JP2012243640A - Compound target, neutron generation method using the same, and neutron generator using the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a target for reducing radioactivation of a member due to protons, and a neutron generating method and a neutron generator for generating low energy neutrons, especially ones for medical use, by colliding protons with the target.SOLUTION: A neutron generating method includes: using a novel target formed by combining a lithium material and a non-metal material for reducing radioactivation of a member due to protons; using protons in a range of 2 MeV to 4 MeV as protons to be applied for generating neutrons containing few harmful fast neutrons; and using a downsized linear accelerator as an accelerator.

Description

  The present invention relates to a target for generating neutrons by causing protons to collide with a target, a neutron generation method for causing protons to collide with the target, and a neutron generator by generating protons into neutrons. More specifically, the present invention provides a new target for generating neutrons using protons having lower energy than conventional ones, a neutron generation method using a new target, and a neutron generator using a new target. In particular, the present invention provides a device with excellent compactness for generating medical neutrons.

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 describes 11 MeV accelerated by RFQ linac and drift tube linac.
A target for generating neutrons by colliding a proton beam of a degree or more with a metal target is disclosed. 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 lithium deposited on an iron, tantalum, or vanadium substrate.

Patent Document 12 describes a lithium target for generating a neutron by colliding a proton having an energy of about 2.5 MeV with a target, and the structure of the target for preventing lithium melting is a cone-shaped transmission having a cooling mechanism. It is characterized in that a palladium thin film is provided on the surface of the hot plate, and a lithium thin film is adhered 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 described above, a large accelerator for generating a proton beam or deuteron beam is necessary, and significant activation of a member by a high energy proton beam occurs. A relatively thick target is necessary to prevent a target from being melted in the case of a solid target, a large-scale cooling device for cooling the target is required, a liquid target is not easy to handle If the material is attached to a thermally conductive metal support, and the target material for generating neutrons is made of a metal such as heavy metal, it is extremely harmful to the human body and the activation of the device members is high. Since neutrons are generated in a mixed manner, a large-scale reduction device is required to decelerate the primary neutrons, and harmful and highly active proton beams are neutral. And that nuclear reaction is by-product material requires a special safety management system for absorbing or removing, a problem in the reaction embrittlement prevention of the target material with the active hydrogen by-product, practically equal. In particular, as shown in Patent Document 6, when using a beryllium solid target, it is essential to remove heat generated by the target, 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 efficiently generating low-energy low-energy thermal neutrons and epithermal neutrons using protons with low activation ability and lower activation energy than conventional ones. However, there are currently no known targets that can solve the above problems.

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 Publication No. 2010/0067640

“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, the present invention is a new target for generating neutrons using protons having lower energy than conventional ones, a neutron generation method by colliding protons having lower energy than conventional ones with new targets, And it aims at providing a neutron generator. In more detail, it is possible to reduce the activation of the member by protons and neutrons, it is possible to reduce harmful and high activation neutrons, fundamentally the problem of heat of target materials and hydrogen embrittlement It is an object of the present invention to provide a new neutron generation target that can be solved, a neutron generation method using the target, and a neutron generation apparatus using the target.

  As a result of intensive studies to achieve the above-mentioned problems, the inventors of the present invention can significantly reduce the activation of proton members by using protons with lower energy than before, and more than before. We have found that a composite target composed of a combination of light element materials and non-metallic materials is very effective as a target for generating neutrons by colliding low-energy protons, and the present invention has been completed based on this finding. It came to do.

That is, the present invention
1. A composite target characterized in that a target for generating protons and generating neutrons is a composite target formed by combining a lithium material and a non-metallic material.
2. Composite target according to the above 1, wherein the non-metallic material is isotropic high density graphite in the range of bulk density ^{1.5g / cm 3 ~3.5g / cm 3} .
3. High density graphite isotropic non-metallic material is in a range of bulk density 1.5g / cm ³ ~3.5g / cm ³ and is the non-metallic material formed by combining it with at least one non-metallic materials 2. The composite target according to 1 above, wherein
4). 4. The composite target according to any one of 1 to 3, wherein the surface of the composite target is uneven.
5. The composite type target according to claim 1, wherein at least a surface in contact with the atmosphere in the composite type target is coated.
6). 5. The composite target according to any one of the above 1 to 4, further comprising a cooling mechanism provided with a refrigerant flow path at least on either the side or the inside of the target.
7). The target for generating a neutron by colliding with a proton is the composite type target according to any one of 1 to 4 above, and at least a surface in contact with the atmosphere in the composite type target is coated, and A composite target comprising a cooling mechanism provided with a refrigerant flow path at least on either the side or inside of the composite target.
8). A neutron generation method using a composite target, characterized in that neutrons are generated by causing a proton of 2 MeV or more and less than 4 MeV to collide with the composite target described in 7 above in a vacuum.
9. 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 neutrons by colliding the protons of the irradiation unit,
The accelerator is a linear accelerator;
The target is the composite target according to 7 above,
A neutron generator using a composite target, wherein the composite target is disposed in the proton irradiation section.
10. 10. The neutron generator according to 9 above, wherein the linear accelerator is a linear accelerator capable of accelerating protons in a range of 2 MeV to 4 MeV.

  Since the present invention is a composite target formed by combining a lithium material and a non-metallic material, a nuclear reaction caused by collision with a proton can be shared by the above two types of materials. Due to the unique properties of lithium materials and non-metallic materials with respect to protons and neutrons, not only can the activation of members such as targets by protons and neutrons be significantly reduced than before, but also by using protons with lower energy than before, It is possible to generate low energy neutrons with reduced harmful and high activation fast neutrons, and dramatically improve the surface area of lithium materials by devising the surface shape of lithium and non-metallic materials. Therefore, it is possible to easily remove the heat generated by the target, and low melting point lithium (melting point: about 180 ° C.) that has been difficult to use as a solid target by this efficient heat removal. ) However, it can be used as a solid target, can prevent hydrogen embrittlement of the target material, Ability to prevent peeling at the bonding interface of the metal material, the effect of the like can be obtained. In the target of the present invention, since the non-metallic material can function as a support material and a coolant for the lithium material, it is possible to prevent the melting and melting of lithium even when lithium that is thinner than conventionally used lithium is used. An effect is obtained. Due to these effects, the target of the present invention can reduce activation by using protons having lower energy than before, and stably generate low energy neutrons.

Moreover, the neutron generation method of the present invention uses protons with lower energy than conventional protons for generating neutrons, and the composite target as a target. For this reason, the neutron generation method of the present invention has a feature that it can remarkably reduce the activation of members such as targets by protons and neutrons, and can generate neutrons suitable for medical use such as BNCT by a small-scale method. .

