Neutron generation method and neutron generator

Abstract

To efficiently obtain directive neutrons.SOLUTION: A neutron generation method includes a step of providing a target (1) containing deuterium, and an irradiation step of generating a neutron beam (8) having directivity by irradiating the target (1) with a beam (5).SELECTED DRAWING: Figure 2

Description

[Technical Field]

[0001] The present invention relates to a neutron generation method and a neutron generator. [Background technology]

[0002] Neutrons have the property of having no electric charge but a magnetic charge, and are therefore used in a wide range of applied research. For example, Non-Patent Document 1 discloses a method for analyzing magnetic field structures using polarized neutrons with aligned magnetic charge directions (magnetic moment and spin directions). [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Republished Patent Publication WO2019 / 039477 [Non-patent literature]

[0004] [Non-Patent Document 1] "Introductory Course: How Neutrons are Made" [online], Internet<https: / / www.jstage.jst.go.jp / article / hamon / 28 / 3 / 28_144 / _pdf> Summary of the Invention [Problem to be solved by the invention]

[0005] Conventional neutron generation methods have a problem in that the ratio of the number of neutrons transmitted to the test subject to the number of neutrons generated by the neutron generator (hereinafter referred to as neutron transmission efficiency) is extremely low.

[0006] That is, in conventional neutron generation methods, neutrons generated by a neutron generator are radiated isotropically, and only neutrons radiated in the direction of the subject are selected by a collimator. Furthermore, when low-energy neutrons with uniform energy are used, a process is required to reduce the energy of the neutrons using a moderator, and many neutrons are excluded in this process. Furthermore, when monoenergetic neutrons are used, only neutrons of a specific energy are selected by a chopper. Furthermore, when polarized neutrons are used, only neutrons with uniform spins are selected by a spin filter. Through the above process, the neutron transmission efficiency is typically 10 -12 It will be about that amount.

[0007] One aspect of the present invention has been made in consideration of the above problems, and has an object to efficiently obtain directional neutrons. [Means for solving the problem]

[0008] In order to solve the above problem, a neutron generating method according to one aspect of the present invention includes a step of preparing a target containing deuterium, and an irradiation step of generating a directional neutron beam by irradiating the target with a beam.

[0009] Furthermore, a neutron generating method according to one aspect of the present invention may include a polarization step of polarizing the nuclear spin of the deuterium in the target, and in the irradiation step, the target may be irradiated with a beam to generate the neutron beam with polarized neutron spins.

[0010] The beam may be a laser beam, a pulsed laser beam, an electron beam, a proton beam, or a deuterium beam.

[0011] In addition, in a neutron generation method according to one aspect of the present invention, the beam may be a laser beam, an electron beam, a proton beam, or a deuterium beam, and in the irradiation step, the beam may be irradiated onto the target from a direction that is not perpendicular to the direction in which the nuclear spin of the deuterium is polarized.

[0012] In the neutron generating method according to one aspect of the present invention, in the irradiation step, the beam may be irradiated onto the target along a direction in which the nuclear spin of the deuterium is polarized.

[0013] The beam may also be polarized gamma rays.

[0014] In addition, in a neutron generating method according to one aspect of the present invention, the beam may be polarized gamma rays, and in the irradiation step, the polarized gamma rays may be irradiated onto the target so that the oscillation direction of the electric field of the polarized gamma rays is not perpendicular to the direction in which the nuclear spin of the deuterium is polarized.

[0015] Furthermore, in a neutron generating method according to one aspect of the present invention, in the irradiation step, the polarized gamma rays may be irradiated onto the target so that the oscillation direction of the electric field of the polarized gamma rays is along the direction in which the nuclear spin of the deuterium is polarized.

[0016] In addition, in the neutron generation method according to one embodiment of the present invention, the beam may be a gamma ray having an energy of 2.224 MeV to 2.225 MeV, an electron beam having an energy of 2.7 MeV to 2.8 MeV, or a proton beam having an energy of 3.5 MeV to 3.6 MeV.

[0017] In addition, in a neutron generation method according to one aspect of the present invention, in the irradiation step, the beam may be irradiated onto the target while maintaining the nuclear spin of the deuterium in a polarized state by applying a magnetic field to the target.

