JP5697021B2 - Composite type target, neutron generation method using composite type target, and neutron generator using composite type target - Google Patents

Description

  The present invention relates to a target for generating neutrons by causing a proton to collide with a target, a neutron generation method for causing a proton to collide with the target, and a neutron generator by causing a proton to collide with the target. 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.

Boron Neutron Capture Therapy (BNCT), which has been expected as a selective cancer treatment in recent years
Research and development of neutron generation methods and devices for Neutron Capture Therapy) are being actively conducted. These are disclosed in, for example, Patent Documents 1, 2, 3, 4, 5, 6, and 7.

Patent Document 1 discloses that Li (d, n) is produced by causing a 30-40 MeV deuteron beam of a radio frequency quadrupole linear accelerator (RFQ linac) to collide with lithium.
) It is characterized by generating reaction and generating neutrons, and 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 neutron generation method and apparatus using 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 cyclotron type proton storage ring, with a beryllium target provided in the ring. It is characterized by adjusting neutrons 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 of about 11 MeV or more accelerated by an RFQ linac or a drift tube linac with 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 discloses that a linear accelerator is used to generate a fast neutron of 10 keV or more by causing a proton beam of 11 MeV to collide with a beryllium target, and the fast neutron is passed through a moderator such as heavy water to be less than 10 keV. It is characterized by adjusting to an epithermal neutron of 0.5 eV or less.

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 large cooling device for cooling the target is required, the thickness of the target for neutron generation is 1 mm or more, and the target material for neutron generation is made of a metal such as heavy metal. Extremely harmful and fast activation neutrons of the equipment members are generated in a mixture of fast neutrons. Therefore, a large speed reduction device is required to decelerate primary neutrons. There are practical problems such as the need for a special safety management system for absorbing or removing protons, neutrons, and nuclear reaction by-products.
In order to solve the above problems, a target for efficiently generating low-energy low-energy thermal neutrons and epithermal neutrons using low-activation proton beams with lower acceleration energy than conventional ones is used. Although the development has been eagerly desired, 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

  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.

  As a result of intensive studies to achieve the above object, the present inventors have significantly reduced the activation of members by protons by using protons with lower energy than before, and more than before. It was found that a composite target including a nonmetallic material and beryllium was very effective as a target for generating neutrons by colliding with low energy protons, and based on this knowledge, the present invention was completed. .

That is, the present invention
1. A composite target in which a target for generating protons and generating neutrons is composed of a non-metallic material and beryllium for reducing activation .
2. 2. The composite target according to 1 above, wherein the target is composed of a substrate made of a non-metallic material and beryllium having a thickness of 0.01 mm or more and less than 1 mm attached to one surface of the substrate.
3. Non-metallic materials to reduce activation, characterized in that it is isotropic graphite in the range of bulk density 1.5g / cm ³ ~3.5g / cm ³ according to any one of the above 1 and 2 Composite type target.
4). 4. The composite target according to any one of 1 to 3 above, wherein a cooling mechanism provided with a refrigerant flow path in a side portion and / or inside of the target is attached.
5. By colliding a proton target for generating neutrons, bulk density 1.5g / cm ³ ~3.5g / cm in the range of ³ isotropic graphite substrate and thickness is deposited on one surface of the substrate 0 .0
A composite target, which is made of beryllium having a size of 1 mm or more and less than 1 mm, and has a cooling mechanism provided with a refrigerant flow path in a side portion and / or inside of the target.
6). In a neutron generation method for generating a neutron by causing a proton to collide with a target, the proton is a proton of 4 MeV or more and less than 11 MeV, the target is the composite target of 5 above, and the proton collides with the target under vacuum A neutron generation method characterized by generating neutrons by nuclear reaction and removing heat generated by the nuclear reaction by a cooling mechanism of the target.
7). 7. The neutron generation method according to 6 above, wherein the beryllium surface of the composite target faces the traveling direction of the proton beam.
8). Hydrogen ion generator for proton generation, accelerator for accelerating protons generated in the hydrogen ion generator, proton irradiation unit for irradiating protons accelerated by the accelerator, and protons in the irradiation unit collide with neutrons In the neutron generator including a target for generating, the accelerator is a linear accelerator, the target is the composite target of the above 5, and the proton irradiation so that the beryllium surface of the target faces the traveling direction of the proton A neutron generator characterized by being arranged at the end of the part.
9. 9. The neutron generator according to 8 above, wherein the linear accelerator is a linear accelerator capable of accelerating protons in a range of 4 MeV or more and less than 11 MeV.