  In addition, the neutron generator of the present invention is harmful by using a linear accelerator, which is a dramatically smaller accelerator than conventional synchrotrons and cyclotrons, and a proton beam having a lower energy and a higher current than that generated by the linear accelerator. A new composite target capable of efficiently generating low-performance medical neutrons is used. As a result, the neutron generator of the present invention does not necessarily require a large-scale decelerator and a large-scale activation prevention device for controlling harmful and high-activation fast neutrons (fast neutrons), which were conventionally required. It has the feature of not. Therefore, the neutron generator of the present invention can be installed in a smaller medical institution than before.

The composite target in the present invention is a composite target made of a lithium material and a nonmetallic material. The main reason for making the target a composite target composed of a lithium material and a non-metallic material is to share the nuclear reaction caused by the collision with the proton between the two materials. ⁷ Li (p, n) reaction is caused on the lithium material side of the composite target, and ¹² C (p, n) is used on the nonmetallic material side of the composite target, for example, when the nonmetallic material is carbon. Cause a reaction. As described above, since the nuclear reaction is shared by the lithium material and the non-metallic material, in the composite target in the present invention, due to the unique properties of the lithium material and the non-metallic material such as carbon with respect to protons and neutrons, In addition to significantly reducing activation of the target such as the target by protons and neutrons, it is possible to use protons having a relatively lower energy than conventional ones, and therefore, it is possible to generate neutrons with lower energy. In the composite target according to the present invention, it is possible to fundamentally solve the thermal problem of the target, the problem of embrittlement of the target material due to active hydrogen by-produced by the reaction, and the like.

The role of the lithium material in the composite target of the present invention is to generate neutrons by collision with protons. The lithium material in the present invention refers to lithium (only a single element of lithium element) made from only lithium element, a lithium compound made from lithium element, and a lithium composite material. Examples of lithium compounds include lithium oxide (Li ₂ O), lithium nitride (Li ₃ N), lithium carbonate (Li ₂ CO ₃ ), lithium sulfate (Li ₂ SO ₄ ), lithium nitrate (LiNO ₃ ), and phosphoric acid. Lithium (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), Titanium Lithium oxide (Li ₄ Ti ₅ O ₁₂ ), Lithium titanate (Li ₂ TiO ₃ )
, Lithium niobate (LiNbO ₃ ), lithium tantalate (LiTaO ₂ ), lithium cobaltate (LiCoO ₂ ), and the like, but are not limited thereto. Examples of the lithium composite material include, but are not limited to, lithium borate glass, lithium alloy, lithium glass ceramic, lithium solid solution ceramic, and the like. The reason why the lithium material in the present invention is the above-mentioned lithium, lithium compound, and lithium composite material is that all of these lithium materials cause ⁷ Li (p, n) reaction. Of these ⁷ Li (p, n) reactions, the lithium material used in the present invention is preferably a lithium material having a lower nuclear reaction threshold, more preferably a lithium material having a higher neutron generation efficiency, and less likely to be activated. Lithium material is preferable, lithium material with low absorption of thermal and epithermal neutrons is preferable, lithium material with high neutron moderating effect is preferable, lithium material with high radiation durability is preferable, and high melting point to withstand heat load The lithium material is more preferable, the lithium material having excellent thermal conductivity for removing heat generated by the collision with the proton is preferable, and the lithium material having excellent adhesion to the nonmetallic material is more preferable. As such a lithium material, lithium made only of lithium element is preferable. Lithium is preferable because it has a low melting point (melting point: about 180 ° C.) but a low threshold for nuclear reaction (threshold for ⁷ Li (p, n) reaction: about 2 MeV).

The main reason for making the composite target of the present invention a non-metallic material is to reduce activation by protons and neutrons, and generate low energy neutrons with reduced harmful and high activation fast neutrons. This is because a non-metallic material is preferable compared to metals. Moreover, it is because a nonmetallic material is excellent in thermal diffusivity compared with metals. The non-metallic material of the present invention includes each of carbon and silicon that are group 4 elements in the periodic table, nitrogen and phosphorus that are group 5 elements, oxygen and sulfur that are group 6 elements, and halogen that is a group 7 element. Among the elements (these elements are referred to as non-metallic elements in the present invention), they are a single material of each element, a compound of each element, and a composite material of each element. The non-metallic material used in the present invention is preferably a non-metallic material that is difficult to be activated among these non-metallic materials, more preferably a non-metallic material that has a high neutron generation efficiency, Non-metallic materials with less absorption are preferred, non-metallic materials with a high neutron moderation effect are preferred, non-metallic materials with high density are preferred for efficient reaction with protons, and radiation durability is preferred, A non-metallic material having a high melting point is preferable to withstand a heat load, a non-metallic material having excellent thermal diffusibility to diffuse the heat generated by the target is preferable, and a non-metallic material having excellent adhesion to a lithium material is preferable. A metal material is more preferable. Examples of such non-metallic materials include isotropic high density graphite, porous carbon, diamond, diamond-like carbon, glassy carbon, carbon nanotube, fullerene, polyacetylene, carbine, graphene, carbon fiber, carbon nitride, silicon carbide. , Silicon, silicon nitride, and composite materials thereof, but are not limited thereto. Among these materials, isotropic high-density graphite not only has the above-mentioned well-balanced physical properties, but is particularly excellent in thermal diffusibility and is a material that does not easily generate radionuclides. It is most preferable because it also has the property of hardly causing hydrogen embrittlement. High density graphite material isotropy in the present invention are typically those bulk density is in the range of 1.5g / cm ³ ~3.5g / cm ³ can be used. In the present invention, the bulk density is 1.5 g /
Isotropic high density graphite less than cm ³ is not unusable, but if the bulk density is less than 1.5 g / cm ³ , collisions between carbon atoms, protons and neutrons may be insufficient. The bulk density is preferably 1.5 g / cm ³ or more. Further, when the bulk density exceeds 3.5 g / cm ³ , the stable phase under normal pressure is diamond, so the maximum value of the bulk density of the isotropic high-density graphite existing as a substance is 3.5 g / cm ³ . is there. As the isotropic high-density graphite used in the present invention, isotropic high-density graphite used as a conventional industrial material can be used, and isotropic high-density graphite improved to a higher density is preferable.

Non-metallic material in the present invention, by combining the most preferred bulk density 1.5g / cm ³ ~3.5g / cm density graphite and other non-metallic materials isotropic in the range of ³ in non-metallic materials It can be set as the nonmetallic composite material. One or more non-metallic materials may be combined. Examples of such non-metallic materials include porous carbon, diamond, diamond-like carbon, glassy carbon, carbon nanotube, fullerene, polyacetylene, carbine, graphene, carbon fiber, carbon nitride, silicon carbide, silicon, and the like mentioned above. Although silicon nitride and these composite materials can be mentioned, it is not limited to these. Composites with isotropic high-density graphite include, for example, pasting of molded bodies of isotropic high-density graphite and other non-metallic materials, mixing of isotropic high-density graphite and other non-metallic materials, etc. It can be carried out by a combination of isotropic high density graphite and other non-metallic materials. The component ratio of the isotropic high-density graphite is not particularly limited, but is usually 50% or more. By doing so, it is possible to provide a favorable cooperative effect between the isotropic high-density graphite and other non-metallic materials. For example, it is possible to further improve the thermal conductivity and thermal diffusibility of the target by combining isotropic high-density graphite and diamond or carbon nanotubes having excellent thermal conductivity.

