JP2007242422A - Neutron generator and neutron irradiation system - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To improve the degree of freedom of irradiating neutrons in executing a BNCT. <P>SOLUTION: This neutron generator 102 is provided with a target 1 for generating neutrons by being irradiated with high-energy protons. A neutron deceleration part 3B for decelerating the neutrons generated from the target by the irradiation of the protons is arranged around the target 1. A reflector 5B for reflecting the neutrons generated from the target 1, multiplying them and guiding them to the neutron deceleration part 3B is arranged outside the neutron deceleration part 3B. The neutron deceleration part 3B revolves about the Y-axis parallel to the traveling direction of the protons. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a technology for generating neutrons, and more particularly to a neutron generator and target capable of generating neutrons suitable for boron neutron supplement therapy, and a neutron irradiation system.

Boron Neutron Capture Therapy (BNCT) uses boron compounds to collect in cancer cells and selectively cancer cells using ⁷ Li and α particles generated when boron absorbs neutrons. It is a cure that destroys and treats. In boron neutron supplemental therapy (hereinafter referred to as BNCT), it is necessary to irradiate the affected area with neutrons, and neutron irradiation equipment is always required when performing BNCT. Regarding neutron irradiation equipment used for BNCT, for example, Patent Document 1 discloses a neutron radiation equipment provided with a filter that filters neutrons in the outside spectrum from a low energy neutron beam to a specific energy.

JP-T-2002-524219

  In Patent Document 1, since neutrons are irradiated from one direction, the degree of freedom in irradiating neutrons is low, and depending on the site irradiated with neutrons, the patient may be forced to take an unreasonable posture. As a result, there is a risk that neutron irradiation may be insufficient, or a long time may be required to ensure an effective irradiation time.

  Therefore, the present invention has been made in view of the above, and an object thereof is to provide a neutron generator and a neutron irradiation system capable of improving the degree of freedom of neutron irradiation when performing BNCT.

  In order to solve the above-described problems and achieve the object, a neutron generator according to the present invention includes a proton passage through which high-energy protons pass, a target that emits neutrons when irradiated with the high-energy protons, and A neutron moderator that is disposed around the target and decelerates neutrons generated from the target by irradiation of the protons, and reflects and multiplies the neutrons generated from the target and guides them to the neutron moderator A reflector and a support that supports at least the neutron moderator and the reflector so as to be able to rotate around the proton path with the traveling direction of the proton as a rotation axis. And

  Since this neutron generator can rotate the neutron moderating portion around the proton passage, the irradiation direction of epithermal neutrons can be changed. Thereby, an appropriate neutron moderator can be selected and used according to the site irradiated with epithermal neutrons. As a result, when performing BNCT, the degree of freedom of neutron irradiation can be improved.

  In the neutron generator according to the next aspect of the present invention, in the neutron generator, the neutron moderating unit moves in the neutron generator in the neutron generator as the neutron generated in the target travels in the direction of travel. The cross-sectional area perpendicular to the direction in which the angle travels increases.

  Since this neutron generator has the configuration of the neutron generator, the same actions and effects as the neutron generator can be obtained. Further, in this neutron generator, the neutron generator is conical and irradiated with neutrons decelerated from the bottom of the cone. As a result, the reflector can more efficiently reflect neutrons to the irradiation side, so that the irradiation time of epithermal neutrons required for treatment is reduced.

  In the neutron generator according to the present invention, in the neutron generator, the solid angle of the reflector when the proton collides with the target is larger than 180 degrees and smaller than 300 degrees. It is characterized by that.

  Since this neutron generator has the configuration of the neutron generator, the same actions and effects as the neutron generator can be obtained. Furthermore, in this neutron generator, the solid angle of the reflector when the proton collides with the target is set to be larger than 180 degrees and smaller than 300 degrees. As a result, the reflector can more efficiently reflect neutrons to the irradiation side, so that the irradiation time of epithermal neutrons required for treatment is reduced. Moreover, the irradiation amount to parts other than the affected part of a patient can be reduced.

  In the neutron generator according to the next aspect of the present invention, in the neutron generator, the target is a plate-like member, and a cross section in which a cooling medium flows on the opposite side to the surface irradiated with the proton on the target A plurality of rectangular cooling channels are joined.

  Since this neutron generator has the configuration of the neutron generator, the same actions and effects as the neutron generator can be obtained. Further, in this neutron generator, a plurality of cooling channels having a rectangular cross section through which the cooling medium flows are joined to the side opposite to the surface where the target is irradiated with protons. Thus, the target can be cooled with a simple configuration.

  In the neutron generator according to the next invention, in the neutron generator, the target is provided with a plurality of partition members provided in a proton irradiation unit irradiated with protons, and a slit into which an end of the partition member is fitted. The partition member and the target support are joined in a state where the slit is fitted in the partition member, and the proton irradiation unit, the partition member, and the target support The enclosed space is configured as a cooling flow path.

  Since this neutron generator has the configuration of the neutron generator, the same actions and effects as the neutron generator can be obtained. Furthermore, this neutron generator forms a plurality of cooling channels inside by the target having the above-described configuration. And a partition member and a target support body are reliably joined by the above structures. As a result, the strength of the target can be improved, and a decrease in heat transfer performance due to poor bonding can be minimized.