  Since the target of the present invention is a composite target composed of beryllium and a non-metallic material, a nuclear reaction caused by collision with a proton can be shared by the above two kinds of materials. The unique physical properties of protons and neutrons of beryllium and non-metallic materials that make up composite targets can reduce activation by protons and neutrons, and absorption of low-energy neutrons with reduced harmful and high-activation fast neutrons Effects such as being low, the generation of fast neutrons due to neutron deceleration being suppressed, and the removal of heat from the nuclear reaction heat being easy due to the sharing of nuclear reactions. Further, in the composite type target of the present invention, since the non-metallic material can function as a support material and a coolant for beryllium, beryllium can be cut or melted even if beryllium is thinner than the beryllium conventionally used as a target. A secondary effect that can be prevented is obtained. Due to these features, the composite target of the present invention can use lower-energy protons than before, reduce activation, and stably generate low-energy neutrons.

  In the neutron generation method of the present invention, a proton having a lower energy than conventional ones is used as a proton for generating neutrons, and a composite target based on a nonmetallic material is used as a target. For this reason, the neutron generation method of the present invention has the features that the activation of the member by protons can be significantly reduced, and neutrons suitable for medical use such as BNCT can be selectively generated by a small-scale method.

In addition, the neutron generator of the present invention uses a linear accelerator, which is a dramatically smaller accelerator than conventional synchrotrons and cyclotrons, and a proton beam with lower energy and higher current than that generated by the linear accelerator. A new composite target that can efficiently generate medical neutrons with low toxicity is used. Accordingly, the neutron generator of the present invention has a feature that a large speed reduction device and a large activation prevention device for controlling harmful and high activation neutrons (fast neutrons) are not necessarily required. Therefore, the neutron generator of the present invention can be installed in a small medical institution.

It is a section lineblock diagram illustrating the composition of the compound type target concerning an embodiment. It is a cross-sectional block diagram which illustrates the structure of the composite type target which attached the cooling mechanism. It is the schematic which illustrates the neutron generation method which concerns on embodiment. It is the schematic which illustrates the neutron generator which concerns on embodiment.

In the present invention, neutrons are generated by colliding a proton having lower energy than that of a conventional target composed of beryllium and a nonmetallic material. On the beryllium side of the composite target, a nuclear reaction ⁹ Be (p, n) reaction occurs. On the non-metallic material side of the composite target, a ¹² C (p, n) reaction occurs when the non-metallic material is carbon.

  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.

  FIG. 1 is a schematic view illustrating the configuration of a composite target according to this embodiment. In FIG. 1, a composite target 3 according to this embodiment for generating neutrons by colliding protons is composed of a nonmetallic material 2 and beryllium 1, and the surface of the beryllium 1 and the nonmetallic material 2. Have a structure in which the surface of the surface is in contact via a boundary surface. By doing so, it is possible to share the nuclear reaction caused by proton collision between the two types of materials. The reason for choosing beryllium (beryllium 1) as one material constituting the composite target 3 is that the level of activation is very low compared to heavy metals, and the rate of harmful and high activation due to nuclear reaction with protons. The generation rate of low-energy neutrons with reduced neutrons is relatively high, the handling is easier than conventional liquid targets such as mercury and liquid lithium, and the melting point of beryllium is relatively high at 1278 ° C. Etc.

  For example, as shown in FIG. 1, when the surface of beryllium 1 is directed so as to face the traveling direction of protons, the proton is made beryllium 1 by making the thickness of beryllium 1 thinner than the theoretical range of protons. It can be designed to cause a nuclear reaction by some protons in the process of passing through and a nuclear reaction by the remaining protons in the process of passing through the nonmetallic material 2. Therefore, since the heat load due to the nuclear reaction does not concentrate on one kind of material, the heat load borne by the material can be reduced.

The thickness of the beryllium 1 in the composite target 3 can be made much thinner than the theoretical range of protons in beryllium. This is because the non-metallic material 2 can function as a support material and a coolant for the beryllium 1. Moreover, it is because the thermal load which each material bears for the said reason is reduced. For example, since the theoretical range of 11 MeV protons in beryllium is about 0.94 mm, in the case of a target composed only of conventional beryllium, the beryllium needs to have a thickness of 1 mm or more. However, the beryllium 1 in the composite target 3 according to the present embodiment can be made considerably thinner than 1 mm. The beryllium thickness in the composite target of the present invention is preferably 0.01 mm or more.
less than 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 will be significantly reduced.
It is preferable that it is m or more. Moreover, 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.