  In addition, the nonmetallic material in the present invention can be appropriately added with a reinforcing material as desired in order to improve the mechanical strength in use. 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 remove the heat generated by the target. Usually, 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 more than the heat load of the target. . For example, the maximum proton power required to generate medical neutrons such as BNCT is about 30 kW maximum.
Since it is estimated to be ～60KW, for example, the surface area of the target is assumed to be 30 cm ^2, the heat load is also a ^{10MW / m 2 ~20MW / m 2} . Conventionally, since one type of target material has been used, for example, when a target material having a surface area of 30 cm ² is used, it is difficult to directly cool the surface of the target material by water cooling. A cooling method via a conductive plate 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. In contrast, the composite target of the present invention, which is a composite of a lithium material and a non-metallic material, can share the thermal load between the two materials of the lithium material and the non-metallic material. Although effective to solve the problem, as described below, the composite of lithium material and non-metallic material in the composite target of the present invention is very effective.

  Since the heat generated in the target is removed in principle by heat conduction or heat diffusion at the material interface, in the composite target of the present invention, lithium material and non-metal material are used to increase heat conductivity and heat diffusion. Is made. That is, the main reason for performing the composite of the lithium material and the nonmetallic material in the composite target of the present invention is that the thermal conductivity at the interface between the two materials is increased by increasing the specific surface area of the lithium material and the nonmetallic material. It is to improve thermal diffusivity. By increasing the specific surface area of the target constituent material, the actual surface area of the target can be made larger than the plane area, so the heat generated inside the target is quickly conducted to the target surface by heat conduction and thermal diffusion. This makes it possible to efficiently remove heat by an indirect or direct cooling mechanism provided on the side or inside of the target. The specific surface area is a surface area of a material having a unit mass. The substantial surface area of the target is the sum of the specific surface areas of the lithium material and the non-metallic material that constitute the target. Further, the plane area of the target is an area when the surface of the target is projected onto the parallel plane. In the composite target of the present invention, a structure in which the surface of the lithium material and the surface of the nonmetallic material are in contact with each other through the boundary surface by the composite of the lithium material and the nonmetallic material is formed. As the structure of the boundary surface, a simple planar shape or various complicated shapes are formed, but a curved surface shape or an uneven shape boundary surface is preferable because it has a larger surface area than a flat surface. In addition, it is preferable that the boundary surface is made of a combination of a lithium material and a non-metallic material because direct heat conduction is performed through the boundary surface. In addition, secondary effects of the combination of lithium material and non-metallic material include such effects as improved adhesion between lithium material and non-metallic material, relaxation of thermal stress at the interface, and prevention of delamination at the interface. It is done.

  As described above, the composite target of the present invention can make the specific surface area of the target larger than the plane area by combining lithium material and non-metallic material. The standard for actively expanding the specific surface area of the target is preferably at least twice the plane area of the target. If the specific surface area of the target is more than twice the plane area, heat conduction to the target surface will be faster, and efficient heat removal will be possible without providing a large heat conduction plate for heat removal on the target surface. Therefore, it is preferable.

As a specific embodiment of the composite target of the present invention, for example, a lithium material and a nonmetallic material are bonded to each other and formed into a target. A mixture of a material and a powdered non-metallic material is formed on a target. A fine particle of lithium material is dispersed in a porous non-metallic material, and this is formed on a target. A powdered non-metallic material is coated with a lithium material. However, the present invention is not limited to these, and the like. For example, it is possible to increase the specific surface area of the target by several times the plane area by molding the surface of a lithium material or non-metallic material with a concavo-convex shape on the target. Since the powdery material is much larger than the specific surface area of the bulk material, the specific surface area of the target is about 100 times the plane area by molding a mixture of powdered lithium material and powdered non-metallic material on the target. It is possible to improve. For the same reason, it is possible to increase the specific surface area of the target by about 1000 times the plane area by forming a target in which fine particles of lithium material are dispersed in a non-metallic material.

The composite method in the composite target of the present invention is appropriately determined according to the composite form, the type and thickness of the lithium material and non-metal material used, and is not limited to a specific processing method. For example, the lithium material is lithium, and the composite of lithium and a nonmetallic material can be combined by hot pressing, HIP treatment, vapor deposition, or the like. In the case where a relatively thick lithium and a nonmetallic material are bonded together, hot pressing or HIP treatment is preferable, and in the case where a relatively thin lithium and a nonmetallic material are bonded together, vapor deposition is preferable. Hot pressing of lithium and non-metallic materials can usually be performed at a temperature from room temperature (23 ° C.) to 180 ° C. (melting point of lithium at normal pressure) and a pressure of 10 ³ kilopascals to 10 ⁵ kilopascals. The HIP treatment is usually performed at a temperature from room temperature to 180 ° C., 10 ⁴ kilopascals to 1
0 can be carried out under pressure ⁶ kPa, deposition room temperature non-metallic materials substrate to 1
The reaction can be performed at a temperature of up to 80 ° C. and a pressure of 10 ⁻³ Pascal to 10 ⁻⁶ Pascal. The unevenness treatment of the lithium material surface or the non-metallic material surface can be performed by a conventional method such as laser ablation, etching, or mold forming. Lithium material and non-metallic material can be pulverized by conventional methods such as mechanical pulverization, freeze pulverization, plasma atomization, and spray drying. The coating of lithium material on non-metallic materials is, for example, CVD (
This is possible by chemical vapor deposition. The fine particles of the lithium material can be dispersed in the nonmetallic material by, for example, an impregnation method for catalyst preparation. In addition, the coating of the non-metallic material surface with the lithium material by the CVD method, for example, allows the gaseous lithium material precursor to pass through the surface of the non-metallic material under a high temperature in an inert atmosphere and thermally decomposes the precursor. It can be performed by a method of depositing a lithium material. In addition, the dispersion of the fine particles of the lithium material into the non-metallic material by the impregnation method is performed by, for example, impregnating a porous non-metallic material with an aqueous solution of a precursor of the lithium material and then firing it in a reducing or oxidizing atmosphere. This can be performed by supporting fine particles of the material on the pores of the nonmetallic material.

