JP2013054889A - Compound type target, neutron generation method using compound type target, and neutron generator using compound type target - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a compound type target which reduces the radioactivation of members which is caused by protons, a neutron generation method which uses the compound type target, and a neutron generator which uses the compound type target.SOLUTION: A compound type target 8 has a target 3, having a form of a composite body formed by overlapping a beryllium material ( or lithium material) 1 with a crystal orientation carbon material 2, and a cooling mechanism 6, having refrigerant passages 5 on a side surface of the target 3 and in the target 3, as ancillary components. As the refrigerant passages 5, not only liquid refrigerant passages but also gas refrigerant passages may be provided. A vacuum seal 4 for sealing a surface of the crystal orientation carbon material 2 positioned at the atmosphere side is provided in the target 3.

Description

  The present invention relates to a target for generating neutrons by causing protons to collide with the target. More specifically, the present invention provides a new target for generating neutrons using low-energy protons, for solving the thermal problem of the target, and for reducing activation of target members by protons and neutrons. It provides a target.

In recent years, research and development of a neutron generation method and apparatus for boron neutron capture therapy (BNCT), which is expected as a selective cancer treatment, have been actively conducted. These are disclosed in Patent Documents 1 to 12, for example.

Patent Document 1 discloses that a deuteron beam of 30 MeV to 40 MeV, for example, of a radio frequency quadrupole linear accelerator (RFQ linac) collides with lithium to cause Li (d, n) reaction to generate neutrons. It is characterized by generating thermal and epithermal neutrons for treatment via a neutron moderator.

  Patent Document 2 relates to a target for generating neutrons, and Nb, Pt, Au, Al, Be, Cr, which are low hydrogen absorbers, in order to improve the corrosion resistance of the target to which a high-intensity proton beam collides. It is characterized by using tungsten coated with stainless steel or its alloy.

  Patent Document 3 discloses that neutrons are generated by inducing a non-thermofusion reaction by colliding a deuterium ion beam against the surface of an alloy with liquid lithium or a metal having a catalytic action for a fusion reaction. It is characterized by.

In Patent Document 4, neutrons containing spallation reactants are generated by colliding a proton beam generated by a cyclotron or the like with a heavy metal such as tantalum or tungsten with a proton beam having an energy of 20 MeV or more. It is characterized by generating therapeutic thermal neutrons and epithermal neutrons by removing harmful spallation reactants and fast neutrons through a configured filter.

Patent Document 5 discloses a method and apparatus for generating neutrons by a fixed field alternating gradient (FFAG) -Emittance Recovery Internal Target (ERIT) method. Patent Document 5 is generated by colliding a proton beam or deuteron beam having an energy of 11 MeV or more and less than 15 MeV, which is circulated and enhanced by a cyclone type proton storage ring, with a beryllium target provided in the ring. The neutrons are adjusted to therapeutic thermal neutrons and epithermal neutrons through a moderator such as heavy water.

  Patent Document 6 discloses a target for generating a neutron by colliding a proton beam accelerated by an RFQ linac or a drift tube linac with an output of about 30 kW and about 11 MeV or more against a metal target. It is also disclosed that the target is a metal target, preferably beryllium. Patent Document 6 discloses that the thickness of the target is approximately equal to or slightly larger than the range of the proton beam in the target, and is equal to or more than the heat transfer area of the target to cool the target. It cools through the metal plate which has the heat-transfer area of.

Patent Document 7 uses a linear accelerator to generate, for example, an 11 MeV proton beam against a beryllium target to generate fast neutrons of 10 keV or more and pass the fast neutrons through a moderator such as heavy water to less than 10 keV. It is characterized by adjusting to an epithermal neutron of 0.5 eV or less.

  Patent Document 8 is characterized in that the method of manufacturing a lithium target is a method of pressing a rolled lithium thin film onto a copper substrate.

  Patent Document 9 describes a lithium target for generating a neutron by colliding a proton with energy slightly higher than a threshold value of Li (p, n) reaction (about 2 MeV) on the target. This structure is characterized in that a block having a cooling mechanism is formed with a conical cut, and a beryllium-covered lithium thin film attached on a backing foil substrate is attached to the conical cut surface.

  Patent Document 10 describes a lithium target for generating neutrons, in which lithium particles have a structure of lithium particles for preventing lithium particles from melting and preventing leakage of lithium liquefied by heat generation. The lithium particles are made of sintered carbon, silicon carbide, zirconium carbide. It is characterized by a structure that is sequentially covered in order.

  Patent Document 11 is characterized in that a lithium target for BNCT is a lithium target deposited on an iron substrate, a tantalum substrate, or a vanadium substrate.

Patent Document 12 describes a lithium target for generating a neutron by colliding a proton having an output of 20 mA-50 kW and an energy of about 2.5 MeV with the target. The structure of the target for preventing melting of lithium has a cooling mechanism. It has a structure in which a palladium thin film is provided on the surface of a conical heat transfer plate having a lithium thin film attached on the palladium thin film.

However, the methods and apparatuses disclosed in Patent Documents 1 to 7 require high-energy proton beams in which the acceleration energy of the proton beam or deuteron beam colliding with the target is at least 11 MeV. Therefore, in the methods and apparatuses disclosed in Patent Documents 1 to 7, a large accelerator for generating proton beams or deuteron beams is necessary, and significant activation of a member such as a target by high energy proton beams is performed. In order to prevent the target from fusing, the large cooling device for cooling the target is necessary, the handling is not easy in the case of a liquid target, and the target is blown out in the case of a solid target. If a thick target material is attached to a thermally conductive metal support, and if the target material for neutron generation is made of a metal such as heavy metal, it is extremely harmful to the human body and the activation ability of the device members High-speed neutrons are generated in a considerable mixture, which means that a large-scale decelerator is needed to decelerate the primary neutrons. In practice, special safety management systems for absorbing or removing protons, neutrons, and nuclear reaction by-products are necessary, and measures to prevent embrittlement of target materials by active hydrogen, which is a reaction by-product, etc. There was a problem. In particular, the problem of activation by a member such as a target using proton beams and neutrons is a problem of radiation exposure received from the activation member, and is an important problem to be solved. In addition, as seen in Patent Document 6, when a beryllium solid target is used, heat removal from the heat generated by the target is essential, so the heat transfer area of the metal support material for supporting the target However, it has been difficult to prevent the peeling of the adhesive interface due to thermal stress and the embrittlement and peeling of the support material due to active hydrogen. Further, in the case of the solid target made of lithium disclosed in the above Patent Documents 8 to 12, in order to prevent the melting of lithium having a low melting point (melting point: about 180 ° C.), the transmission as a support for the lithium thin film There are proposals on the structure of the hot plate and methods for coating lithium particles with a high melting point material, but since these methods are not expected to dramatically improve cooling efficiency, it is difficult to prevent melting of lithium. It is believed that there is. In order to solve the above problems, the development of a target for solving the thermal problem of the target caused by the collision of protons and reducing the activation of the member such as the target by protons and neutrons has been desired. Until now, there is no known target that can solve the above problem. Therefore, the inventors previously filed Japanese Patent Application No. 2010-264724, Japanese Patent Application No. 2011-048187, and Japanese Patent Application No. 2011-113950, and were able to solve the problems described above. Proposed. Since the composite target is a composite target made of a beryllium material (or lithium material) and a non-metallic material, a nuclear reaction caused by collision with a proton can be shared by the two kinds of materials. In addition, the composite target can reduce activation by protons and neutrons due to the unique physical properties of protons and neutrons of the beryllium material (or lithium material) and non-metallic materials that constitute the target, Low-energy neutron absorption with reduced high-speed neutrons, low-energy neutron decelerating function of non-metallic materials suppresses the generation of fast neutrons, easy removal of heat generated by the target, Since a non-metallic material can function as a support and coolant for a beryllium material (or lithium material), beryllium (or lithium) can be used even if beryllium (or lithium) is thinner than the beryllium (or lithium) conventionally used as a target. It has remarkable effects such as prevention of cutting and melting of lithium)