  In the neutron generator according to the next aspect of the present invention, in the neutron generator, the cooling channel has a dimension in a direction parallel to the proton irradiation surface rather than a dimension in a direction orthogonal to the proton irradiation surface. Is large.

  Since this neutron generator has the configuration of the neutron generator, the same actions and effects as the neutron generator can be obtained. Furthermore, this neutron generator includes a cooling channel having a rectangular cross section in the target, which has a dimension larger in the direction perpendicular to the direction of proton travel than in the direction parallel to the direction of proton travel. Thereby, the target can be cooled more efficiently.

  The neutron irradiation system according to the next aspect of the present invention includes an accelerator that irradiates accelerated protons on a target included in the neutron generator, and irradiates an epithermal neutron irradiation target with epithermal neutrons extracted from the neutron generator. It is characterized by.

  Since this neutron irradiation system includes the neutron generator, an appropriate neutron moderator can be selected and used in accordance with the site irradiated with epithermal neutrons. Thereby, when performing BNCT, the freedom degree of neutron irradiation can be improved.

  According to this invention, when performing BNCT, the freedom degree of neutron irradiation can be improved.

  Hereinafter, the present invention will be described in detail with reference to the drawings. The present invention is not limited by the best mode for carrying out the invention (hereinafter referred to as an embodiment). In addition, constituent elements in the following embodiments include those that can be easily assumed by those skilled in the art or those that are substantially the same.

(Embodiment 1)
The neutron generator according to Embodiment 1 is used for BNCT, and reflects neutrons obtained when a proton accelerated to 20 MeV or more by an accelerator collides with a target and reflects a substance that causes an (n, xn) reaction. It is characterized in that it is reflected and amplified as a body, decelerated by a neutron moderator, and epithermal neutrons are extracted.

  FIG. 1 is an overall view showing a neutron irradiation system including a neutron generator according to the first embodiment. The neutron irradiation system 200 includes the accelerator 2 and the neutron generator 100 according to the first embodiment. When protons are irradiated from the accelerator 2 to the neutron generator 100, the neutron generator 100 generates epithermal neutrons in the direction of the BNCT treatment room 20. There is a patient K who undergoes BNCT in the BNCT treatment room 20, and the epithermal neutron is irradiated to the affected part of the patient. Here, the affected part is a cancer cell in which boron compounds are collected, and is a target for neutron irradiation. As the accelerator 2, for example, a cyclotron can be used. In the first embodiment, a cyclotron is used. The type of the accelerator 2 is not limited to this.

  Next, the neutron generator 100 according to the first embodiment will be described. FIGS. 2A and 2B are explanatory diagrams illustrating an overview of the neutron generator according to the first embodiment. FIG. 2-2 shows a state in which the cross section at Y = 0 of the neutron generator 100 shown in FIG. 2-1, that is, the XZ plane at Y = 0, is viewed from the proton traveling direction side. FIG. 2-3 is an enlarged view of the target portion of FIGS. 2-1 and 2-2. In the drawings, the symbol p (lower case) represents a proton, and n (lower case) represents a neutron (the same applies hereinafter).

  The neutron generator 100 includes a target 1, a neutron moderator 3, and a reflector 5. The target 1, the neutron moderating unit 3, and the reflector 5 are disposed in the radiation shield 9 and are configured to minimize neutrons and γ rays leaking outside the neutron generator 100. Here, the radiation shield 9 is made of, for example, concrete.

  A bismuth (Bi) layer 4 is disposed on the epithermal neutron emission side of the neutron moderator 3 for the purpose of shielding γ rays generated from the target 1 and secondary γ rays generated from other portions. Furthermore, a thermal neutron absorption layer 6 is disposed on the Bi layer 4 on the epithermal neutron emission side via a reflector 5. The thermal neutron absorption layer 6 is for absorbing decelerated thermal neutrons, and is made of, for example, polyethylene containing Li.

  The target 1 is a heavy nuclide such as tantalum (Ta) or tungsten (W). Protons accelerated by the accelerator 2 are irradiated to the target 1 through the vacuum proton passage 8, and neutrons are generated from the target 1. The generated neutrons are guided to the neutron moderator 3 where they are decelerated to become epithermal neutrons having an energy of about 4 eV to 40 keV. The epithermal neutrons are reduced by the collimator 7 and the direction of the neutrons are determined in order to reduce the amount irradiated to the part other than the affected part as much as possible and increase the intensity of the epithermal neutrons applied to the affected part. Irradiates to cancer cells.

  As shown in FIGS. 2-1 and 2-2, the neutron generator 100 according to this embodiment includes a plurality of neutron moderators in a direction orthogonal to the traveling direction of protons. In this embodiment, the neutron moderator 3 and the collimator 7 are provided in a direction parallel to the X axis and a direction parallel to the Z axis, respectively. As a result, the neutron generator 100 according to this embodiment can irradiate epithermal neutrons in two directions: a direction parallel to the X axis and a direction parallel to the Z axis.