The thickness of the lithium material in the composite target of the present invention is not particularly limited because it is possible to share the neutron generation reaction caused by the collision of protons with the nonmetallic material, but the theoretical flight of the proton in the lithium material is not limited. It can be made much thinner. This is because the non-metallic material functions as a support material and a coolant for the 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 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, a thickness of 2 mm or more is required. Met. However, lithium in the composite target of the present invention can be made 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 lithium material and the non-metallic material in the thickness direction. In the composite target of the present invention, the ratio can be appropriately set according to the lithium material or non-metallic material to be used and the acceleration energy of the irradiation proton. Usually, the thickness of the non-metallic material is the thickness of the lithium material. Set to 10 times or more. The main reason for this is that the neutron generation efficiency of non-metallic materials is usually one order of magnitude smaller than that of lithium materials.

  The composite target of the present invention can be a composite target having an uneven surface. The main reason for forming the uneven shape on the target surface is to suppress excessive heat concentration on the target surface by increasing the surface area of the surface. The roughening treatment of the target surface can be performed by a conventional method such as laser ablation, etching, or molding.

  The composite target of the present invention can cover at least the surface of the composite target that is in contact with the atmosphere. This main purpose is to prevent oxidative degradation in an oxidizing atmosphere due to contact with the air by placing the composite target under vacuum. The coating may be a coating only on the surface of the composite target in contact with the atmosphere, or may be a coating on the entire surface of the composite target. The coating material for coating is not particularly limited, but light metal materials and non-metal 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, titanium, titanium nitride, magnesium, aluminum, boron, tin, zinc, silicon, various ceramic materials, and the like. Of these, titanium is preferable because of its excellent radiation durability and corrosion resistance. Examples of non-metallic materials include, but are not limited to, epoxy resins and glass fibers.

  The composite target of the present invention can be accompanied by a cooling mechanism for removing heat generated in the target. The cooling mechanism is preferably a cooling mechanism in which at least one of the side part and the inside of the target is provided with a refrigerant flow path in order to increase the cooling efficiency. When a cooling mechanism is provided on the side of the target, it is preferable to perform water cooling via a heat transfer plate having high thermal conductivity. Further, when a cooling mechanism is provided inside the target, it is preferable to provide a coolant channel inside the non-metallic material in the target. As the refrigerant, it is preferable to use a gas having high thermal conductivity such as helium gas. The target of the present invention can have a cartridge type structure in which the target and the cooling mechanism are integrated. By doing so, it is possible to efficiently exhaust heat generated in the target, and when the target is deteriorated, it is possible to easily attach and detach it with a new one by remote control.

  The neutron generation method of the present invention is a neutron generation method of generating neutrons by colliding a composite target of the present invention with protons of 2 MeV or more and 4 MeV or less under vacuum. The composite target of the present invention is a cooling system in which at least the surface of the composite target that contacts the atmosphere is coated, and at least one of the side part and the inside of the composite target is provided with a coolant channel. A composite target with a mechanism can be used. The composite target with the surface coating and the cooling mechanism attached to the composite target was prevented from oxidative deterioration in an oxidizing atmosphere due to the target being in contact with the atmosphere, and occurred in the target. This is for efficient heat removal.

In the neutron generation method of the present invention, the protons are allowed to collide with the composite target under vacuum in order to prevent the intensity of the irradiated protons from being reduced and to prevent air pollution. Therefore, although it is never over the high vacuum, the degree of vacuum is usually in the range of 10 ⁻⁴ Pascal to 10 ⁻⁸ Pascal. The reason why the acceleration energy of irradiated protons is 2 MeV or more and 4 MeV or less is to generate low energy neutrons with reduced fast neutrons. The acceleration energy of the protons needs to be set appropriately depending on the type of lithium material constituting the composite target of the present invention.

In the neutron generation method of the present invention, when the lithium material is lithium and a composite target composed of lithium and a nonmetallic material is used, the acceleration energy of the irradiation proton is preferably 2 MeV or more and 4 MeV or less. Since the threshold value of the ⁷ Li (p, n) reaction of lithium is about 2 MeV, if the proton acceleration energy is less than 2 MeV, the generation efficiency of neutrons is significantly reduced. Therefore, the proton acceleration energy used in the present invention is 2 MeV. The above is preferable. 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.

Neutrons that can be generated by the neutron generation method 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. The 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 having an acceleration energy of 2 MeV or more and 4 MeV or less used in the present invention are irradiated to the composite target of the present invention (lithium is used as a lithium material), neutrons having an average energy of about 0.3 MeV can be generated.

  The neutron generator of the present invention includes a hydrogen ion generator for generating protons, an accelerator for accelerating protons generated in the hydrogen ion generator, and a proton irradiation unit for irradiating protons accelerated by the accelerator, And a target for generating neutrons by colliding the protons irradiated by the proton irradiation unit, a linear accelerator is provided as the accelerator, the composite target of the present invention is used as the target, and a composite type It can be set as the neutron generator which has arrange | positioned the target in the said proton irradiation part. As the composite target of the present invention, at least the surface of the composite target that is in contact with the atmosphere is coated, and at least one of the side part and the inside of the composite target is provided with a coolant channel. A composite target with a mechanism can be used. The above-mentioned composite type target that is coated with a surface and has a cooling mechanism is used to prevent oxidative degradation in an oxidizing atmosphere due to the target coming into contact with the atmosphere, and to occur in the target. This is for efficient heat removal.

The hydrogen ion generator in the neutron generator of the present invention is provided with a hydrogen ion generator for generating protons or negative hydrogen ions. The hydrogen ion generator that can be used in the neutron apparatus of the present invention is not particularly limited, and a conventional hydrogen ion generator can be used. The hydrogen ions generated in the hydrogen ion generator are usually sent to an accelerator for accelerating protons through the charged particle conversion membrane. When negative hydrogen ions are generated in the hydrogen ion generator, the negative hydrogen ions are converted into protons by passing through the charged particle conversion membrane. The converted protons are then sent to an accelerator for acceleration.

The accelerator used in the neutron generator of the present invention is a linear accelerator, but is not particularly limited as long as it is a linear accelerator, and a 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 generates high-current protons in a smaller device than electrostatic accelerators, but also generates very little radiation such as gamma rays and X-rays. More preferred.

  The proton irradiator in the neutron generator of the present invention is configured to irradiate the target with protons accelerated by an accelerator, and generally performs target convergence, proton energy classification, etc. with a target for generating neutrons. And a proton beam adjusting means. The proton irradiation unit is not particularly limited, and a proton irradiation unit including a conventional quadrupole electromagnet or deflection electromagnet can be used.

The neutron generator of the present invention can use a linear accelerator capable of accelerating protons in a range of 2 MeV to 4 MeV as a linear accelerator for accelerating protons. In the neutron generator of the present invention, a linear accelerator capable of accelerating protons in the range of 2 MeV to 4 MeV is used because of the low energy in which fast neutrons that are harmful and have high activation ability are reduced by a relatively small linear accelerator. This is to generate neutrons.

