JP5522564B2 - Radioisotope production method and apparatus - Google Patents

Description

In the present invention, radioactive isotopes used for radiodiagnostics and the like are used as radioactive wastes composed of a wide range of isotopes (for example, strontium 90 to cesium 137) having a high intensity and a long half-life without using nuclear fuel material ²³⁵ U. The present invention relates to a manufacturing method and an apparatus which can be generated efficiently and inexpensively without generating a large amount and enable stable supply.

  At present, in the medical field, radiation and radioisotopes (radioisotopes; hereinafter also referred to as RI) are indispensable for diagnosing and treating diseases. Radiation emitted from RI can be reliably detected and quantified even if the amount of the substance itself is very small, and examination and diagnosis are performed by scintigraphy using this property. The pharmaceutical used for this is called a so-called “radiopharmaceutical”, and the RI used for the radiopharmaceutical or the like is suitable to emit a gamma ray having a short half-life and a large permeability.

Examples of RI used for radiopharmaceuticals and examples of use thereof include, for example, ^99m Tc for brain / thyroid / bone scintigraphy, ⁶⁷ Ga for breast cancer / lung cancer / malignant lymphoma treatment, ²⁰¹ Tl for parathyroid gland / tumor / myocardium Scintigraphy, ⁶⁰ Co is a gamma knife radiation source, ³² P is leukemia treatment, ³⁵ S is DNA base sequence / gene chromosome arrangement determination, ⁵¹ Cr is measurement of circulating blood volume / recirculating red blood cell volume, ⁵⁹ Fe is binding to total iron in serum (TIBC) measurement, ⁸⁹ Sr, ¹⁵³ Sm, ¹⁸⁶ Re for pain relief, ⁹⁰ Y for malignant lymphoma treatment, ¹⁰³ Pd for prostate cancer treatment, ¹²⁵ I for tumor marker, ¹³¹ I for hyperthyroidism and thyroid cancer treatment ¹³³ Xe is a local lung ventilation function test, etc.

Of these RIs, ^99m Tc, ⁹⁰ Y, ¹³¹ I, and ¹³³ Xe are currently fissioned by neutron irradiation in a nuclear reactor using highly enriched ²³⁵ U enriched with ²³⁵ U from 36% to 93%. It is manufactured by reacting and extracting from its fission products. This method of using enriched ²³⁵ U is particularly problematic from the viewpoint of non-proliferation, and the International Atomic Energy Agency (IAEA) and others are working to switch to technologies that use low-enriched raw materials with a ²³⁵ U enrichment of 20% or less. The technology development corresponding to it is advanced all over the world. However, despite 30 years of work, most RIs in the world are still produced using highly enriched ²³⁵ U. On the other hand, when low-concentration ²³⁵ U with a ²³⁵ U enrichment of 20% or less is used as a raw material for RI production, a new problem arises that the amount of plutonium produced increases about 25 times. Therefore, the target RI is irradiated with thermal neutrons (0.025 eV) from the reactor, such as ⁶⁰ Co, ³² P, ³⁵ S, ⁵¹ Cr, ⁵⁹ Fe, ⁸⁹ Sr, ¹⁵³ Sm, and ¹⁸⁶ Re, and the generated RI is extracted. Methods are also being used. A method of irradiating a target with charged particles from a cyclotron, such as ⁶⁷ Ga, ²⁰¹ Tl, ¹⁰³ Pd, and ¹²⁵ I, is also used.

Some RIs are manufactured in Japan, but most of them rely on imports from overseas. However, in 2007, it became difficult to obtain radiopharmaceuticals because of a problem with a Canadian reactor. In August 2008, a Dutch reactor supplying approximately 26% of ⁹⁹ Mo to the global market stopped operation due to partial corrosion deformation of the bottom structure of the primary cooling system, and started operation in mid-February 2009. It was resumed. However, in May 2009, a heavy water leak was detected again in a Canadian reactor, and the operation was halted. The recovery is considered to be early as of the end of March 2010. In this way, if most of RI is relied on by imports from other countries, it is expected that a stable supply system cannot be maintained due to domestic circumstances in other countries, aging of reactors, maintenance, troubles, etc., and stable supply of RI Has become an important and urgent issue. In particular, in Canada, where Japan relies on imports of most RIs, it is expected that the nuclear reactors for the supply will reach the operation permit deadline in 2011. There is no realistic plan from a long-term perspective. In the United States and Europe, the stable supply of RI including ⁹⁹ Mo is eagerly awaited, but a realistic system that can cope with it has not been taken, and it is necessary to establish the system as soon as possible ( Non-patent document 1). In addition, if most of RI is dependent on imports from overseas, the price of RI used in medical treatments will rise, and this will cause a rise in overall medical costs. In 2007, the sales price of radiopharmaceuticals reached 44 billion yen (Non-patent Document 2: Page 5).

In addition, when ²³⁵ U is fissioned in a nuclear reactor, various nuclides are generated in addition to the desired RI as shown in FIG. 1 (Non-Patent Document 3), and storage, management, processing, etc. of unnecessary nuclear waste are generated. Became enormous and very annoying.