JP-A-11-169470 JP 2000-162399 A JP 2003-130997 A JP 2006-47115 A JP 2006-155906 A JP 2006-196353 A JP 2008-22920 A JP 2007-303983 A JP 2009-047432 A US Pat. No. 4,597,936 International Publication No. 08/060663 US Patent Application 2010/0067640

M. A. Lone, et.al., Nucl. Instr. Meth. 143 (1977) 331. Title: Neutron characteristics of coupled liquid hydrogen cold neutron source, authors: Yoshiaki Onagi, Hideki Kobayashi, Hirokatsu Iwasa, Bulletin of the Faculty of Engineering, Hokkaido University, 151: 101-109 (1990-07-30) Radiation facility screening calculation manual, 2007, supervised by Nuclear Safety Technology Center K. Shibata, O. Iwamoto, T. Nakagawa, N. Iwamoto, A. Ichihara, S. Kunieda, S. Chiba, K. Furutaka, N. Otuka, T. Ohsawa, T. Murata, H. Matsunobu, A. Zukeran, S. Kamada, and J. Katakura, “JENDL-4.0: A New Library for Nuclear Science and Engineering”, J. Nucl. Sci. Technol. 48 (2011) 1-30.

  In view of the above circumstances, an object of the present invention is to provide a novel target for generating neutrons using low-energy protons. More specifically, neutrons can be generated by irradiation with low-energy protons, activation of members such as targets by protons and neutrons can be reduced, and thermal problems of target materials and problems of hydrogen embrittlement can be solved. The object is to provide a new neutron generation target that can be fundamentally solved.

  As a result of intensive studies to achieve the above object, the present inventors have used a crystal-oriented carbon material as a non-metallic material that constitutes the composite target previously proposed by the present inventors and the like. By making a composite of beryllium material (or thium material) and the above-mentioned crystal orientation carbon material, it is possible to reduce the activation of components by protons and neutrons, and to reduce harmful and high activation neutrons. In addition, it has been found that the thermal problem of the target material and the problem of hydrogen embrittlement can be fundamentally solved more effectively than the effects of the invention previously proposed by the present inventors, The present invention has been completed based on this finding.

That is, the present invention
1. A composite target in which a target for generating a neutron by colliding with a proton is a composite formed by superimposing a crystal orientation carbon material and one of a beryllium material and a lithium material.
2. 2. The composite type target according to 1 above, wherein the composite type target attaches a vacuum seal to a surface of the composite type target.
3. 2. The composite type target according to 1 above, wherein the composite type target attaches a vacuum seal to a surface of the composite type target, and attaches a cooling mechanism having a coolant channel to the composite type target.
4). In the neutron generation method for generating neutrons by colliding protons with the target,
Proton is a proton of 2 MeV or more and less than 11 MeV,
The target is the composite target of 3 above,
A method of generating neutrons, wherein neutrons are generated by a nuclear reaction by causing the proton to collide with the composite type target under vacuum and the target is cooled by a cooling mechanism of the composite type target.
5. A hydrogen ion generator for proton generation;
An accelerator for accelerating protons generated in the hydrogen ion generator,
A proton irradiation unit for irradiating protons accelerated by an accelerator;
A target for generating protons and generating neutrons,
The accelerator is a linear accelerator;
The neutron generator according to claim 3, wherein the target is the above-mentioned composite target. 6). 6. The neutron generator according to 5 above, wherein the linear accelerator is a linear accelerator capable of accelerating protons in a range of 2 MeV to less than 11 MeV.

One aspect of the present invention is a composite target in which the target is a composite formed by superimposing a beryllium material (or lithium material) and a crystal orientation carbon material, and one of the targets is a vacuum seal attached. One is a composite target in which the composite target is attached with a vacuum seal and a cooling mechanism, and one is the composite type in which the vacuum seal and the cooling mechanism are attached as a neutron generation source. A neutron generation method using a target, and the other is a neutron generation apparatus using the above-mentioned composite target with a vacuum seal and a cooling mechanism as a neutron generation source. The functions of the composite target of the present invention are “reduction of activation of members by protons and neutrons” and “effective cooling of the target” in addition to “neutron generation by nuclear reaction” as main functions. Since the present invention is a composite target composed of the two types of materials described above, the function of the target can be divided between the two types of materials. In other words, low energy neutrons can be generated using low energy protons due to the unique properties of beryllium materials (or lithium materials), and protons possessed by crystal orientation carbon materials and the unique properties of neutrons. The heat generated by the target can be quickly conducted along the orientation plane due to the high thermal conductivity and thermal diffusivity of the crystal orientation carbon material, which can significantly reduce the activation of the target and other members by neutrons. Furthermore, since a plurality of the composites can be laminated so that both materials are alternately overlapped, the thermal load of the target can be dispersed in each composite. That is, since the heat transfer area can be dramatically improved by increasing the number of layers of the composite, it is possible to more efficiently conduct heat generated in the target along the orientation plane more quickly. The target can be efficiently cooled by exhausting the transferred heat out of the system by a cooling mechanism attached to the target. This efficient cooling can also be used with low melting point lithium (melting point: about 180 ° C.), which has been difficult to use as a solid target in the past, can prevent hydrogen embrittlement of the target material, beryllium material ( Or lithium material) and the crystal orientation carbon material can be prevented from being peeled off at the bonding interface, and the crystal orientation carbon material can function as a support material and a coolant for the beryllium material (or lithium material). Even if beryllium (or lithium) thinner than beryllium (or lithium) is used, secondary effects such as prevention of melting and melting of beryllium (or lithium) can be obtained. Moreover, the nuclear reaction under vacuum is possible by the vacuum seal attached to the composite type target, and furthermore, oxidative deterioration of the target material due to contact with the atmosphere can be prevented. In addition, the cooling mechanism provided in the composite target enables the cooling of the target by the actual exhaust heat of the heat generated in the target to the outside of the system. Due to these effects, the composite target of the present invention can solve the thermal problem of the target, and can stably generate low-energy neutrons while reducing activation of members such as the target.

  In addition, a linear accelerator, which is a significantly smaller accelerator than a conventional synchrotron or cyclotron, can be used as a generation source of protons that collide with the composite target of the present invention. It is possible to generate medical neutrons such as BNCT by being provided in a small linear accelerator that can be installed in a medical institution of scale.

The target according to the embodiment is a target in which a beryllium material (or lithium material) and a crystal-orientated carbon-based material are superimposed, a vacuum seal is applied to the surface of the target, and a coolant channel is provided in the target. It is sectional drawing which illustrates that it is a composite type target accompanying the cooling mechanism which has this. And it is sectional drawing which illustrates the compound type target with which the cooling mechanism which provided the refrigerant | coolant flow path was attached to the side surface of the target, and the refrigerant | coolant flow path was independently provided also inside the target. The target according to the embodiment is a target formed by superposing a beryllium material (or lithium material) and a crystal orientation carbon material, a vacuum seal is applied to the surface of the target, and a coolant channel is provided to the target. It is sectional drawing which illustrates that it is a composite type target which has the cooling mechanism which has. A cooling mechanism having a refrigerant flow path is attached to the side surface of the target, a refrigerant flow path is also provided inside the target, and the internal refrigerant flow path is connected to the refrigerant flow path of the cooling mechanism. It is sectional drawing which illustrates a composite type target. A target according to an embodiment, wherein the target is a composite in which a plurality of composites formed by superimposing a beryllium material (or lithium material) and a crystal orientation carbon material are stacked so that the two materials are alternately overlapped, and the target It is sectional drawing which illustrates that it is a composite type target attached with the cooling mechanism in which the vacuum seal was given to the surface of this, and provided the refrigerant | coolant flow path in this target. And it is sectional drawing which illustrates the composite type target which the cooling mechanism which provided the refrigerant | coolant flow path was attached to the side surface of the target. It is the schematic which illustrates the neutron generation method using this invention composite type target which concerns on embodiment. It is the schematic which illustrates the neutron generator which used this invention composite type target which concerns on embodiment. It is sectional drawing which illustrates the target for a comparison.