[0018] The target may include a compound containing deuterium, or may include hydrogen molecules containing deuterium.

[0019] In order to solve the above problems, a neutron generator according to one aspect of the present invention comprises a placement unit for placing a target containing deuterium, and an irradiation unit for generating a directional neutron beam by irradiating the target with a beam. [Effects of the Invention]

[0020] According to one aspect of the present invention, directional neutrons can be obtained efficiently. [Brief explanation of the drawings]

[0021] [Figure 1] 1 is a schematic configuration diagram showing a neutron generator according to a first embodiment of the present invention. [Figure 2] 3 is a schematic diagram showing a method of irradiating a target with an electron beam in the irradiation section of the neutron generator. FIG. [Figure 3] 3 is a schematic diagram showing a method of irradiating a target with a proton beam in the irradiation section of the neutron generator. FIG. [Figure 4] 3 is a schematic diagram showing a method of irradiating a target with deuterium rays in the irradiation section of the neutron generator. FIG. [Figure 5] FIG. 1 is a schematic configuration diagram showing a neutron generator according to a second embodiment of the present invention. [Figure 6] 2 is a schematic diagram showing a method for irradiating a target with polarized gamma rays in the irradiation section of the neutron generator. FIG. [Figure 7] FIG. 2 is a diagram showing the nuclear decomposition of deuterium by the polarized gamma rays. [Figure 8] FIG. 1 is a diagram showing how polarized neutrons are generated from polarized deuterium. [Figure 9] 10 is a graph showing the distribution of directional neutrons generated when non-spin-polarized deuterium is irradiated with polarized gamma rays and unpolarized gamma rays, according to a third embodiment of the present invention. [Figure 10] 1 is a graph showing a theoretical calculation prediction of the energy spectrum of neutrons generated when deuterium is irradiated with gamma rays having an energy slightly higher than the binding energy of deuterium. [Figure 11] FIG. 1 is a diagram showing a theoretical calculation prediction of the directionality of neutrons generated when deuterium contained in a target is irradiated with gamma rays having energy slightly higher than the binding energy of deuterium. DETAILED DESCRIPTION OF THE INVENTION

[0022] [Embodiment 1] (Schematic configuration of neutron generator 100) Fig. 1 is a schematic diagram showing the configuration of a neutron generator 100 according to a first embodiment of the present invention. As shown in Fig. 1, the neutron generator 100 includes an irradiation unit 10, a placement unit 20, and a polarization unit 30. Hereinafter, "polarizing nuclear spins" means creating a biased distribution of nuclear spin orientations.

[0023] The irradiation unit 10 irradiates the target 1 with a beam (quantum beam) to generate a neutron beam 8 in which the neutron spins are polarized (hereinafter referred to as a polarized neutron beam 8). The irradiation unit 10 is, for example, a laser irradiation device including a laser oscillator 11, a laser amplifier 12, a pulse compressor 14, and a condenser 15. The laser oscillator 11 emits pulsed laser light 2. The laser oscillator 11 emits a fundamental wave or a harmonic wave of an ultrashort pulse laser using, for example, a Ti:Sapphire laser (wavelength 800 nm), a Yb fiber laser (wavelength 1040 nm), a Nd glass laser (wavelength 1053 nm), or a Nd:YAG (Yttrium Aluminum Garnet) laser (wavelength 1064 nm). The laser amplifier 12 amplifies the laser light 2 emitted from the laser oscillator 11. Pulse compressor 14 compresses the time width (pulse width) of laser light 2 amplified by laser amplifier 12. Collector 15 focuses laser light 2 compressed by pulse compressor 14 toward target 1. Irradiation unit 10 focuses laser light 2 toward target 1 and irradiates target 1 with a beam such as laser light 2, thereby generating polarized neutron beam 8 from target 1 (see FIGS. 2 to 4).

[0024] The placement unit 20 is a member for placing the target 1 containing deuterium. Examples of the placement unit 20 include a needle-shaped member that is inserted into the target 1 to fix the target 1, a member that holds the target 1 by clamping it, or a table on which the target 1 is placed. The placement unit 20 may be configured to apply a magnetic field to the target 1 so that the nuclear spin of deuterium remains polarized until irradiation with a beam by the irradiation unit 10.