In consideration of such problems, the present applicants have, ²³⁵ without using a ^U, efficiently producing a highly radioactive molybdenum ^{99 Mo} which is the parent nuclide of radioactive technetium ^{99m Tc,} which is often used as a radioactive diagnostic agent The technique which performs is proposed (patent document 1). In the proposed method, an aqueous Mo solution in which a Mo compound is dissolved in water is irradiated with neutrons in an irradiation capsule installed in the core of a nuclear reactor to generate ⁹⁹ Mo by a ⁹⁸ Mo (n, γ) reaction. It is intended to produce ⁹⁹ Mo efficiently by recovering Mo aqueous solution continuously or batchwise. Likewise Patent Document 2, using a ^{98 Mo,} a technique for generating radioactive molybdenum ^{99 Mo} by thermal neutron capture reaction is proposed. However, in the case of using these thermal neutron capture reactions, since the reactor is used, the production site is limited, and in addition to being largely dependent on the operation mode of the reactor, the production cost is expensive and the reaction cross section is small. The specific activity was low and there was a problem in production efficiency. In addition, considering the safety of nuclear reactors, for example, there may be a situation where it is necessary to stop the operation for half a year, for example, during periodic inspections. In order to easily and stably supplying the ^{99 Mo} facilities such as hospitals these circumstances, it was necessary further technical devices.

  On the other hand, it is also performed to generate a RI by irradiating a raw material target with a proton or heavy ion beam using an accelerator. In the case of protons, by making the accelerator used compact, it can be easily used in facilities such as hospitals. However, when generating RI using protons emitted from such a small accelerator, it can only cope with RI of light nuclides, and avoiding enlargement of the accelerator when trying to cope with RI of heavy nuclides. There was a problem that could not. That is, when generating a RI using protons, the proton has a positive charge, so to react with the target nucleus of a heavy nuclide (although it is a nucleus with many positively charged protons) Because there is a repulsive interaction between positive charges, we have to overcome this and get inside the nucleus. For that purpose, the energy of the incident protons needs to be sufficiently high. Furthermore, when protons are incident on the target material, the proton energy in the target is greatly reduced, so that the thickness of the target that can be used is limited, and as a result, the efficiency of generating sufficient RI is often not high. On the other hand, the energy loss in the target increases the temperature of the target, and the use intensity of the proton beam may be limited for a target having a low melting point. By the way, the proton beam is generated by an accelerator and transported through the vacuum pipe to a nearby location where the target is set. However, when the target is set on the atmosphere side, it is necessary to maintain the vacuum in the vacuum pipe and shut off the atmosphere side portion. The material used for blocking is required to be as thin as possible in order to suppress a decrease in the energy and intensity of the proton beam. However, if this material is continuously irradiated with a proton beam, it is destroyed as a result of radiation damage, so that it is difficult to use a high-intensity proton beam for a long time. In order to manufacture various RI according to the purpose, if the target material can be set in the atmosphere, the shape and material of the target can be selected flexibly, which is practically very convenient. However, as described above, RI generation using a proton beam has a problem. These circumstances are similar for heavy ion beams. The problem is greater than the amount of positive charges more than protons.

JP 2008-102078 A Special Table 2002-504231

“Accelerating production of medical isotopes” Nature Vol 457, 29 January 2009 Science Council of Japan Basic Medical Committee / General Engineering Committee Meeting Task Review Subcommittee on Radioactive and Radioactive Utilization “Proposal: Stable Supply System of Radioisotopes in Japan” July 24, 2008 Nuclear Physics A462 (1987) 85-108 North-Holland, Amsterdam

The present invention solves the above-mentioned problems of the prior art, does not use the enrichment ²³⁵ U, does not use the nuclear reactor facility, and does not generate a large amount of radioactive waste, and can be efficiently and inexpensively and simply. It is an object of the present invention to provide a method and an apparatus capable of realizing a stable supply of a radioisotope.

  In order to solve the above problems, the present invention provides the following technical methods or means.

[1] power supply for applying a voltage to accelerate the charged particle beam consisting of deuterium or protons, the voltage from the power source is applied, an acceleration tube for accelerating the charged particle beam, and, provided on the accelerator exit section Rutotomoni, tritium is disposed a fast neutron generator target of occluded titanium, with fast neutron generator which the charged particle beam is accelerated to generate a fast neutron irradiated, of one neutron A value obtained by adding 0.5 to the threshold value of (n, 2n) reaction that emits two neutrons upon irradiation [unit: MeV] is the lower limit value, and the (n, 2n) reaction at an energy value other than the lower limit value is the lower limit value. (n, 2n) in the value with a scale small accelerator enough to fast neutrons Ru is generated having an energy value within a range that the reaction upper limit energy value equal to the cross-sectional area of the reaction, prior to The fast neutrons are generated by the charged particle beam irradiation irradiated to the solid raw material target, (n, 2n) to cause a reaction, radioactive isotopes (excluding Mo) to be produced by directly or beta decay the A method for producing a characteristic radioisotope.

[2] In the first invention, one or more targets selected from the following Table 1, Table 2, Table 3, Table 4, Table 5, Table 6, Table 7 as target nuclei of the solid source target A method for producing a radioisotope, characterized by irradiating a solid source target containing nuclei with fast neutrons.

[3] In the first or second invention, the solid source target is irradiated with fast neutrons in a state in which the solid source target is in close contact with or separated from the fast neutron generator provided in the accelerator emitting unit. A method for producing a radioisotope characterized by the above.

[4] power source for applying a voltage to accelerate the charged particle beam consisting of deuterium or protons, the voltage from the power supply is applied, an acceleration tube for accelerating the charged particle beam, and, provided on the accelerator exit section Rutotomoni, tritium is disposed a fast neutron generator target of occluded titanium, with fast neutron generator which the charged particle beam is accelerated to generate a fast neutron irradiated, of one neutron A value obtained by adding 0.5 to the threshold value of (n, 2n) reaction that emits two neutrons upon irradiation [unit: MeV] is the lower limit value, and the (n, 2n) reaction at an energy value other than the lower limit value is the lower limit value. (n, 2n) in the value with a small accelerator size enough to Ru to generate fast neutrons with the energy value in a range that the reaction upper limit energy value equal to the cross-sectional area of the reaction, the solid Comprising a target support means for supporting the charge target, the fast neutrons is generated by the charged particle beam irradiation irradiated to the solid raw material target, excluding (n, 2n) reaction cause, radioisotopes (However, Mo ) Is produced directly or by beta decay, a radioisotope production apparatus.