As described above, the main reason for making the composite target of the present invention a composite formed by superposing a beryllium material (or lithium material) and an oriented carbon material is that the function of the target is the above-mentioned two kinds of materials as described above. It is to share functions. The reason for using beryllium material and lithium material is mainly to generate low energy neutrons by collision with low energy protons, and beryllium materials undergo ⁹ Be (p, n) reaction by 4 MeV to 11 MeV protons. Lithium materials can cause ⁹ Li (p, n) reactions with 2 MeV to 4 MeV protons. In addition, the reason for using the crystal orientation carbon material as another material of the target is mainly that the activation by protons and neutrons is reduced, and the high thermal conductivity and thermal diffusivity in the orientation plane of the crystal orientation carbon material is provided. This is because the heat generated by the target is quickly conducted along the alignment plane. Moreover, although the crystal orientation carbon material has a lower neutron generation efficiency than the beryllium material and the lithium material, it is possible to generate neutrons by collision with protons.

  The beryllium material in the present invention is a single element material of a beryllium element selected from group 2 elements in the periodic table (being a single metal of beryllium element, hereinafter referred to as beryllium), a beryllium compound, and a beryllium composite material That is. The lithium material in the present invention is a single element material of lithium element selected from the group elements in the periodic table (a simple metal of lithium element, hereinafter referred to as lithium), a lithium compound, and lithium It is a composite material. In the present invention, beryllium, beryllium compounds, and beryllium composite materials are collectively referred to as beryllium materials, and lithium, lithium compounds, and lithium composite materials are collectively referred to as lithium materials because the neutron generation principle is specific to a specific element. This is because it is based on the reaction. In other words, the principle of neutron generation by irradiating the target with accelerated protons is based on a physical nuclear reaction between the proton and the atom of the specific element contained in the target. This is because neutrons are produced by the nuclear reaction similar to the case of the specific element alone even when the material is used. That is, in the present invention, in addition to beryllium and lithium, beryllium compounds and beryllium composite materials, lithium compounds and lithium composite materials can be used. When a compound or composite material of the specific element is used as a target, elements other than the specific elements (beryllium element and lithium element) contained in the compound or composite material are not activated by protons or neutrons. In addition, it is desirable that the element does not generate harmful substances by reaction with by-product hydrogen atoms. Examples of such elements include boron, carbon, silicon, nitrogen, phosphorus, oxygen, and sulfur.

The beryllium material in the present invention is beryllium, a beryllium compound, and a beryllium composite material. Examples of beryllium compounds include beryllium oxide (BeO),
Beryllium nitride (Be ₃ N ₂ ), beryllium carbide, beryllium hydroxide (Be (OH) ₂ ), beryllium acetate (Be (CH ₃ CO ₂ ) ₂ ), beryllium carbonate (BeCO ₃ ), beryllium sulfate (BeSO ₄ ), Beryllium nitrate (Be (NO ₃ ) ₂ ), beryllium phosphate (Be ₃ (PO ₄ ) ₂ ), beryllium silicate (Be ₂ SiO ₄ ), beryllium aluminate (Be (AlO ₂ ) ₂ ), beryllium titanate ( Examples include, but are not limited to, BeTiO ₃ ), beryllium niobate (Be (NbO ₃ ) ₂ ), beryllium tantalate (Be (TaO ₂ ) ₂ ), and the like. The beryllium composite materials mainly include beryllium glass such as beryllium borate glass and beryllium metaphosphate glass, beryllium glass ceramic containing beryllium glass as a main component, beryllium alloys such as magnesium beryllium alloy and aluminum beryllium alloy, and beryllium oxide. Examples thereof include, but are not limited to, beryllium ceramics included as components, beryllium solid solution ceramics in which beryllium elements are dissolved, and beryllium-encapsulated fullerenes. Among the above beryllium materials, beryllium and beryllium oxide have a relatively high ⁹ Be (p, n) reaction threshold (about 4 MeV), but have a high melting point (beryllium melting point: about 1278 ° C., beryllium oxide melting point: 2570 ° C.) Therefore, it is most preferable. Beryllium glass, beryllium ceramic, and beryllium-containing endohedral fullerenes are preferable because the beryllium element does not elute.

The lithium material in the present invention refers to lithium, a lithium compound, and a lithium composite material. Examples of the lithium compound include lithium oxide (Li ₂ O), lithium nitride (Li ₃ N), lithium carbide, lithium hydroxide (LiOH), lithium acetate (LiCH ₃ CO ₂ ), and lithium carbonate (Li ₂ CO ₃ ). , Lithium sulfate (Li ₂ SO ₄ ), lithium nitrate (LiNO ₃ ), lithium phosphate (Li ₃ PO ₄ ), lithium silicate (Li ₄ SiO ₄ ), lithium aluminate (LiAlO ₂ ), lithium iron phosphate ( LiFePO ₄ ), lithium iron phosphate (Li ₂ FePO ₄ F), lithium titanate (Li ₄ Ti ₅ O ₁₂ ), lithium titanate (Li ₂ TiO ₃ ), lithium niobate (LiNbO ₃ ), tantalate Examples thereof include lithium (LiTaO ₂ ), but are not limited thereto. The lithium composite material includes lithium glass such as lithium borate glass, lithium silicate glass, and lithium disilicate glass, lithium glass ceramic containing lithium glass as a main component, lithium magnesium alloy, lithium aluminum alloy, etc. Examples include, but are not limited to, lithium alloys, lithium ceramics containing lithium oxide as a main component, lithium solid solution ceramics in which lithium element is dissolved, lithium atom-containing fullerenes, and the like. Among the above lithium materials, although lithium has a low melting point, ⁷ Li (p,
n) Most preferred because of low reaction threshold (about 2 MeV). Lithium glass, lithium glass ceramic, and lithium atom-encapsulating fullerene are preferable because lithium alone does not elute.

  The main reason why another material of the composite target of the present invention is a crystal-oriented carbon material is that it is effective for reducing activation by protons and neutrons compared to metals, and This is because the thermal conductivity and thermal diffusivity of the heat generated by the target are even better. Moreover, it is because a crystal orientation carbon material is preferable compared with metals in generating low energy neutrons in which fast neutrons that are harmful and have high activation ability are reduced.

  The crystal orientation carbon material is preferably a material that is not easily activated, preferably absorbs less thermal neutrons and epithermal neutrons, preferably has a high neutron moderating effect, and preferably has high radiation durability. In order to withstand heat load, it is preferable to have a high melting point, heat conductivity for conducting and diffusing the heat generated by the target, and heat diffusibility are preferred, and beryllium material (or lithium material) The material is preferably excellent in adhesiveness, and is preferably a material capable of generating neutrons.

