 and the shielding T204 on the side of the raw material target T201, or only between the bremsstrahlung generation target A103 in front of the raw material target T201 and the raw material target T201, or may be installed in multiple of these locations.

[0086] The neutron absorber T202 and the neutron moderator T203 may be stacked on top of each other or spaced apart from each other. The neutron absorber T202 and the neutron moderator T203 may be stacked in single layers or alternately stacked in multiple layers. Stacking the neutron absorber T202 and the neutron moderator T203 alternately can improve neutron shielding performance in a limited space.

[0087] Figure 4 shows the relationship between the energy of neutrons incident on a neutron absorber and their absorption cross section. In Figure 4, the horizontal axis represents the energy [eV] of neutrons incident on the neutron absorber, and the vertical axis represents the neutron absorption cross section [b] of the neutron absorber. The dotted line is the absorption curve for the (n,X) reaction of radium-226. The solid line is the absorption curve for the (n,2n) reaction of radium-226. The dashed line is the absorption curve for the (n,α) reaction of boron-10.

[0088] Materials exhibit a relatively large cross section for neutron capture reactions with thermal neutrons. As shown in Figure 4, boron-10 exhibits a relatively large absorption cross section in the thermal neutron kinetic energy range of 5 to 500 meV. On the other hand, the higher the neutron kinetic energy, the smaller the neutron absorption cross section. High-energy neutrons emitted by materials surrounding the raw material target T201 may not be sufficiently shielded by the neutron absorber T202 alone.

[0089] In such a case, it is preferable that the neutrons R303 emitted from the material around the raw material target T201 are moderated by the neutron moderator T203 to a range of kinetic energies that can be absorbed by the neutron absorber T202. It is preferable that the neutron moderator T203 moderates the kinetic energy of the neutrons R303 emitted from the neutron generating source around the raw material target T201 to an upper limit value of the range of kinetic energies of the neutrons R303 at which the neutron absorber T202 shows a maximum value of the neutron absorption cross section.

[0090] The range of kinetic energies of neutrons R303 to be shielded in the radionuclide production system A100, i.e., the range of kinetic energies of neutrons R303 shielded by the combination of the neutron absorber T202 and the neutron moderator T203, is preferably 0.5 meV or more and 1 MeV or less. When the shielding target is 1 MeV or less, as shown in FIG. 4, the (n, 2n) reaction of radium-226 can be utilized while suppressing the (n, X) reaction of radium-226. Therefore, the generation of impurity nuclides can be suppressed while the by-produced neutrons can be utilized for the production of radionuclides. Furthermore, when the shielding target is 0.5 meV or more, shielding can be performed using a general neutron absorber that absorbs thermal neutrons.

[0091] Fig. 5 is a diagram showing an example of the arrangement of neutron absorbers in a radionuclide production system according to an embodiment of the present invention. Fig. 5 shows the configuration around the raw material target T201 inside the irradiation chamber T200 of the radionuclide production system A100. As shown in Fig. 5, the neutron absorber T202 can be installed between the raw material target T201 and the shielding T204 behind the raw material target T201, or between the shielding T204 on the side of the raw material target T201 and the raw material target T201, so as to be spaced apart from the raw material target T201 and close to the shielding T204.

[0092] In Figure 2, the neutron absorber T202 is installed so as to surround the raw material target T201 from the rear, sides, and front in the traveling direction of the charged particle beam R301. The raw material target T201 is surrounded on all sides by the neutron absorber T202. With this arrangement, the following problems (1) to (4) may occur depending on the type of radionuclide to be produced and the type of neutron absorber T202.

[0093] (1) The neutron absorber T202 acts as a moderator for the neutrons R303 emitted by the neutron generation source around the raw material target T201. Because the neutrons R303 are slowed down, the number of thermal neutrons incident on the raw material target T201 increases. When the number of thermal neutrons increases, impurity nuclides are more likely to be generated by (n,X) reactions, etc.

[0094] (2) The neutron absorber T202 acts as a shield against the bremsstrahlung radiation R302 emitted by the bremsstrahlung radiation generating target A103. Since the bremsstrahlung radiation R302 incident on the raw material target T201 is attenuated, the amount of radioactive nuclides produced by the raw material target T201 is reduced.

[0095] (3) The neutron absorber T202 is deteriorated by the thermal load caused by the incidence of the charged particle beam R301 and the bremsstrahlung radiation R302.

[0096] (4) The neutron absorber T202 absorbs useful neutrons emitted by the bremsstrahlung target A103. The fast neutrons emitted by the bremsstrahlung target A103 due to self-shielding can be used to produce radioactive nuclides. For example, 226 Ra(n,2n) 225 The neutron absorption reaction, denoted Ra, can be used to produce actinium-225 via beta decay from radium-225. When such neutrons are absorbed, the production of radionuclides by the feedstock target T201 is reduced.

[0097] From the viewpoint of countermeasures against the problems (1) to (4), it is preferable that the neutron absorber T202 is provided outside the irradiation field of the charged particle beam R301 and the bremsstrahlung radiation R302, and it is preferable that it is provided in front of the raw material target T201 in the direction of travel of the charged particle beam R301, and not between the beam outlet of the charged particle beam R301 and the raw material target T201.

[0098] Specifically, it is preferable that the neutron absorber T202 be provided outside the imaginary contact surface (dashed line shown in FIG. 5) between the bremsstrahlung target A103 and the raw material target T201, where the shielding T204 is located. It is also preferable that the neutron absorber T202 not be provided inside the imaginary contact surface (dashed line shown in FIG. 5) between the bremsstrahlung target A103 and the raw material target T201, where the raw material target T201 is located.

