Neutron profile measuring device and neutron profile measuring method

Abstract

To easily measure a neutron profile.SOLUTION: A neutron profile measurement device 10 includes: a plurality of metal plate converters 12a to 12e containing a metal element that is converted into other radioisotope that beta decays by a threshold reaction of absorbing neutrons; and a fixing jig 14 for fixing the plurality of metal plate converters 12a to 12e so that the plurality of metal plate converters 12a to 12e overlap each other in a predetermined axial direction. Two or more of the plurality of metal plate converters 12a to 12e are made of the same material.SELECTED DRAWING: Figure 2

Description

[Technical field]

[0001] The present invention relates to a neutron profile measuring device and a measuring method. [Background technology]

[0002] There is a known inspection method that uses neutron beams to non-destructively see inside materials, and it is called neutron radiography testing (NRT) or neutron imaging. Neutron imaging is mainly used to inspect materials that contain elements with small atomic numbers that are difficult to inspect with X-rays, and can be used to inspect, for example, water, oil, or resin that contains hydrogen (H), and materials that contain lithium (Li) or boron (B). As a neutron source, for example, an accelerator neutron source is used, which generates neutron beams by irradiating a target with a particle beam such as a proton beam accelerated by an accelerator.

[0003] Since the mode of interaction between neutrons and materials changes depending on the neutron energy, it is necessary to appropriately adjust and measure the energy (spectrum) of the neutron beam used in the inspection. As a method for measuring the neutron spectrum, a method has been proposed in which multiple types of metal foil converters are irradiated with neutron beams, and the intensity of radiation emitted from each of the multiple types of metal foil converters activated by the neutron beam irradiation is transferred onto a transfer plate and measured (for example, Patent Document 1). [Prior art documents] [Patent documents]

[0004] [Patent Document 1] JP 2020-24105 A Summary of the Invention [Problem to be solved by the invention]

[0005] It is known that the neutron beam emitted from an accelerator neutron source has a directivity according to the energy of the neutron. In order to operate the accelerator neutron source appropriately, it is preferable to be able to measure the neutron profile, which is the spatial distribution of the neutron beam.

[0006] An exemplary object of an embodiment of the present invention is to provide a technique for easily measuring a neutron profile. [Means for solving the problem]

[0007] A neutron profile measurement device according to an embodiment of the present invention includes a plurality of metal plate converters each containing a metal element that is converted into another radioisotope that undergoes beta decay by a threshold reaction of absorbing a neutron, and a fixing jig that fixes the plurality of metal plate converters so that the plurality of metal plate converters overlap each other in a predetermined axial direction, wherein two or more of the plurality of metal plate converters are made of the same material.

[0008] Another aspect of the present invention is a neutron profile measurement method using the neutron profile measurement device of an aspect of the present invention, which includes irradiating a plurality of metal plate converters fixed by a fixing jig with a neutron beam, imaging a two-dimensional intensity distribution of radiation emitted from each of the plurality of metal plate converters activated by the irradiation with the neutron beam to generate image data, and generating three-dimensional profile data of the neutron beam based on the image data.

[0009] Any combination of the above components or mutual substitution of the components or expressions of the present invention between methods, devices, systems, etc. are also valid as aspects of the present invention. Effect of the Invention

[0010] According to the present invention, the neutron profile can be measured easily. [Brief description of the drawings]

[0011] [Figure 1]FIG. 2 is a diagram showing a schematic diagram of a neutron beam emitted from an accelerator neutron source. [Diagram 2] 1 is a side view showing a schematic configuration of a neutron profile measurement apparatus according to a first embodiment. [Diagram 3] 1 is a table showing the characteristics of metal elements used in a metal plate converter. [Figure 4] FIG. 2 is a rear view showing a schematic configuration of the metal plate converter. [Diagram 5] 3 is a rear view diagrammatically illustrating the configuration of the neutron profile measurement apparatus of FIG. 2. [Figure 6] FIG. 2 is a cross-sectional view illustrating a schematic configuration of a transfer device. [Figure 7] 7(a) to (e) are diagrams showing examples of transferred images of a plurality of metal plate converters. [Figure 8] 1 is a graph showing an example of a three-dimensional profile of a neutron beam. [Figure 9] 1 is a graph showing an example of the directivity of a neutron beam. [Figure 10] 1 is a flowchart showing the flow of a neutron spectrum measuring method. [Figure 11] FIG. 11 is a side view showing a schematic configuration of a neutron profile measurement apparatus according to a second embodiment. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0012] Hereinafter, the embodiment of the present invention will be described in detail. Note that the configuration described below is an example and does not limit the scope of the present invention in any way. In addition, in the description of the drawings, the same elements are given the same reference numerals, and duplicated descriptions are omitted as appropriate. In addition, in the drawings referred to in the following description, the size and thickness of each component are for convenience of explanation, and do not necessarily indicate the actual dimensions or ratios.

[0013] The present embodiment relates to a technique for measuring a neutron profile, which is a spatial distribution of neutrons emitted from a neutron source. In particular, the present embodiment relates to a technique for easily measuring a three-dimensional profile of fast neutrons emitted from an accelerator neutron source. In this specification, "fast neutrons" refers to high-energy neutrons with neutron energy of 1 MeV or more.

[0014] FIG. 1 is a diagram showing a schematic diagram of a neutron beam NB emitted from an accelerator neutron source 90. The accelerator neutron source 90 includes an accelerator 92 and a target 94. The accelerator 92 is a device for accelerating a particle beam PB to be irradiated onto the target 94, and is, for example, a cyclotron. The particle beam PB is, for example, a proton beam or an alpha beam. The accelerator 92 generates a proton beam accelerated to, for example, 10 MeV or more. The target 94 generates high-speed neutrons by a nuclear reaction caused by irradiation with the particle beam PB. An example of the target 94 is metallic beryllium, but other materials such as lithium may be used.