[0025] The target 1 contains deuterium. The target 1 may contain a compound containing deuterium. The compound containing deuterium may be, for example, a solid organic material containing deuterium. The target 1 may also contain hydrogen molecules containing deuterium.

[0026] The polarization unit 30 polarizes the nuclear spins of deuterium in the target 1 containing deuterium. The polarization unit 30 polarizes the nuclear spins of deuterium, for example, by triplet DNP (Dynamic Nuclear Polarization). In this case, the polarization unit 30 performs DNP by irradiating the target 1, which is placed in a uniform static magnetic field, with laser light and then irradiating the target 1 with microwaves. Here, the laser light excites electron spins to a triplet state. The microwaves resonate with the electron spins and the nuclear spins of deuterium, polarizing the nuclear spins of deuterium. The target 1 contains organic molecules that serve as a polarization source. By using such triplet DNP, the polarization unit 30 can polarize the nuclear spins of deuterium using a relatively small and low-cost device. A detailed method for implementing nuclear spin polarization using triplet DNP is described, for example, in Patent Document 1 mentioned above. Instead of the triplet DNP described above, the polarization unit 30 may polarize the nuclear spin of deuterium by applying a strong magnetic field of several tesla to deuterium cooled to an ultra-low temperature.

[0027] The pulse compressor 14, the collector 15, the positioning unit 20, and the polarization unit 30 are provided inside the vacuum vessel 13. The laser light 2 amplified by the laser amplifier 12 passes through a window 13a of the vacuum vessel 13 and enters the pulse compressor 14. The polarized neutron beam 8 generated by the target 1 passes through a window 13b of the vacuum vessel 13 and is irradiated (transmitted) to the subject A.

[0028] FIG. 2 is a schematic diagram showing a method of irradiating a target 1 with an electron beam 5. FIG. 3 is a schematic diagram showing a method of irradiating a target 1 with a proton beam 6. FIG. 4 is a schematic diagram showing a method of irradiating a target 1 with a deuterium beam 7. With reference to FIGS. 2 to 4, the methods of irradiating the target 1 with the electron beam 5, proton beam 6, and deuterium beam 7 as beams will be described below. Note that in FIGS. 2 to 4, only polarized deuterium contained in the target 1 is shown as the target 1.

[0029] As shown in FIG. 2, when the target 1 is irradiated with the electron beam 5, the irradiation unit 10 includes an electron generation target 3 arranged upstream of the target 1 (on the condenser 15 side). The electron generation target 3 is made of, for example, aluminum foil. The laser light 2 collected by the condenser 15 is irradiated onto the electron generation target 3. As a result, the electron beam 5 is generated from the electron generation target 3. The electron beam 5 generated from the electron generation target 3 is irradiated onto the target 1 as a beam.

[0030] As shown in FIG. 3, when a proton beam 6 is irradiated onto a target 1, the irradiation unit 10 includes a proton generation target 4 arranged upstream of the target 1. The electron generation target 3 may be made of, for example, the same organic material as that contained in the target 1 (however, it does not have to contain deuterium). As in the example shown in FIG. 2, the laser light 2 collected by the collector 15 is irradiated onto the proton generation target 4. As a result, a proton beam 6 is generated from the proton generation target 4. The proton beam 6 generated from the proton generation target 4 is irradiated onto the target 1 as a beam.

[0031] As shown in Fig. 4, when target 1 is irradiated with deuterium beam 7, laser beam 2 collected by collector 15 is directly irradiated onto target 1. This causes electrons to be generated from target 1, and the generated electrons accelerate protons and deuterium in target 1. Therefore, deuterium beam 7 is generated in target 1 and is irradiated as a beam onto other deuterium in target 1. When laser beam 2 is directly irradiated onto target 1, electron beam 5 and proton beam 6 are also generated simultaneously.