FIG. 1 (composite target 3 according to the present embodiment) does not particularly limit the surface area of the beryllium surface in the composite target of the present invention. Normally, the maximum value of the heat load per unit area of the target is regarded as the proton output divided by the proton irradiation area, so the heat removal capability from the beryllium surface must be designed to be greater than the target heat load. I must. For example, the proton output necessary for generating medical neutrons such as BNCT is estimated to be about 30 kW at the maximum. For example, the proton acceleration energy is 12 MeV, and the proton irradiation area is the diameter. If it is 60 mm, the heat load is about 10 MW / m ² . Conventionally, since one type of target material has been used, for example, when beryllium having a thickness of 2 mm and a diameter of 60 mm is used, the direct cooling method by water cooling of the beryllium surface is difficult, so that the surface area is larger than that of beryllium. A direct cooling method via a large heat conduction plate has been proposed (Patent Document 6). However, in the present invention, since the thermal load of beryllium can be reduced by using a composite target composed of two kinds of materials, there is no need to limit the surface area of beryllium.

Another reason for using a composite target as a non-metallic material is mainly to reduce activation by irradiated protons and generated 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. The non-metallic material constituting the composite target of the present invention is preferably a material that has high neutron generation efficiency and is difficult to be activated, preferably has little absorption of thermal and epithermal neutrons, and has a high neutron moderating effect It is preferable to have a high density in order to efficiently carry out a nuclear reaction with protons, to have a high radiation resistance, to have a high melting point in order to withstand a heat load, and to generate heat generated from beryllium. In order to remove heat, it is preferable to have excellent thermal conductivity, and it is preferable to have excellent adhesion to beryllium. Examples of such non-metallic materials include isotropic graphite , diamond, diamond-like carbon, glassy carbon, silicon carbide, silicon nitride, and composite materials thereof. Among these materials, isotropic graphite is most preferable because it has the above-mentioned balanced physical properties. Isotropic graphite 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. Conventional isotropic graphite can be used, and isotropic graphite improved to a higher density is more preferable.

  Note that the present invention does not particularly limit the ratio of the beryllium and the nonmetallic material in the thickness direction in the composite target. In the present invention, the ratio can be appropriately set according to the acceleration energy of the nonmetallic material to be used and the irradiation proton, but usually the thickness of the nonmetallic material is set to 10 times or more the thickness of beryllium. .

  As shown in FIG. 1, the composite target 3 according to the present embodiment has a structure in which the surface of the beryllium 1 and the surface of the nonmetallic material 2 are in contact via a boundary surface. In the case of the relatively thick beryllium 1, such a structure can be produced, for example, by subjecting the one surface of the nonmetallic material 2 to hot pressing or HIP treatment. On the other hand, in the case of relatively thin beryllium, for example, it can be produced by vapor-depositing beryllium on one surface of a nonmetallic material.

  In addition, the entire target of the non-metallic material in the composite target according to the present invention is coated with a radiation-resistant / corrosion-resistant metal material such as titanium as desired, and the entire target is placed under vacuum, so that the atmosphere Oxidation degradation in an oxidizing atmosphere due to contact with the substrate can be prevented.

FIG. 2 is a schematic view illustrating a composite target with a cooling mechanism according to the embodiment. As shown in FIG. 2, the composite target 7 with the cooling mechanism according to the present embodiment includes a beryllium 1, a nonmetallic material 2, a cooling mechanism 4 provided on the side of the composite target, and the inside of the composite target. Provided with a cooling mechanism 5 and a heat transfer plate 6.

  The composite target of the present invention preferably has a cooling mechanism attached to remove the heat of reaction generated by the nuclear reaction at the target. The cooling mechanism is preferably a cooling mechanism in which a refrigerant flow path is provided on the side and / or inside of the composite target in order to increase the cooling efficiency. As shown in FIG. 2, when a cooling mechanism (cooling mechanism 4) is provided on the side of the composite target, a method of water cooling through a metal plate (heat transfer plate 6) having high thermal conductivity is preferable. In the case where a cooling mechanism (cooling mechanism 5) is provided inside the composite target, it is preferable to provide a coolant channel inside the non-metallic material of the composite target, and heat conduction such as helium gas as the coolant. It is preferable to use a gas having high properties. Further, the composite target of the present invention can have a cartridge type structure in which the target and the cooling mechanism are integrated.