[0015] The neutron beam NB emitted from the target 94 has a directivity according to the energy of the neutron. FIG. 1 shows schematic direction angles θ1, θ2, and θ3 of neutron beams NB1, NB2, and NB3 with different energies. The first neutron beam NB1 is a fast neutron with relatively high energy (e.g., 10 MeV) and exists within a range of a relatively small first directivity angle θ1. The second neutron beam NB2 is a fast neutron with medium energy (e.g., 5 MeV) and exists within a range of a second directivity angle θ2 larger than the first directivity angle θ1. The third neutron beam NB3 is a fast neutron with relatively low energy (e.g., 1 MeV) and exists within a range of a third directivity angle θ3 larger than the second directivity angle θ2.

[0016] In this way, the beam angles θ1 to θ3 tend to become smaller as the energy of the neutrons emitted from the target 94 increases. Although low-energy neutrons of less than 1 MeV can also be emitted from the target 94, the low-energy neutrons tend to be emitted isotropically from the target 94. The object of this embodiment is to measure the spatial distribution of fast neutrons having a directionality as shown in FIG.

[0017] (First embodiment) 2 is a side view showing a schematic configuration of a neutron profile measurement apparatus 10 according to the first embodiment. The neutron profile measurement apparatus 10 includes a plurality of metal plate converters 12a, 12b, 12c, 12d, and 12e (collectively referred to as metal plate converters 12) and a fixing jig 14. The neutron profile measurement apparatus 10 may further include a positioning plate 20.

[0018] The metal plate converter 12 is a flat metal plate with a uniform thickness. The metal plate converter 12 is used to measure the two-dimensional intensity distribution of the incident neutron beam NB. The metal plate converter 12 contains a metal element that is activated by a threshold reaction that absorbs neutrons. When the metal plate converter 12 is irradiated with the neutron beam NB, a radioisotope corresponding to the energy of the irradiated neutrons is generated inside the metal plate converter 12. By measuring the two-dimensional intensity distribution of the radiation emitted from the metal plate converter 12 after the irradiation with the neutron beam NB, the two-dimensional intensity distribution in a specific energy region of the neutron beam NB irradiated to the metal plate converter 12 can be calculated.

[0019] The metal plate converters 12a-12e are arranged perpendicular to a predetermined axial direction (z direction), and the thickness direction of the metal plate converters 12a-12e coincides with the axial direction. The predetermined axial direction corresponds to the incident direction of the neutron beam NB to be measured. In FIG. 2, the incident direction of the neutron beam NB is set to the +z direction. The metal plate converters 12a-12e are arranged so as to overlap each other in the axial direction. The metal plate converters 12a-12e are arranged at intervals such that their positions in the axial direction (z direction) are different from each other, for example, so as to be equally spaced in the axial direction.

[0020] The metal plate converters 12a-12e are made of the same material. By making the metal plate converters 12a-12e of the same material, the measurement conditions of the metal plate converters 12a-12e can be made the same, and only the measurement positions in the axial direction can be changed. As a result, the two-dimensional intensity distribution of neutrons in a specific energy region can be measured at multiple positions different in the axial direction, and a three-dimensional profile of the neutron beam NB can be obtained. In the illustrated example, five metal plate converters 12a-12e are used, but the number of metal plate converters 12 is not limited to five, and may be at least two or more, and may be three or four, or may be six or more. In other words, it is sufficient that there are at least two or more metal plate converters using the same material.

[0021] FIG. 3 is a diagram showing the characteristics of the metal element used in the metal plate converter 12. For example, zinc (Zn), aluminum (Al), magnesium (Mg), gadolinium (Gd), molybdenum (Mo) or gold (Au) can be used as the metal element used in the metal plate converter 12. These metal elements are easy to measure the two-dimensional intensity distribution of radiation with high accuracy because the radioisotopes generated by the threshold reaction undergo beta decay and emit beta rays. In addition, these metal elements are highly convenient in terms of time in measuring radiation because the half-life of the radioisotopes is 0.1 hours or more and 200 hours or less.

[0022] In the case of zinc (Zn), various natural isotopes exist, and the isotopic abundance ratio is as follows: 64 Zn is 48.63%, 66 Zn is 27.90%, 67 Zn is 4.10%, 68 Zn is 18.75%, 70 Zn is 0.62%. 64 Zn decays to β with a half-life of 12.7 hours in the (n,p) reaction with a threshold energy of 0.9 MeV. - Decay 64 Cu is produced. 66 Zn decays to β with a half-life of 5.12 minutes in the (n,p) reaction with a threshold energy of 1.887 MeV. - Decay 66Cu is produced. 66 Since the half-life of Cu is less than 0.1 hours, the preparation time from the completion of neutron beam NB irradiation to the start of radiation measurement 66 The amount of remaining Cu is drastically reduced. Therefore, by waiting 30 minutes to an hour after irradiation with neutron beam NB and then measuring the radiation, 64 Only the contribution of Cu can be measured. Therefore, by using a Zn plate for the metal plate converter 12, the two-dimensional intensity distribution of neutrons having an energy of 0.9 MeV or more can be measured.