[0099] Similarly, it is preferable that the neutron moderator T203 be provided outside the imaginary contact surface (dashed line shown in FIG. 5) between the bremsstrahlung target A103 and the raw material target T201, where the shielding T204 is located. It is also preferable that the neutron moderator T203 not be provided inside the imaginary contact surface (dashed line shown in FIG. 5) between the bremsstrahlung target A103 and the raw material target T201, where the raw material target T201 is located.

[0100] As shown in Figure 4, 226 Ra(n,2n) 225 The neutron absorption reaction, represented by Ra, has a threshold at approximately 10 MeV. The raw material target T201 containing radium-226 is converted into radium-225 by this neutron absorption reaction only when neutrons with energies above the threshold are incident, and actinium-225 is produced by beta decay. On the other hand, the (n,X) reaction that produces impurity nuclides becomes less likely to occur as the kinetic energy of the neutrons increases. Therefore, it is preferable that the neutron moderator T203 be provided outside the irradiation field of the charged particle beam R301, and not provided in front of the raw material target T201 in the direction of travel of the charged particle beam R301.

[0101] Ordinary neutron absorbers mainly absorb thermal neutrons. The main source of thermal neutrons is often the shielding T204 behind the raw material target T201 in the direction of travel of the charged particle beam R301. This is because the charged particle beam R301 accelerated by the accelerator A101 and the bremsstrahlung radiation R302 generated by the bremsstrahlung generation target A103 penetrate the raw material target T201 and enter the shielding T204 behind the raw material target T201.

[0102] Therefore, since the shielding T204 behind the raw material target T201 is the main neutron generation source, it is preferable that the neutron absorber T202 and the neutron moderator T203 are installed at least between the raw material target T201 and the shielding T204 behind the raw material target T201 in the traveling direction of the charged particle beam R301. Furthermore, since the shielding T204 on the sides of the raw material target T201 also tends to emit neutrons, it is more preferable that they be installed between the raw material target T201 and the shielding T204 on the sides and behind the raw material target T201.

[0103] 5, the neutron absorber T202 is installed so as to surround the raw material target T201 from the rear and sides in the traveling direction of the charged particle beam R301, and is installed between the raw material target T201 and the shielding T204 behind the raw material target T201, and between the raw material target T201 and the shielding T204 on the side of the raw material target T201. The neutron absorber T202 is not installed between the bremsstrahlung generation target A103 in front of the raw material target T201 and the raw material target T201.

[0104] With this arrangement, it is possible to absorb neutrons R303 emitted from the shielding T204 behind the raw material target T201, which is the main neutron generation source, and from the surrounding shielding T204, while opening the irradiation field of the charged particle beam R301 and bremsstrahlung radiation R302 to the raw material target T201. This makes it possible to reduce attenuation of bremsstrahlung radiation R302 incident on the raw material target T201, heat load on the neutron absorber T202 due to the incidence of the charged particle beam R301 and bremsstrahlung radiation R302, and absorption of useful neutrons emitted by the bremsstrahlung generation target A103.

[0105] In Fig. 5, the neutron absorber T202 is installed close to the shielding T204 and away from the raw material target T201. This arrangement allows the raw material target T201 to be easily installed and retrieved. It also prevents the raw material target T201 and the neutron absorber T202 from being subjected to a concentrated heat load from the charged particle beam R301 or the like. However, the neutron absorber T202 can also be installed integrally with the shielding T204 or the beam dump T212.

[0106] Fig. 6 is a diagram showing an example of the arrangement of neutron absorbers in a radionuclide production system according to an embodiment of the present invention. Fig. 6 shows the configuration around the source target T201 inside the irradiation chamber T200 of the radionuclide production system A100. As shown in Fig. 6, the source target T201 can be formed by a source material T251 and a source container T252 that contains the source material T251. The neutron absorber T202 can be supported by the source container T252.

[0107] The source material T251 is a material containing a source nuclide that is transmuted into a predetermined radionuclide by a nuclear reaction. The source material T251 can be in any physical state or chemical form. The source material T251 can be solid, liquid, semi-liquid, or gaseous. The source material T251 can be a simple substance of the source nuclide element, a compound containing the source nuclide element, an alloy containing the source nuclide element, or a mixture of these simple substances, compounds, or alloys.

[0108] The source container T252 is a container that contains the source material T251 and is used for handling the source material T251 and for holding the source material T251 relative to the beam axis. The source container T252 may be a sealed container that holds the source material T251 in a sealed state, or an open container that holds the source material T251 in an open state. When the source material T251 is gaseous or when the source material T251 emits gaseous radioactive material, it is preferable to use a sealed container.

[0109] The source container T252 can be formed from metals such as aluminum, aluminum alloys, stainless steel, low-alloy steel, nickel alloys, and zirconium alloys; ceramics such as silicon carbide; glass such as quartz glass; or resins such as epoxy resins, polyimides, polyetherimides, polyetherketones, polysulfones, and polyethersulfones.

[0110] 6, the neutron absorber T202 is supported so as to cover the surface of the source container T252. The neutron absorber T202 is installed so as to surround the source target T201 from the rear and sides in the traveling direction of the charged particle beam R301, and is installed between the source target T201 and the shielding T204 behind the source target T201, and between the source target T201 and the shielding T204 to the side of the source target T201. The neutron absorber T202 is not installed between the bremsstrahlung generation target A103 and the source target T201.

[0111] With this arrangement, it is possible to absorb neutrons R303 emitted from the shielding T204 behind the raw material target T201, which is the main neutron generation source, and from the surrounding shielding T204, while opening the irradiation field of the charged particle beam R301 and bremsstrahlung radiation R302 to the raw material target T201. This makes it possible to reduce attenuation of bremsstrahlung radiation R302 incident on the raw material target T201, heat load on the neutron absorber T202 due to the incidence of the charged particle beam R301 and bremsstrahlung radiation R302, and absorption of useful neutrons emitted by the bremsstrahlung generation target A103.