FIG. 1 is a cross-sectional view illustrating that the target according to the embodiment is a composite target having a shape in which a lithium material and a nonmetallic material are bonded to each other. FIG. 2 is a cross-sectional view illustrating that the target according to the embodiment is a composite target having a shape in which a lithium material is bonded to a nonmetallic material having an uneven surface. FIG. 3 is a cross-sectional view illustrating that the target according to the embodiment is a composite target having a shape in which a lithium material and a nonmetallic material are bonded to each other, and the lithium material has an uneven surface. FIG. 4 is a cross-sectional view illustrating that the target according to the embodiment is a composite target formed by molding a mixture of a lithium material and a nonmetallic material. FIG. 5 is a cross-sectional view illustrating that the target according to the embodiment is a composite target formed by molding a nonmetallic material in which fine particles of lithium material are dispersed. FIG. 6 is a cross-sectional view illustrating that the target according to the embodiment is a composite target in which a non-metallic composite material obtained by combining isotropic high-density graphite and another non-metallic material and a lithium material are bonded together. FIG. FIG. 7 is a cross-sectional view illustrating that the target according to the embodiment is a composite target having a shape in which the surface of the composite target is surface-coated. As the composite target, any one of composite targets as shown in FIGS. 1 to 6 can be used. FIG. 8 shows that the target according to the embodiment is a composite target having a shape with a cooling mechanism provided with a coolant channel in at least one of the side and the inside of the composite target. It is sectional drawing which illustrates this. As the composite target, any one of composite targets as shown in FIGS. 1 to 6 can be used. FIG. 9 shows an example in which the target according to the embodiment is provided with a cooling mechanism in which the surface of the composite target is surface-coated and a refrigerant flow path is provided in at least one of the side and the inside of the composite target. It is sectional drawing which illustrates that it is the composite type target of the cartridge type structure which is doing. As the composite target, any one of composite targets as shown in FIGS. 1 to 6 can be used. FIG. 10 is a schematic view illustrating a neutron generation method using the composite target of the present invention according to the embodiment. As the composite target of the present invention, a composite target having a cartridge type structure as shown in FIG. 9 can be used. FIG. 11 is a schematic view illustrating a neutron generator using the composite target of the present invention according to the embodiment. As the composite target of the present invention, a composite target having a cartridge type structure as shown in FIG. 9 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 the present embodiment for generating neutrons by colliding with protons is a composite target formed by combining a lithium material and a nonmetallic material, and the surface of the lithium material and the nonmetallic material passes through an interface. The target has a structure in contact with each other. As a lithium material, lithium can be mentioned as a preferred material. Moreover, as a nonmetallic material, isotropic high density graphite can be mentioned as a preferable material. Examples of the target having a structure in which the surface of the lithium material and the nonmetallic material are in contact with each other through the interface include, for example, a target in which the lithium material and the nonmetallic material are bonded to each other, a powdered lithium material, and a powdered nonmetallic material A target made by molding a mixture of the above, a target made by molding a non-metallic material in which fine powder of lithium material is dispersed, a target in which a lithium material and a non-metallic material are bonded by the combination of both materials, etc. Although it can illustrate, it is not limited to these. The non-metallic material may be a single material or a non-metallic composite material obtained by combining a plurality of non-metallic materials.

  As shown in FIG. 1, the composite target 3 according to this embodiment is a composite target in which a lithium material 2 and a nonmetallic material 1 are bonded together.

  As shown in FIG. 2, the composite target 5 according to the present embodiment is a composite target in which a lithium material 2 is bonded onto a nonmetallic material 4 having an uneven surface 40.

  As shown in FIG. 3, the composite target 7 according to this embodiment is a composite target in which a lithium material 6 having an uneven surface 60 and a nonmetallic material 1 are bonded together.

  As shown in FIG. 4, the composite target 9 according to the present embodiment is a composite target made by molding a mixture 8 of a lithium material and a nonmetallic material.

  As shown in FIG. 5, the composite target 11 according to the present embodiment is a composite target made by molding a target material 10 in which fine particles of a lithium material are dispersed in a nonmetallic material.

  As shown in FIG. 6, the composite target 13 according to the present embodiment is a composite type in which a nonmetallic composite material 12 formed by combining isotropic high-density graphite and another nonmetallic material and a lithium material 2 are bonded together. Is the target.

  As shown in FIG. 7, the composite target 16 according to this embodiment is a composite target in which a surface coating 15 is applied to the surface of the composite target 14. The composite target 14 is any one of the composite targets as shown in FIGS.

As shown in FIG. 8, the composite target 20 according to the present embodiment includes a target attached with a cooling mechanism 18 in which a coolant channel 17 is provided in at least one of the side part and the inside of the composite target 14. This is a cartridge-type target with an integrated cooling mechanism. As the composite target 14, any one of the composite targets as shown in FIGS. 1 to 6 can be used. Further, a heat transfer plate 19 can be provided between the cooling mechanism 18 and the composite target 14 as necessary.

  As shown in FIG. 9, the composite type target 21 according to the present embodiment has a surface coating 15 applied to the surface of the composite type target 14, and a refrigerant flow path at least on one side or inside of the composite type target 14. 17 is a composite target of a cartridge type structure with a cooling mechanism 18 provided with 17. As the composite target 14, any one of the composite targets as shown in FIGS. 1 to 6 can be used. Further, a heat transfer plate 19 can be provided between the cooling mechanism 18 and the composite target 14 as necessary.

  In the neutron generation method according to the present embodiment, low-energy neutrons that are reduced in harmful and high-activation fast neutrons by colliding protons with relatively low energy compared to the prior art into the composite target of the present invention under vacuum. This is a method of generating neutrons.

  FIG. 10 is a schematic view illustrating a neutron generation method according to the embodiment. As shown in FIG. 10, in the neutron generation method according to the present embodiment, a low-energy neutron is generated by causing a proton 23 having a predetermined acceleration energy (2 MeV or more and 4 MeV or less) to collide with the composite target 22 of the present invention in a vacuum. This is a neutron generation method for generating 24. As the composite target 22 of the present invention, a composite target having a cartridge type structure with a surface coating as shown in FIG. 9 and an accompanying cooling mechanism can be used.

  FIG. 11 is a schematic view illustrating a neutron generator according to the embodiment. As shown in FIG. 11, the neutron generator according to this embodiment includes a hydrogen ion generator 29, a linear accelerator 30, a proton irradiation unit 31, and a composite target 32 provided in the proton irradiation unit. The hydrogen ion generator 29 is provided with a hydrogen ion generator, and the generated hydrogen ions 25 are usually introduced into the linear accelerator 30 through the charged particle conversion film and accelerated. The protons 26 accelerated to a predetermined energy by the linear accelerator 30 are introduced into the proton irradiation unit 31 connected to the tip of the linear accelerator 30 and collide with the composite target 32 provided in the proton irradiation unit 31. Thus, low energy neutrons 28 are generated. The linear accelerator 30 is not particularly limited as long as it is a linear accelerator capable of generating protons of 2 MeV or more and 4 MeV or less. The proton irradiation unit 31 is usually provided with a quadrupole electromagnet or a deflection electromagnet. As the composite target 32, a composite target having a cartridge structure with a surface coating as shown in FIG. 9 and an accompanying cooling mechanism can be used.