[0023] In the case of aluminum (Al), the isotope abundance ratio is: 27 It is 100% Al. 27 Al decays to β with a half-life of 9.458 minutes in the (n,p) reaction with a threshold energy of 1.896 MeV. - Decay 27 Mg is produced and decays to β with a half-life of 14.959 hours in the (n,α) reaction with a threshold energy of 3.249 MeV. - Decay 24 Immediately after irradiation with neutron beam NB, Na is produced. 24 It has a shorter half-life than Na 27 However, after 1-2 hours from the irradiation of the neutron beam NB, Mg is generated in large quantities. 27 The remaining amount of Mg has decreased dramatically, and the half-life of 24 For example, by measuring radiation for about one hour after irradiation with neutron beam NB, 27 Only the Mg contribution can be measured, and by measuring radiation in the subsequent period, 24 Therefore, by using an Al plate for the metal plate converter 12, it is possible to measure the two-dimensional intensity distribution of neutrons having an energy of 1.896 MeV or more and the two-dimensional intensity distribution of neutrons having an energy of 3.249 MeV or more.

[0024] In the case of magnesium (Mg), the isotope abundance ratio is: 24 Mg is 78.99%, 25 Mg is 10.00%, 26Mg is 11.01%. 24 Mg decays to β with a half-life of 14.96 hours in the (n,p) reaction with a threshold energy of 4.931 MeV. - Decay 24 Therefore, by using an Mg plate for the metal plate converter 12, it is possible to measure the two-dimensional intensity distribution of neutrons having energies of 4.931 MeV or more.

[0025] In the case of gadolinium (Gd), the isotope abundance ratio is 152 Gd is 0.20%, 154 Gd is 2.18% 155 Gd is 14.80%, 156 Gd is 20.47% 157 Gd is 15.65%, 158 Gd is 24.84%, 160 Gd is 21.86%. 160 Gd undergoes the (n,2n) reaction with a threshold energy of 7.498 MeV in 18.479 hours. - Decay 159 Gd is produced. 158 Gd is mainly reacting with (n,γ) in the resonance region below 1 MeV. 159 Gd is generated. 159 Since Gd is the same isotope, it is not possible to separate them based on the difference in half-life. However, since low-energy neutrons of less than 1 MeV are emitted isotropically from the target 94, their effect on the relative shape of the two-dimensional intensity distribution of directional fast neutrons is small. Therefore, by using a Gd plate in the metal plate converter 12, it is possible to measure the two-dimensional intensity distribution of neutrons with energies of 7.498 MeV or more.

[0026] In the case of molybdenum (Mo), the isotope abundance ratio is: 92 Mo is 14.84%, 94 Mo is 9.25%, 95 Mo is 15.92%, 96 Mo is 16.68%, 97 Mo is 9.55%, 98 Mo is 24.13%, 100 Mo is 9.63%.100 Mo decays to β with a half-life of 65.94 hours via the (n,2n) reaction with a threshold energy of 8.373 MeV. - Decay 99 Mo is produced, and the reaction is mainly in the (n,γ) region below 1 MeV, resulting in a β reaction with a half-life of 14.61 minutes. - Decay 101 Mo is produced. 101 Mo is 99 The half-life of Mo is shorter than that of Mo, at 14.61 minutes. Therefore, by measuring radiation at least one hour after irradiation with neutron beam NB, 99 Only the contribution of Mo can be measured. 98 Mo is mainly excited by the (n,γ) reaction in the resonance region below 1 MeV. 99 Mo is generated. 99 Since Mo is the same isotope, it is not possible to separate them based on the difference in half-life. However, since low-energy neutrons of less than 1 MeV are emitted isotropically from the target 94, their effect on the relative shape of the two-dimensional intensity distribution of directional fast neutrons is small. Therefore, by using a Mo plate in the metal plate converter 12, it is possible to measure the two-dimensional intensity distribution of neutrons with energies of 8.373 MeV or more.

[0027] In the case of gold (Au), the isotope abundance ratio is: 197 It is 100% Au. 197 Au decays in the (n,2n) reaction with a threshold energy of 8.114 MeV and a half-life of 6.183 days. - Decay 196 Au is generated. 197 Au decays primarily in the (n,γ) reaction in the resonance region below 1 MeV, with a half-life of 2.695 days. - Decay 198 Au is produced. 197 In the case of Au, the reaction cross section in the resonance region is extremely large. 196 Compared to Au 198 A large amount of Au is generated. 198 Since Au has a relatively long half-life, 196It is difficult to separate only the contribution of Au in a short time. Therefore, when an Au plate is used for the metal plate converter 12, a filter made of an Au plate may be added in front of the incident direction of the neutron beam NB, and the neutrons in the resonance region may be absorbed by the filter. This causes mainly fast neutrons to be incident on the metal plate converter 12, which is an Au plate, and makes it possible to separate the contribution of the resonance region. Therefore, when an Au plate is used for the metal plate converter 12, by combining an Au plate filter, it is possible to measure the two-dimensional intensity distribution of neutrons having energies of 8.114 MeV or more. 198 By measuring radiation after about four times the half-life of Au (for example, 11 days), 196 It is also possible to measure only the contribution of Au, in which case there is no need to combine it with an Au plate filter.

[0028] Considering practicality such as price and ease of handling, the material of the metal plate converter 12 is preferably Zn, Al, or Mo. The metal plate converter 12 is preferably made of a material containing 95% or more or 99% or more of the metal element used. When Al is used as an example, the metal plate converter 12 is made of an Al plate containing 99% or more of Al and has a thickness of about 0.1 mm to 5 mm. Since the reaction cross section of the fast neutron to be measured is extremely small, even if the thickness of the metal plate converter 12 is set to about several mm, the intensity of the fast neutron before and after passing through the metal plate converter 12 is almost the same. Therefore, the influence of attenuation of the fast neutron due to passing through the multiple metal plate converters 12a to 12e can be almost negligible.

[0029] 4 is a rear view that typically illustrates the configuration of the metal plate converter 12. The metal plate converter 12 has a center hole 22, notches 24a, 24b, a fixing hole 26, and scribe lines 28a, 28b.