[0032] In the irradiation method shown in FIGS. 2 to 4, when the beam has energy exceeding the binding energy of deuterium (approximately 2.2 MeV), deuterium undergoes nuclear decomposition (nuclear fission). At this time, neutrons in deuterium are emitted in a direction approximately parallel to the irradiation direction of the beam. That is, the irradiation unit 10 can generate a directional neutron beam 8 by irradiating the target 1 with a beam. Furthermore, since the nuclear spin of the deuterium contained in the target 1 is polarized, a polarized neutron beam 8 with polarized neutron spins can be obtained. Here, the irradiation unit 10 may irradiate the target 1 with the beam along the direction in which the nuclear spin of deuterium is polarized. This can improve the directionality and polarization of the neutron beam 8. Furthermore, the direction in which the nuclear spin of deuterium is polarized (the direction of the nuclear spin) may be aligned with the direction in which the beam travels. Furthermore, by controlling the energy of the laser light 2 and using a monoenergetic beam, a polarized neutron beam 8 with monoenergetic or uniform energy can be generated. In the irradiation method shown in Fig. 3, the protons in the proton beam 6 may be spin-polarized by polarizing the nuclear spins of hydrogen contained in the proton generation target 4. Similarly, in the irradiation method shown in Fig. 4, the deuterium in the deuterium beam 7 may be spin-polarized. By polarizing the nuclear spins of deuterium contained in the target 1, the deuterium in the deuterium beam 7 also becomes spin-polarized. This improves the degree of polarization of the neutron beam 8.

[0033] (Neutron generation method) The neutron generation method will be described below. First, a target 1 containing deuterium is placed in a placement unit 20 (preparation step S1). Next, the polarization unit 30 polarizes the nuclear spin of the deuterium contained in the target 1 (polarization step S2). Next, the irradiation unit 10 irradiates the target 1 with a beam (irradiation step S3). This causes a directional polarized neutron beam 8 to be generated from the target 1. The directional polarized neutron beam 8 is transmitted to the subject A.

[0034] (Advantages of neutron generation methods) The neutron generation method according to this embodiment makes it possible to generate a directional polarized neutron beam 8 directly from the target 1. Furthermore, by using a monoenergetic beam, it is possible to generate a monoenergetic polarized neutron beam 8 directly from the target 1. Therefore, devices such as a collimator, moderator, chopper, and spin filter required in conventional neutron generation methods are not required. Therefore, compared to conventional neutron generation methods, the neutron generation method according to this embodiment does not require neutron selection using the above-mentioned devices, and therefore can dramatically improve neutron transmission efficiency. Furthermore, the neutron generator 100 does not require devices such as a collimator, moderator, chopper, and spin filter, and therefore can be made smaller.

[0035] For example, in the neutron generation method according to this embodiment, if the distance from the placement unit 20 to the subject A is ideally brought down to about 30 cm, the neutron transmission efficiency will be about 0.1. This is the neutron transmission efficiency (10 -12 ) of 10 11 In this case, the efficiency is 10 times higher per second, which allows for simplified radiation shielding of target 1. 5 pieces / cm 2 The number of neutrons generated is 10 per second, which is equivalent to the number of neutrons generated using conventional accelerators. 4 pieces / cm 2 of polarized neutrons will be available to subject A.

[0036] Furthermore, in the neutron generation method according to this embodiment, a beam is irradiated onto the target 1 by an irradiation unit 10 using laser light 2. Therefore, compared to conventional neutron generation methods using accelerators, the pulse width of the polarized neutron beam 8 can be made extremely short, and the time resolution can be dramatically improved. Therefore, for example, the diagnostic accuracy of neutron measurement of the subject A can be dramatically improved.

[0037] For example, if the laser oscillator 11 in the irradiation unit 10 is a Yb fiber laser (wavelength 1040 nm), the irradiation unit 10 can generate laser light 2 with, for example, 10 mJ energy per pulse, a repetition rate of 100 Hz, and a pulse width of 100 fs. When the laser light 2 is focused to a diameter of 2 μm by the condenser 15 and directly irradiated onto the target 1 (in the case of the irradiation method shown in FIG. 4 ), the irradiation unit 10 accelerates polarized deuterium to an energy of approximately 100 keV and generates a monoenergetic polarized neutron beam 8 of approximately 2.5 MeV. Here, monoenergetic means single-energy. Such an irradiation unit 10 can generate 100 neutrons per pulse (10,000 neutrons per second). Furthermore, because the neutron pulse width is approximately 10 ps, ​​the time resolution of neutron measurement is 100 million times higher than the time resolution (1 ms) of conventional accelerator-based neutron generation methods.