[0112] 6, the neutron absorber T202 is installed integrally with the source container T252, separated from the source target T201. With this arrangement, even when the neutron absorber T202 is installed, the source target T201 can be easily installed and retrieved. In addition, it is possible to avoid concentration of heat load on the source target T201 and the neutron absorber T202 due to the charged particle beam R301, etc.

[0113] The neutron absorber T202 can be supported on the source container T252 by coating the surface with powder of the neutron absorber T202 or by fixing bulk of the neutron absorber T202 to the surface. Coating methods include thermal spraying, painting, and atomization. Fixing methods include joining with connecting parts such as screws, and bonding with an adhesive.

[0114] For example, if a powder mixture of boron oxide or boron carbide powder and metallic aluminum powder is sprayed onto the surface of the source container T252, the boron or aluminum can be immobilized on the surface of the source container T252 while increasing the thermal conductivity of the neutron absorber T202, enabling efficient heat removal. Also, if a paint containing powder such as gadolinium oxide and a binder is prepared and then applied to the surface of the source container T252 and dried, gadolinium and other substances can be immobilized.

[0115] The neutron absorber T202 can be supported on the source container T252 by using the neutron absorber T202 as the material of the source container T252 or by blending the neutron absorber T202 into the material of the source container T252. Examples of blending the neutron absorber T202 into the material include dispersing a powder of a single substance or a powder of a compound, or adding the neutron absorber T202 as an additive element to a metal or ceramic.

[0116] For example, boron-blended borosilicate glass, boron carbide, hafnium, etc. can be used as the material for the source container T252. Also, a composite material in which the neutron absorber T202 is dispersed can be formed by mixing boron oxide, boron carbide, cadmium oxide, cadmium chloride, hafnium, hafnium hydride, hafnium oxide, samarium oxide, gadolinium, gadolinium oxide, etc. with the metal, ceramics, or resin that is the material for the source container T252.

[0117] The source container T252 supporting the neutron absorber T202 is preferably equipped with a cooling mechanism for removing the heat load caused by the charged particle beam R301, etc. Furthermore, the neutron absorber T202 is preferably made of a material with high heat resistance or high thermal conductivity. This is because if the neutron absorber T202 is integrally supported by the source container T252, the heat load caused by the charged particle beam R301, etc. on the source container T252 and the neutron absorber T202 will be greater than if the neutron absorber T202 is separated from the source container T252.

[0118] 6, the neutron absorber T202 is integrally supported by the source container T252, but the neutron absorber T202 may be blended into the source material T251. Methods for blending the neutron absorber T202 into the source material T251 include dispersing a powder of a single element or a powder of a compound, or adding the neutron absorber T202 as an additive element to a metal or ceramic.

[0119] In the configuration in which the neutron absorber T202 is supported on the source container T252 or in which the neutron absorber T202 is blended with the source material T251, the neutron absorber T202 is disposed close to the source material T251, so that the neutrons R303 incident on the source material T251 can be suppressed with a minimum amount of neutron absorber T202. This reduces the amount of radioactive waste generated by the activation of the neutron absorber T202 and the installation costs of the neutron absorber T202. In addition, because the neutron absorber T202 is disposed so as to cover the source material T251, it is possible to more reliably suppress the neutrons R303 emitted by the neutron generating source around the source target T201 from reaching the source target T201.

[0120] FIG. 7 is a diagram showing an example of the arrangement of neutron absorbers in a radionuclide production system according to an embodiment of the present invention. FIG. 7 shows the configuration around the source target T201 inside the irradiation chamber T200 of the radionuclide production system A100. As shown in FIG. 7, the source target T201 can be formed by a source material T251 and a source container T252 that contains the source material T251. The source target T201 can be contained in a source cover T205. The neutron absorber T202 can be supported by the source cover T205.

[0121] The source cover T205 is a container that houses the source target T201 and is used to prevent radioactive materials from scattering in the event of damage to the source container T252. The source cover T205 is a sealed container that keeps the source target T201 sealed. The source target T201 is supported inside the source cover T205 so that it is positioned in the irradiation field of the bremsstrahlung radiation R302. The source cover T205 is used as a contamination prevention measure, for example, when the source nuclides or the radioactive nuclides being produced have high dose rates. Alternatively, it is used to prevent gas leakage when gaseous radioactive materials are generated.

[0122] From the viewpoint of reducing the heat load due to the charged particle beam R301 etc., the source cover T205 is preferably provided with a structure in which the container wall is thinner than that of the source container T252. The source cover T205 can be formed from metals such as aluminum, aluminum alloy, stainless steel, low-alloy steel, nickel alloy, zirconium alloy, etc., or ceramics such as silicon carbide, etc. From the viewpoint of avoiding activation by the charged particle beam R301 or bremsstrahlung radiation R302, the source cover T205 is preferably made of light elements or low-density materials.

[0123] The source cover T205 is preferably provided with a cooling mechanism to remove the heat load caused by the charged particle beam R301 etc. This is because if the source target T201 is housed in the source cover T205, the heat load on the source material T251 and the source container T252 caused by the charged particle beam R301 etc. will be large.

[0124] The cooling mechanism may be a heat exchange mechanism that circulates a coolant inside the material cover T205 to perform heat exchange, a conduction cooling mechanism that cools the material cover T205 and the material target T201 by thermal conduction, an air cooling mechanism that cools the material cover T205 by forced air cooling, an immersion cooling mechanism that cools the material cover T205 by immersing it in a coolant, etc. The coolant may be water such as light water or heavy water, oil such as paraffinic oil, naphthenic oil, or aromatic oil, gas such as carbon dioxide or an inert gas, or a fluid neutron absorber T202 or neutron moderator T203.