[0030] The center hole 22 is a through hole provided in the center of the metal plate converter 12, and is a mark indicating the center position in the x-direction and the y-direction perpendicular to the axial direction (z-direction). The notches 24a and 24b are V-shaped or U-shaped cutouts provided at some locations on the outer periphery of the metal plate converter 12. The notches 24a and 24b are marks for identifying the orientation of the metal plate converter 12 in the x-direction and the y-direction. The fixing hole 26 is a through hole provided in the outer periphery of the metal plate converter 12, and is used for fixing by the fixing jig 14. In the illustrated example, the outer shape of the metal plate converter 12 is a square, and the fixing holes 26 are provided at each of the four corners of the square. The scribed lines 28a and 28b are marks indicating the center position in the x-direction and the y-direction. The first scribed line 28a is drawn as a straight line extending in the y-direction through the center hole 22, and the second scribed line 28b is drawn as a straight line extending in the x-direction through the center hole 22.

[0031] The notches 24a, 24b are also marks for identifying the front surface (e.g., the incident side of the neutron beam NB) and the back surface (e.g., the exit side of the neutron beam NB) of the metal plate converter 12. The notches 24a, 24b are provided at a plurality of positions that are asymmetric with respect to the central hole 22. In the illustrated example, when the U-shaped second notch 24b is on the left side of the V-shaped first notch 24a in the transfer result, it is indicated that the transfer result is on the front surface (the surface on the incident side of the neutron beam NB) of the converter.

[0032] The metal plate converters 12a-12e have the same shape, and each has the shape shown in Fig. 4. The metal plate converters 12a-12e each have a through hole (center hole 22) provided in the center, and are arranged so that the through holes are aligned in the axial direction (z direction). The metal plate converters 12a-12e each have cutouts (notches 24a, 24b) provided in the outer periphery, and are arranged so that the cutouts are aligned in the axial direction (z direction).

[0033] The shape of the metal plate converter 12 is not limited to that shown in FIG. 4, and may be any other shape such as a rectangle or a circle. The metal plate converter 12 may be provided with a notch or a through hole other than the center hole 22 and the notches 24a and 24b as a mark for identifying the position and orientation in the x and y directions. For example, instead of providing two notches 24a and 24b, for example, only one of the first notch 24a or the second notch 24b may be provided. In addition, notches or through holes may be provided at multiple positions asymmetrical with respect to the center hole 22 in order to identify the front and back of the metal plate converter 12. A fixing hole 26 may be used as a mark for identifying the position and orientation in the x and y directions. For example, multiple fixing holes 26 may be provided at positions asymmetrical with respect to the center hole 22.

[0034] Returning to FIG. 2, the fixing jig 14 is configured to fix the plurality of metal plate converters 12a to 12e to each other. The fixing jig 14 prevents the arrangement of the plurality of metal plate converters 12a to 12e from changing with respect to the neutron beam NB during irradiation. The fixing jig 14 includes a spacer 16 and a fastening member 18. The spacer 16 is disposed between the plurality of metal plate converters 12a to 12e and maintains the intervals between the plurality of metal plate converters 12a to 12e. The fastening member 18 is a bolt, a screw, or the like, and fastens and fixes the plurality of metal plate converters 12a to 12e and the spacer 16 to each other. The fixing jig 14 is configured to allow the plurality of metal plate converters 12a to 12e and the spacer 16 to be disassembled, for example, by removing the fastening member 18. After irradiation with the neutron beam NB, the plurality of metal plate converters 12a to 12e are separately disassembled, so that the two-dimensional intensity distribution of the radiation emitted from each of the plurality of metal plate converters 12a to 12e can be measured with high accuracy.

[0035] The positioning plate 20 is a metal plate having marks used for positioning when installing the neutron profile measurement device 10. The positioning plate 20 is fixed to the multiple metal plate converters 12a-12e by a fixing jig 14. The positioning plate 20 is disposed, for example, on the near side of the multiple metal plate converters 12a-12e in the incident direction of the neutron beam NB. The positioning plate 20 is fixed, for example, by being sandwiched between the metal plate converter 12a and a fastening member 18.

[0036] Fig. 5 is a rear view showing a schematic configuration of the neutron profile measurement device 10 of Fig. 2, as viewed from the opposite side to the incidence direction of the neutron beam NB. The positioning plate 20 has scribed lines 28c, 28d which are marks indicating the center positions in the x and y directions. The third scribed line 28c is drawn as a straight line extending in the y direction through the center hole 22, and is provided at a position overlapping with the first scribed line 28a. The fourth scribed line 28d is drawn as a straight line extending in the x direction through the center hole 22, and is provided at a position overlapping with the second scribed line 28b.

[0037] The positioning plate 20 is larger in size in the x and y directions than the metal plate converter 12, and has scribed lines 28c, 28d at locations that do not overlap with the metal plate converter 12 in the axial direction. This prevents the scribed lines 28c, 28d from being hidden by the metal plate converter 12. In the example of FIG. 5, the positioning plate 20 has an octagonal outer shape, but the outer shape of the positioning plate 20 may be any other shape, such as a circle or a diamond. In addition, positioning marks other than the scribed lines 28c, 28d may be provided on the positioning plate 20.

[0038] As shown in FIG. 2, when the neutron profile measurement device 10 is installed in front of the accelerator neutron source 90, the installation position is adjusted using the marking lines 28a, 28b on the rearmost metal plate converter 12e and the marking lines 28c, 28d on the positioning plate 20. The installation position of the neutron profile measurement device 10 is assumed to be, for example, an outlet on an extension line of the radiation direction of the neutron beam NB emitted from the center of the accelerator neutron source 90. Since the neutron beam NB cannot usually be directly observed with the naked eye, a cross laser is irradiated from a laser marking device so as to match the designed position of the radiation source center and the designed radiation direction of the radiation NB, and a reference coordinate axis is set. Next, the neutron profile measurement device 10 is positioned so that the cross laser and the marking lines 28a to 28d match. For example, by using a stand (not shown) that supports the neutron profile measurement device 10, the three-dimensional position can be adjusted based on the cross laser. This allows the neutron profile measurement device 10 to be installed on an extension of the radiation direction of the designed neutron beam NB.