  Thus, since the neutron generator 100 according to this embodiment can irradiate epithermal neutrons in a plurality of directions, the degree of freedom in the direction in which epithermal neutrons can be irradiated on the affected area increases. As a result, epithermal neutrons can be more appropriately irradiated to the affected area of the patient K who is undergoing treatment. In this embodiment, in the XZ plane, a plurality (two in this embodiment) of neutron moderators 3 are arranged so that the central angle about the proton passage 8 is about 90 degrees apart. . However, the arrangement of the neutron moderator 3 is not limited to this.

  As illustrated in FIG. 2C, the target 1 is disposed to be inclined with respect to the X axis and the Z axis. As a result, the distance that the neutron travels through the target 1 can be shortened as much as possible, so that the generated neutron can be efficiently guided to the neutron moderator 3. Further, by making the inclination angles θx and θz of the target 1 with respect to the X axis and the Z axis substantially equal, the intensity and distribution of epithermal neutrons emitted from the collimators 7 through the neutron moderators 3 are substantially uniform. Can be.

  Further, as shown in FIG. 2A, the neutron generator 100 according to this embodiment tilts the target 1 with respect to a direction (X-axis direction) orthogonal to the proton traveling direction. As a result, the area on which the target 1 is irradiated with protons is increased, so that the amount of heat generated per unit area of the target 1 due to irradiation with protons can be reduced. Thereby, since the thermal load of the target 1 can be reduced, the cooling capacity of the target 1 can be improved.

  In this embodiment, the affected part is irradiated with neutrons in a direction substantially orthogonal to the traveling direction of protons. By tilting the target 1 with respect to a direction (X-axis direction) orthogonal to the traveling direction of protons, The traveling distance of neutrons in the target 1 can be shortened. Thereby, attenuation of neutrons in the target 1 can be suppressed, so that neutrons generated in the target 1 can be efficiently guided to the neutron moderating unit 3.

  The number of neutron moderators 3 provided in the neutron generator 100 is not limited to two. However, as the number of neutron moderators 3 increases and the intensity of epithermal neutrons that can be irradiated from one neutron moderator 3 decreases, the number of neutron moderators 3 is set in consideration of the output of the accelerator 2.

  When a plurality of neutron moderators 3 are provided, in order to prevent epithermal neutrons from being radiated from the collimator 7 of the neutron moderator 3 that is not used for treatment, the collimator 7 from the portion where the neutrons enter the neutron moderator 3 It is preferable to provide a means for blocking neutrons and γ-rays up to or outside the collimator 7.

The neutron blocking means can be configured, for example, by providing a shutter-like structure that can be opened and closed in the epithermal neutron irradiation section 7r of the collimator 7. The material used for the neutron shielding portion, for example, or a polymer material containing much hydrogen having neutron absorbing capability, the B ¹⁰ having neutron absorbing capability can be used a material containing stainless, aluminum, or the like .

  As shown in FIGS. 2A and 2B, in the neutron generator 100 according to this embodiment, the epithermal neutron irradiation unit 7r of the collimator 7 is irradiated from the surface 100p of the neutron generator 100 with the epithermal neutron irradiation side. Protruding. A part of the surface 6 p of the thermal neutron absorption layer 6 is formed in a truncated cone shape, and the top portion of the truncated cone becomes the epithermal neutron irradiation portion 7 r of the collimator 7. When the epithermal neutron irradiation part 7r of the collimator 7 is substantially flush with the surface of the thermal neutron absorption layer 6, depending on the posture of the patient K, the affected part that can irradiate epithermal neutrons may be limited. However, if the epithermal neutron irradiation part 7r of the collimator 7 protrudes from the surface 100p of the neutron generator 100 as in the neutron generator 100 according to this embodiment, the restriction can be reduced.

  For example, when irradiating epithermal neutrons from the temporal region of patient K, if epithermal neutron irradiation part 7r of collimator 7 is substantially flush with surface 100p of neutron generator 100, epithermal neutrons are caused by patient K's shoulder. The distance between the irradiation unit 7r and the temporal region of the patient K is increased. However, if the epithermal neutron irradiation part 7r of the collimator 7 protrudes from the surface 100p of the neutron generation apparatus 100 as in the neutron generation apparatus 100 according to this embodiment, the epithermal neutron irradiation part 7r and the temporal region of the patient K Therefore, epithermal neutrons can be effectively irradiated to the affected area.

Next, the neutron moderating unit 3 will be described. The neutron moderator 3 can be composed of, for example, iron (Fe) 3a and a fluorine compound 3f. The neutrons generated from the target 1 are decelerated by the iron 3a and then the fluorine compound 3f to become epithermal neutrons. As the fluorine compound 3f, for example, AlF ₃ (69 wt%)-Al (30 wt%)-LiF (1 wt%) can be used (the composition of Li is not limited). The neutron moderating unit 3 can extract a high epithermal neutron flux from the neutrons generated at the target 1.

  In the first embodiment, the neutron guided to the neutron moderating unit 3 is near 90 degrees with respect to the proton traveling direction (proton beam direction) -Y (FIGS. 2A and 2B), or near 90 degrees. It is preferable to use neutrons generated in the direction of a large angle, that is, behind the proton traveling direction. The reason for this will be described.