[0125] The neutron absorber T202 can be supported on the raw material cover T205 by coating the surface with powder of the neutron absorber T202 or by fixing bulk of the neutron absorber T202 to the surface. Coating methods include thermal spraying, painting, and atomization. Fixing methods include joining with connecting parts such as screws, and bonding with an adhesive.

[0126] In addition, methods for supporting the neutron absorber T202 on the source cover T205 include using the neutron absorber T202 as the material for the source cover T205, or blending the neutron absorber T202 into the material for the source cover T205. Methods for blending the neutron absorber T202 into the material include mixing a powder of a single substance or a powder of a compound, and adding the neutron absorber T202 as an additive element to metals or ceramics.

[0127] In the configuration in which the neutron absorber T202 is supported by the source cover T205, it is possible to avoid concentration of heat load on the neutron absorber T202, etc., due to the charged particle beam R301, etc., compared to a configuration in which the neutron absorber T202 is integrated into the source container T252. Furthermore, compared to a configuration in which the neutron absorber T202 is installed away from the source target T201, it is possible to suppress neutrons incident on the source material T251 with fewer neutron absorbers T202. Therefore, it is possible to reduce the amount of radioactive waste generated by activation of the neutron absorber T202 and the installation costs of the neutron absorbers T202.

[0128] Fig. 8 is a diagram showing an example of the arrangement of neutron absorbers in a radionuclide production system according to an embodiment of the present invention. Fig. 8 shows the configuration around the raw material target T201 inside the irradiation chamber T200 of the radionuclide production system A100. As shown in Fig. 8, the neutron absorber T202 can be combined with a neutron moderator T203 to form a composite material T206. The composite material T206 can be installed around the raw material target T201 between the neutron generation source and the raw material target T201.

[0129] The composite material T206 can be formed by blending the neutron absorber T202 with the neutron moderator T203, which serves as a matrix, or by blending the neutron absorber T202 and the neutron moderator T203 with another matrix. The neutron absorber T202 and the neutron moderator T203 blended with another matrix can be in powder or particulate form. It is preferable that the neutron absorber T202 be uniformly dispersed with a high degree of dispersion in the matrix.

[0130] A specific example of the composite material T206 is boron-doped high-density polyethylene. Boron-doped high-density polyethylene is produced by adding boron oxide, boron carbide, borate, or the like to high-density polyethylene. The amount of boron added to boron-doped high-density polyethylene is usually 1% by mass or more and 20% by mass or less. The shielding ability of boron-doped high-density polyethylene is adjusted by the amount of boron added.

[0131] For example, the composite material T206 can be a material obtained by compounding a neutron absorbing material T202 such as boron, boron oxide, boron carbide, borate, or lithium fluoride with a base material made of a resin material such as polyethylene or polypropylene, which is a neutron moderator T203. Alternatively, a material can be used in which a neutron absorbing material T202 such as gadolinium oxide and a neutron moderator T203 such as beryllium oxide are compounded with a base material made of a resin material such as silicone rubber or acrylic resin.

[0132] As the neutron absorber T202 forming the composite T206, boron or a boron-containing compound such as boron oxide, boron carbide, or borate is particularly preferred. As the neutron moderator T203 forming the composite T206, polyethylene is preferred, and high-density polyethylene is particularly preferred. Boron-containing polyethylene has high neutron shielding performance, is lightweight, and is highly processable, so it can be appropriately placed around the raw material target T201 or on the surface of structural materials inside the irradiation chamber T200.

[0133] 8, the composite material T206 is installed behind the raw material target T201 in the traveling direction of the charged particle beam R301, and is installed between the raw material target T201 and a shielding T204 behind the raw material target T201. It is preferable that the composite material T206 is installed at least between the raw material target T201 and the shielding T204 behind the raw material target T201, which is the main neutron generation source.

[0134] However, the composite material T206 can be installed at any position between the neutron generation source around the feedstock target T201 and the feedstock target T201. The composite material T206 can be installed between the feedstock target T201 and at least one of the shielding T204 surrounding the feedstock target T201 and the bremsstrahlung target A103. The composite material T206 may be installed only between the feedstock target T201 and the shielding T204 behind the feedstock target T201 in the traveling direction of the charged particle beam R301, only between the shielding T204 on the side of the feedstock target T201 and the feedstock target T201, only between the bremsstrahlung target A103 in front of the feedstock target T201 and the feedstock target T201, or at multiple positions among these.

[0135] By installing the neutron absorber T202 as the composite material T206, the shielding ability against neutrons incident on the raw material target T201 can be adjusted by adjusting the amount of neutron absorber T202 mixed into the composite material T206. Therefore, by adjusting the amount of neutron absorber T202 mixed depending on the output of the accelerator A101 and the position of the composite material T206, the installation cost of the neutron absorber T202 can be reduced. In addition, by adjusting the mixing ratio of neutron absorber T202 and neutron moderator T203 to the base material, shielding properties that shield neutrons in a specified energy range can be obtained. The amounts of neutron absorber T202 and neutron moderator T203 used can be reduced depending on the energy of neutrons R303 emitted by neutron generation sources around the raw material target T201.

[0136] Fig. 9 is a diagram showing an example of the arrangement of neutron absorbers in a radionuclide production system according to an embodiment of the present invention. Fig. 9 shows the configuration around the source target T201 inside the irradiation chamber T200 of the radionuclide production system A100. As shown in Fig. 9, the source target T201 can be housed in a source cover T207. Inside the source cover T207, a coolant T211 can be circulated between the source cover T207 and the coolant container T210. The neutron absorber T202 can be contained in the coolant T211.

[0137] The source cover T207 is provided as a sealed container that is liquid-tight. Inside the source cover T207, a source target T201 is supported so as to be positioned in the irradiation field of the bremsstrahlung radiation R302, and a coolant T211 is circulated and maintained. The source cover T207 is connected to a coolant vessel T210 via a coolant pipe T208. The inside of the source cover T207 communicates with the inside of the coolant vessel T210 via the coolant pipe T208.