[5] In the fourth invention, the solid source target is one or more selected from the following Table 1, Table 2, Table 3, Table 4, Table 5, Table 6, and Table 7 as the source target nucleus. An apparatus for producing a radioisotope, which is a solid source target including a target nucleus.

[6] In the fourth or fifth invention, the solid source target is set in a state of being in close contact with or separated from a fast neutron generator provided in the accelerator emission unit. Radioisotope production equipment.

[7] In any one of the fourth, fifth, and sixth inventions, the fast neutron generator provided in the accelerator emitting portion includes a cooling means, and the fast neutron generator is provided in the vacuum chamber and the atmosphere side. The radioactive isotope production apparatus is characterized in that it is set in a state in which the solid source target is in close contact with or separated from the fast neutron generator.

According to the present invention, the high-speed neutrons are generated by the charged particle beam irradiation from the small accelerator solid raw material target is irradiated, since so as to produce a RI (n, 2n) by the reaction, using a concentrated ^{235 U} Without using a nuclear reactor facility, it is possible to reduce the generation of high-strength and long-lived radioactive waste and to stably supply RI efficiently and inexpensively .

  In addition, the RI manufacturing apparatus according to the present invention does not need to be regulated by nuclear fuel materials and can be miniaturized. Therefore, there is an advantage that it can be easily used in facilities such as hospitals.

  Furthermore, according to the present invention, since the RI is generated by irradiating the raw material target with neutrons having no charge, the case of a heavy target nuclide is lighter than when the target is irradiated with a proton beam having a positive charge. As with target nuclides, it can be handled with a small-scale accelerator, and it is not bothered by energy loss due to electromagnetic interaction in the target and the heat generation of the target, resulting in about 100 times more than in the case of proton beams. It is possible to irradiate a heavy target at a time, and the amount of RI generated can be increased. In addition, since the target can be placed in the atmosphere, there is an advantage that the degree of freedom in target placement and material selection is increased. This is considered to give immense convenience to various users.

It is a figure which shows the production amount distribution of the nuclide produced | generated by ²³⁵ U nuclear fission in a nuclear reactor. It is a graph which shows the reaction cross-section evaluation value of a raw material target and a fast neutron. It is a figure showing typically RI manufacture device by one embodiment of the present invention. It is a figure which shows typically the sample container used when produced | generated RI is gas. It is a figure which shows typically the principal part of RI manufacturing apparatus by another embodiment of this invention. It is a block diagram which shows the manufacturing procedure of RI by this invention. The fast neutrons are generated by the charged particle beam irradiation from the small accelerator, the measurement data of 811keV gamma-rays emitted along with the beta decay of the generated ^{58 Co} by irradiating the raw material target containing target nuclei ^{59 Co} FIG.

Hereinafter, the present invention will be described in detail based on embodiments.
In the present invention, a radioisotope used for radioactive diagnostic agents, etc., a high-speed neutrons are generated by the charged particle beam irradiation from the small accelerator solid raw material target is irradiated, two neutrons by the irradiation of a single neutron It is produced directly or by beta decay by initiating a (n, 2n) reaction that releases. In the present invention, fast neutron means neutron having energy of 0.1 MeV or more.

When the raw material target is irradiated with fast neutrons, (n, 2n) reaction, (n, ⁴ He) reaction, (n, p) reaction, (n, 3n) reaction, (n, np) reaction, (n, n ′) ) Various reactions such as reactions occur, but the raw material target of the present invention has a very large reaction cross-section in the (n, 2n) reaction, which is inferior to that of reactor-based radioisotope production. It was confirmed that radioactive isotopes can be obtained efficiently without any problems. According to the present invention, a desired radioisotope can be produced with reduced radioactivity without generating a large amount of radioactive waste as in the case of using a nuclear reactor.

FIG. 2 is a graph showing, as an example, evaluation values of neutron energy and reaction cross-section when a raw material target having ¹⁴⁸ Nd as a target nucleus is irradiated with fast neutrons. From FIG. 2, it can be seen that when the raw material target is irradiated with fast neutrons, the (n, 2n) reaction cross section is close to the maximum value depending on the value of neutron energy and has a much larger reaction cross section than other reactions.

In the present invention, using the target nuclei shown in Table 1, Table 2, Table 3, Table 4, Table 5, Table 6, and Table 7 below, radioisotopes (product nuclei) are directly obtained using the (n, 2n) reaction. Or by beta decay. Examples of the target to be used are shown in Table 1, Table 2, Table 3, Table 4, Table 5, Table 6, and Table 7 below.

Of these, ⁴⁷ Sc, ⁴⁹ V (target nucleus ⁵⁰ Cr), ⁵⁷ Co, ⁸³ Rb, ⁹¹ Nb, ⁹⁵ Tc, ⁹⁷ Tc, ¹⁰¹ Rh, ¹⁰⁵ Ag, ¹¹¹ In, ¹²⁹ Cs, ¹³¹ Cs, ¹³⁵ La, ¹⁴³ Pm, ¹⁴⁷ Pm, ¹⁴⁹ Pm, ¹⁵⁵ Tb, ¹⁵⁷ Tb, ¹⁶⁷ Tm, ¹⁶¹ Ho, ¹⁷⁹ Ta, ¹⁸³ Re, ¹⁸⁹ Ir, ¹⁹⁵ Au are obtained by beta decay and can be made carrier-free.