  FIG. 3A is a conceptual diagram illustrating the relationship between the proton traveling direction F and the neutron generation direction. FIG. 3-2 is an explanatory diagram illustrating the relationship between the neutron flux intensity and the energy of neutrons after deceleration, using the generation direction of neutrons generated from the target as a parameter. The generation direction of neutrons generated from the target 1 (the direction of the neutron beam) is expressed by an inclination angle with respect to the proton traveling direction F (see FIG. 3A). The proton traveling direction F means 0 degree. Here, the proton traveling direction F side is referred to as the proton traveling direction front, and the opposite side of the paper traveling direction F is referred to as the proton traveling direction rear.

As can be seen from FIG. 3-2, fast neutrons having high energy of about 10 ⁷ eV have the fewest neutrons that are generated in the vicinity of 90 degrees with respect to the inclination angle θ with respect to the traveling direction F of protons (A in FIG. 3-2). Part shown by). Therefore, if neutrons generated at an inclination angle θ of around 90 degrees are guided to the neutron moderator 3, the amount of fast neutrons transmitted from the neutron generator 100 to the BNCT treatment room 20 side can be reduced. It will be advantageous.

  In order to reduce the amount of transmission of the fast neutrons, when the inclination angle θ between the direction of generation of neutrons generated from the target 1 and the traveling direction F of protons is in the range of 90 ° -0, + 90 °, the neutron moderating unit 3 It is preferable to acquire neutrons for guidance. That is, it is preferable to use the neutrons generated behind the proton in the traveling direction as neutrons for guiding the neutron moderator 3. By doing in this way, the quantity of the fast neutron which reaches | attains the patient K of the BNCT treatment room 20 from the neutron generator 100 can be reduced. Further, as described above, the neutron generated in the vicinity of 90 degrees with respect to the traveling direction F of the proton is guided to the neutron moderator 3 to be an epithermal neutron, so that a plurality of neutron moderators 3 around the target 1 as described above. The structure which arrange | positions can be implement | achieved easily.

  Further, as shown in FIG. 3A, the target 1 is preferably arranged to be inclined with respect to a direction orthogonal to the proton traveling direction F. This is because the irradiation area of the target 1 with respect to the proton beam is increased, the thermal load of the target 1 is lowered, and neutron attenuation in the target 1 is suppressed. That is, when the target 1 is arranged orthogonally to the proton traveling direction F, neutrons generated at an inclination angle of about 90 degrees with respect to the proton traveling direction F reach the neutron moderating unit 3 before reaching the neutron moderating unit 3. Attenuates as it travels through 1. As a result, the number of neutrons that can be extracted as epithermal neutrons is reduced. If the target 1 is arranged to be inclined with respect to the direction orthogonal to the proton traveling direction F, the distance that neutrons travel through the target 1 can be shortened, so that the generated neutrons can be efficiently guided to the neutron moderating unit 3.

  When the target 1 is arranged orthogonal to the proton traveling direction F, the shape when the proton collides with the target 1 is substantially circular, but the target 1 is tilted with respect to the direction orthogonal to the proton traveling direction F. When the is placed, the shape when the proton collides with the target becomes an ellipse. Thereby, compared with the case where the target 1 is arranged orthogonal to the traveling direction F of the proton, the area when the proton collides with the target 1 can be increased, so that the heat generation density of the target 1 can be lowered. As a result, for example, when a cooling medium having the same cooling capacity is used, the target 1 can be cooled more easily.

  Therefore, from the above viewpoint, it is preferable that the target 1 is disposed to be inclined with respect to the proton traveling direction F. Here, when the target thickness tp with respect to the traveling direction of the protons exceeds the range tc (for example, about 2.8 mm when tantalum is used and the energy of the proton is about 50 MeV), the proton irradiated to the target 1 is the target 1. As a result, the amount of heat generated by the target 1 is extremely increased. This increase in calorific value is called the Bragg peak.

  When the target tilt angle β is increased, the distance of protons traveling in the target 1 increases, and the proton P completely stops in the target 1, which may cause a Bragg peak. In order to avoid the Bragg peak, in the neutron generator 100 of the first embodiment, the target inclination angle β is made smaller than the proton range tc. Therefore, the target thickness tp with respect to the proton traveling direction F is configured to satisfy the relationship of (tp = t / cos β) <tc.

  With such a configuration, protons that have collided with the target 1 are transmitted, and the protons are prevented from stopping in the target 1. Further, the target 1 is cooled by the cooling medium flowing on the emission surface (heat transfer surface 1h), and heat generation is suppressed. Thereby, heat_generation | fever of the target 1 can be suppressed and durability can be improved. Note that there is almost no change in the number of generated neutrons between when the proton is stopped in the target 1 and when it is transmitted.

  The proton range increases as the proton energy increases. Therefore, when the proton energy is low, the range becomes small. For example, when the tantalum is used for the target 1 and the proton energy is 30 MeV, the range is about 1.2 mm. The target thickness in the traveling direction of protons may be larger than the proton range. Therefore, when the proton energy is small, the proton is stopped in the target and the target 1 is sufficiently cooled to suppress the temperature rise of the target 1 due to the kinetic energy given by the proton stopping.