[0138] A circulation pump T209 is connected to the coolant pipe T208. A magnetic pump, a diaphragm pump, or the like is preferably used as the circulation pump T209. These pumps are designed to not require sealing materials, which can prevent leakage of activated coolant T211 caused by radiation deterioration of the sealing materials.

[0139] The coolant container T210 is a container that temporarily stores the coolant T211. The coolant container T210 is provided with a capacity that allows the coolant T211 to circulate at a constant flow rate. The coolant container T210 may be installed inside the irradiation chamber T200, but is preferably installed outside the irradiation chamber T200. When the coolant container T210 is installed outside the irradiation chamber T200, the heat load and activation of the coolant T211 due to the charged particle beam R301, etc. can be minimized.

[0140] The coolant vessel T210 may be equipped with a cooler for forcibly cooling the coolant T211. The cooler may be a plate-type heat exchanger such as a brazed plate type, an immersion coil type heat exchanger, or an air-cooling cooling fan.

[0141] A coolant T211 for cooling the raw material target T201 is sealed in a circulation system consisting of the raw material cover T207, the coolant container T210, etc. The raw material cover T207, the coolant piping T208, the circulation pump T209, and the coolant container T210 constitute a cooling mechanism that removes heat from the raw material target T201 by heat exchange with the coolant T211, which is a working fluid. The coolant T211, which is a working fluid, contains a neutron absorber T202.

[0142] The coolant T211 is circulated between the material cover T207 and the coolant container T210 by a circulation pump T209. The material target T201 housed in the material cover T207 is immersed in the coolant T211. The coolant T211, which has received heat from the material target T201, is sent to the coolant container T210 through the coolant piping T208 and dissipates heat. The coolant T211 is circulated at a flow rate that is sufficient to remove heat from the material target T201.

[0143] The raw material cover T207, the coolant piping T208, the circulation pump T209, and the coolant container T210 are preferably made of materials with high chemical stability. This is because if these elements in contact with the coolant T211 are exposed to radicals and active oxygen species generated by the charged particle beam R301 and bremsstrahlung radiation R302 and oxidatively deteriorate, there is a risk of causing leakage of the activated coolant T211. Examples of materials with high chemical stability include SUS316 and SUS316L.

[0144] The coolant T211 can be either liquid or gas, as long as it removes the heat load on the raw material target T201 caused by the charged particle beam R301 or the like and circulates the neutron absorber T202 around the raw material target T201. The coolant T211 may be made of a material with a large neutron scattering cross section that functions as the neutron moderator T203. The coolant T211 can be water such as light water or heavy water, oil such as paraffinic oil, naphthenic oil, or aromatic oil, air, dry nitrogen, or a rare gas.

[0145] The neutron absorber T202 can be incorporated into the coolant T211 by dispersing a powder of the neutron absorber T202 element or a powder of a compound in the coolant T211, or by dissolving the neutron absorber T202 in the coolant T211. For example, the coolant T211 can be a boron-containing compound such as boron oxide or boron carbide, or light water to which boric acid has been added. The concentration of the neutron absorber T202 per coolant T211 can be adjusted to any desired concentration depending on the dose of neutrons R303 emitted by the neutron generation source around the raw target T201.

[0146] 9, the neutron absorber T202 is used by being contained in the coolant T211, but the neutron absorber T202 can also be used as the coolant T211 itself. For example, xenon can be circulated as the coolant T211 in the circulation system formed by the raw material cover T207, the coolant container T210, etc.

[0147] In the case where the neutron absorber T202 is contained in the coolant T211 or where the neutron absorber T202 is used as the coolant T211 itself, the coolant T211 can remove the heat load on the raw material target T201 caused by the charged particle beam R301, etc., while the neutron absorber T202 circulating around the raw material target T201 can prevent neutrons R303 emitted by the neutron generating source from entering the raw material target T201.

[0148] Fig. 10 is a diagram showing an example of the arrangement of neutron absorbers in a radionuclide production system according to an embodiment of the present invention. Fig. 10 shows the configuration around the raw material target T201 inside the irradiation chamber T200 of the radionuclide production system A100. As shown in Fig. 10, a forced cooling dump T213 can be installed behind the raw material target T201 in the traveling direction of the charged particle beam R301. The forced cooling dump T213 can circulate the absorber T217 between itself and the absorber container T216. The neutron absorber T202 can be supported by the forced cooling dump T213.

[0149] The forced cooling dump T213 is a device that receives radiation and attenuates its intensity, and is used to forcibly cool the heat load caused by radiation. The forced cooling dump T213 is installed behind the raw material target T201 in the direction of travel of the charged particle beam R301. The charged particle beam R301, bremsstrahlung radiation R302, etc. that have passed through the raw material target T201 are incident on and absorbed by the forced cooling dump T213. The forced cooling dump T213 prevents the charged particle beam R301, bremsstrahlung radiation R302, etc. from leaking outside the irradiation chamber T200.

[0150] The forced cooling dump T213 is provided as a sealed container that is liquid-tight. An absorbent T217 is circulated and held inside the forced cooling dump T213. An absorbent container T216 is connected to the forced cooling dump T213 via an absorbent piping T214. The inside of the forced cooling dump T213 communicates with the inside of the absorbent container T216 via the conduit of the absorbent piping T214.

[0151] A circulation pump T215 is connected to the absorber pipe T214. A magnetic pump, a diaphragm pump, or the like is preferably used as the circulation pump T215. These pumps are designed to not require a sealant, which can prevent leakage of activated absorber T217 caused by radiation deterioration of the sealant.