In the present invention, in order to produce RI, without using a reactor, fast neutrons which are generated by the charged particle beam irradiation using a small accelerator to irradiate the solid raw material target. In this way, unnecessary radioactivity can be reduced without generating a large amount of radioactive waste as compared with the case where radioactive isotopes are generated by fission reaction in a nuclear reactor.

As a small accelerator for accelerating a charged particle beam for generating fast neutrons, for example, a commercially available small accelerator may be used, or the Japan Atomic Energy Agency (NES) Fusion Neutron Engineering Neutron Source Facility (FNS), which is the facility of the present applicant. You may use facilities, such as DT neutron source.

  The energy of fast neutrons used in the present invention is the (n, 2n) reaction at energy values other than the lower limit, with a value [unit: MeV] obtained by adding 0.5 to the (n, 2n) reaction threshold. The target nuclei are irradiated with fast neutrons having an energy value within a range where the upper limit is the energy value at which the reaction cross-sectional area is equal to the reaction cross-sectional area of the (n, 2n) reaction at the lower limit.

In the accelerator for neutron generation, for example, deuterium ( ² H) beam is irradiated to tritium ( ³ H), and fast neutrons can be generated together with helium ( ⁴ He) in the next reaction.

² H + ³ H → ⁴ He + n
The neutron energy (En) generated by this reaction is given by the following relational expression.

4 × En = Ed + 2 × {2 × Ed × En} ^1/2 × cos θ + 3 × Q
Here, Ed is deuterium energy, Q is the generated energy of the reaction, and Q = 17.6 MeV. θ is the angle between the generated neutrons and incident deuterium. From this equation, it can be seen that 14 MeV fast neutrons can be obtained by using, for example, 0.35 MeV low energy deuterium. At the International Fusion Materials Irradiation Facility (IFFIF), which is currently underway, liquid lithium (Li) is irradiated with deuterium to produce high-intensity fast neutrons. Furthermore, even if metal Li, metal beryllium (Be), or carbon (C) is irradiated with protons or deuterium, fast neutrons can be generated.

Here, the production efficiency of RI by fast neutrons will be examined by taking ⁹⁹ Mo production by a ¹⁰⁰ Mo (n, 2n) reaction as an example. The amount of ⁹⁹ Mo produced by fission in the nuclear reactor (Y _furnace ) is given below.

²³⁵ U: Concentration 20%. The fission cross section due to the reaction between thermal neutrons and ²³⁵ U is 585 burns. Among them, the production ratio of ⁹⁹ Mo is 6% (see FIG. 1). From the above, the amount of ⁹⁹ Mo generated in this U = 0.20 × 585 × 0.06 = 7 burns.

¹⁰⁰ Mo: natural abundance ratio 9.6%. ⁹⁹ Mo production reaction cross section by fast neutron is 1.5 burn. From the above, the amount of ⁹⁹ Mo produced from natural Mo (Y _{high speed} ) = 0.096 × 1.5 = 0.14 burn.

That is, the ratio of Y _{high speed} to Y _furnace = Y _{high speed} / Y _furnace = 0.14 / 7 = 0.02 Formula (1)
The amount of ⁹⁹ Mo produced by fast neutrons is 2% in the case of a nuclear reactor, excluding the amount of neutrons.

By the way, as for the amount of neutrons, the thermal neutron amount of the _reactor φ _Reactor : In the case of Japan Nuclear Energy Agency Research Reactor Facility JRR3, φ _Reactor = 10 ¹⁴ pieces / (cm ² · second)
Formula (2)
Amount of fast neutrons φ _Fast : In the case of IFMIF, φ _fast = 10 ¹⁴ pieces / (cm ² · sec)
Formula (3)
That is, the ratio of the fast neutron amount to the reactor amount is: φ _fast / φ _reactor = 1 formula (4)
It becomes. Above, in view of the neutron amount, the ratio of the fast neutron ^{99 Mo} production amount by utilizing a reactor ^{99 Mo} production amount by the use it is given below.
0.02 × 1 = 0.02 Formula (5)
Here, considering that a high concentration of ¹⁰⁰ Mo can be obtained relatively easily (for example, assuming 100% concentration), the ratio of equation (5) is calculated from equations (1) and (4):
0.02 ÷ 9.6 × 100 = 0.21 Formula (6)
It becomes. In other words, according to the present invention, it can be seen that even using fast neutrons, ⁹⁹ Mo can be produced in an amount sufficiently comparable to the amount produced in the nuclear reactor. The above also applies to each target that is the subject of the present invention.

In addition, when irradiated with protons to generate neutrons metal Li (lithium), the reaction neutron energy generated by ^{{p + 7 Li → n +} 7 Be} (En) is given by the following equation.
En = {R × cos θ + (1−R ² × sin ² θ) ^1/2 } ² × {M _Be × (E _cm + Q) / (M _Be + M _n )}
R = [M _n × M _p × E _cm / {M _Be × M _Li × (E _cm + Q)}] ^1/2
E _cm = M _Li × E _p / (M _Li + M _p )
Here, E _p is the energy of protons, and M _p , M _n , M _Li , and M _Be are the static masses of protons, neutrons, Li, and Be. Further, θ is an angle formed between the neutron generated by this reaction and the proton beam axis. Q is the threshold of this reaction, which is -1.644 MeV.