  As described above, the present invention is a novel target for generating a neutron by causing a proton to collide with the target, and a neutron generation method and apparatus using the target. In the embodiments described so far, the acceleration energy of the irradiation protons is a relatively low energy proton of 2 MeV or more and 4 MeV or less, so that the activation of the member such as the target by the proton is remarkably reduced, and the harmful high speed. Neutron generation is suppressed, acceleration protons can be generated with a small linear accelerator, and a composite target composed of a composite of lithium and non-metallic materials is used as a target, which is harmful and highly radioactive. Low-energy neutron generation with reduced fast neutrons is possible, heat removal from the target is easy to remove, and a cooling mechanism is attached to the target for efficient cooling. In addition, since it is possible to make a cartridge type structure in which the target and the cooling mechanism are integrated, Min provided, has the feature that the removable exchange with new upon target degradation can be simplified by remote control.

In addition, as described above, the nonmetallic material included in the target of the present invention can have a neutron moderating effect, so that the generation of fast neutrons is reduced. Thereby, in embodiment described above, the deceleration mechanism for decelerating the generated neutron can be reduced in size compared with the past.

  Therefore, the neutron generator according to the present invention can be installed in a medical institution smaller than before as a medical neutron generator for generating medical neutrons such as BNCT.

  The present invention will be specifically described below with reference to examples.

[Example 1]
A neutron generation experiment was performed using a target of a composite target having a cartridge type structure as shown in FIG. 9, a neutron generation method as shown in FIG. 10, and a neutron generator as shown in FIG. The target of the cartridge type structure has a thickness of 0.1 on one side of isotropic high-density graphite (manufactured by Toyo Tanso Co., Ltd .: IG15, bulk density 1.9 g / cm ³ ) having a diameter of 165 mm × thickness 30 mm. 1 is a composite target produced by pressing a 2 mm lithium sheet under HIP processing conditions of 150 ° C.-1000 atm. A thin titanium film with a thickness of 0.1 mm is 150 ° C.-1000 on the surface of the target. It is a cartridge type structure target in which a surface coating is applied by pressure bonding under atmospheric pressure HIP processing conditions, and a cooling mechanism is integrated with a target in which a cylindrical water cooling jacket is provided on the side of the target. This is attached to a proton irradiation part provided at the tip of an RFQ linac having a length of about 6.5 m via a flange so that the lithium surface is perpendicular to the traveling direction of the proton, and an acceleration proton with an output of 30 kW and 3 MeV. ^Were collided under a vacuum of 10 ^-6 Pascals to generate neutrons. The target was cooled by introducing 10 liters of water at about 5 ° C. per minute into the water cooling jacket. The energy distribution of generated neutrons after 100 hours of operation was measured with a gas radiation detector. The degree of activation of the target after the experiment was measured by a survey meter. Moreover, the state of the target after the experiment was observed.

[Example 2]
A neutron generation experiment was performed by the same method and apparatus as in Example 1 except that the target portion of the composite target having the cartridge type structure as shown in FIG. 9 was changed to the following composite type target as shown in FIG. The composite target is formed by applying laser ablation (light source: YAG laser) on one side of isotropic high-density graphite (Toyo Tanso Co., Ltd. product: IG15, bulk density 1.9 g / cm ³ ) having a diameter of 165 mm and a thickness of 30 mm The composite target shown in FIG. 2 was prepared by roughening the surface by applying a lithium sheet having a thickness of 0.2 mm under HIP treatment conditions of 150 ° C. to 1000 atm. This is a composite target having a surface coated by pressure bonding a thin titanium layer with a thickness of 0.1 mm on the surface under HIP processing conditions of 150 ° C.-1000 atm. As in Example 1, the energy distribution of the generated neutrons, the degree of activation of the target, and the state of the target were examined.

[Example 3]
A neutron generation experiment was performed by the same method and apparatus as in Example 1 except that the target portion of the composite target having the cartridge type structure as shown in FIG. 9 was changed to the following composite type target as shown in FIG. The composite type target has a lattice shape by laser ablation on one side of isotropic high-density graphite (manufactured by Toyo Tanso Co., Ltd .: IG15, bulk density 1.9 g / cm ³ ) having a diameter of 165 mm and a thickness of 30 mm. Irregularities (concave part: 8 mm x 8 mm x dent 0.2 mm, convex part: width 1 mm) are applied, and a 0.2 mm thick lithium sheet is layered on the irregular surface and pressure-bonded under HIP processing conditions of 150 ° C-1000 atm. It is a composite type target as shown in FIG. 2 prepared by removing lithium protruding after embedding lithium in the recess, and a thin titanium film with a thickness of 0.1 mm on the surface of the target is 150 ° C. to 1000 atm. It is a composite target that has been surface-coated by pressure bonding under HIP processing conditions. As in Example 1, the energy distribution of the generated neutrons, the degree of activation of the target, and the state of the target were examined.

[Example 4]
A neutron generation experiment was performed by the same method and apparatus as in Example 1 except that the target portion of the composite target having a cartridge type structure as shown in FIG. 9 was changed to the following composite type target as shown in FIG. . The composite type target has a lithium sheet having a thickness of 0.2 mm on one side of isotropic high-density graphite (manufactured by Toyo Tanso Co., Ltd .: IG15, bulk density 1.9 g / cm ³ ) having a diameter of 165 mm and a thickness of 30 mm. A shape as shown in FIG. 3, which is pressure-bonded under HIP processing conditions of 150 ° C. to 1000 atm, and has a concavo-convex shape (lattice-shaped groove having a width of 10 microns × depth of 10 microns × pitch of 10 mm) by laser ablation on the lithium surface. This is a composite target in which a surface of the target is coated by press-bonding a thin titanium layer having a thickness of 0.1 mm under HIP treatment conditions of 150 ° C. to 1000 atm. Although the amount of lithium used was reduced by about 2% due to the formation of irregularities on the lithium surface by the laser ablation, the surface area of the lithium surface was increased about 4 times. As in Example 1, the energy distribution of the generated neutrons, the degree of activation of the target, and the state of the target were examined.