[0152] The absorbent container T216 is a container that temporarily stores the absorbent T217. The absorbent container T216 is provided with a capacity that allows the absorbent T217 to circulate at a constant flow rate. The absorbent container T216 may be installed inside the irradiation chamber T200, but is preferably installed outside the irradiation chamber T200. When the absorbent container T216 is installed outside the irradiation chamber T200, the thermal load and activation of the absorbent T217 due to the charged particle beam R301, etc. can be minimized.

[0153] The absorbent container T216 may be equipped with a cooler for forcibly cooling the absorbent T217. As the cooler, a plate-type heat exchanger such as a brazed plate type, an immersion coil-type heat exchanger, or an air-cooling cooling fan can be used.

[0154] The radiation absorbing material T217 is sealed in the circulation system consisting of the forced cooling dump T213 and the absorber container T216. The forced cooling dump T213, the absorber piping T214, the circulation pump T215, and the absorber container T216 constitute a cooling mechanism attached to the beam dump that removes heat from the forced cooling dump T213 by circulating the absorber T217, which is the working fluid.

[0155] The absorbent T217 is circulated between the forced cooling dump T213 and the absorbent container T216 by a circulation pump T215. The charged particle beam R301 and the like that have passed through the raw material target T201 are absorbed by the absorbent T217 stored in the forced cooling dump T213. The absorbent T217 that has been heated by the incidence of the charged particle beam R301 and the like is sent to the absorbent container T216 through the absorbent piping T214 and dissipates heat. The absorbent T217 is circulated at a flow rate that allows the forced cooling dump T213 to sufficiently remove heat.

[0156] The forced cooling dump T213, the absorber piping T214, the circulation pump T215, and the absorber container T216 are preferably made of a material with high chemical stability. This is because if these elements in contact with the absorber T217 are exposed to radicals or active oxygen species generated by the charged particle beam R301 or bremsstrahlung radiation R302 and oxidatively deteriorate, there is a risk of leakage of the activated absorber T217. Examples of materials with high chemical stability include SUS316 and SUS316L.

[0157] The absorber T217 can be either liquid or gas, as long as it can absorb the charged particle beam R301 and the like that have passed through the raw material target T201 and can remove the heat load on the forced cooling dump T213 caused by the charged particle beam R301 and the like. The absorber T217 may be made of a material with a large neutron scattering cross section that functions as the neutron moderator T203. The absorber T217 can be water such as light water or heavy water, oil such as paraffinic oil, naphthenic oil, or aromatic oil, or liquid metal.

[0158] The neutron absorber T202 is preferably disposed at least between the forced cooling dump T213 behind the raw material target T201 and the raw material target T201, since the forced cooling dump T213 behind the raw material target T201 is the main neutron generation source. In addition to being disposed between the forced cooling dump T213 and the raw material target T201, the neutron absorber T202 may also be disposed at any position between the neutron generation source around the raw material target T201 and the raw material target T201.

[0159] In Fig. 10, the neutron absorber T202 is supported on the front surface of the forced cooling dump T213. Methods for supporting the neutron absorber T202 on the forced cooling dump T213 include coating the surface with powder of the neutron absorber T202 or fixing bulk of the neutron absorber T202 to the surface. Coating methods include thermal spraying, painting, and atomization. Fixing methods include joining with connecting parts such as screws, and bonding with an adhesive.

[0160] 10, the neutron absorber T202 is supported on the front surface of the forced cooling dump T213, but the neutron absorber T202 may be contained in the absorber T217 of the forced cooling dump T213, or may be used as the absorber T217 itself of the forced cooling dump T213. Methods for containing the neutron absorber T202 in the absorber T217 include dispersing a powder of the neutron absorber T202 simple substance or a powder of a compound in the absorber T217, dissolving the neutron absorber T202 in the absorber T217, and the like.

[0161] In the configurations in which the neutron absorber T202 is supported on the forced cooling dump T213, the configuration in which the neutron absorber T202 is contained in the absorber T217, and the configuration in which the neutron absorber T202 is used as the absorber T217 itself, the absorber T217 absorbs and attenuates the charged particle beam R301 and the like that has passed through the raw material target T201, and also removes the heat load on the forced cooling dump T213 due to the charged particle beam R301 and the like, while the neutron absorber T202 can prevent neutrons R303 emitted by the neutron generating source behind the raw material target T201 from entering the raw material target T201. Since it is possible to increase the intensity of the charged particle beam R301 and the bremsstrahlung R302, the amount of radioactive nuclides produced can be increased.

[0162] FIG. 11 is a diagram showing an example of the arrangement of neutron absorbers in a radionuclide production system according to an embodiment of the present invention. FIG. 11 shows the configuration around the raw material target T201 inside the irradiation chamber T200 of the radionuclide production system A100. As shown in FIG. 11, a beam dump T218 can be installed behind the raw material target T201 in the traveling direction of the charged particle beam R301. The bremsstrahlung generation target A103 can also be provided with a forced cooler T219. The forced cooler T219 can circulate a coolant T223 between the coolant container T222 and the coolant T223. The neutron absorber T202 can be supported by the beam dump T218 or the forced cooler T219.

[0163] The beam dump T218 is a device that receives radiation and attenuates its intensity. The beam dump T218 is installed behind the raw material target T201 in the direction of travel of the charged particle beam R301. The charged particle beam R301, bremsstrahlung radiation R302, etc. that have passed through the raw material target T201 are incident on and absorbed by the beam dump T218. The beam dump T218 prevents the charged particle beam R301, bremsstrahlung radiation R302, etc. from leaking outside the irradiation chamber T200.

[0164] The forced cooler T219 is a device that removes the heat load on the bremsstrahlung generation target A103 caused by the charged particle beam R301, etc., by forced cooling. The forced cooler T219 exchanges heat between the bremsstrahlung generation target A103 and the coolant T223, thereby cooling the bremsstrahlung generation target A103 that has been heated by the incidence of the charged particle beam R301, etc.