  From this equation, it can be seen that, for example, when a low energy proton of 16 MeV is used, fast neutrons of about 14 MeV can be obtained in the proton beam axis direction. Since neutrons are mainly emitted in the proton beam direction, it is important to set the target in the beam axis direction.

  FIG. 3 schematically shows an RI manufacturing apparatus according to an embodiment of the present invention.

  In the figure, 1 is a high voltage power source, 2 is a power cable, 3 is an accelerator terminal, 4 is an accelerator tube, 5 is a deuteron transport line, 6 is a fast neutron generator, 7 is a cooling tube, 8 cooling system, 9 is a raw material Targets 10 are target support frames or sample containers, 11 is a target support, and 12 is an RI container (target storage) with radiation shielding. FIGS. 3A and 3B respectively show a state in which the raw material target 9 is in close contact with the fast neutron generator 6 and a state in which the source target 9 is separated.

  The generation efficiency of RI increases when the raw material target 9 is brought into close contact with the fast neutron generator 6 as shown in FIG. In this case, the raw material target 9 or the sample container 10 containing it is brought into close contact with the tips of the fast neutron generator 6 and the cooling tube 7 via a cooling member made of, for example, Cu. In this case, the cooling member provided in the fast neutron generator 6 has a partition function between the vacuum chamber of the deuteron transport line 5 and the atmosphere side where the raw material target 9 is located. In some cases, as shown in FIG. 3B, the raw material target 9 may be separated from the fast neutron generator 6 by about 10 mm, and this distance is not limited.

  The high voltage power supply 1 outputs a high voltage for making the deuterium beam energy of about 0.35 MeV in order to generate a large amount of neutrons by the neutron generation reaction. The power cable 2 is for applying the high voltage of the high voltage power supply 1 to the acceleration tube 4 in contact with the accelerator terminal 3. In the fast neutron generator 6, a metal plate having excellent thermal conductivity such as Cu is provided with a deposition film such as titanium occluded with deuterium, for example. It plays the role of generating a large amount of neutrons by causing the neutron generation reaction. The cooling system 8 serves to cool the metal plate by the cooling pipe 7 in order to prevent thermal diffusion of the deuterium in the metal plate irradiated with the deuterium beam. Cooling is performed by water cooling or the like. The metal plate may be a fixed type or a rotary type.

  As the raw material target 9 of the present invention, a natural target element or a material concentrated to a natural abundance ratio of the target element or more is used as an oxide powder or the like, or a powder obtained by compressing and molding this powder into a high density. A material having a bulk density of 60% or more can be used (for example, Japanese Patent Application Laid-Open No. 55-22102). Moreover, when using the concentrated target element, it is necessary to perform an electromagnetic separation collection method etc. as the pretreatment. In the case of using a powder of a target element oxide or the like, it is necessary to seal it in a quartz tube and then seal it in an aluminum metal irradiation container. When using pelletized powder of target element oxide or the like, it is directly sealed in a metal irradiation container. This metal irradiation container is the sample container 10. Furthermore, a target element metal can also be used as a target. However, in this case, dissolution with nitric acid or the like is required for extraction of the target element metal.

When using a pelletized material as the raw material target 9, for example, a size having a diameter of 10 mm and a thickness of 0.5 mm can be used, but of course, this is an example and is not limited thereto. Considering the irradiation energy, yield and the like of fast neutrons, the shape and size can be appropriately set. In that case, if the thickness of the raw material target 9 is too thick, a problem of neutron scattering occurs and the generation efficiency is lowered. Therefore, it is necessary to consider this point. Neutrons are emitted from the accelerator terminal 3 in all directions, and the neutron flux (pieces / cm ² · sec) decreases at 1 / r ² . For this reason, when the raw material target 9 is brought into close contact with the neutron generator 6 of the accelerator terminal 3, the RI generation efficiency is maximized. Here, r is the distance from the neutron source.

  The raw material target 9 is fixed or accommodated in the target support frame or the sample container 10. The target support 11 serves to fix the target support frame or the sample container 10. The RI container 12 includes a radiation shield, and the generated RI is put in this, taken out of the laboratory, and transported and moved to a required place. Each member other than the RI container 12 also shields radiation as necessary.

The solid source target is irradiated with neutrons using the apparatus configured as described above, and the irradiation time can be set in consideration of the half-life of the nuclide to be generated. In addition, when the half-life is longer than 5 days, a desired amount of RI can be obtained if the irradiation time is about 5 days. In this case, since the use of fast neutrons is generated by the charged particle beam irradiation from the accelerator, without a large amount of radioactive waste generated since it does not utilize nuclear fission, also relatively large reaction cross-sectional area (n, 2n) Since the reaction is used, the desired RI can be stably supplied with high efficiency. Furthermore, since the apparatus configuration can be very downsized using a commercially available accelerator, RI can be manufactured and used easily and stably in a facility such as a hospital.

In addition, when the reaction threshold of the target target is 15 MeV or more, an apparatus having the following configuration is used. In order to generate a large amount of neutrons by the neutron generation reaction, the high voltage power supply 1 outputs a high voltage for making the proton beam energy of about 25 MeV, for example. The power cable 2 is for applying the high voltage of the high voltage power supply 1 to the acceleration tube 4 in contact with the accelerator terminal 3. The fast neutron generator 6 is set with a metallic Li thin film provided on a metal plate excellent in thermal conductivity such as Cu, and the fast neutron generator 6 causes the above neutron generation reaction, It plays a role in generating neutrons. The cooling system 8 serves to cool the metal plate by the cooling pipe 7 in order to prevent Li on the surface of the Cu metal plate irradiated with the proton beam from being thermally diffused. Cooling is performed by water cooling or the like. The metal plate may be a fixed type or a rotary type. In this case, most of the neutrons are emitted from the fast neutron generator 6 along the proton beam axis, and the neutron flux (pieces / cm ² · sec) decreases at 1 / r ² . Therefore, it is preferable that the raw material target 9 is disposed in close contact with the fast neutron generating unit 6 or in proximity (separated to about 10 mm).