In general, the carbon material is a single element material (hereinafter referred to as carbon) of a carbon element selected from the group 14 elements in the periodic table, and therefore the carbon material in the present invention also follows this definition. In general, crystallinity means that atoms and molecules constituting a substance are arranged in a spatially repeating pattern, and orientation means that the directions of molecules and crystals are aligned. Therefore, the crystal orientation in the present invention also follows this definition. In other words, the crystal-oriented carbon material in the present invention is a carbon that is a crystalline carbon composed of carbon atoms or carbon molecules and that has a uniform crystal orientation. Examples of the crystal orientation carbon material in the present invention include single crystal graphite, highly oriented pyrolytic graphite (HOPG), carbon fiber, carbon nanofiber, and vapor grown carbon fiber (VGCF) described below. -grown carbon fiber), carbon whiskers, carbon nanotubes, graphenes, single crystal diamond, epitaxial diamond, and the like, but are not limited thereto. Single-crystal graphite has a honeycomb-shaped layer (called a graphite layer) in which six-membered rings of carbon atoms (including cases where some of them contain a five-membered ring) are connected in a plane, and is bonded by a weak van der Waals force. Thus, a layered structure is formed, and the layered structure is regularly arranged like a crystal, and the plane of the graphite layer (hereinafter referred to as a graphite plane) is oriented in the same direction in an orderly manner. HOPG is a graphite material having high crystal orientation similar to that of single crystal graphite, although it is not perfect crystal orientation like single crystal graphite. Carbon fiber, carbon nanofiber, VGCF, and carbon whisker are graphite materials in which graphite microcrystals are aggregated in a fiber shape and the graphite layer is oriented in the fiber axis direction. Carbon nanotubes are carbon materials that have a hollow at the center of the molecule and are composed of one or more graphite layers so as to cover the hollow. Graphenes are carbon materials whose molecules are composed of one to several graphite layers. Single crystal diamond is diamond in which the diamond structure is continuous without interruption. Epitaxial diamond is a thin-film diamond crystal obtained by growing a diamond crystal on a crystal serving as a substrate, and the crystal growth is diamond aligned in alignment with the crystal plane of the underlying substrate. Of the crystal-oriented carbon materials in the present invention, single-crystal graphite usually has a thermal conductivity value on the graphite surface of 1500 Wm ⁻¹ K ⁻¹ , thermal diffusivity (thermal conductivity per specific heat capacity). ) Is about 3.4 m ² h ⁻¹ . On the other hand, the thermal conductivity of copper, which is well known as a metal material having high thermal conductivity, is 400 Wm ⁻¹ K ⁻¹ , and the thermal diffusivity is about 0.42 m ² h ⁻¹ . Therefore, among the crystal orientation carbon materials in the present invention, HOPG, carbon fiber, carbon nanofiber, VGCF, carbon whisker, carbon nanotubes, and graphenes having crystal orientation similar to single crystal graphite and single crystal graphite are: It is preferable as a heat conducting material for quickly conducting and diffusing heat generated in the target along the graphite surface. Single crystal diamond has a thermal conductivity value of 2300 Wm ⁻¹ K ⁻¹ and a thermal diffusivity of about 4.6 m ² h ⁻¹ . Therefore, among the crystal orientation carbon materials in the present invention, single crystal diamond or epitaxial diamond whose crystal orientation is similar to single crystal diamond conducts and diffuses heat generated in the target isotropically (three-dimensionally) quickly. It is preferable as a heat conductive material for the purpose. The crystal orientation carbon material in the present invention usually has a bulk density of 1.5 g.
Those in the range of cm ^{−3 to} 3.5 gcm ⁻³ can be used. In the present invention, the bulk density is not unusable crystalline orientation carbon material of less than 1.5Gcm ^-3, bulk density insufficient collisions between the carbon atoms and the protons and neutrons is less than 1.5Gcm ^-3 Therefore, the bulk density is preferably 1.5 gcm ⁻³ or more. Further, when the bulk density exceeds 3.5 gcm ⁻³ , the stable phase under normal pressure is diamond, so the maximum value of the bulk density of the carbon material existing as a substance is about 3.5 gcm ⁻³ . As the crystal orientation carbon material used in the present invention, a crystal orientation carbon material used as a conventional industrial material can be used, and a crystal orientation carbon material improved to a higher density is more preferable.

  Among the above crystal orientation carbon materials, single crystal graphite, HOPG, carbon fiber, single crystal diamond, and epitaxial diamond are manufactured as industrial materials and not only have the above-mentioned balanced physical properties, It is more preferable because it is excellent in heat conduction and thermal diffusivity, is a material that hardly generates a radionuclide, and unexpectedly has a property of hardly causing hydrogen embrittlement.

The crystal orientation carbon material in the present invention is a composite of at least one material selected from the above-mentioned single crystal graphite, HOPG, carbon fiber, single crystal diamond, and epitaxial diamond and other carbon-based materials. The carbon-based composite material can be made. One or more carbon-based materials may be combined. Examples of such a carbon-based material include, but are not limited to, isotropic graphite, porous carbon, diamond, diamond-like carbon, glassy carbon, fullerene, polyacetylene, carbon nitride, and silicon carbide. Not what you want. For example, the composite with isotropic graphite can be performed by laminating a composite formed by superimposing a beryllium material (or lithium material) and a crystal orientation carbon material and a block-shaped formed body of isotropic graphite. The component ratio of isotropic graphite is not particularly limited, but is usually 50% or more. By doing so, the heat generated in the target can be conducted to the bottom surface of the target, so that the target can be cooled more efficiently.

It is known that the average energy of neutrons generated at the target is about one fifth of the energy of incident protons (Non-Patent Document 1). Thus, for example, the average energy of neutrons generated when 8 MeV protons collide with a beryllium material is about 1.6 MeV, which is 3 MeV.
It is expected that the average energy of neutrons generated by colliding protons with lithium materials is about 0.6 MeV. Since the average energy value of this neutron is in the energy range of fast neutrons, in order to use the generated neutrons for medical purposes such as BNCT, it is necessary to decelerate to the energy of thermal neutrons or epithermal neutrons with a moderator. . Carbon-based materials such as light water (H ₂ O), heavy water (D ₂ O), beryllium (Be), beryllium oxide (BeO), and graphite (C) are ferrous metals such as iron, non-ferrous metals such as copper, And neutron moderation ratio (the value of neutron moderation divided by the neutron absorption capability, the better the moderator. However, it is generally used as a neutron moderator for nuclear reactors and the like. Among them, carbon-based materials such as graphite are larger than the neutron moderation ratio of light water, and the neutron moderation distance (the travel distance from fast neutrons to thermal neutrons, given as the square root of Fermi age τcm ² ) Is about 20cm, which is relatively short (about 4 times the neutron moderation distance of light water and about 2 times the neutron moderation distance of heavy water) (Non-patent document 2). Neutron moderation to obtain thermal or epithermal neutrons It is a material suitable as a material. In addition, since carbon-based materials such as graphite are expected to have neutron permeability similar to that of water, neutron transmittance (I / I ₀ : against the intensity of incident neutrons) in carbon-based materials such as graphite The ratio of neutron intensity after transmission) is measured data of neutron transmittance of water (I / I ₀ = 10 ^−0.08T , where Tcm is the transmission distance of neutron and incident neutron is 1 MeV) ( Based on Non-Patent Document 3), for example, the thickness of the graphite material in the present invention is 3
Assuming cm, the neutron transmittance is estimated to be about 60%, so that it is expected that transmission of about 40% of fast neutrons can be suppressed. Further, for example, when the thickness of the graphite material in the present invention is 20 cm or more, it is expected that transmission of fast neutrons is almost completely suppressed and thermal neutrons and epithermal neutrons are obtained.

  In addition, the crystal orientation carbon material in the present invention can be appropriately added with a reinforcing material as desired in order to improve the mechanical strength and the like when used. The reinforcing material is preferably a material that is difficult to be activated. Examples of such materials include, but are not limited to, epoxy resins, glass fibers, and various ceramic materials.