[0038] (Variation 1) The deuterium contained in the target 1 does not have to be spin-polarized. That is, the polarization step S2 may be omitted in the neutron generation method according to embodiment 1. Even in this case, a directional neutron beam 8 can be generated by irradiating the target 1 with a beam using the irradiation method shown in FIGS.

[0039] (Variation 2) The irradiation unit 10 only needs to irradiate the beam onto the target 1 from a direction that is (at least) not perpendicular to the direction in which the deuterium nuclear spin is polarized. Even in this case, the degree of neutron polarization, directivity, and neutron transmission efficiency can be improved compared to conventional neutron generation methods.

[0040] [Embodiment 2] Other embodiments of the present invention will be described below. For ease of explanation, the same reference numerals will be used to designate components having the same functions as those described in the above embodiment, and the description thereof will not be repeated.

[0041] (Configuration of neutron generator 200) Fig. 5 is a schematic diagram showing the configuration of a neutron generator 200 according to a second embodiment of the present invention. As shown in Fig. 5, the neutron generator 200 includes an irradiation unit 210, an electron synchrotron 220, an arrangement unit 20, and a polarization unit 30. Note that the polarization unit 30 is not shown in Fig. 5.

[0042] The irradiation unit 210 is a laser irradiation device that is larger in scale than the irradiation unit 10 according to embodiment 1. The irradiation unit 210 includes an incident unit 211 and a condensing unit 212. The condensing unit 212 includes mirrors 213a to 213d, lenses 214a and 214b, and a wavelength conversion unit 215.

[0043] Laser light 2 in the infrared range (1040 nm) enters condensing unit 212 from incident unit 211 via mirror 213a (half mirror or dichroic mirror). Laser light 2 entering condensing unit 212 is converted into laser light 2 in the ultraviolet range (260 nm) by wavelength conversion unit 213. The laser light 2 is further condensed to condensing spot P (100 μmφ) by lens 214a. Laser light 2 passing through condensing spot P is collimated by lens 214b, reflected by mirrors 213b to 213d, and again condensed to condensing spot P by lens 214a.

[0044] The electron synchrotron 220 passes electrons accelerated to nearly the speed of light through a focused spot P.

[0045] With the above configuration, the laser light 2 focused by the lens 214a and the electrons 201 accelerated by the electron synchrotron 220 collide at the focused spot P.

[0046] FIG. 6 is a schematic diagram showing a method of irradiating a target 1 with polarized gamma rays 202. FIG. 7 is a diagram showing the nuclear decomposition of deuterium by polarized gamma rays 202. FIG. 8 is a diagram showing the generation of polarized neutrons from polarized deuterium. With reference to FIGS. 6 to 8, a method of irradiating a target 1 with polarized gamma rays 202 as a beam to generate polarized neutrons 8 will be described below. Note that in FIGS. 6 to 8, only polarized deuterium contained in the target 1 is shown as the target 1. Also, in FIG. 7, only one neutron 8 contained in the polarized neutron beam 8 is shown as the neutron beam 8. Also, the oscillation of the polarized gamma rays 202 shown in FIGS. 6 to 8 indicates the oscillation of the electric field of the polarized gamma rays 202.

[0047] 6, the laser light 2 focused by the lens 214a and the electrons 201 accelerated by the electron synchrotron 220 collide at a focused spot P. This causes the laser light 2 to scatter (inverse Compton scattering) and become polarized gamma rays 202. The polarized gamma rays 202 are irradiated as a beam onto the target 1. The target 1 may contain, for example, gaseous deuterium sealed in an arrangement portion 20 serving as a sealing member.

[0048] As shown in Fig. 7, polarized gamma rays 202 are irradiated onto deuterium contained in target 1. When deuterium is irradiated with polarized gamma rays 202 having energy exceeding the binding energy of deuterium (approximately 2.2 MeV), the deuterium undergoes nuclear decomposition. At this time, protons 9 and neutrons 8 constituting the deuterium are emitted in opposite directions, each of which is approximately parallel to the vibration direction of the electric field of the polarized gamma rays 202 (the Y-axis direction in Fig. 7). If the spin of deuterium were not polarized, the neutrons 8 would be emitted in both the positive and negative directions of the Y-axis.