  When the generated RI is a gas, a sample container 10 as shown in FIG. In this case, as the sample container 10, a highly airtight container such as stainless steel is used. The sample container 10 is provided with a vacuum valve 10A, and the generated RI can be discharged. Such a sample container 10 is used when a gas RI is generated by irradiating a solid target nucleus with fast neutrons.

  When the gas RI is generated, an alkali solution such as sodium hydroxide or an acid solution such as hydrochloric acid is placed in the sample container 10 and stirred to dissolve the gas RI generated by the nuclear reaction. Thereafter, the vacuum valve 10A is connected to the air collection system 13 as shown in FIGS. Here, the sample container is heated, and the dissolved gas RI is discharged into the vacuum and introduced into the air collection system 13. In the air collection system 13, for example, the gas RI is adsorbed by an adsorbent such as molecular sieve. At this time, the air collection system 13 is cooled with liquid nitrogen or the like as necessary. The remaining solid target can be reused.

  Next, another embodiment of the present invention will be described.

  FIG. 5 is a diagram schematically showing a main part of an RI manufacturing apparatus according to another embodiment of the present invention. FIG. 5A is a schematic diagram seen from a direction perpendicular to the deuterium beam traveling direction, and a fast neutron generator. (B) is a schematic view seen from the traveling direction of the deuterium beam. (B) is a case where the fast neutron generator is separated from the raw material target.

  In the figure, 21 is a deuterium beam, 22 is a rectangular parallelepiped vacuum beam tube, 23 is a copper plate having a titanium film adsorbing tritium (tritium), 24 is a raw material target, 25 is a cooling member, and 26 is a proton beam. . The cooling member 25 may be integrated with the copper plate 23. In this case, the copper plate 23 has an inner wall and an outer wall, and a titanium film adsorbing deuterium on the surface of the copper plate 23 on the inner wall (vacuum chamber side). The raw material target 24 is disposed in close contact with or spaced from the surface of the copper plate on the outer wall (atmosphere side) so that a cooling medium such as water passes through the space between the inner wall and the outer wall. Yes.

The fast neutrons generated by irradiating the deuterium ( ² H ⁺ ) beam 21 to the deuterium ( ³ H) isotropically in almost the entire space regardless of the incident direction of the deuterium beam 21. Has the property of being released. For this reason, in order to make maximum use of neutrons generated in a limited neutron utilization time, the raw material target 24 is arranged as follows. As the raw material target 24, for example, a natural target element or a pellet-like one obtained by compressing and solidifying and sintering a powder of oxide of a concentrated target element may be used. Metals can also be used.

In order to prevent the high-intensity deuterium beam 21 irradiated to the copper plate 23 provided with the tritium-containing titanium film from raising the temperature of titanium and causing thermal diffusion of the deuterium, the tritium-containing titanium film was provided. The copper plate 23 is cooled by the cooling pipe 25. In order to use a higher-intensity deuterium beam 21 within a given cooling capacity range, it is conceivable to reduce the heat load per unit area provided by the deuterium beam 21. Therefore, the size of the deuterium beam 21 is changed from the usual 5 mm diameter to, for example, 10 mm diameter by changing the beam transport system of the accelerator. As a result, the heat load per unit area can be reduced to ¼, so that the intensity is four times that of a conventional deuterium beam, and the resulting neutrons can be used four times as much. Further, since fast neutrons are isotropically emitted into the entire space, the raw material target 24 is set not only in front of the deuterium beam 21 but also on the side surface as shown in FIG.

The deuterium beam 21 is irradiated to a copper plate 23 having a tritium-containing titanium film through a beam transport system in which a vacuum is maintained by a vacuum beam tube 22 which is a rectangular parallelepiped. Then ^{2 H + + 3 H → 4} He + n fast neutrons generated by the reaction, placed (closest distance) on the atmosphere side of the cooling member 25 (the copper plate 23) is irradiated to the raw material target 24. On the other hand, in order to efficiently use fast neutrons emitted backward with respect to the deuterium beam 21 incident at a right angle to the copper plate 23 having a tritium-containing titanium film, a vacuum beam tube (a rectangular parallelepiped) close to the fast neutron generation site. ) Four surfaces of 22 are processed and the raw material target 24 is embedded as shown. With such a configuration, fast neutrons are isotropically emitted into the entire space, so that RI generation is performed with higher efficiency.

  Moreover, when using a faster neutron, as mentioned above, a proton etc. are irradiated to Li or Be. In this case, most of the neutron flux is emitted along the direction of the proton beam. Therefore, the arrangement of the raw material target 24 is in front of the fast neutron generator as shown in FIGS. 5D and 5E. FIG. 5D shows the case where the raw material target 24 is brought into close contact with the fast neutron generator, and FIG. 5E shows the case where the raw material target 24 is spaced from the fast neutron generator. As described above, according to the present invention, since the raw material target 24 can be arranged not on the vacuum but on the atmosphere side, there is an advantage that the shape of the raw material target 24 and the degree of freedom in arrangement are increased.