The temperature of the target 1 that is irradiated with protons rises due to the energy of the protons. For this reason, while the neutron generator 100 is in operation, the target 1 is cooled by a cooling medium such as water (H ₂ O) or a liquid metal (for example, mercury (Hg)). In the neutron generator 100 of Embodiment 1, the target 1 is cooled from the surface opposite to the surface irradiated with the protons accelerated by the accelerator 2. More specifically, the target 1 is cooled by bringing a cooling medium into contact with the heat transfer surface 1 h provided on the opposite side of the proton irradiation surface 1 p of the target 1. The cooling medium whose temperature has been raised is taken out of the neutron generator 100, the temperature is lowered by the heat exchanger 50, and it is sent again to the target 1 by the pump 52. Next, the cooling structure of the target 1 used in this embodiment will be described.

  FIG. 4 is an explanatory diagram illustrating a target cooling structure according to the first embodiment. The target 1 is attached to the target support 40 and configured as an integral structure. The target 1 is provided with a plurality of partition members 41. In this embodiment, for example, by cutting a thick tantalum plate, the proton irradiation unit 1A of the target 1 irradiated with protons and the partition member 41 are integrally configured. Thus, since the proton irradiation part 1A and the partition member 41 are integrally formed from the same material, the strength of the target 1 can be improved and the heat transfer performance can be prevented from being lowered due to poor bonding. The target 1 may be configured by joining the partition member 41 to the proton irradiation unit 1A of the target 1 by welding or the like.

  The target support 40 is provided with a slit 40s into which the end of the partition member 41 is fitted. In the target 1 and the target support 40, the end portion of the partition member 41 included in the target 1 is fitted into the slit 40 s of the target support 40. And the partition member 41 and the target support body 40 are joined by welding etc., and the target 1 and the target support body 40 unite | combine. With such a structure, a space surrounded by the partition member 41, the proton irradiation unit 1 </ b> A of the target 1, and the target support 40 becomes a cooling flow path 42 through which a cooling medium flows. A plurality of cooling channels 42 are formed on the side opposite to the proton irradiation side of the target 1. Since the partition member 41 plays a role of a rib in a state where the target 1 and the target support body 40 are integrated, it contributes to an improvement in the strength of the target 1. Moreover, since the end part of the partition member 41 is inserted in the target support body 40, and both are joined by welding etc., both can be welded reliably. As a result, the strength of the target 1 is improved, and a decrease in heat transfer performance due to poor bonding can be minimized.

  An inlet-side header 43a and an outlet-side header 43b are attached to the respective ends of the target 1 on the side where the cooling flow path 42 is open. The inlet side header 43a and the outlet side header 43b and the target 1 are joined by welding, for example. The inlet header 43a is provided with a plurality of inlet nozzles 46a that form inlets for the cooling medium. Thereby, the flow velocity distribution of the cooling medium flowing into the plurality of cooling channels 42 can be made uniform. The outlet header 43b is provided with an outlet nozzle 46b that forms an outlet for the cooling medium. Thereby, the flow velocity distribution in the vicinity of the outlet of the cooling channel 42 can be made uniform.

  When the target 1 is irradiated with protons to generate neutrons, a cooling medium is flowed from the inlet header 43a toward the outlet header 43b. As a result, the cooling medium flows to the cooling flow path 42 formed in the target support 40, and the cooling medium takes away the heat generated by the target 1, so that the target 1 can be cooled. In this embodiment, the planar shape of the target 1 is rectangular in consideration of ease of manufacture.

  FIG. 5 is a cross-sectional view illustrating another cooling structure of the target according to the first embodiment. In this cooling structure, a cooling flow path 42 is formed by attaching a plurality of cooling pipes 44 whose cross-sectional shape perpendicular to the pipe axis direction is rectangular (substantially square in this embodiment) to the target 1. A spacer 45 is provided between adjacent cooling pipes 44, and the spacer 45 is sandwiched between the support plate 46 and the target 1. Here, the target 1 and the cooling pipe 44 are joined by welding. The spacer 45 is joined to the target 1 and the support plate 46 by welding. When the target 1 is irradiated with protons to generate neutrons, the cooling medium flows into the cooling flow path 42 in the cooling pipe 44 joined to the support plate 46, and the cooling medium takes away the heat generated by the target 1. Therefore, the target 1 can be cooled.

  The target 1 and the spacer 45 may have an integrated structure by cutting, for example. Further, instead of using the cooling pipe 44, a space surrounded by the target 1, the spacer 45, and the support plate 46 may be used as a cooling flow path. In this way, if the cooling pipe 44 is not used, the labor of welding the cooling pipe 44 can be saved, so that the manufacturing process can be simplified. Further, since there is no deterioration in heat transfer performance due to poor welding of the cooling pipe 44, stable cooling performance can be exhibited.

FIG. 6A is an explanatory diagram illustrating a change in heat transfer coefficient depending on the shape of the cooling flow path. FIG. 6B is an explanatory diagram of a cross section of the cooling channel. As can be seen from FIG. 6A, the smaller the equivalent diameter de (= 4 × X × Y / (2 × X + 2 × Y) = 2 × X × Y / (X + Y)), the smaller the heat transfer coefficient dd (W / m ² · K) increases. In addition, the heat transfer coefficient dd increases as the length (dimension) in the direction (Y direction) perpendicular to the cooling surface (that is, the proton irradiation surface) 1 pc is smaller. Therefore, the cooling flow path 42 has a large X / Y, that is, the dimension in the direction parallel to the proton irradiation surface is larger than the dimension in the direction orthogonal to the proton irradiation surface, and the equivalent diameter de is small. It is preferable to do so. Next, returning to FIGS. 2-1 and 2-2, the reflector 5 provided in the neutron generator 100 according to this embodiment will be described.