  FIG. 3 is a schematic view illustrating a neutron generation method according to the embodiment. An arrow 8 in FIG. 3 indicates the flow of protons that collide with the composite target 7. Moreover, the arrow 9 in FIG. 3 shows the flow of generated neutrons.

In the neutron generation method according to the present embodiment, low energy in which fast neutrons that are harmful and have high activation ability are reduced by colliding a proton of lower energy than that in the past with the composite target 7 shown in FIG. 2 under vacuum. Generate neutrons. In this embodiment, as a target, a composite target 7 composed of a substrate made of isotropic graphite (nonmetallic material 2) and beryllium 1 having a thickness of 0.01 mm or more and less than 1 mm attached to one surface of the substrate is used. Use. Thereby, in the neutron generation method according to the present embodiment, the activation level is very low compared to heavy metals, and the generation efficiency of low energy neutrons with reduced harmful and high activation fast neutrons compared to heavy metals. As a result, it is possible to prevent the heat load associated with the nuclear reaction from being borne only by beryllium, so that the cooling mechanism for removing heat can be made compact. Moreover, since the cooling mechanism provided with the refrigerant flow path in the side and / or inside of the target is attached, the cooling efficiency of the composite target 7 can be increased. As shown in FIG. 3, when the cooling mechanism 4 is provided on the side portion of the composite target 7, a method of water cooling via a metal plate (heat transfer plate 6) having high thermal conductivity is preferable. Further, when the cooling mechanism 5 is provided inside the composite target 7, it is preferable to provide a refrigerant flow path inside the non-metallic material 2 of the composite target 7, and heat conductivity such as helium gas as the refrigerant. It is preferable to use a high gas.

  The acceleration energy of protons used in the neutron generation method in the present invention is preferably 4 MeV or more and less than 11 MeV, more preferably 6 MeV or more and 8 MeV or less. When the proton acceleration energy is less than 4 MeV, the generation efficiency of neutrons is remarkably reduced. Therefore, the proton acceleration energy used in the present invention is preferably 4 MeV or more. In addition, when the acceleration energy of the proton is 11 MeV or more, not only the activation of the member becomes remarkable, but also the generation of fast neutrons increases, and a highly toxic radioactive material such as tritium may be by-produced. The acceleration energy of the proton used is preferably less than 11 MeV. More preferable proton acceleration energy is 6 MeV or more and 8 MeV or less in order to reduce the activation of the member and selectively generate low energy neutrons with reduced harmful and high activation fast neutrons.

  In the neutron generation method according to this embodiment, the collision between the proton and the composite target 7 is performed under vacuum in order to prevent air scattering and air contamination of the proton.

In the present embodiment, as shown in FIG. 3, the beryllium 1 surface of the composite target 7 is provided so as to face the proton traveling direction, so that a large part of the nuclear reaction with the proton occurs in the first reaction. This is because beryllium is preferable. Although it is possible to direct the surface of the non-metallic material in the direction of the proton, the density of the non-metallic material is low, so a thick material is required to slow down the irradiated proton, and the surface of the beryllium is advanced by the proton. It is not preferable as compared with the case of turning in the direction.

  Neutrons that can be generated by the neutron generation method of the present invention are low-energy neutrons that contain a large amount of thermal neutrons or epithermal neutrons. Low-energy neutrons are neutrons that are reduced from harmful and high activation fast neutrons. Fast neutrons are biologically harmful and have a very high activation ability because their energy is two orders of magnitude higher than thermal neutrons or epithermal neutrons. Types of neutrons include fast neutrons, epithermal neutrons, thermal neutrons, and cold neutrons, but these neutrons are not clearly separated in terms of energy, but are reactor physics, shielding, dosimetry, analysis Energy categories differ depending on the medical field. 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 referred to in the present invention means a neutron in which fast neutrons of 0.5 MeV or more are reduced. When the irradiation proton energy exceeds 8 MeV, neutrons of 0.5 MeV or more may be included, but the degree can be considerably reduced as compared with the conventional primary neutrons.

  FIG. 4 is a schematic view illustrating the configuration of the neutron generator according to the embodiment. As shown in FIG. 4, the neutron generator according to this embodiment includes a composite target 7, a hydrogen ion generator 13, a linear accelerator 14, and a proton irradiation unit 15.

  In FIG. 4, the accelerator for generating protons in the neutron generator according to the present embodiment is a linear accelerator (linear accelerator 14). Conventionally, large accelerators such as synchrotrons and cyclotrons have been used to use high energy protons of 11 MeV or higher as protons for colliding with the target. However, since the present invention uses protons of 4 MeV or more and less than 11 MeV, linear accelerators are used. However, it is possible to generate sufficiently high-current protons. In addition, the arrow 11 in FIG. 4 shows the flow of acceleration protons.