  Next, a method for manufacturing RI according to the present invention will be described.

Manufacturing method of the RI according to the present invention basically a solid raw material target containing the target nucleus is irradiated with fast neutrons caused by the charged particle beam irradiation from the small accelerator, two by irradiation of one neutron (N, 2n) reaction is caused to emit neutrons, and RI is generated directly or by beta decay.

  Hereinafter, an example of an RI manufacturing method according to the present invention will be described with reference to the block diagram of the manufacturing procedure of FIG.

  First, for example, using a natural target element, a powder such as an oxide is compressed, molded, and sintered to produce a pellet-shaped raw material target (step S1).

  Next, a raw material target is put in a sample container and set at a neutron irradiation position (step S2).

Next, a deuterium beam of 0.35 MeV, for example, is irradiated from a neutron generator to a titanium film occluded with tritium provided on the cooling copper plate. As a result, 14 MeV fast neutrons are generated (step S3) .
In the solid source target that is the subject of the present invention, the (n, 2n) reaction predominates due to this fast neutron irradiation, and RI is generated (step S4).

  After performing neutron irradiation for an appropriate time, the irradiation is stopped, the sample container containing the RI is taken out, and the desired RI is obtained (step S5).

  Thus, for the raw material target of the present invention, even when using fast neutrons generated by irradiating a metal beam Li (lithium) or metal Be (beryllium) or carbon (C) with a proton beam or deuterium beam, By applying a similar technique, it is possible to efficiently produce a desired RI without producing a large amount of radioactive waste.

  In addition, when the production nucleus and the target nucleus according to the present invention are the same element, the irradiated target (the target and the reaction product coexist) can be dissolved in an aqueous solution (or acid or alkali) and used for the production of the production nucleus. it can.

  Further, when the produced nucleus is a long-life RI relative to the short-lived RI of the daughter nuclide, the milking can be performed by a system called a cow milking system or a generator system.

  Although an example of the manufacturing method has been described above, of course, the manufacturing method of the present invention is not limited to this example, and each step can be performed using the various methods described above.

The present inventors have carried out following experiment to confirm such that a fast neutron beam generated by the charged particle beam irradiation from the small accelerator can generate RI by irradiating the solid raw material target.
<Experimental purpose>
* Confirmation that ⁹⁹ Mo is generated with 14 MeV fast neutrons using a natural Mo sample with the expected reaction cross section * Generated with 14 MeV neutrons using the ⁹³ Nb sample used to determine the absolute value of the above reaction cross section Measurement of ⁹² Nb radiation and confirmation that it can be used to determine the cross-sectional area * ⁹⁹ Quantitative evaluation of residual radioisotope produced in association with Mo production reaction * ² H + ³ H → ⁴ He + n reaction Verifying 14MeV neutron is stable generated by the neutron intensity to be expected ^{(3 H} target performance evaluation)
* Confirmation that ² H (deuterium beam) for inducing the above reaction is supplied stably (Verification that small accelerator operates stably)
* Confirmation that Mo and Nb targets can be easily and flexibly installed and removed from the neutron irradiation site <Experiment location> Neutron Source Facility for Fusion Neutron Engineering, Japan Atomic Energy Agency (FNS)
<Experiment date>
Neutron irradiation experiment: January 27 to January 30, 2009 (6 hours of irradiation per day)
Measurement of generated Mo radioactivity: January 27 to February 5, 2009 <Sample> Natural Mo
Sample 1: Diameter: about 10 mm, thickness: 50 microns (0.05 mm), weight 40.214 mg
Sample 2: Diameter: about 10 mm, thickness: 5 microns (0.005 mm), weight 3.663 mg
Sample 1 was measured after 6 hours of irradiation.

Sample 2 was measured after neutron irradiation until the last day.
<Sample> ⁹³ Nb
Sample 3: diameter 10 mm, thickness: 0.1 mm, weight 69.4 mg
<Mo target installation location>
² Location 10 cm away from the neutron generation site in the direction of extension of the H beam axis.
<Neutral irradiation conditions>
* 14 MeV neutron production reaction
² H + ³ H → ⁴ He + n: ² H beam energy: 0.35 MeV
* Neutron generation amount 1.8 × 10 ¹¹ n / cm ² · sec [January 27] to 1.5 × 10 ¹¹ n / cm ² · sec [January 30]
^<99 Mo production reaction>
¹⁰⁰ Mo + n → ⁹⁹ Mo + 2n
< ⁹² Nb production reaction>
⁹³ Nb + n → ⁹² Nb + 2n
<Measurement of ⁹⁹ Mo and residual radioactivity (measured with FNS)>
* Measurement conditions: Start measurement after cooling time of approximately 1 hour after neutron irradiation * Measurer: Ge semiconductor detector * ⁹⁹ Mo sample and ⁹² Nb sample placement: Set 5 cm away from Ge detector <Result>
* Confirm that ⁹⁹ Mo is produced in the amount originally predicted * Confirm that ⁹³ Nb sample can be used to determine ⁹⁹ Mo cross-sectional area * Quantitative determination of residual radioisotope generated accompanying ⁹⁹ Mo formation reaction Evaluation. (Check that it is a small amount compared to the amount of ⁹⁹ Mo).

* Confirmed that 14 MeV neutrons generated by ² H + ³ H → ⁴ He + n reaction are stably generated with the expected neutron intensity ( ³ H target could be evaluated to have high performance)
* It was confirmed that ² H (deuterium beam) for inducing the above reaction was stably supplied.

(Verification of stable operation of small accelerators)
* It was confirmed that the Mo target and Nb target can be easily and flexibly installed and removed from the neutron irradiation site.