In neutron generation by proton-target collision, it is very important how to efficiently exhaust heat generated by the target. Normally, the maximum value of the heat load per unit surface area of the target is regarded as the proton output divided by the surface area of the target, so the heat removal capacity from the target surface must be designed to be greater than the heat load of the target. . For example, it has been estimated that the proton power required to generate medical neutrons such as BNCT is at least about 30 kW, so if the surface area of the target is 30 cm ² , for example, the thermal load will be 10 MWm ⁻² . Also become. The higher the output, the higher the output of the proton, the more the neutron generation dose.Therefore, there is no reason to set it as high as possible, but since one type of target material was used in the past, For example, a 30 kW proton beam with a surface area of 30 c
When irradiating the target material of m ² , it is difficult to directly cool the surface of the target material by water cooling. Therefore, a cooling method through a metal heat conduction plate having a surface area larger than that of the target material has been proposed. (Patent Document 6). However, in this method, it is almost difficult to use a solid target using a material having a low melting point such as lithium. On the other hand, the composite target of the present invention, which is a composite of a beryllium material (or lithium material) and a crystal orientation carbon material, has high thermal conductivity and thermal diffusivity that the crystal orientation carbon material has. Since the heat generated in the target can be quickly discharged out of the system by using it, the proton output can be made larger than the conventional output value, for example, a proton with an output of about 100 kW. But it can be used. The composite target of the present invention is effective for solving the thermal problem of the target as described above.

  In the present invention, the reason why the target is a composite formed by superimposing the beryllium material (or lithium material) and the crystal orientation carbon material is that the heat generated by the target has high thermal conductivity. This is because the superposition of both materials is effective for exhausting heat outside the system using the thermal diffusivity. For example, when using a crystal orientation carbon material, such as single crystal graphite, where the thermal conductivity of the graphite surface is orders of magnitude higher than the thermal conductivity of the surface orthogonal to the graphite surface, the graphite surface of the single crystal graphite And a beryllium material (or lithium material) in a composite form, heat generated in the target can be quickly conducted and diffused along the graphite layer to the target surface. The heat thus conducted is quickly exhausted by the cooling mechanism provided on the target, and as a result, the target can be efficiently cooled. In this case, it is effective to provide the cooling mechanism at a position perpendicular to the graphite surface, that is, the side surface of the target. In addition, for example, even when using a material that has higher thermal conductivity than a metal material such as single crystal diamond as the crystal orientation carbon material and that conducts heat isotropically like a metal material, By making a composite of the surface of single crystal diamond and beryllium material (or lithium material), it is possible to conduct and diffuse heat generated in the target from any direction of the crystal plane of the diamond to the target surface. . Thus, the heat conducted in all directions is quickly exhausted by the cooling mechanism provided in the target, and as a result, the target can be efficiently cooled. In this case, the cooling mechanism can be provided on the side surface of the target, the inside of the target, or the lower surface of the target. Further, for example, when a material having crystal orientation in the fiber axis direction such as carbon fiber is used as the crystal orientation carbon material, the surface of the sheet-like carbon fiber in which the carbon fibers are aligned and bundled in the fiber axis direction By forming a composite in which the beryllium material (or lithium material) is superimposed, heat generated in the target can be conducted and diffused along the fiber axis of the carbon fiber to the target surface. The heat thus conducted is quickly exhausted by the cooling mechanism provided on the target, and as a result, the target can be efficiently cooled. In this case, it is effective to provide a cooling mechanism on the side surface of the target. The number of composites used for the composite target of the present invention is not limited. By making the composite a composite in which both materials are alternately stacked, it is possible to dramatically increase the heat transfer area, so that the heat generated by the target can be further increased. It is possible to conduct efficiently to the target surface. The heat conducted quickly to the target surface by heat conduction or heat diffusion as described above is transferred to the outside of the actual system by an indirect or direct cooling mechanism provided on the side, inside, or bottom of the target. Heat can be exhausted, thereby cooling the target.

  As a specific aspect of the composite target of the present invention, for example, a thin beryllium material (or lithium material) formed by superposing a single beryllium material (or lithium material) and a crystal orientation carbon material and then forming the target on the target is used. ) And a crystallographically oriented carbon material are laminated so that both materials are alternately laminated, and then formed into a target. However, the present invention is not limited thereto. Although the number of stacked layers is not limited, it is possible to dramatically increase the heat transfer area by increasing the number of stacked layers.

The molding method of the composite target of the present invention is appropriately determined according to the type and thickness of the material used, and is not limited to a specific processing method. For example, formation of a composite by superimposing a beryllium material and a crystal orientation carbon material can be performed by hot pressing, HIP processing (hot isostatic pressing), vapor deposition, or the like. The composite made up of a relatively thick beryllium material and a crystallographic orientation carbon material is preferably subjected to hot pressing or HIP treatment. The formation of a composite made up of a relatively thin beryllium material and a crystallographic orientation carbon material is Vapor deposition is preferred. The hot pressing of the beryllium material and the crystal orientation carbon material can be normally performed at a temperature from 200 ° C. to the melting point of the beryllium material at normal pressure, and a pressure of 10 ³ kilopascals to 10 ⁵ kilopascals. Is usually 10
It can be performed under the temperature from 0 ° C. to the melting point of the beryllium material at normal pressure, under the pressure of 10 ⁴ kilopascals to 10 ⁶ kilopascals, and the deposition is performed from the temperature of the carbon-based material substrate to the melting point of the beryllium material. At a temperature of 10 ⁻³ Pascals to 10 ⁻⁶ Pascals. For example, beryllium carbide can be generated at the bonding interface by superimposing beryllium and the crystal-oriented carbon material by HIP treatment at 900 ° C. or higher, which can improve the adhesion. In addition, for example, formation of a composite formed by superimposing a lithium material and a crystal orientation carbon material can be performed by hot pressing, HIP treatment, vapor deposition, or the like. Formation of a composite composed of a stack of a relatively thick lithium material and a crystal orientation carbon material is preferably performed by hot pressing or HIP treatment. Formation of a composite composed of a stack of a relatively thin lithium material and a crystal orientation carbon material Is preferably an evaporation method. The hot pressing of the lithium material and the crystal orientation carbon material can be usually performed at a temperature from room temperature (23 ° C.) to a melting point of the lithium material at normal pressure and a pressure of 10 ³ kilopascals to 10 ⁵ kilopascals. The HIP treatment can be usually performed at a temperature ranging from room temperature to the melting point of the lithium material at normal pressure, and at a pressure of 10 ⁴ kilopascals to 10 ⁶ kilopascals. Can be carried out at a temperature from room temperature to the melting point of the lithium material, and at a pressure of 10 ⁻³ Pascal to 10 ⁻⁶ Pascal. A target obtained by stacking a plurality of composites composed of a stack of a thin beryllium material (or lithium material) and a crystal orientation carbon material is, for example, a beryllium material (or lithium material) on a thin crystal orientation carbon material. A sheet produced by vapor deposition of a beryllium material (or lithium material) and a sheet produced by rolling and bonding a thin beryllium material (or lithium material) to a thin crystal orientation carbon material. It can be manufactured by laminating oriented carbon materials so that they are alternately in contact with each other and press-molding them into a target shape by hot pressing, HIP treatment or the like. The beryllium material or the lithium material can be coated on the crystal orientation carbon material by, for example, a CVD method (chemical vapor deposition).