[Example 5]
A neutron generation experiment was conducted by the same method and apparatus as in Example 1 except that the target portion of the composite target having a cartridge type structure as shown in FIG. 9 was changed to the following composite type target as shown in FIG. The composite target is composed of powdered lithium (average particle size: 10 microns) and powdered isotropic high-density graphite (manufactured by Toyo Tanso Co., Ltd .: average particle size 50 microns, bulk density 2.2 g / cm ^3). 4) prepared by HIP treatment of a mixture of powdered lithium (powdered lithium: powdered isotropic high-density graphite mass ratio = 1: 500) at 150 ° C. to 1000 atm. FIG. 4 shows a diameter of 165 mm × thickness of 30 mm. Such a composite target is a composite target in which a surface of the target is coated by pressing a 0.1 mm thick titanium thin film under a HIP treatment condition of 150 ° C. to 1000 atm. The surface area of lithium contained in the target was calculated to be about 100 times larger than the surface area of block-like lithium. As in Example 1, the energy distribution of the generated neutrons, the degree of activation of the target, and the state of the target were examined.

[Example 6]
A neutron generation experiment was conducted by the same method and apparatus as in Example 1 except that the target portion of the composite target having a cartridge type structure as shown in FIG. 9 was changed to the following composite type target as shown in FIG. The composite target is composed of lithium atom-encapsulated C ₆₀ fullerene (containing one lithium atom per fullerene molecule) and powdered isotropic high-density graphite (manufactured by Toyo Tanso Co., Ltd .: average particle size 50). A mixture of micron and bulk density 2.2 g / cm ³ (lithium-encapsulated fullerene: powder isotropic high-density graphite mass ratio = 1: 5) in a nitrogen gas atmosphere under conditions of 1000 ° C. to 1000 atm. 5 is a composite type target having a diameter of 165 mm and a thickness of 30 mm as shown in FIG. 5, and a titanium thin film having a thickness of 0.1 mm is pressure-bonded to the surface of the target under HIP processing conditions of 1000 ° C. to 1000 atm. This is a composite target having a surface coating. As in Example 1, the energy distribution of the generated neutrons, the degree of activation of the target, and the state of the target were examined.

[Example 7]
A neutron generation experiment was conducted by the same method and apparatus as in Example 1 except that the target portion of the composite target having a cartridge type structure as shown in FIG. 9 was changed to the following composite type target as shown in FIG. The above composite target is lithium titanate (Li ₄ Ti ₅ O ₁₂ ) (
Ishihara Sangyo Co., Ltd. manufactured product: LT-017, average particle size 20 microns) and powdered isotropic high density graphite (Toyo Tanso Co., Ltd. manufactured product: average particle size 50 microns, bulk density 2.2 g / cm ³ ) 165 mm diameter and thickness produced by HIP treatment of a mixture of (lithium titanate: powdered isotropic high-density graphite mass ratio = 1: 5) in a nitrogen gas atmosphere at 1000 ° C. to 1000 atm. A composite target as shown in FIG. 5 with a thickness of 30 mm, and a surface coating is applied by pressure-bonding a thin titanium layer with a thickness of 0.1 mm to the surface of the target in a nitrogen atmosphere under HIP processing conditions of 1000 ° C. to 1000 atmospheres. Composite target. As in Example 1, the energy distribution of the generated neutrons, the degree of activation of the target, and the state of the target were examined.

[Example 8]
A neutron generation experiment was conducted by the same method and apparatus as in Example 1 except that the target portion of the composite target having a cartridge type structure as shown in FIG. 9 was changed to the following composite type target as shown in FIG. The composite target is composed of powdered lithium disilicate (Li ₂ O.2SiO ₂ ) glass ceramic (average particle size 20 microns) and powdered isotropic high-density graphite (manufactured by Toyo Tanso Co., Ltd .: average particle size) A mixture (powdered lithium disilicate glass ceramic: mass ratio of powdered isotropic high density graphite = 1: 5) having a diameter of 50 microns and a bulk density of 2.2 g / cm ^{3 is} 1000 in a nitrogen gas atmosphere. A composite target as shown in FIG. 5 having a diameter of 165 mm and a thickness of 30 mm produced by HIP treatment under the condition of ° C.-1000 atm. A titanium thin film with a thickness of 0.1 mm is formed on the surface of the target in a nitrogen gas atmosphere. It is a composite target that has been surface-coated by pressure bonding under the HIP processing conditions of 1000 ° C. to 1000 atm. As in Example 1, the energy distribution of the generated neutrons, the degree of activation of the target, and the state of the target were examined.

[Example 9]
A neutron generation experiment was conducted by the same method and apparatus as in Example 1 except that the target portion of the composite target having a cartridge type structure as shown in FIG. 9 was changed to the following composite type target as shown in FIG. The composite target is composed of powdered lithium tantalate-alumina solid solution (average particle size: 20 microns, mass ratio of lithium tantalate: alumina = 1: 5) and powdered isotropic high-density graphite (Toyo Tanso Co., Ltd.) Company product: average particle size 50 microns, bulk density 2.2 g / cm ³ ) (powdered lithium tantalate-alumina solid solution: powdered isotropic high density graphite mass ratio = 1: 5) A composite target as shown in FIG. 5 having a diameter of 165 mm and a thickness of 30 mm produced by HIP treatment under conditions of 1000 ° C. and 1000 atmospheres in a nitrogen gas atmosphere, and having a thickness of 0.1 mm on the surface of the target. This is a composite type target that has been surface-coated by pressure bonding titanium thin film in a nitrogen gas atmosphere under HIP processing conditions of 1000 ° C. to 1000 atm. As in Example 1, the energy distribution of the generated neutrons, the degree of activation of the target, and the state of the target were examined.

[Example 10]
A neutron generation experiment was performed by the same method and apparatus as in Example 1 except that the target portion of the composite target having the cartridge type structure as shown in FIG. 9 was changed to the following composite type target as shown in FIG. The composite type target is a porous carbon material (average particle size 200 microns, specific surface area 600 m ² / g, average pore size 10 nanometers, bulk density 1.5 g /
cm ³ )), lithium fine particles (lithium loading ratio: 2% by mass) are adjusted by supporting fine particles of lithium on the surface by impregnation method, and powdery isotropic high density graphite. (Product manufactured by Toyo Tanso Co., Ltd .: average particle size 100 microns, bulk density 2.2 g / c
m ³ ) (lithium-supported carbon material: mass ratio of powdered isotropic high-density graphite = 1:
10) is a composite target as shown in FIG. 5 having a diameter of 165 mm and a thickness of 30 mm produced by HIP treatment at 150 ° C.-1000 atm, and a titanium thin film with a thickness of 0.1 mm on the surface of the target. Is a composite type target that is surface-coated by pressure bonding under a HIP treatment condition of 150 ° C. to 1000 atm. The surface area of lithium contained in the target was calculated to be about 1000 times larger than the surface area of block-like lithium. Similarly to Example 1, the energy distribution of generated neutrons, the degree of activation of the target after the experiment, and the state of the target after the experiment were examined.

