Neutron generator

Abstract

To provide a neutron generator with simple constitution that can obtain an enough neutron bundle used for boron neutron capture therapy (BNCT).SOLUTION: A neutron generator 1 comprises: a vacuum chamber 2; a plurality of targets 3 provided on an inner wall thereof, and generating neutrons by collision of ions; an ion source 4 generating the ions in the vacuum chamber 2 toward the plurality of targets 3; and a shroud 6 covering the respective targets 3. The shroud 6 damps recoil electrons, generated when the ions generated by the ion sources 4 collides against the targets 3 biased negatively to the ion source 4, with a magnetic field in the shroud 6 to annihilate them.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a neutron generator that generates neutrons by bombarding a target with ions. [Background technology]

[0002] BACKGROUND ART Conventionally, a neutron generator is known that bombards a target with ions to generate neutrons used in boron neutron capture therapy (BNCT) (see, for example, Patent Document 1).

[0003] In the device of Patent Document 1, deuterium ions are generated by a deuterium ion source and supplied into an acceleration chamber. The supplied deuterium ions pass through an electron suppression shroud that prevents backflow electrons, which can damage the device, from returning to the ion source, and are then strongly attracted to and collide with a negatively biased titanium target.

[0004] This results in a deuterium-deuterium (DD) nuclear reaction, which produces fast neutrons that are then shaped by a beam shaper into a neutron beam with a spot size useful for neutron irradiation of tumors. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Patent Publication No. 2022-140253 Summary of the Invention [Problem to be solved by the invention]

[0006] However, according to the device of Patent Document 1, the neutron flux of the obtained neutron beam is at most 9 × 10 6 n / s / cm 2 This is about the same as the 10 required for BNCT (boron neutron capture therapy). 9 n / s / cm 2On the other hand, if a plurality of such devices are used to increase the neutron flux, the overall size of the device increases.

[0007] An object of the present invention is to provide a neutron generator with a simple configuration that can obtain a neutron flux sufficient for use in BNCT. [Means for solving the problem]

[0008] The neutron generator of the present invention comprises a vacuum chamber, a plurality of targets provided on the inner wall of the vacuum chamber and generating neutrons through ion collisions, an ion source that generates the ions within the vacuum chamber and directs the ions toward the plurality of targets, and a shroud that covers each target.

[0009] The shroud uses a magnetic field within the shroud to control the movement of recoil electrons that are generated when ions generated by the ion source are attracted to and collide with the target, which is negatively biased with respect to the ion source, and prevents the recoil electrons from heading toward the ion source.

[0010] According to the present invention, since multiple neutron sources, each consisting of an ion source and multiple targets, are arranged in a single vacuum chamber, it is possible to provide a neutron generator with a simple configuration that can obtain a larger neutron flux. Therefore, with this neutron generator, it is possible to easily obtain the neutron flux necessary and sufficient for BNCT. [Brief explanation of the drawings]

[0011] [Figure 1] 1 is a simplified cross-sectional view showing the configuration of a neutron generator according to one embodiment of the present invention. [Figure 2] FIG. 2 is a cross-sectional view taken along line II-II in FIG. [Figure 3] FIG. 2 is a diagram showing a model for simulating the neutron flux obtained by the neutron generator of FIG. 1 by particle transport Monte Carlo calculation. [Figure 4]FIG. 4 is a diagram showing a model for similarly simulating the neutron flux when the number of targets in the model of FIG. 3 is one, as a comparative example. [Figure 5] FIG. 10 is a diagram showing a model for simulating the neutron flux obtained by a neutron generator according to another embodiment of the present invention, using particle transport Monte Carlo calculations. [Figure 6] FIG. 6 is a diagram showing, as a comparative example, a model for obtaining neutron flux by particle transport Monte Carlo calculation when the number of targets in the model of FIG. 5 is one. DETAILED DESCRIPTION OF THE INVENTION

[0012] Hereinafter, an embodiment of the present invention will be described with reference to the drawings. Fig. 1 shows a cross section of a neutron generator according to an embodiment of the present invention, passing through the central axis of its vacuum chamber. Fig. 2 shows a cross section taken along line II-II in Fig. 1.