  Neutrons generated from the target 1 are directed not only in the direction of the neutron moderating unit 3 but also in all directions of 360 degrees centering on the portion where the target 1 is irradiated with protons. In order to more efficiently guide the neutrons generated from the target 1 to the neutron moderating unit 3, the target 1 is disposed inside the reflector 5. In the first embodiment, the reflector 5 is made of a substance that causes a (n, xn) reaction when reflecting neutrons.

  Here, the substance causing the (n, xn) reaction must be a heavy nuclide and a substance containing a nuclide that does not cause a fission reaction by neutron irradiation. For example, lead (Pb) or iron (Fe ) Etc. can be used. Particularly, since lead also has a function of shielding γ rays, it is preferable to use lead for the reflector 5 because it can shield γ rays generated slightly when protons collide with the target 1.

  The reflector 5 made of such a material reflects not only neutrons but also one neutron when reflecting neutrons obtained by irradiating the target 1 with high-energy protons. In addition, x new neutrons are generated. That is, the reflector 5 can not only reflect neutrons generated at the target 1 but also multiply the neutrons. As a result, the neutron generator 100 according to the first embodiment can introduce more neutrons to the neutron moderator 3 and generate epithermal neutrons with a high neutron flux.

  Here, the high energy proton means a proton accelerated to 20 MeV or more and 500 MeV or less. Then, when neutrons obtained by irradiating the target 1 with such protons enter a substance that causes (n, xn) reaction, (n, xn) reaction occurs. Thus, in the neutron generator according to Embodiment 1, the target 1 is irradiated with high energy protons to generate neutrons, and the generated neutrons are generated using the reflector 5 that generates an (n, xn) reaction. Multiply. As a result, the amount of epithermal neutrons emitted from the neutron moderator 3 can be increased by about an order of magnitude compared to the case of using a reflector that does not cause (n, xn) reaction. As a result, more neutrons can be guided to the neutron moderating unit 3, so that epithermal neutrons can be efficiently obtained. Next, an example of treatment equipment using the neutron generator 100 according to this embodiment will be described.

  7 and 8 are explanatory diagrams illustrating examples of treatment facilities using the neutron generator according to the first embodiment. The treatment facility 210 shown in FIG. 7 is provided with different treatment rooms on different floors of the building. In this treatment facility 210, the epithermal neutron irradiation parts 7r of the two collimators 7 provided in the neutron generator 100 according to this embodiment are arranged in the first treatment room 211 and the second treatment room 212, respectively. The patient K in the first treatment room 211 is irradiated with epithermal neutrons from the temporal region, and the patient K in the second treatment room 212 is irradiated with epithermal neutrons from the frontal region. At this time, it is only necessary for the patient K to lie on his back on the bed 213, and his / her posture does not need to be changed greatly according to the site of irradiation with epithermal neutrons (the position of the affected area).

  In the treatment facility 220 shown in FIG. 8, the epithermal neutron irradiation parts 7r of the two collimators 7 included in the neutron generator 100 according to this embodiment are arranged on the work table 221 side and the lower side of the neutron generator 100, respectively. Is done. The patient K on the work table 221 side is irradiated with epithermal neutrons from the temporal region, and the patient K below the neutron generator 100 is irradiated with epithermal neutrons from the frontal region. At this time, it is only necessary for the patient K to lie on his back on the bed 213, and his / her posture does not need to be changed greatly according to the site of irradiation with epithermal neutrons (the position of the affected area).

  As described above, if the neutron generator 100 according to this embodiment is used, it is possible to appropriately irradiate the affected part of the patient K undergoing treatment with epithermal neutrons. Therefore, it is possible to reduce the burden of treatment. Moreover, since the patient K can take a more natural posture during the irradiation of epithermal neutrons, the epithermal neutrons can be efficiently irradiated to the affected area.

(Modification)
Although the neutron generator which concerns on the modification of Embodiment 1 is the structure substantially the same as the neutron generator which concerns on Embodiment 1, the shapes of a reflector and a neutron deceleration part differ. Other configurations are the same as those of the first embodiment. Here, the solid angle means a solid angle when the target is irradiated with protons.

  FIG. 9 is a conceptual diagram illustrating the structure of a neutron generator according to a modification of the first embodiment. FIG. 10 is an explanatory diagram showing the relationship between the solid angle of the reflector and the maximum irradiation time of epithermal neutrons required for treatment. The neutron generator 101 has a spherical shape as a whole, and the solid angle α1 of the reflector 5A is larger than 180 degrees. Along with this, the shape of the neutron moderating portion 3A is conical. Here, the solid angle α2 of the neutron moderator 3A is (360−α1) degrees.

  With the above configuration, the neutron moderating unit 3A is directed toward the emitting unit 3Ao from the incident unit 3Ai of neutrons generated in the target 1, that is, as the neutrons travel in the neutron moderating unit 3A. The cross-sectional area of becomes larger. Here, the cross-sectional area of the neutron moderator 3A is an area of a cross section orthogonal to the direction in which neutrons travel in the neutron moderator 3A.