The thickness of the beryllium material (or lithium material) in the composite target of the present invention is not particularly limited because the neutron generation reaction due to proton collision can be shared with the crystal orientation carbon material. (Or lithium material) can be much thinner than the theoretical range of protons. This is because the crystal-oriented carbon material functions as a support material and a coolant for the beryllium material (or lithium material). Moreover, it is because the thermal load which each material bears for the said reason is reduced. The theoretical range can be calculated from the incident energy of protons and the stopping power of matter. For example, when the target material is beryllium, the theoretical range of 11 MeV protons in beryllium is about 0.94 mm. Therefore, in the case of a target composed only of conventional beryllium, the thickness is 1 mm or more. Was necessary. However, the beryllium in the target of the present invention can be considerably thinner than 1 mm. When the beryllium material in the target of the present invention is beryllium, the thickness of beryllium is preferably 0.01 mm or more and less than 1 mm. More preferably, the thickness of beryllium is 0.1 mm or more and 0.5 mm or less. If the beryllium thickness is less than 0.01 mm, the heat resistance is remarkably lowered, so that it is preferably 0.01 mm or more. Further, in order to share part of the nuclear reaction caused by proton collision with beryllium, the thickness of beryllium is preferably less than 1 mm. Similarly, when the target material is lithium, the theoretical range of 11 MeV protons in lithium is about 2 mm. Therefore, in the case of a target composed only of conventional lithium, the thickness is 2 mm or more. It was necessary. However, when the lithium material in the composite target of the present invention is lithium, the thickness of lithium can be considerably thinner than 2 mm. The thickness of lithium in the composite target of the present invention is preferably 0.01 mm or more and 1 mm or less. More preferably, it is 0.05 mm or more and 0.5 mm or less. When the thickness of lithium is less than 0.01 mm, the heat resistance is lowered, so that the thickness is preferably 0.01 mm or more. Further, in order to share a part of the reaction caused by proton collision with lithium, the thickness of lithium is preferably 1 mm or less. In order to maintain heat resistance and share a part of the nuclear reaction caused by proton collision with lithium, the thickness of lithium is preferably 0.05 mm or more and 0.5 mm or less.

  The composite target of the present invention does not limit the ratio of the beryllium material (or lithium material) and the crystal orientation carbon material in the thickness direction. The composite target of the present invention can be appropriately set according to the target material using the ratio and the acceleration energy of the irradiation proton, and the thickness of the crystal orientation carbon material is usually made of a beryllium material (or lithium material). Set to more than 10 times the thickness. The main reason for this is that the neutron generation efficiency of the crystal-oriented carbon material is usually smaller by one digit or more than the neutron generation efficiency of the beryllium material (or lithium material).

  The composite type target of the present invention can attach a vacuum seal to the surface of the composite type target. The main reason for attaching a vacuum seal is that in the present invention, since the target is irradiated with protons under vacuum, the target is handled and operated under vacuum. Further, as a secondary effect of attaching the vacuum seal, there is an effect of preventing oxidative deterioration in an oxidizing atmosphere due to contact with the atmosphere. The vacuum seal may be a seal of a portion where the target is in contact with the atmosphere, or a seal of the entire target. The sealing material for vacuum sealing is not particularly limited, but light metal materials and non-metallic materials are preferable because they are less likely to be activated than heavy metals. Examples of the light metal material include, but are not limited to, magnesium, aluminum, boron, tin, zinc, silicon, alloys of these light metal materials, various ceramic materials, and the like. Further, examples of the non-metallic material include glass, epoxy resin, glass fiber reinforced plastic, and the like, but are not limited thereto.

  Further, the composite type target of the present invention can be attached with a vacuum seal on the surface of the composite type target, and can be attached with a cooling mechanism having a refrigerant flow path on the composite type target. The main reason for doing this is to cool the target by effectively exhausting heat generated in the target out of the system. The location where the cooling mechanism is provided on the composite target is not particularly limited. However, when the cooling mechanism is provided on the side surface of the composite target, water cooling may be performed via a heat transfer plate having high thermal conductivity if necessary. Is possible. When a cooling mechanism is provided inside the composite type target, it is possible to provide a refrigerant flow path inside the crystal orientation carbon material, and the beryllium material (or lithium material) and the crystal orientation carbon material are overlapped. It is also possible to stack a plurality of combined composites and provide a refrigerant flow path in the gap between adjacent composites. As the refrigerant in this case, for example, a liquid such as cooling water or a gas having high thermal conductivity such as helium gas is preferably used. It is also possible to provide a cooling mechanism on the bottom surface of the composite target. In this case, it is preferable to use a material that hardly causes the problem of activation by neutrons. An example of such a material is a crystal orientation carbon material in the present invention. Further, the composite target of the present invention can have a cartridge type structure in which the target and the cooling mechanism are integrated. In this way, the heat generated in the target can be efficiently exhausted out of the system, and when the target is deteriorated, it can be easily replaced with a new one by remote control.

Neutrons that can be generated using the composite target of the present invention are low-energy neutrons containing a large amount of thermal neutrons or epithermal neutrons. Low-energy neutrons are neutrons that have reduced harmful and high activation fast neutrons. Fast neutrons are biologically harmful and have a very high activation capacity because their energy is two orders of magnitude higher than thermal neutrons or epithermal neutrons. Types of neutrons include fast neutrons (also called fast neutrons), epithermal neutrons, thermal neutrons, and cold neutrons, but these neutrons are not clearly separated in terms of energy, Energy categories vary depending on areas such as shielding, dosimetry, analysis, and medical care. For example, according to the basic term of nuclear disaster prevention, “Fast neutrons are those that have a large momentum among fast neutrons (fast neutrons), and this value varies depending on fields such as reactor physics, shielding, and dosimetry. However, it is common for fast neutrons to be 0.5 MeV or higher. " In the medical field, epithermal neutrons are generally neutrons in the range of 1 eV to 10 keV, and thermal neutrons are generally neutrons of 0.5 eV or less. The low energy neutron in the present invention means a neutron in which fast neutrons of 0.5 MeV or more are reduced. When protons with acceleration energy used in the present invention of 2 MeV or more and 4 MeV or less are irradiated to the composite target of the present invention (a target made of a composite of a lithium material and a crystal orientation carbon material), the average energy is about 0.3 MeV. Can generate neutrons. In addition, when protons having an acceleration energy of 6 MeV or more and 8 MeV or less used in the present invention are irradiated to the composite target of the present invention (a target formed by superposing a beryllium material and a crystal orientation carbon material), the acceleration energy is 0.5 MeV or more. The generation amount of fast neutrons can be reduced by at least about 30% compared to a conventional beryllium-only target.

Neutrons can be generated by using the composite target of the present invention and causing low-energy protons to collide with the target in a vacuum. The low-energy protons are protons having energies ranging from a threshold of proton energy (referred to as a nuclear reaction threshold) that can cause a nuclear reaction by collision with a target to several times the threshold. The reason why the acceleration energy of irradiated protons is set to the threshold value of the nuclear reaction or several times the threshold value is to generate low energy neutrons with reduced fast neutrons. The acceleration energy of the proton needs to be set as appropriate depending on the type of target material constituting the composite target of the present invention. When a beryllium material is used as the target material, the acceleration energy of the irradiation protons is preferably 4 MeV or more and less than 11 MeV, and more preferably 6 MeV or more and 8 MeV or less. ^{7 Since} the threshold value of the Be (p, n) reaction is about 4 MeV, if the acceleration energy of the proton is less than 4 MeV, the generation efficiency of neutrons is significantly reduced. Therefore, the acceleration energy of the proton used in the present invention is 4 MeV or more. Preferably there is. In addition, when the acceleration energy of the proton is 11 MeV or more, not only the activation of the member such as the target becomes remarkable but also the generation of fast neutrons increases. Therefore, the acceleration energy of the proton is preferably less than 11 MeV. More preferable protons are 6 MeV or more and 8 MeV or less for generating low energy neutrons with reduced harmful and high activation fast neutrons. Further, the acceleration energy of irradiation protons when a lithium material is used as the target material is preferably 2 MeV or more and 4 MeV or less. ^{7 Since} the threshold of Li (p, n) reaction is about 2 MeV, if the acceleration energy of protons is less than 2 MeV, the generation efficiency of neutrons is significantly reduced. Therefore, the acceleration energy of protons used in the present invention is 2 MeV or more. Preferably there is. Moreover, when the acceleration energy of protons exceeds 4 MeV, not only the activation of the target or the like becomes remarkable, but also the generation of fast neutrons increases. Therefore, the acceleration energy of protons is preferably 4 MeV or less. More preferable protons are 2 MeV or more and 4 MeV or less for generating low energy neutrons in which harmful and high activation fast neutrons are reduced. The reason why the proton collides with the composite target under vacuum is to prevent the irradiation proton from being reduced in intensity and to prevent air pollution. Therefore, although it has never passed over to a high vacuum, the degree of vacuum is usually in the range of 10 ⁻⁴ Pascal to 10 ⁻⁸ Pascal.