[0165] The forced cooler T219 can be provided with a cooling space for accommodating and immersing the bremsstrahlung target A103 to cool it, and a cooling channel for passing a coolant T223 so as to come into contact with the bremsstrahlung target A103. The forced cooler T219 is connected to a coolant vessel T222 via a coolant pipe T220. The cooling space and cooling channel of the forced cooler T219 communicate with the interior of the coolant vessel T222 via the conduit of the coolant pipe T220.

[0166] A circulation pump T221 is connected to the coolant pipe T220. As the circulation pump T221, it is preferable to use a magnet pump, a diaphragm pump, or the like. These pumps are designed to not require a seal, so that leakage of activated coolant T223 caused by radiation deterioration of the seal can be avoided.

[0167] The coolant container T222 is a container that temporarily stores the coolant T223. The coolant container T222 has a capacity that allows the coolant T223 to circulate at a constant flow rate. The coolant container T222 may be installed inside the irradiation chamber T200, but is preferably installed outside the irradiation chamber T200. When the coolant container T222 is installed outside the irradiation chamber T200, the thermal load and activation of the coolant T223 due to the charged particle beam R301, etc. can be minimized.

[0168] The coolant vessel T222 may be equipped with a cooler for forcibly cooling the coolant T223. The cooler may be a plate-type heat exchanger such as a brazed plate type, an immersion coil type heat exchanger, or an air-cooling cooling fan.

[0169] A coolant T223 for cooling the bremsstrahlung target A103 is sealed in a circulation system consisting of the forced cooler T219, the coolant container T222, etc. The forced cooler T219, the coolant piping T220, the circulation pump T221, and the coolant container T222 constitute a cooling mechanism that removes heat from the bremsstrahlung target A103 by heat exchange with the coolant T223, which is the working fluid.

[0170] The coolant T223 is circulated between the forced cooler T219 and the coolant container T222 by the circulation pump T221. The bremsstrahlung target A103 is cooled by immersion in the coolant T223 in the cooling space or by the coolant T223 flowing through the cooling channel. The coolant T223 that has received heat from the bremsstrahlung target A103 is sent to the coolant container T222 through the coolant piping T220 and dissipates heat. The coolant T223 is circulated at a flow rate that is sufficient to remove heat from the bremsstrahlung target A103.

[0171] The forced cooler T219, coolant piping T220, circulation pump T221, and coolant container T222 are preferably made of materials with high chemical stability. This is because if these elements in contact with the coolant T223 are exposed to radicals and active oxygen species generated by the charged particle beam R301 and bremsstrahlung radiation R302 and oxidatively deteriorate, there is a risk of causing leakage of activated coolant T223. Examples of materials with high chemical stability include SUS316 and SUS316L.

[0172] The coolant T223 can be either liquid or gas as long as it can remove the heat load of the bremsstrahlung generation target A103 caused by the charged particle beam R301 or the like. The coolant T223 may be made of a material with a large neutron scattering cross section that functions as the neutron moderator T203. The coolant T223 can be water such as light water or heavy water, oil such as paraffinic oil, naphthenic oil, or aromatic oil, air, dry nitrogen, or a rare gas.

[0173] The neutron absorber T202 is preferably disposed at least between the beam dump T218 behind the feedstock target T201 and the feedstock target T201, since the beam dump T218 behind the feedstock target T201 is the neutron generation source. The neutron absorber T202 is preferably disposed at least between the bremsstrahlung target A103 and the feedstock target T201, since the bremsstrahlung target A103 is the neutron generation source. The neutron absorber T202 may be disposed at any position between the neutron generation source around the feedstock target T201 and the feedstock target T201, in addition to between the beam dump T218 and the feedstock target T201 or between the bremsstrahlung target A103 and the feedstock target T201.

[0174] In Fig. 11, the neutron absorber T202 is supported on the front surface of the beam dump T218 and the rear surface of the forced cooler T219. Methods for supporting the neutron absorber T202 on the beam dump T218 or the forced cooler T219 include coating the surface with powder of the neutron absorber T202 or fixing bulk of the neutron absorber T202 to the surface. Coating methods include thermal spraying, painting, and atomization. Fixing methods include joining with connecting parts such as screws, and bonding with an adhesive.

[0175] 11, the neutron absorber T202 is supported on the rear surface of the forced cooler T219, but the neutron absorber T202 may be contained in the coolant T223 of the forced cooler T219, or may be used as the coolant T223 itself of the forced cooler T219. Methods for containing the neutron absorber T202 in the coolant T223 include dispersing a powder of the neutron absorber T202 simple substance or a powder of a compound in the coolant T223, dissolving the neutron absorber T202 in the coolant T223, and the like.

[0176] For example, the coolant T223 can be a boron-containing compound such as boron oxide or boron carbide, or light water with boric acid added. The concentration of the neutron absorber T202 per coolant T223 can be adjusted to any concentration depending on the dose of neutrons R303 emitted by the bremsstrahlung target A103. Xenon can also be circulated as the coolant T223 in the circulation system consisting of the forced cooler T219, coolant vessel T222, etc.

[0177] According to the configuration in which the neutron absorber T202 is supported by the forced cooler T219, the configuration in which the neutron absorber T202 is contained in the coolant T223, or the configuration in which the neutron absorber T202 is used as the coolant T223 itself, it is possible to remove the heat load of the bremsstrahlung target A103 due to the charged particle beam R301 etc., while preventing the neutron absorber T202 from causing the neutrons R303 emitted from the bremsstrahlung target A103 to impinge on the raw material target T201. Since the heat load of the bremsstrahlung target A103 is reduced, it is possible to reduce melting and damage to the bremsstrahlung target A103.