[0013] 1 and 2, this neutron generator 1 includes a cylindrical vacuum chamber 2, multiple targets 3 that are provided inside the sidewall of the vacuum chamber 2 and generate neutrons through ion collisions, and an ion source 4 that generates ions toward each of the targets 3. The multiple targets 3 are provided by forming the material that makes up the targets 3 into a cylindrical shape and supporting it inside the sidewall of the vacuum chamber 2.

[0014] The ion source 4 is provided in the vacuum chamber 2 at a predetermined distance from one bottom surface 5 of the vacuum chamber 2. Each target 3 is covered by a shroud 6. The shroud 6 has a function of using a magnetic field within the shroud to control the movement of recoil electrons that are generated when ions generated by the ion source 4 are attracted to the target 3, which is negatively biased with respect to the ion source 4, and collide with the target 3 to form an ion beam BM, thereby preventing the recoil electrons from heading toward the ion source 4.

[0015] That is, a magnetic field that helps to control the direction and speed of recoil electrons is formed inside the shroud 6. This magnetic field captures, brakes, and deflects recoil electrons generated by collisions, preventing them from heading toward the ion source 4. Therefore, recoil electrons can be handled with a simple structure that simply includes a magnet placed inside the shroud 6, without the need for externally supplied energy.

[0016] A cooling water channel 7 is provided on the outside of the side wall of the vacuum chamber 2 to cool the targets 3 that generate heat through neutron bombardment. The multiple targets 3 are arranged at equal central angular intervals around the central axis CL on a plane perpendicular to the central axis CL of the vacuum chamber 2. In this embodiment, four targets 3 are arranged at central angular intervals of 90°.

[0017] A deuterium-tritium ion source is used as the ion source 4. A titanium target is used as the target 3. By using such an ion source 4 and target 3, the generation of fast neutrons by the DT reaction (deuterium-tritium reaction) is promoted when ions (deuterium-tritium ions) from the ion source 4 collide with the target 3.

[0018] In this configuration, the neutron generator 1 is driven with a potential difference and current of, for example, 200 kV and 100 mA between the ion source 4 and each target 3. During this time, deuterium-tritium ions generated by the ion source 4 toward each target 3 are attracted to each target 3, which is negatively biased with respect to the ion source 4, pass through the shroud 6 of each target 3, and collide with each target 3.

[0019] During this collision, recoil electrons are generated at each target 3, but these recoil electrons are controlled by the magnetic field inside the corresponding shroud 6 and are prevented from proceeding to the ion source 4. In other words, backflow electrons that could damage the device are prevented from being accelerated back into the ion source 4. Therefore, the neutron generator 1 can be driven without any problems by the above-mentioned 200 kV and 100 mA.

[0020] During this time, a DT nuclear reaction occurs due to the collision of deuterium-tritium ions with each target 3, and high-speed neutrons are generated. The generated neutrons are emitted in approximately isotropic directions. For example, the number of such neutrons is up to 1×10 per target 3. 13 Therefore, when the target 3 that generates neutrons is close to the position where the neutrons are used, the generated neutrons are used efficiently without being affected by the direction of the ion beam BM.

[0021] Figure 3 shows a model for simulating the neutron flux obtained by the neutron generator 1 of Figure 1 by particle transport Monte Carlo calculation. In this model, elements corresponding to those of the neutron generator 1 are denoted by the same reference numerals. Also, as in Figure 1, this model is shown in a cross section passing through the central axis CL of the vacuum chamber 2.

[0022] In Figure 3, the x, y, and z axes are shown in a left-handed system, with the center C of the bottom surface of the vacuum chamber 2 as the origin. The z axis coincides with the central axis CL of the vacuum chamber 2. The size of each part is indicated by the scale [cm] graduated on the x, y, and z axes.

[0023] In this model, the vacuum chamber 2 is made of aluminum AL, including the wall portion corresponding to the cooling water passage 7 and the portion corresponding to the shroud 6 of the neutron generator 1 in Figure 1. The portion corresponding to the cooling water passage 7 and the empty portion of the vacuum chamber 2 other than the wall and shroud 6 are voids 8.

[0024] The aluminum AL that constitutes the vacuum chamber 2 and the air 9 that covers the vacuum chamber 2 function as moderators that scatter and decelerate neutrons. A virtual detector (tally) 10 is set at a point 66.05 cm on the z-axis. The neutron flux in the region where the virtual detector 10 is located is obtained and evaluated by particle transport Monte Carlo calculations.