The composite target of the present invention, a hydrogen ion generation unit for generating protons, an accelerator for accelerating protons generated in the hydrogen ion generation unit, and a proton irradiation unit for irradiating the target with protons accelerated by the accelerator It is possible to generate neutrons with a neutron generator equipped with A linear accelerator may be provided as the accelerator, the composite target of the present invention may be used as the target, and the composite target may be provided in the proton irradiation unit. The hydrogen ion generator is provided with a hydrogen ion generator for generating hydrogen ions. The hydrogen ion generator is not particularly limited, and a conventional hydrogen ion generator can be used. The generated hydrogen ions are sent to an accelerator for acceleration. Although the said accelerator is a linear accelerator, if it is a linear accelerator, it will not specifically limit, The conventional linear accelerator can be used. Examples of such a linear accelerator include a high frequency quadrupole linear accelerator, an electrostatic linear accelerator, a normal conduction linear accelerator, a superconducting linear accelerator, and the like. The high-frequency quadrupole linear accelerator not only can generate high-current protons in a small device compared to the electrostatic accelerator, but also generates very little radiation such as gamma rays and X-rays.
More preferable than electrostatic linear accelerator. As the linear accelerator, a linear accelerator capable of accelerating protons in the range of 2 MeV to less than 11 MeV generates low-energy neutrons that are reduced in harmful and high-activation fast neutrons by a relatively small linear accelerator. It is effective for. The proton irradiator is for irradiating the target with protons accelerated by an accelerator. The target for generating neutrons and the protons for normally performing proton convergence, diffusion, scanning, proton energy classification, etc. Beam adjusting means are provided. The proton irradiation unit is not particularly limited, and a proton irradiation unit including a conventional quadrupole electromagnet or deflection electromagnet can be used.

  Hereinafter, an aspect of the present invention will be described in detail as an embodiment (hereinafter also referred to as “this embodiment”) with reference to the drawings.

  The composite target according to this embodiment for generating neutrons by colliding with protons is a composite target that is a composite formed by superimposing a beryllium material (or lithium material) and a crystal orientation carbon material. Each material in the composite target has a structure in contact with the interface. As such a target, a target having the following shape is possible. For example, a target obtained by forming a composite formed by stacking a beryllium material (or lithium material) and a crystalline orientation carbon material into a target shape, and a target formed by forming a composite formed by stacking a plurality of the composites into a target shape However, the present invention is not limited to these examples. The crystal orientation carbon material may be a single material or a carbon-based composite material in which a plurality of crystal orientation carbon materials are combined. Further, the composite type target may be a composite type target with a vacuum seal, and the composite type target may have a vacuum seal and a cartridge type structure with a cooling mechanism having a coolant channel. Is possible. Further, if necessary, a cut groove can be formed on the surface of the composite target in order to prevent separation of the beryllium material (or lithium material) and the crystal orientation carbon material in the composite target. It is also possible to provide a heat transfer plate between the cooling mechanism and the target in order to reliably conduct the generated heat to the cooling mechanism.

  FIG. 1 is a schematic view of a composite target according to the present embodiment. As shown in the figure, the composite target 8 of the present invention includes a target 3 having a composite shape formed by superposing a beryllium material (or lithium material) 1 and a crystal orientation carbon material 2, and a side surface and an inside of the target. This is a composite target 8 with a cooling mechanism 6 having a refrigerant flow path 5. As the refrigerant flow path 5, not only a liquid refrigerant flow path but also a gas refrigerant flow path can be provided. The target 3 is provided with a vacuum seal 4 for sealing the surface of the carbon material located on the atmosphere side. Moreover, the groove | channel 7 for partitioning and adhering a beryllium material (or lithium material) to the single side | surface of a carbon material as needed can be provided.

FIG. 2 is a schematic view of the composite target according to the present embodiment. As shown in the figure, the composite type target 8 includes a target 3 having a composite shape formed by superposing a beryllium material (or lithium material) 1 and a crystal orientation carbon material 2, and a side surface and an inside of the target. The composite target 8 is accompanied by a cooling mechanism 6 provided with a flow path 5. As the refrigerant flow path 5, a common refrigerant flow path can be provided inside the target and on the side of the target. The target 3 is provided with a vacuum seal 4 for sealing the surface of the carbon material located on the atmosphere side. Moreover, the groove | channel 7 for partitioning and adhering a beryllium material (or lithium material) to the single side | surface of a carbon material as needed can be provided.

  FIG. 3 is a schematic view of the composite target according to the present embodiment. As shown in the figure, the composite target 8 of the present invention has a shape in which a plurality of composites formed by superposing a beryllium material (or lithium material) 1 and a crystal orientation carbon material 2 are laminated so that both materials are alternately superposed. And a target 8 having a cooling mechanism 6 provided with a refrigerant flow path 5 on the target 3. The refrigerant flow path 5 may be a liquid refrigerant flow path. The target 3 is provided with a vacuum seal 4 for sealing the surface of the carbon-based material located on the atmosphere side.

  FIG. 4 is a schematic view illustrating a neutron generation method using the composite target of the present invention according to the embodiment. As shown in the figure, it is possible to generate neutrons 11 of low energy by causing a proton 10 having a predetermined acceleration energy (2 MeV or more and less than 11 MeV) to collide under vacuum in the composite target 9 of the present invention.

  FIG. 5 is a schematic view illustrating a neutron generator using the composite target of the present invention according to the embodiment. As shown in the figure, in the neutron generator according to this embodiment, a hydrogen ion generator 17, a linear accelerator 18, and a proton irradiation unit 19 are connected via a flange 20. And the composite type target 12 is provided in a proton irradiation part. The hydrogen ion generator 17 is provided with a hydrogen ion generator, and the generated hydrogen ions 13 are introduced into the linear accelerator 18 and accelerated. The proton 14 accelerated to a predetermined energy by the linear accelerator 19 is introduced into the proton irradiation unit 18 connected to the tip of the linear accelerator 15, and collides with the composite target 12 provided in the proton irradiation unit 19. Thus, the low energy neutron 15 is generated. The linear accelerator 18 is not particularly limited as long as it is a linear accelerator capable of generating protons of 2 MeV or more and less than 11 MeV. The proton irradiation unit 19 is usually provided with a quadrupole electromagnet or a deflection electromagnet.

  FIG. 6 is a schematic cross-sectional view illustrating a conventional target in which beryllium (or lithium) 21 is attached to a metal support 22.

  As described above, the present invention is a novel target for generating neutrons by colliding protons with a target. As in the embodiments described above, since the target is a composite formed by superimposing a beryllium material or a lithium material and a crystal orientation carbon material, harmful and high activation fast neutrons are reduced. It is possible to generate energy neutrons, it is easy to exhaust heat generated by the target, the cooling mechanism is attached to the target, so that efficient cooling is possible, the target and the cooling mechanism, Therefore, the target is provided at the tip of the proton irradiation unit, and when the target is deteriorated, it can be easily attached and detached with a new one by remote control.

  In addition, as described above, the crystal orientation carbon material that is a constituent material of the composite target of the present invention can have a neutron moderating effect, so that generation of fast neutrons is reduced. Thereby, in embodiment described above, it is possible to reduce in size the deceleration mechanism for decelerating generated neutrons.

  Moreover, since the acceleration energy of the irradiated protons is a relatively low energy proton of 2 MeV or more and less than 11 MeV, activation of the member such as the target by the proton is remarkably reduced, and generation of harmful fast neutrons is suppressed. The effect that acceleration protons can be generated with a small linear accelerator can be obtained.