[0039] Next, a method for measuring radiation emitted from activated metal plate converters 12 will be described. Fig. 6 is a cross-sectional view showing a schematic configuration of a transfer device 30. The transfer device 30 is a cassette for transferring the two-dimensional intensity distribution of radiation emitted from the multiple metal plate converters 12a-12e onto a transfer plate 32 to form an image. The transfer device 30 includes a transfer plate 32, a buffer material 34, and a shielding container 36.

[0040] The transfer plate 32 is an imaging plate (IP) for generating an image corresponding to the radiation intensity distribution in response to radiation. For example, a plate using a photostimulable phosphor can be used as the transfer plate 32. The photostimulable phosphor mainly reacts to beta rays to fluoresce, and has a memory function (optical memory function) in which the area that reacted to the radiation emits light again when a readout light is irradiated thereafter. As a result, a highly sensitive image can be obtained compared to the case where a general phosphor that does not have photostimulability is used, and image data with a wide dynamic range can be obtained. In addition, by using the transfer device 30, the irradiation environment of the neutron beam NB and the transfer environment to the transfer plate 32 can be separated, and the high dose of gamma rays generated in the irradiation environment of the neutron beam NB can be prevented from adversely affecting the transfer process.

[0041] The activated metal plate converters 12a-12e are housed in the shielding container 36 with one side of each converter in close contact with the transfer plate 32. For example, the side of the metal plate converter 12 that is the incident side of the neutron beam NB is brought into close contact with the transfer plate 32. The cushioning material 34 is a sponge-like resin material or rubber material, and presses the transfer plate 32 against the metal plate converters 12a-12e. This prevents gaps from being generated between the transfer plate 32 and the metal plate converters 12a-12, and prevents the relative positions of the transfer plate 32 and the metal plate converters 12a-12 from changing during the transfer process. The shielding container 36 blocks light from the outside so that the inside of the container is in a darkroom state during the transfer process.

[0042] 6, the radiation intensity distributions of the multiple metal plate converters 12a-12e are transferred simultaneously using one transfer device 30. This allows the multiple metal plate converters 12a-12e to have the same transfer conditions. Note that multiple transfer devices 30 may be used, and the radiation intensity distributions of the multiple metal plate converters 12a-12e may be imaged using separate transfer devices 30. The radiation intensity distribution transferred to the transfer plate 32 is read using a dedicated reading device (reader or scanner), and image data corresponding to the radiation intensity distribution is generated.

[0043] 7(a) to (e) are diagrams showing an example of a transferred image of a plurality of metal plate converters 12a to 12e. The example in FIG. 7 shows a case where 100 mm×100 mm Al plates are used as the plurality of metal plate converters 12a to 12e, and the axial positions of the plurality of metal plate converters 12a to 12e are changed by 20 mm. A central hole 22 of 3 mm diameter is provided in the center of the Al plate converter. Transfer onto the transfer plate 32 started 1.5 hours after irradiation with the neutron beam NB, so that mainly 24 The radiation emitted from sodium is transferred, and neutrons with energies of 3.249 MeV or more are measured. In the transferred image, the darker (darker) the image is, the higher the radiation intensity and the greater the amount of neutrons, while the lighter (lighter) the image is, the lower the radiation intensity and the smaller the amount of neutrons.

[0044] 7(a) to (e) are arranged in order of distance from the accelerator neutron source 90 to the metal plate converters 12a to 12e. FIG. 7(a) is a transferred image of the metal plate converter 12a arranged at the position closest to the accelerator neutron source 90, and FIG. 7(e) is a transferred image of the metal plate converter 12e arranged at the position farthest from the accelerator neutron source 90. As shown in FIG. 7(a) to (e), it can be seen that the two-dimensional intensity distribution of the neutron beam NB can be imaged with high spatial resolution. The spatial resolution obtained by this method depends on the performance of the reader of the transfer plate 32. In the example of FIG. 7, the spatial resolution is 25 μm, but it is also possible to use a finer reader (for example, with a spatial resolution of 12.5 μm). In addition, since the center of the transferred image becomes darker (thicker) as it gets closer to the accelerator neutron source 90, it can be said that the two-dimensional intensity distribution of the neutron beam NB can be compared at multiple different positions in the axial direction.

[0045] In the center of each of the transferred images in Figs. 7(a)-(e), there is a circular area that is relatively white (light) compared to the surroundings. The circular area in the center corresponds to the center hole 22 of each of the multiple metal plate converters 12a-12e, and the radiation intensity is locally reduced due to the through-hole. For the same reason, there is a circular area corresponding to the fixing hole 26 in each of the four corners of Figs. 7(a)-(e). In the example of Figs. 7(a)-(e), the metal plate converter 12 does not have notches 24a, 24b, but if the notches 24a, 24b are present, V-shaped and U-shaped relatively white (light) areas will be generated at the locations corresponding to the notches 24a, 24b. The area that appears locally white (light) in the transferred image can be used as a mark for identifying the position and orientation of the transferred image in the x and y directions.

[0046] 7(a), it is clear that the position of the highest neutron intensity is misaligned with the position of the central hole 22, and it is also possible to identify the direction and magnitude of the misalignment. Such misalignment is caused by a misalignment between the central axis of the neutron beam NB emitted from the accelerator neutron source 90 and the central axis of the neutron profile measurement device 10 at the time of installation. Therefore, by precisely measuring the central axis of the neutron profile measurement device 10 at the time of installation, it is possible to precisely identify the position and orientation of the central axis of the neutron beam NB from the direction and magnitude of the misalignment based on the transferred image.