[0025] Fig. 4 shows a model for simulating the neutron flux in the virtual detector 10 by particle transport Monte Carlo calculations when there is one target 3 in the model of Fig. 3, as a comparative example for the model of Fig. 3. Parts that are the same as those in the model of Fig. 3 are denoted by the same reference numerals as in Fig. 3.

[0026] Target 3 is located on the z-axis, -5 cm from the origin C of the x, y, and z axes. Shroud 6 is also placed on the z-axis so as to surround target 3. It is assumed that ions from the ion source travel along the z-axis toward shroud 6, pass through shroud 6, and then collide with target 3. The size of each part is indicated by the scale [cm] on the x, y, and z-axes.

[0027] The neutron flux of all neutrons (neutrons in the entire energy range including fast neutrons, thermal neutrons, and epithermal neutrons) in the virtual detector 10 calculated by particle transport Monte Carlo calculation using the models of FIGS. 3 and 4 is 5.18E+08 [n / cm 2 / sec], and in the case of the model in Figure 4, it is 1.87E+08[n / cm 2 / sec].

[0028] Therefore, from the results of this particle transport Monte Carlo calculation, it can be seen that by using four targets 3 as in this embodiment, a neutron flux that is approximately three times as large can be obtained in the virtual detector 10 compared to when there is only one target 3 (comparative example). Therefore, it can be seen that, despite the simple device configuration, it is highly likely that the neutron flux required for BNCT can be obtained outside the bottom surface 5 of the vacuum chamber 2 of this embodiment in FIG.

[0029] As described above, according to this embodiment, four sets of neutron sources, each consisting of an ion source 4 and a target 3, are arranged in one cylindrical vacuum chamber 2. As a result, the neutron generator 1 can obtain a neutron flux necessary or sufficient for BNCT outside the bottom surface 5 of the vacuum chamber 2, despite its simple configuration.

[0030] Furthermore, since the DT reaction is used to generate neutrons, the number of neutrons generated can be improved by about two orders of magnitude compared to when the DD reaction is used.

[0031] Furthermore, since the target 3 is covered with a shroud 6 to protect against recoil electrons, a higher voltage (200 to 260 kV) than is considered effective in the DT reaction can be applied without any problems, and neutrons of a higher intensity (number of neutrons generated) can be generated from one target 3.

[0032] For example, in the case of the DT reaction, increasing the applied voltage from 120 kV to 250 kV can roughly double the number of neutrons generated. In addition, the number of neutrons generated can be increased in proportion to the current value.

[0033] Figure 5 shows a model for particle transport Monte Carlo calculations corresponding to the configuration of a neutron generator according to another embodiment of the present invention. In Figure 5, as in the case of the model in Figure 3, the center C of the bottom surface of the vacuum chamber 2 is set as the origin, and the x, y, and z axes are represented in a left-handed system. The z axis coincides with the central axis CL of the vacuum chamber 2. The size of each part is indicated by the scale [cm] marked on the x, y, and z axes.

[0034] As shown in Figure 5, this model differs from the model in Figure 3 in that each target 3 is supported by quartz glass 11, there is a moderation layer 12 between the vacuum chamber 2 and the virtual detector 10 that slows down neutrons, the sides of the vacuum chamber 2 and the outside of the bottom surface opposite the bottom surface 5 are covered with lead 13, and an opening 15 to the virtual detector 10 is formed with lithium fluoride polymer (Lif Poly) 14.

[0035] The quartz glass 11 has both insulating and heat-resistant properties and also functions as a neutron reflector. The moderation layer 12 is made of lead 13, iron 16, and calcium fluoride 17, which are provided in this order from the bottom surface 5 side of the vacuum chamber 2.

[0036] That is, in this model (i.e., the neutron generator of this embodiment), neutrons emitted in an isotropic direction from the target 3 are effectively utilized at the position of the virtual detector 10 by the reflection and deceleration function of the neutron scattering section composed of the lead 13 covering the vacuum chamber 2, the quartz glass 11, the moderating layer 12, and the lithium fluoride polymer 14.