Then, the present inventors have fast neutrons beam generated by the charged particle beam irradiation from the small accelerator irradiated in the solid raw material target other than Mo, 93 ^Nb, 2 neutrons by the irradiation of a single neutron The following experiment was conducted in order to confirm that it was possible to generate a (n, 2n) reaction to release RI and generate RI.
<Experiment location> Japan Atomic Energy Agency, Neutron Source Facility for Fusion Neutron Engineering (FNS)
<Sample> Natural Co
Diameter: about 10mm, thickness: 1mm, weight 722.3mg
<Mo target installation location>
² Location 10 cm away from the neutron generation site in the direction of extension of the H beam axis.
<Neutral irradiation conditions>
* 14 MeV neutron production reaction
² H + ³ H → 4 He + n: ² H beam energy: 0.35 MeV
* Neutron generation amount 1.8 x 10 ¹¹ n / cm ² · sec at the location where it was generated < ⁵⁸ Co and residual radioactivity measurement (measured with FNS)>
* Measurement conditions: Start measurement 1 hour after neutron irradiation is completed * Measurer: Ge semiconductor detector * ⁵⁸ Co sample placement: Set at a position 5 cm away from Ge detector * Released with ⁵⁸ Co beta decay The 811 keV gamma rays measured by a Ge semiconductor detector are shown in FIG.

  Also for the raw material target of the present invention, fast neutrons generated by irradiating a metal beam Li (lithium), metal Be (beryllium) or carbon (C) with a proton beam, a deuterium beam or a deuterium beam are similarly used. By applying such a technique, it is possible to efficiently produce a desired RI without generating a large amount of radioactive waste.

DESCRIPTION OF SYMBOLS 1 High voltage power supply 2 Power supply cable 3 Accelerator terminal 4 Acceleration tube 5 Deuteron transport line 6 Fast neutron generating part 7 Cooling tube 8 Cooling system 9 Raw material target 10 Target support frame 11 Target support stand or sample container 12 RI container (target storage) Warehouse)
21 Deuterium beam 22 Vacuum transport line 23 Copper plate with a deuterium-containing titanium film 24 Raw material target 25 Cooling tube 26 Proton beam

Claims (7)

Power source for applying a voltage to accelerate the charged particle beam consisting of deuterium or protons, the voltage from the power supply is applied, an acceleration tube for accelerating the charged particle beam, and, Rutotomoni provided to the accelerator exit section, the tritium is disposed a fast neutron generator target occluded titanium, with fast neutron generator which the charged particle beam accelerated in this occurs the fast neutron irradiated, 2 by the irradiation of a single neutron A value obtained by adding 0.5 to the threshold value of (n, 2n) reaction that emits individual neutrons [unit: MeV] is set as the lower limit value, and (n, 2n) reaction at energy values other than the lower limit value is set at the lower limit value ( n, 2n) using a scale small accelerator enough to fast neutrons Ru is generated having an energy value within a range that the reaction upper limit energy value equal to the cross-sectional area of the reaction,
The fast neutrons are generated by the charged particle beam irradiation irradiated to the solid raw material target, (n, 2n) reaction cause, be produced by directly or beta decay of radioactive isotopes (except for Mo) A method for producing a radioisotope characterized by the above. As a target nucleus of the solid source target, fast neutrons are applied to the solid source target including one or more target nuclei selected from the following Table 1, Table 2, Table 3, Table 4, Table 5, Table 6, and Table 7. The method for producing a radioisotope according to claim 1, wherein irradiation is performed.

  3. The radioactive material according to claim 1, wherein the solid material target is irradiated with fast neutrons in a state in which the solid material target is in close contact with or separated from a fast neutron generator provided in the accelerator emission unit. Isotope production method. Power source for applying a voltage to accelerate the charged particle beam consisting of deuterium or protons, the voltage from the power supply is applied, an acceleration tube for accelerating the charged particle beam, and, provided on the accelerator exit section Rutotomoni, the tritium is disposed a fast neutron generator target occluded titanium, with fast neutron generator which the charged particle beam accelerated in this occurs the fast neutron irradiated, 2 by the irradiation of a single neutron A value obtained by adding 0.5 to the threshold value of (n, 2n) reaction that emits individual neutrons [unit: MeV] is set as the lower limit value, and (n, 2n) reaction at energy values other than the lower limit value is set at the lower limit value ( n, 2n) and the degree of scale small accelerator which Ru is generated fast neutrons the cross sections with equal energy value has the energy value within the range of the upper limit of the reaction,
Comprising a target support means for supporting the solid source target;
The fast neutrons are generated by the charged particle beam irradiation irradiated to the solid raw material target, (n, 2n) reaction cause, be produced by directly or beta decay of radioactive isotopes (except for Mo) An apparatus for producing radioisotopes characterized by The solid source target is a solid source target containing one or more target nuclei selected from the following Table 1, Table 2, Table 3, Table 4, Table 5, Table 6, and Table 7 as source target nuclei. The radioisotope manufacturing apparatus according to claim 4.

  The radioisotope production according to claim 4 or 5, wherein the solid source target is set in a state of being in close contact with or separated from a fast neutron generator provided in the accelerator emission unit. apparatus.   A state in which the fast neutron generator provided in the accelerator emission unit has a cooling means, the fast neutron generator has a partition function on the vacuum chamber and the atmosphere side, and the solid source target is in close contact with the fast neutron generator or The radioisotope manufacturing apparatus according to any one of claims 4 to 6, wherein the radioisotope manufacturing apparatus is set in a separated state.

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