[0047] FIG. 8 is a graph showing a three-dimensional profile of the neutron beam NB. Curves A to E in FIG. 8 show the intensity distribution on the diagonal of the transferred image shown in FIG. 7(a) to (e). In FIG. 8, the position of the central hole 22 is set as the origin, and the intensity value at the position of the fixed hole 26 is normalized as 1. In addition, the intensity distribution (dotted line) assuming that there is no central hole 22 is obtained by curve fitting to calculate the peak value, and the full width at half maximum (FWHM) of the intensity distribution at the peak is shown by a dashed line. From FIG. 8, it can be seen that the three-dimensional profile shows that the peak value of the neutron amount decreases and the full width at half maximum Wa, Wb widens as the distance from the accelerator neutron source 90 increases.

[0048] Fig. 9 is a graph showing the directivity of the neutron beam NB, and is a plot of the full width at half maximum of the curves A to E shown in Fig. 8 against the axial position of the multiple metal plate converters 12a to 12e. As shown in the figure, the full width at half maximum of the neutron intensity distribution calculated using each of the multiple metal plate converters 12a to 12e are arranged on a straight line, and it can be seen that the directivity of the neutron beam NB as shown in Fig. 1 can be measured. Since the gradient of the approximation line shown in Fig. 9 is about 0.9, it can be seen that the directivity angle based on the full width at half maximum is about 43 degrees.

[0049] 10 is a flow chart showing the flow of the neutron spectrum measurement method. First, the neutron profile measurement device 10 is positioned with respect to the neutron beam NB to be measured (S10). For example, the origins of the x and y directions are determined based on the position of the target 94 of the accelerator neutron source 90, and the z direction is determined based on the irradiation direction of the particle beam PB irradiated to the target 94. Specifically, the reference coordinate axes can be determined using a surveying instrument such as a laser marking device (laser theodolite). Next, the neutron profile measurement device 10 is installed based on the determined coordinate axes. For example, the installation position of the neutron profile measurement device 10 is adjusted so that the cross laser irradiated from the laser marking device, the marking lines 28a, 28b on the rearmost metal converter 12e, and the marking lines 28c, 28d on the positioning plate 20 coincide with each other.

[0050] Next, the installed neutron profile measurement device 10 is irradiated with a neutron beam NB to be measured (S12). The plurality of metal plate converters 12a-12e included in the neutron profile measurement device 10 are activated by irradiation with the neutron beam NB. After irradiation with the neutron beam NB, radiation emitted from each of the plurality of metal plate converters 12a-12e is transferred to a transfer plate 32 (S14). For example, the neutron profile measurement device 10 is disassembled, and each of the plurality of metal plate converters 12a-12e is accommodated in the transfer device 30, thereby transferring a two-dimensional intensity distribution of the radiation to the transfer plate 32. After the transfer is completed, an image of the two-dimensional intensity distribution of the radiation transferred to the transfer plate 32 is read to generate image data (S16).

[0051] Next, three-dimensional profile data of the neutron beam NB is generated based on the image data (S18). The three-dimensional profile data is any data that indicates the three-dimensional spatial distribution of the neutron beam NB to be measured, such as the graph data of Fig. 8 or Fig. 9, or the numerical data of the beam angle calculated from the graph of Fig. 9.

[0052] According to this embodiment, the three-dimensional profile of the neutron beam NB to be measured can be identified with high spatial resolution using the neutron profile measurement device 10. When an Al plate is used for the metal plate converter 12, the material is inexpensive and the time required for the transfer step of S14 is about one day, so that the three-dimensional profile of the neutron beam NB can be obtained quickly and easily.

[0053] When an Al plate is used for the metal plate converter 12, the transfer process is divided into two steps to obtain three-dimensional profile data by energy. For example, the two-dimensional intensity distribution of radiation emitted from each of the multiple Al plate converters activated by irradiation with the neutron beam NB is transferred onto a first transfer plate to generate first image data. Then, the two-dimensional intensity distribution of radiation emitted from each of the multiple Al plate converters after transfer onto the first transfer plate is transferred onto a second transfer plate to generate second image data. Based on the first image data, three-dimensional profile data of neutrons having an energy of 1.896 MeV or more can be generated. Also, based on the second image data, three-dimensional profile data of neutrons having an energy of 3.249 MeV or more can be generated.

[0054] (Second embodiment) 11 is a side view showing a schematic configuration of a neutron profile measurement apparatus 50 according to a second embodiment. In the second embodiment, a combination of multiple types of metal plate converters is used to obtain a three-dimensional profile by energy. The second embodiment will be described below, focusing on the differences from the first embodiment, and commonalities will be omitted as appropriate.

[0055] The neutron profile measurement device 50 includes a plurality of first metal plate converters 54a, 54b, 54c, 54d, and 54e (collectively referred to as first metal plate converters 54), a plurality of second metal plate converters 56a, 56b, 56c, 56d, and 56e (collectively referred to as second metal plate converters 56), a plurality of third metal plate converters 58a, 58b, 58c, 58d, and 58e (collectively referred to as third metal plate converters 58), and a fixing jig 14. The neutron profile measurement device 50 may further include a positioning plate 20.