  A hydrogen ion generator 13 is provided at one end of the linear accelerator, and hydrogen ions from the hydrogen ion generator 13 enter the acceleration cavity through the charged particle conversion film and are accelerated. An arrow 10 in FIG. 4 indicates the flow of the hydrogen ions. The hydrogen ion generation part (hydrogen ion generator 13 in this embodiment) of the present invention is not particularly limited, and a conventional proton generator, negative hydrogen ion generator, or the like can be used. As the acceleration cavity, a high-frequency acceleration cavity, a DC acceleration cavity, a normal conduction acceleration cavity, a superconductivity acceleration cavity, or the like can be used.

  The proton irradiation unit of the present invention (in this embodiment, the proton irradiation unit 15) is not particularly limited, and a conventional proton irradiation unit including a quadrupole electromagnet and a deflection electromagnet can be used. In addition, the arrow 12 in FIG. 4 shows the flow of irradiation protons. Moreover, the arrow in FIG. 4 shows the flow of generated neutrons.

The proton accelerated by the linear accelerator 14 is guided to the proton irradiation unit 15 connected to the tip of the linear accelerator 14 and collides with the composite target 7 provided at the tip of the proton irradiation unit 15. It generates low energy neutrons with reduced harmful and high activation fast neutrons. The composite type target 7 is a composite type target with a cooling mechanism as shown in FIG. That is, the beryllium surface of the composite target 7 is provided so as to face the traveling direction of protons. The cooling mechanism attached to the composite type target 7 is a cooling mechanism in which a refrigerant flow path is provided on the side and / or inside the composite type target as shown in FIG. As described above, the composite target 7 can have a cartridge structure in which the target and the cooling mechanism are integrated. Since the neutron generator according to the present embodiment is provided at the tip of the accelerator via a vacuum flange having a semi-automatic desorption structure, it can be easily attached and detached with a new one by remote control when the target is deteriorated. It has the feature.

  As described above, the present invention is a novel composite target for causing a proton to collide with a target to generate neutrons, and a neutron generation method and apparatus using the composite target. In the embodiments described above, since the acceleration energy of the irradiation proton is a low energy proton of 4 MeV or more and less than 11 MeV, the activation of the member by the proton is remarkably reduced, and the generation of harmful fast neutrons is suppressed. Acceleration protons can be generated with a small linear accelerator, and a composite target composed of beryllium and a non-metallic material is used as a target. The ability to selectively generate neutrons, the easy removal of reaction heat associated with nuclear reactions, the cooling mechanism attached to the target, efficient cooling, Since it is possible to have a cartridge type structure integrated with the cooling mechanism, the target is provided at the tip of the proton irradiation unit, Upon deterioration of Getto, it has a feature that the attachment and detachment exchange of a new one can be carried out simply by remote control.

  Further, as described above, the nonmetallic material contained in the composite target can have a neutron moderating effect. In the composite target, generation of fast neutrons is reduced. Thereby, in embodiment described above, the deceleration mechanism for decelerating the generated neutron can be reduced in size.

  Therefore, the neutron generator according to the present invention can be installed in a small medical institution 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]
Neutron generation experiments were performed using the method and apparatus shown in FIGS. Hydrogen ions generated by a hydrogen ion generator are introduced into a normal conduction linear accelerator having a length of about 6.5 m, accelerated to 4 MeV under a vacuum of 10 ⁻⁶ Pascal, sent to an irradiation unit, and collided with a composite target. Neutrons were generated. As the composite target, beryllium having a thickness of 0.1 mm was attached to one side of isotropic graphite (manufactured by Toyo Tanso Co., Ltd .: IG15, bulk density 1.90 g / cm ³ ) having a diameter of 165 mm and a thickness of 30 mm. A composite type target was used, and this was attached to the tip of the proton irradiation part via a flange so that the beryllium surface was perpendicular to the traveling direction of the proton. For cooling, a 1 mm-thick copper plate was wound around the side surface of the composite target, and an annular water-cooling jacket was attached thereon, and the entire target was water-cooled. After 100 hours of operation, the degree of activation of the entire neutron generator was measured with a survey meter. The energy distribution of the generated neutrons was measured using a gas radiation detector disclosed in Japanese Patent Application Laid-Open No. 2008-243634.