[0049] As shown in FIG. 8, when spin-polarized deuterium is irradiated with polarized gamma rays 202, neutrons 8 are emitted in one direction (the positive direction of the Y axis in FIG. 8). That is, the irradiation unit 210 can generate a directional neutron beam 8 by irradiating the target 1 with polarized gamma rays 202 as a beam. Furthermore, since the nuclear spin of deuterium contained in the target 1 is polarized, a polarized neutron beam 8 with polarized neutron spins is obtained. Here, the irradiation unit 210 may irradiate the target 1 with the polarized gamma rays 202 so that the oscillation direction of the electric field of the polarized gamma rays 202 is along the direction in which the nuclear spin of deuterium is polarized. This can improve the directionality and polarization of the neutron beam 8. Furthermore, the direction in which the nuclear spin of deuterium is polarized (the direction of the nuclear spin) may be perpendicular to the direction in which the beam travels. Furthermore, by controlling the energy of the laser light 2 and using a monoenergetic beam, a polarized neutron beam 8 with monoenergetic or uniform energy can be generated.

[0050] (Neutron generation method) The neutron generating method according to the embodiment 2 is similar to the neutron generating method according to the embodiment 1. That is, the neutron generating method according to the embodiment 2 includes a preparation step S1, a polarization step S2, and an irradiation step S3.

[0051] (Advantages of neutron generation methods) The neutron generation method according to the second embodiment, which uses polarized gamma rays 202 as the beam irradiated onto the target 1, can generate a low-energy polarized neutron beam 8 more efficiently than the neutron generation method according to the first embodiment, which uses an electron beam 5, a proton beam 6, and a deuterium beam 7. Furthermore, due to the configuration of the irradiation unit 210 and the electron synchrotron 220 described above, more neutrons can be transmitted to the subject A than the neutron generation method according to the first embodiment.

[0052] (Variation 1) In the second embodiment, as in the first modification of the first embodiment, the deuterium contained in the target 1 does not have to be spin-polarized. That is, in the neutron generation method according to the second embodiment, the polarization step S2 may be omitted. Even in this case, a directional neutron beam 8 can be generated by irradiating the target 1 with a beam using the irradiation method shown in Fig. 6. As described above, since deuterium is not spin-polarized, the neutron beam 8 is emitted in both the positive direction of the Y axis shown in Fig. 8 and the negative direction of the Y axis.

[0053] (Variation 2) The irradiation unit 10 only needs to irradiate the target 1 with the polarized gamma rays 202 so that the oscillation direction of the electric field of the polarized gamma rays 202 is not (at least) perpendicular to the direction in which the nuclear spin of deuterium is polarized. Even in this case, the neutron transmission efficiency can be improved compared to conventional neutron generation methods.

[0054] (Variation 3) In the second embodiment, instead of the polarized gamma rays 202, deuterium may be irradiated with a quantum beam having an energy slightly higher than the threshold energy for deuterium nuclear decomposition (e.g., gamma rays of 2.224 MeV to 2.225 MeV, electron beams of 2.7 MeV to 2.8 MeV, or proton beams of 3.5 MeV to 3.6 MeV). When deuterium is irradiated with these quantum beams, most of the energy of these quantum beams is used for deuterium nuclear decomposition, so the energies of the protons 9 and neutrons 8 after deuterium nuclear decomposition are close to zero. On the other hand, since deuterium just before nuclear decomposition is moving due to the momentum of the quantum beam, the protons 9 and neutrons 8 are emitted in the same direction as the quantum beam. In other words, by irradiating deuterium with a quantum beam having an energy slightly higher than the threshold energy for deuterium nuclear decomposition, the irradiation unit 210 can generate a neutron beam 8 with low energy and extremely high directivity. Since all of the energy of gamma rays irradiated onto deuterium is absorbed by the deuterium and used for deuterium nuclear decomposition, the threshold energy for deuterium nuclear decomposition by gamma rays can be said to be the binding energy of deuterium.

[0055] Figure 10 is a graph showing theoretical calculation predictions of the energy spectrum of neutrons generated when deuterium is irradiated with gamma rays having energies slightly higher than the binding energy Eth of deuterium. Spectra 10A and 10B in Figure 10 are the energy spectra of neutrons generated when deuterium is irradiated with gamma rays having energies Eγ1 (=Eth+25 eV) and Eγ2 (=Eth+250 eV), respectively. Eth is the binding energy of deuterium.