[0178] Although the embodiments of the present invention have been described above, the present invention is not limited to the above-described embodiments, and various modifications are possible within the scope of the present invention. For example, the present invention is not necessarily limited to those having all of the configurations of the above-described embodiments. It is possible to replace part of the configuration of an embodiment with another configuration, add part of the configuration of an embodiment to another form, or omit part of the configuration of an embodiment.

[0179] For example, the structures shown in Figures 2, 3, 6, 7, and 9 can be combined with the structures shown in Figures 5, 8, and 10. Furthermore, the structures shown in Figures 2, 3, and 5 to 10 can be combined with the structure shown in Figure 11. [Explanation of symbols]

[0180] A100 Radionuclide Production System A101 accelerator A102 Beam Pipe A103 Bremsstrahlung target A111 Charged particle source A112 solenoid A113 Solenoid A114 Accelerator tube A115 Vacuum Exhaust Device A116 Converging electromagnet system A117 Quadrupole electromagnet A118 Quadrupole electromagnet A119 Bending electromagnet system A120 Bending electromagnet A121 Quadrupole electromagnet A122 Steering electromagnet system A123 Steering electromagnet A124 Steering electromagnet A126 Beam Monitor R301 Charged Particle Beam R302 Bremsstrahlung radiation R303 Neutron T200 irradiation chamber T201 Raw material target T202 Neutron Absorber T203 neutron moderator T204 Shield T205 Raw Material Cover T206 Composite T207 Raw Material Cover T208 Coolant piping T209 Circulation Pump T210 coolant container T211 coolant T212 beam dump T213 Forced Cooling Dump T214 Absorbent piping T215 Circulation Pump T216 Absorbent container T217 Absorbent T218 beam dump T219 Forced cooler T220 Coolant Piping T221 Circulation Pump T222 coolant container T223 Coolant T251 Raw materials T252 Raw material container

Claims

1. A radionuclide production system comprising: an accelerator for accelerating charged particles; and a raw material target for producing radionuclides by a nuclear reaction caused by irradiation with a charged particle beam accelerated by the accelerator or radiation generated by the charged particle beam, wherein a neutron absorbing material that absorbs neutrons generated by irradiation with the charged particle beam or the radiation is provided between the raw material target and at least one of a shield surrounding the raw material target and a radiation generation target that generates the radiation by irradiation with the charged particle beam.

2. 2. The radionuclide production system of claim 1, A radionuclide production system comprising a neutron moderator that slows down the neutrons, between the raw material target and at least one of a shield surrounding the raw material target and a radiation generation target that generates the radiation by irradiation with the charged particle beam.

3. 2. The radionuclide production system of claim 1, A radioactive nuclide production system in which the neutron absorbing material is provided outside the shielding body from an imaginary contact surface between the radiation generating target and the raw material target, and is not provided inside the imaginary contact surface where the raw material target is located.

4. 2. The radionuclide production system of claim 1, A radionuclide production system in which the neutron absorber is formed from a material selected from the group consisting of boron, lithium, beryllium, cadmium, xenon, hafnium, samarium, gadolinium, compounds containing these, alloys containing these, or combinations of these elements alone, compounds containing these, or alloys containing these.

5. 2. The radionuclide production system of claim 1, A radionuclide production system in which the raw material target is formed from a material selected from the group consisting of radium-226, molybdenum-100, zinc-68, germanium-70, hafnium-178, osmium-189, palladium-106, compounds containing these, alloys containing these, or simple substances thereof, or compounds containing these, or alloys containing these.

6. 3. The radionuclide production system of claim 2, A radionuclide production system wherein the neutron moderator is made of polyethylene, polypropylene, dibutyl phthalate, graphite, aluminum, iron, hydrogen, helium, beryllium, beryllium oxide, lithium hydroxide, lithium fluoride, magnesium fluoride, calcium fluoride, light water, heavy water, concrete, paraffin, metal hydride, or a combination thereof.

7. 3. The radionuclide production system of claim 2, A radionuclide production system in which the kinetic energy of neutrons shielded by the neutron absorber and the neutron moderator is 0.5 meV or more and 1 MeV or less.

8. 3. The radionuclide production system of claim 2, A radionuclide production system in which the neutron absorbing materials and the neutron moderating materials are stacked alternately in multiple layers.

9. 3. The radionuclide production system of claim 2, The neutron absorbing material is blended with the neutron moderating material, the neutron absorbing material is boron or a compound containing boron, A radionuclide production system wherein the neutron moderator is polyethylene.

10. 2. The radionuclide production system of claim 1, the source material target is a source material containing a source nuclide that undergoes a nuclear reaction when irradiated with the radiation, or the source material and a source container containing the source material; A radionuclide production system wherein the neutron absorbing material is supported by the source vessel or incorporated into the source material.

11. 2. The radionuclide production system of claim 1, a cooling mechanism for removing heat from the raw material target by heat exchange with a working fluid; A radionuclide production system, wherein the neutron absorbing material is contained in the working fluid.

12. 12. The radionuclide production system of claim 11, A radionuclide production system, wherein the neutron absorbing material is a compound containing boron or boric acid.

13. 3. The radionuclide production system of claim 2, A radionuclide production system in which the neutron moderator is provided outside the imaginary contact surface between the radiation generating target and the raw material target, where the shielding is located, and is not provided inside the imaginary contact surface where the raw material target is located.

14. 2. The radionuclide production system of claim 1, a beam dump for attenuating the charged particle beam that has passed through the raw material target is provided behind the raw material target in the traveling direction of the charged particle beam; A radionuclide production system comprising the neutron absorbing material on the surface of or inside the beam dump.

15. 2. The radionuclide production system of claim 1, the accelerator is an electron accelerator that accelerates electrons, A radionuclide production system comprising a bremsstrahlung target for generating bremsstrahlung radiation by irradiation with an electron beam accelerated by the accelerator.

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