[0056] The neutron profile measurement device 50 includes a plurality of converter sets 52a, 52b, 52c, 52d, and 52e (collectively referred to as converter sets 52). The converter set 52 includes a plurality of types of metal plate converters 54, 56, and 58. The first metal plate converter 54 contains a first metal element. The second metal plate converter 56 contains a second metal element different from the first metal element. The third metal plate converter 58 contains a third metal element different from the first metal element and the second metal element. The first metal element, the second metal element, and the third metal element are Zn, Al, Mg, Gd, Mo, or Au. Each of the plurality of converter sets 52a to 52e may include only two types of metal plate converters, or may include four or more types of metal plate converters.

[0057] The first metal plate converters 54a-54e, the second metal plate converters 56a-56e, and the third metal plate converters 58a-58e are arranged so as to overlap each other in the axial direction (z direction). In the example of FIG. 11, five converter sets 52a-52e are used, and each converter set 52 includes three metal plate converters, so that a total of 15 metal plate converters are used. That is, the neutron profile measurement device 50 includes five first metal plate converters 54a-54e, five second metal plate converters 56a-56e, and five third metal plate converters 58a-58e. The number of converter sets is not limited to five, and may be at least two or more, and may be three or four, or six or more.

[0058] In one example, the first metal plate converter 54 is an Al plate converter and has a thickness of about 1 mm to 5 mm. The second metal plate converter 56 is a Zn plate converter and has a thickness of about 0.1 mm to 1 mm. The third metal plate converter 58 is a Mo plate converter and has a thickness of about 0.1 mm to 1 mm. The multiple types of metal plate converters 54, 56, 58 included in the same converter set 52 are arranged adjacent to each other. By arranging the multiple types of metal plate converters 54, 56, 58 adjacent to each other, it is possible to increase the mechanical strength compared to the case where they are arranged separately. For example, by relatively increasing the thickness of the first metal plate converter 54, the second metal plate converter 56 and the third metal plate converter 58 can be mechanically supported by the first metal plate converter 54. Materials other than Al (Zn, Mg, Gd, Mo, Au) are relatively expensive, so by increasing the thickness of the Al plate converter and decreasing the thickness of the metal plate converters other than Al, it is possible to reduce material costs while maintaining mechanical strength.

[0059] The first metal plate converter 54, the second metal plate converter 56 and the third metal plate converter 58 are configured to have a shape similar to the metal plate converter 12 shown in Figure 4. Thus, each of the first metal plate converter 54, the second metal plate converter 56 and the third metal plate converter 58 has a square outline and includes a central hole 22, notches 24a, 24b, fastening holes 26 and scribe lines 28a, 28b.

[0060] The fixing jig 14 is configured similarly to the first embodiment. The fixing jig 14 fixes the converter sets 52a-52e and prevents the arrangement of the converter sets 52a-52e relative to the neutron beam NB from changing. The spacers 16 are disposed between the converter sets 52a-52e and maintain the intervals between the converter sets 52a-52e. The fastening members 18 fasten and fix the converter sets 52a-52e and the spacer 16 to each other. The metal plate converters 54, 56, 58 of each converter set 52 are sandwiched and fixed between the spacer 16 and the fastening members 18, or between two spacers 16.

[0061] 11, the stacking order of the multiple types of metal plate converters 54, 56, 58 included in one converter set 52 is the same. That is, in any of the multiple converter sets 52a to 52e, the third metal plate converter 58, the second metal plate converter 56, and the first metal plate converter 54 are arranged in this order in the incident direction of the neutron beam NB. This allows the spacing between the multiple first metal plate converters 54a to 54e, the spacing between the multiple second metal plate converters 56a to 56e, and the spacing between the multiple third metal plate converters 58a to 58e to be the same.

[0062] The stacking order of the multiple types of metal plate converters 54, 56, 58 included in each of the multiple converter sets 52a to 52e does not necessarily have to be the same. Also, the types and number of types of metal plate converters included in each of the multiple converter sets 52a to 52e do not have to be the same. For example, only some of the converter sets 52a and 52b may include three types of metal plate converters, Al, Zn, and Mo, and the remaining converter sets 52c to 52e may include only two types of metal plate converters, Al and Zn, or only Al plate converters.

[0063] According to this embodiment, by combining a plurality of types of metal plate converters, three-dimensional profile data of the neutron beam NB can be obtained for a plurality of energy regions. For example, three-dimensional profile data of neutrons having an energy of 8.373 MeV or more can be obtained from a plurality of Mo plate converters. Three-dimensional profile data of neutrons having an energy of 3.249 MeV or more and three-dimensional profile data of neutrons having an energy of 1.896 MeV or more can be obtained from a plurality of Al plate converters. Also, three-dimensional profile data of neutrons having an energy of 0.9 MeV or more can be obtained from a plurality of Zn plate converters. As a result, three-dimensional profile data corresponding to each of the neutron beams NB1 to NB3 having different energies in FIG. 1 can be obtained, and a more detailed three-dimensional profile of the neutron beam NB can be grasped.

[0064] The present invention has been described above based on the embodiments. It will be understood by those skilled in the art that the present invention is not limited to the above embodiments, that various design changes are possible, that various modifications are possible, and that such modifications are also within the scope of the present invention.

[0065] In the above embodiment, a stimulable phosphor is used as the transfer plate 32, but other types of phosphors may be used, or a combination of lead-over intensifying screen and photosensitive film may be used.

[0066] In the above embodiment, the spacer 16 is used to maintain the spacing between the multiple metal plate converters. In another embodiment, the spacing between the multiple metal plate converters may be maintained by the thickness of the metal plate converter itself, rather than using the spacer 16. In this case, the multiple metal plate converters may be arranged adjacent to each other. In the second embodiment, when all (e.g., 15) metal plate converters are arranged adjacent to each other, the spacing between the same type of metal plate converters corresponds to the sum of the thicknesses of the multiple types of metal plate converters 54, 56, 58 included in one converter set 52.