[Example 2]
Except that the acceleration energy of the irradiation proton was 8 MeV and the beryllium thickness of the composite target was 0.5 mm, neutrons were generated in the same manner as in Example 1, and the degree of activation and the energy distribution of the neutrons were measured. did.

[Example 3]
Except that the acceleration energy of irradiated protons was 10 MeV and the beryllium thickness of the composite target was 0.6 mm, neutrons were generated in the same manner as in Example 1, and the degree of activation and the energy distribution of neutrons were measured. did.

[Comparative Example 1]
For comparison, neutrons were generated by irradiating the target with 12 MeV protons accelerated using the linear accelerator of Example 1. A beryllium target having a diameter of 165 mm and a thickness of 2 mm was used as the target. The beryllium target was water cooled by attaching a copper plate having a diameter of 165 mm and a thickness of 1 mm to one side of beryllium, and attaching a water cooling jacket on the copper plate. This target was attached to the tip of the proton irradiation unit via a flange. The degree of activation and the energy distribution of neutrons were measured using the same measuring instrument as in Example 1.

Table 1 shows the experimental results obtained from the degree of activation and the neutron energy distribution measured in Examples 1 to 3 and Comparative Example 1.

  From the above results, using the method and apparatus of the present invention, it is possible to significantly reduce the activation of the member by protons compared to the conventional method and apparatus, and to significantly reduce the generation of fast neutrons without using a moderator. It was confirmed that it was possible. Since the neutron generator of the present invention is a small neutron generator in which a composite target is mounted on a small proton generator equipped with a linear accelerator, it can be easily installed even in a small medical institution.

  Since the present invention uses low energy protons in the range of 4 MeV to less than 11 MeV, activation of the member by protons can be reduced. And this invention can share a part of nuclear reaction with a nonmetallic material by making this proton collide with the composite type target comprised from the nonmetallic material and beryllium which attached the cooling mechanism, Moreover, stable generation of low energy neutrons with reduced harmful fast neutrons is possible. Therefore, the present invention is very useful as a medical neutron generation method and apparatus such as BNCT, and can be easily installed even in a small medical institution.

DESCRIPTION OF SYMBOLS 1 Beryllium 2 Non-metallic material 3 Composite target 4 Cooling mechanism 5 provided in the side part Cooling mechanism 6 provided in the inside 6 Heat transfer plate 7 Composite type target with cooling mechanism 8 Proton flow 9 Neutron flow 10 Hydrogen ion Flow 11 Accelerated proton flow 12 Irradiated proton flow 13 Hydrogen ion generator 14 Linear accelerator 15 Proton irradiation unit

Claims (9)

A target for generating neutrons by bombarding protons reduces activation of isotropic graphite, diamond, diamond-like carbon, glassy carbon, silicon carbide, silicon nitride, or a composite material thereof. A composite target comprising a metal material and beryllium. 2. The composite according to claim 1, wherein the target is composed of a substrate made of a nonmetallic material for reducing the activation and beryllium having a thickness of 0.01 mm or more and less than 1 mm attached to one surface of the substrate. Type target. Non-metallic materials to reduce the activation is in any one of claims 1 and 2, characterized in that it is isotropic graphite in the range of bulk density 1.5g / cm ³ ~3.5g / cm ³ The described composite target. Composite target according to any one of claims 1 to 3, characterized in that supplementary to the sides and or cooling mechanism inside provided a flow path of a refrigerant of said target. By colliding a proton target for generating neutrons, bulk density 1.5g / cm ³ ~3.5g / cm ³ range is adhered to one surface of the isotropic graphite substrate and the substrate with a thickness of 0 .01m
A composite target, which is made of beryllium having a length of m or more and less than 1 mm, and is provided with a cooling mechanism provided with a refrigerant flow path at least on either the side or the inside of the target. In the neutron generation method for generating neutrons by colliding protons with the target,
The proton is a proton of 4 MeV or more and less than 11 MeV,
The target is the composite target of claim 5;
A method of generating neutrons, wherein neutrons are generated by a nuclear reaction by causing the protons to collide with the target in a vacuum, and heat generated by the nuclear reaction is removed by a cooling mechanism of the target. The neutron generation method according to claim 6, wherein the beryllium surface of the composite target faces the traveling direction of protons. 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 claim 5,
A neutron generating apparatus, wherein the beryllium surface of the target is disposed at an end of the proton irradiation section so as to face the proton traveling direction.   The neutron generator according to claim 8, wherein the linear accelerator is a linear accelerator capable of accelerating protons in a range of 4 MeV or more and less than 11 MeV.

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