[0056] As shown in Figure 10, when deuterium is irradiated with gamma rays of energy Eγ1, neutrons with a narrow energy spread and low energy (approximately 650 eV) are obtained. Also, when deuterium is irradiated with gamma rays of energy Eγ2, the energy spread is wider than when deuterium is irradiated with gamma rays of energy Eγ1 (energy spectrum 10A).

[0057] Fig. 11 is a diagram showing a theoretical calculation prediction of the directionality of neutrons generated when deuterium contained in target 1 is irradiated with gamma rays having an energy slightly higher than the binding energy Eth of deuterium. As shown in Fig. 11, when deuterium is irradiated with gamma rays having an energy Eγ1 (=Eth+25 eV), the emission angle of the generated neutrons is approximately 1.3 degrees. Also, when deuterium is irradiated with gamma rays having an energy Eγ2 (=Eth+250 eV), the emission angle of the generated neutrons is approximately 22.6 degrees. In other words, when deuterium is irradiated with gamma rays having an energy that is greater than 0 and not greater than 250 eV relative to the binding energy Eth of deuterium, highly directional neutrons can be obtained.

[0058] For example, when deuterium is irradiated with gamma rays having an energy 10 eV higher than the binding energy Eth of deuterium, the radiation angle of the generated neutrons is 1 degree or less. In other words, it is preferable that the energy of the gamma rays irradiated onto deuterium be close to the binding energy Eth of deuterium.

[0059] The gamma rays described above are generated, for example, by the following method. Specifically, in the irradiation unit 210 shown in FIG. 5, instead of the laser light 2 in the ultraviolet range (260 nm), a laser light 2 of the second harmonic (532 nm) of an Nd:YAG laser is focused at a focused spot P. At the focused spot P, the laser light 2 is collided with electrons accelerated by the electron synchrotron 220 (for example, up to 250 MeV). This causes the laser light 2 to scatter (inverse Compton scattering), generating gamma rays with a maximum energy of 2.224 MeV. In other words, gamma rays with energy slightly higher than the binding energy of deuterium are generated. Furthermore, the irradiation unit 210 may include a highly reflective cavity (supercavity) capable of storing laser light in order to increase the number of reactions between the laser light 2 and electrons.

[0060] Note that heavy water (DO) may be used as the target 1 instead of deuterium. Furthermore, the deuterium may be polarized or unpolarized. When polarized deuterium is used, the neutron generator 200 can generate a more polarized neutron beam 8. Furthermore, as long as gamma rays having an energy slightly higher than the binding energy of deuterium are used, the gamma rays irradiating the deuterium do not need to be polarized.

[0061] Furthermore, the electron beam as the quantum beam may be generated similarly using an electron accelerator, and the proton beam as the quantum beam may be generated similarly using a proton accelerator.

[0062] [Embodiment 3] Other embodiments of the present invention will be described below. For ease of explanation, the same reference numerals will be used to designate components having the same functions as those described in the above embodiment, and the description thereof will not be repeated.

[0063] An experiment was conducted to confirm the distribution of directional neutrons generated when polarized gamma rays are irradiated onto deuterium that is not spin-polarized (hereinafter referred to as unpolarized deuterium). In this embodiment, the directivity of neutrons generated by irradiation with polarized gamma rays will be described.

[0064] Figure 9 is a graph showing the directional distribution of neutrons generated when unpolarized deuterium is irradiated with polarized gamma rays and unpolarized gamma rays. In the graph of Figure 9, the vertical axis represents the number of detected neutrons, and the horizontal axis represents the polar angle. Note that the polar angle here indicates the angle at which the neutrons are detected relative to the axis along the oscillation direction of the electric field of the polarized gamma rays.

[0065] As shown by curve 9B in Fig. 9, neutrons generated when unpolarized gamma rays are irradiated onto unpolarized deuterium are emitted isotropically. On the other hand, as shown by approximation curve 9A in Fig. 9, neutrons generated when unpolarized deuterium is irradiated with polarized gamma rays exhibit directivity in the 0-degree and 180-degree directions. Therefore, as shown in Modification 1 of Embodiment 2, even with unpolarized deuterium, irradiating it with polarized gamma rays can direct neutrons in two directions (0-degree and 180-degree directions; in Fig. 8, the positive and negative directions of the Y axis). Furthermore, using polarized deuterium instead of unpolarized deuterium can further improve neutron directionality.