  Therefore, the composite target of the present invention is effective as a neutron source of a neutron generator for generating medical neutrons such as BNCT that can be installed in a small medical institution.

As described above, the crystal-oriented carbon material in the composite target of the present invention can conduct and diffuse heat generated in the target to the surface of the target as quickly as metal or more or metal. Thus, it is clear that melting and fusing of the beryllium material (or lithium material), which is another target material, can be prevented. The effect of reducing the activation of the target material, which is one of the roles, can also be theoretically proved below.
[Simulation by theoretical calculation]
A simulation was performed to predict activation of the target material. The simulation was performed using JENDL-4.0 (Non-Patent Document 4), which is a theoretical calculation program for the nuclear reaction cross section of the neutron nuclear reaction. An outline of the calculation result will be described below. (1) Nuclear reactions caused by collisions between 6 MeV protons and beryllium are ⁹ Be (p, γ) ¹⁰ B, ⁹ Be (p, n) ⁹ B, ⁹ Be (p, pn) ⁸ Be, and ⁹ Be (p , α) ⁶ Li, the half-life of these nuclides is short, and the effective dose equivalent rate constant Γ _{e of} these nuclides is a measure of the dose of gamma rays emitted from radionuclides: the unit μS _v m ² MBq ^-1 h ^-1
ΜS _v is microsievert, m is meter, MBq is mega becquerel, h is hour)
Zero. (2) Nuclear reactions caused by collision of neutrons and beryllium below 6 MeV are ⁹ Be (n, γ) ¹⁰ Be, ⁹ Be (n, 2n) ⁸ Be, and ⁹ Be (n, α) ⁶ He, These nuclides have short half-lives and their effective dose equivalent rate constant Γ _e is zero. The reason why the acceleration energy of neutron is set to 6 MeV or less is that the maximum energy of neutron generated by collision of 8 MeV protons and beryllium is 6.1 MeV. (3) Nuclear reactions caused by collisions between 3 MeV protons and lithium are ⁶ Li (p, γ) ⁷ Be, ⁶ Li (p, α) ³ He, ⁷ Li (p, γ) ⁸ Be, ⁷ Li (p, n) ⁷ Be and ⁷ Li (p, α) ⁴ He. Among these generated radionuclides, nuclides other than ⁷ Be have short half-lives, and effective dose equivalent rate constant Γ of nuclides other than ⁷ Be. _e was zero or 0.00847. (4) Nuclear reactions caused by 3 MeV neutron-lithium collisions are: ⁶ Li (n, γ) ⁷ Li, ⁶ Li (n, p) ⁶ He, ⁶ Li (n, t) ⁴ He, ⁶ Li (n , α) ³ H
, And ⁷ Li (n, γ) ⁸ Li Among these radionuclides, radionuclides other than tritium (t or ³ H) have short half-lives, and effective dose equivalent rates of radionuclides other than tritium The constant Γ _e was zero or 0.00847. (5) Radionuclides having a relatively long half-life and a relatively high effective dose equivalent rate constant Γ _{e due} to collisions between 6 MeV neutrons and group 0 elements in the periodic table and elements of group 1 to group 8 elements. The resulting elements were Sc, Ti, Mn, Fe, Co, Ni, Cu, and Pt. Among these, radionuclides generated by the activation of iron materials are ⁵⁴ Fe (n, p) ⁵⁴ Mn (half-life 312 days, Γ _e 0.111), ⁵⁴ Fe (n, α) ⁵¹ Cr (half-life 27.7 days, Γ _e 0.0046), ⁵⁶ Fe (n, p) ⁵⁶ Mn (half-life 2.58 hours, Γ _e 0.203), and ⁵⁸ Fe (n, γ) ⁵⁹ Mn (half-life 44.6 days, Γ _e 0.147), copper material The radionuclide produced by the activation of ⁶³ Cu (n, γ) ⁶⁴ Cu (half-life 12.7 hours,
Γ _e 0.0259), ⁶³ Cu (n, γ) ⁶⁰ Co (half-life 5.27 years, Γ _e 0.305), and ⁶⁵ Cu (n, p) ⁶⁵ Ni (half-life 2.52 hours, Γ _e 0.0671).

  From the results of the above theoretical calculation simulation, it was predicted that the crystal-oriented carbon material used for the composite target of the present invention does not generate a radionuclide due to a nuclear reaction with irradiated protons and generated neutrons. On the other hand, conventionally, metal materials such as copper materials and iron materials used as target materials have been expected to generate various radionuclides and to activate the target materials due to nuclear reactions with irradiated protons and generated neutrons.

As described above, from the theoretical calculation results regarding the thermal characteristics of the material composition and the activation characteristics by protons and neutrons in the composite target of the present invention, the composite target of the present invention can significantly reduce the activation compared to the conventional metal target. In addition, it is possible to conduct and diffuse the heat generated in the target to the target surface as quickly as or more than the metal material. The heat conducted and diffused to the target surface is transferred to the composite target. Since it is possible to exhaust heat outside the system by the accompanying cooling mechanism, the neutron generation method and neutron generator using the composite target of the present invention and the composite target of the present invention can be installed in a small-scale medical institution. Effective as a neutron source, neutron generation method, and neutron generator for generating medical neutrons such as BNCT

  In the composite target of the present invention, the target portion is a composite formed by superimposing a beryllium material (or lithium material) and a crystal orientation carbon material, so that the activation of members by protons and neutrons can be reduced. Since a low-energy proton can be used, the generation of fast neutrons can be reduced, the thermal problem of the target can be solved, and the composite target of the cartridge type structure in which the target portion and the cooling mechanism are integrated is a target. The heat generated can be exhausted to the outside of the actual system, and when the target is deteriorated, it can be safely and easily exchanged with a new one by remote control. Further, since the neutron generation method and the neutron generator using the composite target of the present invention can generate low energy neutrons using a small linear accelerator, the composite target of the present invention is used for medical purposes such as BNCT. Very useful in generating neutrons.

1 Beryllium material (or lithium material)
2 Crystal orientation carbon material 3 Target 4 Vacuum seal 5 Refrigerant flow path 6 Cooling mechanism 7 Groove 8 Composite target 9 Composite target 10 Proton flow 11 Neutron flow 12 Composite target 13 Hydrogen ion flow 14 Acceleration proton flow 15 Flow of irradiated protons 16 Flow of generated neutrons 17 Hydrogen ion generation unit 18 Linear accelerator 19 Proton irradiation unit 20 Flange 21 Beryllium (or lithium)
22 Metal support

Claims (6)

  A composite target in which a target for generating a neutron by colliding with a proton is a composite formed by superimposing a crystal orientation carbon material and one of a beryllium material and a lithium material.   The composite type target according to claim 1, wherein the composite type target attaches a vacuum seal to a surface of the composite type target.   2. The composite target according to claim 1, wherein the composite target is attached with a vacuum seal on a surface of the composite target, and a cooling mechanism having a coolant channel is attached to the composite target. . In the neutron generation method for generating neutrons by colliding protons with the target,
Proton is a proton of 2 MeV or more and less than 11 MeV,
The target is the composite target of claim 3,
A method of generating neutrons, wherein neutrons are generated by a nuclear reaction by causing the proton to collide with the composite type target under vacuum and the target is cooled by a cooling mechanism of the composite type target. A hydrogen ion generator for proton generation;
An accelerator for accelerating protons generated in the hydrogen ion generator,
A proton irradiation unit for irradiating protons accelerated by an accelerator;
A target for generating protons and generating neutrons,
The accelerator is a linear accelerator;
A neutron generator, wherein the target is the composite target according to claim 3.   The neutron generator according to claim 5, wherein the linear accelerator is a linear accelerator capable of accelerating protons in a range of 2 MeV or more and less than 11 MeV.

Images