[0037] FIG. 6 shows a comparative example of the model of FIG. 5, which is similar to the model of FIG. 5 except that there is one target 3 and this target 3 is supported on the bottom surface 5 by silica glass 11.

[0038] The neutron flux for only epithermal neutrons in the virtual detector 10 calculated by particle transport Monte Carlo calculation using the models of FIGS. 5 and 6 is 4.25E+08 [n / cm 2 / sec], and in the case of the model in Figure 6, it is 1.39E+08[n / cm 2 / sec].

[0039] Therefore, it can be understood that with regard to the neutron flux of epithermal neutrons used in BCNT, the neutron generator of this embodiment, which corresponds to the model of Figure 5, can obtain a neutron flux of epithermal neutrons at the position of the virtual detector 10 that is approximately three times higher than that of a neutron generator having only one target 3, which corresponds to the model of Figure 6.

[0040] As described above, in the neutron generator of this embodiment corresponding to the model of Fig. 5, four sets of neutron sources, each consisting of an ion source 4 and a target 3, are arranged in one cylindrical vacuum chamber 2. As a result, even when the vacuum chamber 2 is covered with lead 13, a moderating layer 12 is provided between the vacuum chamber 2 and the virtual detector 10, and an opening 15 to the virtual detector 10 is formed with lithium fluoride polymer 14, the neutron flux required for BNCT can be obtained in the virtual detector 10 at the opening 15 with a simple configuration.

[0041] Furthermore, quartz glass 11 is used as the support material for each target 3, which also functions as a reflector, increasing the number of neutrons in the desired direction. Furthermore, the effective placement of reflectors and moderators, such as the moderating layer 12, lithium fluoride polymer 14, and lead 13 covering the entire structure, allows neutrons with an energy distribution and density suitable for BNCT to be irradiated at the intended location.

[0042] Although the embodiments of the present invention have been described above, the present invention is not limited to this. For example, the number of targets is not limited to four, and may be three or more. However, the ion source must generate ions in the direction of the targets corresponding to the number of targets.

[0043] Furthermore, as a configuration for generating neutrons by the DT reaction, a configuration may be adopted in which an ion source that generates only deuterium ions is used, and a target that is previously loaded with tritium is used.

[0044] The vacuum chamber is not limited to a cylindrical one, but may have a regular polygonal cylindrical shape (a cylindrical shape with a regular polygonal cross section), or may have a spherical shape. [Explanation of symbols]

[0045] 1...neutron generator, 2...vacuum chamber, 3...target, 4...ion source, 5...bottom, 6...shroud, 7...cooling water channel, 8...space, 9...air, 10...virtual detector, 11...quartz glass, 12...moderating layer, 13...lead, 14...lithium fluoride polymer (Lif Poly), 15...opening, 16...iron, 17...calcium fluoride, AL...aluminum.

Claims

1. a vacuum chamber; a plurality of targets provided on an inner wall of the vacuum chamber for generating neutrons by collision of ions; an ion source within the vacuum chamber that generates the ions toward the plurality of targets; a shroud covering each target, the shroud controlling, by a magnetic field within the shroud, the movement of recoil electrons generated when the ions are attracted to and collide with the target, which is negatively biased with respect to the ion source, and preventing the recoil electrons from heading toward the ion source.

2. the vacuum chamber has a cylindrical or regular polygonal tubular shape, the target is provided inside a sidewall of the vacuum chamber; 2. The neutron generator according to claim 1, wherein the ion source is provided in the vacuum chamber so as to have a predetermined distance from one bottom surface of the vacuum chamber.

3. 3. The neutron generating device according to claim 2, wherein the plurality of targets are arranged on a plane perpendicular to a central axis of the vacuum chamber at equal central angular intervals about the central axis.

4. 3. The neutron generator according to claim 2, further comprising a neutron scattering unit that scatters neutrons generated by each target in order to obtain a desired neutron flux at a position on the central axis of the vacuum chamber outside the bottom surface where the neutrons are utilized.

5. 5. The neutron generator according to claim 4, wherein the desired neutron flux is a neutron flux suitable for BNCT.

6. 2. The neutron generator according to claim 1, further comprising a target support that supports each target on an inner wall of the vacuum chamber, the target support being made of a material that is insulating and heat-resistant and also functions as a neutron scattering material.

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