[0066] (Additional notes) The neutron generation method shown in the above embodiment can be applied to, for example, neutron radiography, neutron diffraction, magnetic field structure analysis using polarized neutrons, cancer treatment using boron neutron capture therapy, and radioactive waste purification using nuclear transmutation using neutrons.

[0067] The present invention is not limited to the above-described embodiments, and various modifications are possible within the scope of the claims. Embodiments obtained by appropriately combining the technical means disclosed in different embodiments are also included in the technical scope of the present invention. [Explanation of symbols]

[0068] 1 target 2. Laser light 5. Electron beam 6. Proton beam 7 Deuterium line 8 Neutrons, neutron rays, polarized neutrons, polarized neutron rays 10, 210 Irradiation unit 20 Placement section 30 Polarization section 100, 200 Neutron Generator 201 Electronic 202 Polarized Gamma Rays

Claims

1. providing a target containing deuterium; an irradiation step of generating a directional neutron beam by irradiating the target with a beam, A neutron generating method, wherein the beam is a gamma ray having an energy of 2.224 MeV to 2.225 MeV, an electron beam having an energy of 2.7 MeV to 2.8 MeV, or a proton beam having an energy of 3.5 MeV to 3.6 MeV.

2. providing a target containing deuterium; an irradiation step of generating a directional neutron beam by irradiating the target with a beam, A neutron generating method, wherein the beam is laser light.

3. 3. The neutron generating method according to claim 2, wherein the beam is a pulsed laser beam.

4. providing a target containing deuterium; an irradiation step of generating a directional neutron beam by irradiating the target with a beam, A neutron generating method, wherein the beam is an electron beam.

5. a polarization step of polarizing the nuclear spins of the deuterium in the target, The neutron generating method according to claim 1 , wherein in the irradiation step, the target is irradiated with a beam, thereby generating the neutron beam in which the neutrons have spin-polarized polarized neutrons.

6. providing a target containing deuterium; a polarization step of polarizing the nuclear spins of the deuterium in the target; an irradiation step of generating a directional, spin-polarized neutron beam by irradiating the target with a beam, the beam is a laser beam, an electron beam, a proton beam, or a deuterium beam; A neutron generating method, wherein in the irradiation step, the beam is irradiated onto the target from a direction that is not perpendicular to a direction in which the nuclear spins of the deuterium are polarized.

7. 7. The neutron generating method according to claim 6, wherein in the irradiation step, the beam is irradiated onto the target along a direction in which the nuclear spin of the deuterium is polarized.

8. 8. The neutron generating method according to claim 5, wherein in the irradiation step, the target is irradiated with the beam while maintaining the nuclear spin of the deuterium in a polarized state by applying a magnetic field to the target.

9. The neutron generating method according to claim 1 , wherein the target contains a compound containing deuterium.

10. The neutron generating method according to claim 1 , wherein the target contains hydrogen molecules containing deuterium.

11. a placement unit for placing a target containing deuterium; an irradiation unit that generates a directional neutron beam by irradiating the target with a beam, A neutron generator, wherein the beam is a gamma ray having an energy of 2.224 MeV to 2.225 MeV, an electron beam having an energy of 2.7 MeV to 2.8 MeV, or a proton beam having an energy of 3.5 MeV to 3.6 MeV.

12. a placement unit for placing a target containing deuterium; an irradiation unit that generates a directional neutron beam by irradiating the target with a beam, A neutron generator, wherein the beam is laser light.

13. a placement unit for placing a target containing deuterium; an irradiation unit that generates a directional neutron beam by irradiating the target with a beam, A neutron generator, wherein the beam is an electron beam.

14. a placement unit for placing a target containing deuterium; a polarization unit that polarizes the nuclear spins of the deuterium in the target; an irradiation unit that generates a directional, spin-polarized neutron beam by irradiating the target with a beam, the beam is a laser beam, an electron beam, a proton beam, or a deuterium beam; The neutron generator, wherein the irradiation unit irradiates the beam onto the target from a direction that is not perpendicular to a direction in which the nuclear spin of the deuterium is polarized.

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