[0067] In the above-described second embodiment, the multiple types of metal plate converters 54, 56, 58 included in one converter set 52 are arranged adjacent to each other. In another embodiment, spacers may be arranged between the multiple types of metal plate converters 54, 56, 58 included in one converter set 52.

[0068] In the above embodiment, the case of measuring a neutron profile for neutron imaging has been described. The measurement method according to the present embodiment may be applied not only to neutron imaging but also to various fields in which neutron beams are used. For example, the method may be used to evaluate a neutron source used in a neutron doping (NTD) method in which silicon (Si) is converted to phosphorus (P) and doped by irradiating a silicon wafer with a neutron beam. The method may also be used to evaluate a neutron source for medical use, for example, a neutron source used in boron neutron capture therapy (BNCT) in which boron (B) incorporated in cancer tissue is irradiated with a neutron beam to selectively destroy the cancer tissue. [Explanation of symbols]

[0069] 10...neutron profile measuring device, 12...metal plate converter, 14...fixing jig, 16...spacer, 18...fastening member, 20...positioning plate, 22...center hole, 24a, 24b...notch, 26...fixing hole, 28a, 28b, 28c, 28d...scribed lines, 30...transfer device, 32...transfer plate, 50...neutron profile measuring device, 52...converter set, 54...first metal plate converter, 56...second metal plate converter, 58...third metal plate converter, 90...accelerator neutron source, 92...accelerator, 94...target, NB...neutron beam.

Claims

1. a plurality of metal plate converters containing metallic elements that are converted to other radioisotopes that undergo beta decay by a threshold reaction of absorbing neutrons; a fixing jig that fixes the plurality of metal plate converters so that the plurality of metal plate converters overlap each other in a predetermined axial direction, The plurality of metal plate converters include a plurality of first metal plate converters containing a first metal element, and a plurality of second metal plate converters containing a second metal element having an atomic number different from that of the first metal element, Each of the second metal plate converters is disposed adjacent to one of the first metal plate converters; A neutron profile measurement device, wherein each of the plurality of metal plate converters is used to measure a two-dimensional intensity distribution of an incident neutron beam.

2. A neutron profile measuring device as described in claim 1, characterized in that the first metal element is aluminum (Al).

3. A neutron profile measuring device as described in claim 1 or 2, characterized in that the second metal element is zinc (Zn), magnesium (Mg), gadolinium (Gd), molybdenum (Mo) or gold (Au).

4. A method for producing a radioisotope comprising the steps of: (a) providing a plurality of metal plate converters containing a metal element that is converted into another radioisotope that undergoes beta decay by a threshold reaction of absorbing a neutron; a fixing jig that fixes the plurality of metal plate converters so that the plurality of metal plate converters overlap each other in a predetermined axial direction, two or more of the plurality of metal plate converters are made of the same material; A neutron profile measurement device characterized in that the multiple metal plate converters each have a through hole provided in the center, and the respective through holes are arranged so as to be aligned in the axial direction.

5. A method for producing a radioisotope comprising the steps of: (a) providing a plurality of metal plate converters containing a metal element that is converted into another radioisotope that undergoes beta decay by a threshold reaction of absorbing a neutron; a fixing jig that fixes the plurality of metal plate converters so that the plurality of metal plate converters overlap each other in a predetermined axial direction, two or more of the plurality of metal plate converters are made of the same material; A neutron profile measurement device characterized in that the multiple metal plate converters each have a notch or through hole provided on their outer periphery, and each notch or through hole is arranged so as to be aligned in the axial direction.

6. A method for producing a radioisotope comprising the steps of: (a) providing a plurality of metal plate converters containing a metal element that is converted into another radioisotope that undergoes beta decay by a threshold reaction of absorbing a neutron; a fixing jig that fixes the plurality of metal plate converters so that the plurality of metal plate converters overlap each other in a predetermined axial direction, two or more of the plurality of metal plate converters are made of the same material; A neutron profile measurement device further comprising a positioning plate fixed to the plurality of metal plate converters and having a mark indicating a position in a direction perpendicular to the axial direction.

7. 7. The neutron profile measurement apparatus according to claim 1, wherein the fixing jig includes a spacer provided between the plurality of metal plate converters.

8. A neutron profile measurement method using the neutron profile measurement device according to any one of claims 1 to 7, comprising: Irradiating the plurality of metal plate converters fixed by the fixing jig with a neutron beam; generating image data by imaging a two-dimensional intensity distribution of radiation emitted from each of the plurality of metal plate converters activated by the irradiation with the neutron beam; generating three-dimensional profile data of the neutron beam based on the image data.

9. A neutron profile measurement method using a neutron profile measurement device, comprising: The neutron profile measuring device comprises: a plurality of metal plate converters containing metallic elements that are converted to other radioisotopes that undergo beta decay by a threshold reaction of absorbing neutrons; a fixing jig that fixes the plurality of metal plate converters so that the plurality of metal plate converters overlap each other in a predetermined axial direction, two or more of the plurality of metal plate converters are made of the same material; The neutron profile measurement method includes: Irradiating the plurality of metal plate converters fixed by the fixing jig with a neutron beam; generating image data by imaging a two-dimensional intensity distribution of radiation emitted from each of the plurality of metal plate converters activated by the irradiation with the neutron beam; generating three-dimensional profile data of the neutron beam based on the image data; generating the image data includes: transferring a two-dimensional intensity distribution of radiation emitted from each of the plurality of metal plate converters activated by irradiation with the neutron beam onto a first transfer plate to generate first image data; and transferring the two-dimensional intensity distribution of radiation emitted from each of the plurality of metal plate converters after transfer onto the first transfer plate onto a second transfer plate to generate second image data; A neutron profile measurement method, comprising generating three-dimensional profile data of the neutron beam based on the first image data and the second image data.

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