  As shown in FIG. 10, when the solid angle α1 of the reflector 5A is larger than 180 degrees, the maximum irradiation time of epithermal neutrons required for treatment is reduced. However, as the solid angle α1 of the reflector 5A is made larger than 180 degrees, the ratio of fast neutron flux increases, and there is a possibility that the allowable value may be exceeded at 300 degrees. For this reason, the solid angle α1 of the reflector 5A is preferably in a range larger than 180 degrees and smaller than 300 degrees, more preferably in a range larger than 240 degrees and smaller than 300 degrees, and further preferably 270 degrees ± 15. It is a range of degrees.

  FIG. 11 is a cross-sectional view illustrating a configuration example of a neutron generator according to a modification of the first embodiment. As shown in FIG. 11, in this neutron generator 101, the solid angle of the reflector 5A is set to 270 degrees, and the solid angle of the neutron moderator 3A is set to 90 degrees (that is, 360 degrees—the solid angle of the reflector 5A). is there. And in order to make the reflector 5A and the neutron moderating part 3A into a shape close to a sphere, the shape of the reflector 5A is adjusted. In this way, the volume of the reflector 5A can be reduced and the weight can be reduced as compared with the neutron generator 100 (see FIG. 2-1 etc.) shown in the first embodiment. In addition, although the neutron generator 101 shown in FIG. 11 is provided with the single neutron moderator 3A, when providing the several neutron moderator 3A, the structure of the neutron generator 100 which concerns on Embodiment 1 is applied, for example, The neutron moderator 3A and the collimator 7 are arranged in the part indicated by D in FIG.

  As described above, in the first embodiment and the modification thereof, a plurality of neutron moderators are provided around the target, and the epithermal neutrons can be irradiated from the plurality of neutron moderators. A neutron moderator can be selected and used. Thereby, when performing BNCT, the freedom degree of neutron irradiation can be improved. Note that the configurations disclosed in the first embodiment and its modifications can also be applied to the following embodiments. Moreover, if it has the same structure as the structure disclosed in Embodiment 1 and its modifications, the same operations and effects as in Embodiment 1 and its modifications are achieved.

(Embodiment 2)
The neutron generator according to the second embodiment has the same configuration as that of the neutron generator according to the first embodiment except that the neutron generator can rotate around the proton path. Other configurations are the same as those of the neutron generator according to the first embodiment.

  12A and 12B are general views illustrating the configuration of the neutron generator according to the second embodiment. FIGS. 13-1 to 13-3 are conceptual diagrams showing states when irradiating epithermal neutrons in the neutron generator according to the second embodiment. The neutron generator 102 is rotatably supported by the support member 110 and is driven by the driving device 111 to rotate around the proton passage 8. When the neutron generator 102 rotates, the epithermal neutron irradiator 7r of the collimator 7 sets the distance between the rotation axis (Y axis) of the neutron generator 102 and the epithermal neutron irradiator 7r around the proton path 8 as the radius. Move on the circumference you want.

  As shown in FIGS. 13-1 to 13-3, by adjusting the relationship between the position of the epithermal neutron irradiation part 7 r of the collimator 7 and the position of the neutron irradiation part with respect to the patient K, it is appropriate for the affected part. Epithermal neutrons can be irradiated from the direction. For example, in the state shown in FIG. 13A, epithermal neutrons are irradiated to the top of the patient K's head. In the state shown in FIG. 13B, epithermal neutrons are irradiated between the top of the patient K and the frontal region. In the state shown in FIG. 13C, epithermal neutrons are irradiated to the frontal region of the patient K.

  FIG. 14 is a cross-sectional view of the neutron generator according to the second embodiment. As in the neutron generator 101 (see FIG. 11) according to the modification of the first embodiment, the neutron generator 102 makes the solid angle of the reflector 5B larger than 180 degrees (270 degrees in this example). The solid angle of the neutron moderator 3B is 90 degrees (that is, 360 degrees—the solid angle of the reflector 5B). And in order to make the reflector 5B and the neutron moderating part 3B into a shape close to a sphere, the shape of the reflector 5B is adjusted. At this time, the shape of the reflector 5B is adjusted so that the center of gravity in the cross section orthogonal to the rotation axis (Y axis) of the neutron generator 102 is positioned in the vicinity of the rotation axis (Y axis) of the neutron generator 102. Is preferred. If it does in this way, the driving force at the time of rotating the neutron generator 102 can be reduced.

  In the neutron generator 102 according to this embodiment, the target 1 is fixed to the proton passage 8. When the neutron generator 102 rotates, the neutron moderator 3B and the epithermal neutron irradiation unit 7r of the collimator 7 rotate relative to the target 1. Here, the target 1 may be rotated together with the neutron moderator 3 </ b> B and the collimator 7 of the neutron generator 102. In this way, epithermal neutrons can be generated while maintaining a state where the distance that the neutrons generated in the target 1 pass through the target 1 is minimized.

  As described above, in this embodiment, since the neutron moderator can be rotated around the proton path, the irradiation direction of epithermal neutrons can be changed. Thereby, an appropriate neutron moderator can be selected and used according to the site irradiated with epithermal neutrons. As a result, when performing BNCT, the degree of freedom of neutron irradiation can be improved. In addition, if the same configuration as the configuration disclosed in the second embodiment is provided, the same operations and effects as the second embodiment are achieved.