[Example 11]
A neutron generation experiment was conducted by the same method and apparatus as in Example 1 except that the target portion of the composite target having the cartridge type structure as shown in FIG. 9 was changed to the following composite type target as shown in FIG. The composite target is composed of powdered isotropic high-density graphite (manufactured by Toyo Tanso Co., Ltd .: average particle size 50 microns, bulk density 2.2 g / cm ³ ), powdered industrial diamond (Showa Denko Co., Ltd.) Manufactured product: average particle size 20 microns) and a mixture of carbon nanotubes (Ryosan Trading Co., Ltd. product: CVD-MWNT) (powder isotropic high density graphite: powdered industrial diamond: mass of carbon nanotubes Ratio = 8: 1: 1) was subjected to HIP treatment at 500 ° C.-1000 atm to prepare a carbon molded body having a diameter of 165 mm × thickness of 30 mm, and then a 150 mm lithium sheet having a thickness of 0.2 mm was formed on one side of the molded body. A composite target as shown in FIG. 6 produced by pressure bonding under the HIP processing conditions of ℃ -1000 atmospheres, and a thin titanium film with a thickness of 0.1 mm is 150 ℃ on the surface of the target. A composite target which has been subjected to surface coating by crimped HIP process conditions 1000 atm. As in Example 1, the energy distribution of the generated neutrons, the degree of activation of the target, and the state of the target were examined.

[Example 12]
A neutron generation experiment was conducted by the same method and apparatus as in Example 1 except that the target portion of the composite target having the cartridge type structure as shown in FIG. 9 was changed to the following composite type target as shown in FIG. The composite target is a silicon carbide molded body having a diameter of 165 mm and a thickness of 30 mm [mixture of silicon carbide powder and silicon powder using a belt-type high-temperature and high-pressure apparatus (silicon carbide: silicon mass ratio = 9: 1). 6 was prepared by pressing a lithium sheet having a thickness of 0.2 mm on one side of H.sub.2 at a temperature of 150.degree. C. to 1000 atm. It is a composite type target as shown in the figure, and is a composite type target that is surface-coated by pressure bonding a thin titanium layer with a thickness of 0.1 mm to the surface of the target under HIP processing conditions of 150 ° C. to 1000 atm. As in Example 1, the energy distribution of the generated neutrons, the degree of activation of the target, and the state of the target were examined.

[Comparative Example 1]
For comparison, a lithium target having a diameter of 165 mm × thickness of 0.2 mm was prepared by pressure bonding to a cylindrical copper plate having a diameter of 165 mm × length of 30 mm × thickness of 1 mm under HIP processing conditions of 150 ° C. to 1000 atm. A neutron generation experiment was performed by the same method and apparatus as in Example 1 except that a lithium target was used and a cylindrical water cooling jacket was provided on this side to cool the water. As in Example 1, the energy distribution of the generated neutrons, the degree of activation of the target, and the state of the target were examined.

  The experimental results of Examples 1 to 11 and Comparative Example 1 are shown in Table 1.

[Simulation by theoretical calculation]
In order to theoretically explain the experimental results of the above examples and comparative examples, activation simulation was performed, and the results shown in Table 2 were obtained. The simulation was performed using JENDL-4.0 (Non-patent Document 1), which is a theoretical calculation program for the nuclear reaction cross section of the neutron nuclear reaction.

  From the above results, it was confirmed that the composite target of the present invention has higher heat resistance than the conventional target, is not easily activated, and has excellent durability against hydrogen embrittlement. The experimental results of proton and neutron activation were also supported theoretically. Moreover, it was confirmed that the generation of fast neutrons can be reduced by the neutron generation method and the neutron generator using the composite target of the present invention.

  Since the target of the present invention is a composite target composed of a composite of a lithium material and a non-metallic material, the activation of a member by protons and neutrons can be reduced. The target of the cartridge type structure that can reduce the generation of neutrons and can solve the thermal problem of the target by combining the lithium material and the non-metallic material. It is possible to remove the heat efficiently, and it is possible to safely and easily perform replacement and replacement with a new one by remote control when the target is deteriorated. Moreover, low energy neutrons can be generated using a small linear accelerator by a neutron generation method and a neutron generator using the composite target of the present invention. Therefore, the present invention is very useful in generating medical neutrons such as BNCT.

DESCRIPTION OF SYMBOLS 1 Nonmetallic material 2 Lithium material 3 Composite type target 4 Nonmetallic material 5 which has an uneven | corrugated surface 5 Composite type target 6 Lithium material which has an uneven | corrugated surface 7 Composite type target 8 Molded object of mixture of lithium material and nonmetallic material 9 Composite type target DESCRIPTION OF SYMBOLS 10 Nonmetallic material compact 11 in which fine particles of lithium material are dispersed 11 Composite target 12 Compact 13 formed by combining isotropic high density graphite material and other nonmetallic material 13 Composite target 14 Composite target 15 Surface Coating 16 Composite type target 17 Refrigerant flow path 18 Cooling mechanism 19 Heat transfer plate 20 Composite type target 21 Composite type target 22 Cartridge type target 22 Composite type target 23 Proton flow 24 Neutron flow 25 Hydrogen ion flow 26 Acceleration proton flow 27 Flow of irradiated protons 28 Flow of generated neutrons 29 Hydrogen ion generator 0 linac 31 proton irradiation unit 32 combined type target

Claims (10)

  A composite target characterized in that a target for generating protons and generating neutrons is a composite target formed by combining a lithium material and a non-metallic material. Composite target according to claim 1, wherein the non-metallic material is isotropic high density graphite in the range of bulk density ^{1.5g / cm 3 ~3.5g / cm 3} . It said non-metallic material is a bulk density 1.5g / cm ³ ~3.5g / cm ³ density graphite and isotropic in the range, which at least one non-metallic material with a non-metallic material comprising in combination The composite target according to claim 1, wherein the target is a composite target.   The composite target according to any one of claims 1 to 3, wherein the surface of the composite target is uneven.   The composite type target according to any one of claims 1 to 4, wherein at least a surface of the composite type target that is in contact with air is coated.   The composite type target according to any one of claims 1 to 4, further comprising a cooling mechanism provided with a refrigerant flow path at least in one of a side portion and an inside of the composite type target. .   The target for generating a neutron by colliding with a proton is the composite type target according to any one of claims 1 to 4, wherein at least a surface in contact with the atmosphere in the composite type target is coated, and A composite target comprising a cooling mechanism provided with a refrigerant flow path at least on one of the side and the inside of the composite target.   A neutron generation method using a composite target, wherein neutrons are generated by causing a proton of 2 MeV or more and less than 4 MeV to collide with the composite target according to claim 7 under vacuum. 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 the accelerator;
A target for generating neutrons by colliding the protons irradiated by the proton irradiation unit,
The accelerator is a linear accelerator;
The target is a composite target according to claim 7,
A neutron generator using a composite target, wherein the composite target is disposed in the proton irradiation section.   The neutron generator according to claim 9, wherein the linear accelerator is a linear accelerator capable of accelerating protons in a range of 2 MeV to 4 MeV.

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