  As described above, the neutron generator, the target, and the neutron irradiation system according to the present invention are useful for BNCT, and are particularly suitable for efficiently generating neutrons suitable for BNCT.

1 is an overall view showing a neutron irradiation system including a neutron generator according to Embodiment 1. FIG. It is explanatory drawing which shows the outline | summary of the neutron generator which concerns on Embodiment 1. FIG. It is explanatory drawing which shows the outline | summary of the neutron generator which concerns on Embodiment 1. FIG. It is an enlarged view of the target part of FIGS. 2-1 and 2-3. It is a conceptual diagram which shows the relationship between the advancing direction F of a proton, and the generation | occurrence | production direction of a neutron. It is explanatory drawing which represented the generation | occurrence | production direction of the neutron generated from the target as a parameter about the relationship between the neutron flux intensity | strength after deceleration and the energy of a neutron. FIG. 3 is an explanatory diagram illustrating a target cooling structure according to the first embodiment. It is sectional drawing which shows the other cooling structure of the target which concerns on Embodiment 1. FIG. It is explanatory drawing which shows the change of the heat transfer rate by the shape of a cooling flow path. It is explanatory drawing which shows the cross section of a cooling flow path. It is explanatory drawing which shows the example of the treatment equipment using the neutron generator which concerns on Embodiment 1. FIG. It is explanatory drawing which shows the example of the treatment equipment using the neutron generator which concerns on Embodiment 1. FIG. It is a conceptual diagram explaining the structure of the neutron generator which concerns on the modification of Embodiment 1. It is explanatory drawing which shows the relationship between the solid angle of a reflector, and the irradiation time maximum value of the epithermal neutron required for a treatment. It is sectional drawing which shows the structural example of the neutron generator which concerns on the modification of Embodiment 1. It is a general view which shows the structure of the neutron generator which concerns on Embodiment 2. FIG. It is a general view which shows the structure of the neutron generator which concerns on Embodiment 2. FIG. It is a conceptual diagram which shows the state at the time of irradiating an epithermal neutron in the neutron generator which concerns on Embodiment 2. FIG. It is a conceptual diagram which shows the state at the time of irradiating an epithermal neutron in the neutron generator which concerns on Embodiment 2. FIG. It is a conceptual diagram which shows the state at the time of irradiating an epithermal neutron in the neutron generator which concerns on Embodiment 2. FIG. It is sectional drawing of the neutron generator which concerns on Embodiment 2. FIG.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Target 1h Heat transfer surface 1p Proton irradiation surface 2 Accelerator 3a Iron 3f Fluorine compound 3, 3A, 3B Neutron decelerating part 3Ai Incident part 3Ao Output part 4 Bismuth (Bi) layer 5, 5A, 5B Reflector 6 Thermal neutron absorption layer 7 Collimator 7r Epithermal neutron irradiation part 8 Proton passage 9 Radiation shield 20 Treatment room 40 Target support body 41 Partition member 42 Cooling flow path 43a Inlet side header 43b Outlet side header 44 Cooling pipe 45 Spacer 46 Support plate 100, 101, 102 Neutron Generator 110 Support member 200 Neutron irradiation system 210, 220 Treatment facility

Claims (7)

A proton passage through which high energy protons pass,
A target that is irradiated with the high-energy protons to generate neutrons;
A neutron moderator that is disposed around the target and decelerates neutrons generated from the target by irradiation of the protons;
A reflector for reflecting and multiplying the neutrons generated from the target and leading to the neutron moderator,
A support portion that supports at least the neutron moderator and the reflector so as to be able to rotate around the proton path, with the traveling direction of the proton as a rotation axis;
The neutron generator characterized by comprising.   The neutron moderator has a cross-sectional area that is perpendicular to the direction in which the neutron travels in the neutron generator as the neutron generated by the target travels in the neutron generator. The neutron generator according to claim 1.   3. The neutron generator according to claim 2, wherein a solid angle of the reflector when a portion where the proton collides with the target is the center is larger than 180 degrees and smaller than 300 degrees.   The target is a plate-shaped member, and a plurality of cooling channels having a rectangular cross section through which a cooling medium flows are joined to a side opposite to a surface on which the proton is irradiated to the target. The neutron generator of any one of 1-3. The target is
A plurality of partition members provided in the proton irradiation unit irradiated with protons;
A target support provided with a slit into which an end of the partition member is fitted, and
The partition member and the target support are joined in a state where the slit is fitted in the partition member, and a space surrounded by the proton irradiation unit, the partition member, and the target support is configured as a cooling channel. The neutron generator according to any one of claims 1 to 3, wherein   The neutron generation according to claim 4 or 5, wherein the cooling channel has a dimension in a direction parallel to the proton irradiation surface larger than a dimension in a direction orthogonal to the proton irradiation surface. apparatus. The target with which the neutron generator of any one of Claims 1-6 is equipped is equipped with the accelerator which irradiates the accelerated proton,
A neutron irradiation system that irradiates an epithermal neutron irradiation target with epithermal neutrons extracted from the neutron generator.

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