JP2024032148A - Neutron source position measuring device and neutron source position measuring method - Google Patents

Abstract

An object of the present invention is to easily measure the position of a neutron beam source. A neutron source position measuring device (10) includes a metal plate converter (12) containing a metal element that is converted into another radioactive isotope that undergoes beta decay by a threshold reaction of absorbing neutrons, and a reference point of the metal plate converter (12). The metal plate is placed away from the metal plate converter 12 toward the neutron source 96 on the reference axis 22 passing through the reference point 20 and the marker for identifying the position of the metal plate 20, and has a neutron absorption coefficient of energy at which a threshold reaction occurs. A neutron absorber 14 made of a material larger than the converter 12 is provided. [Selection diagram] Figure 2

Description

The present invention relates to a neutron source position measuring device and method.

BACKGROUND ART An inspection method for non-destructively looking through a substance using a neutron beam is known, and is called neutron radiography testing (NRT) or neutron imaging. Neutron imaging is mainly used to inspect substances containing elements with low atomic numbers that are difficult to inspect with X-rays, such as water, oil, or resin containing hydrogen (H), lithium (Li), and boron ( It can be used to test substances containing B). As a neutron source, for example, an accelerator neutron source is used that generates a neutron beam by irradiating a target with a particle beam such as a proton beam accelerated using an accelerator.

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

Japanese Patent Application Publication No. 2020-24105

In the case of an accelerator neutron source, the source of the neutron beam is where the particle beam interacts with the target. In order to properly operate an accelerator neutron source, it is preferable to be able to accurately measure the position of the neutron beam source.

One exemplary object of an embodiment of the present invention is to provide a technique for easily measuring the position of a neutron source.

A neutron source position measuring device according to an embodiment of the present invention includes a metal plate converter containing a metal element that is converted into another radioactive isotope that undergoes beta decay by a threshold reaction of absorbing neutrons, and a reference point of the metal plate converter. A marker for identifying the position and a material that is placed away from the metal plate converter toward the neutron source side on the reference axis passing through the reference point and has a neutron absorption coefficient larger than that of the metal plate converter for the energy at which the threshold reaction occurs. a first neutron absorber configured.

Another aspect of the present invention is a neutron source position measuring method using the neutron source position measuring device of a certain aspect. This method involves irradiating a metal plate converter with neutron beams from a neutron beam source through a first neutron absorber, and a two-dimensional intensity distribution of radiation emitted from the metal plate converter that is activated by the neutron beam irradiation. , the distance from the metal plate converter to the first neutron absorber on the reference axis, the size of the first neutron absorber, and the number of first neutron absorbers included in the image data. The distance to the neutron source on the reference axis is calculated using the size of the projected image, and the distance to the neutron source on the reference axis is calculated based on the position of the projected image of the first neutron absorber with respect to the position of the marker included in the image data. and calculating the position of the neutron source relative to the position of the neutron source.

Note that arbitrary combinations of the above-mentioned constituent elements and mutual substitution of constituent elements and expressions of the present invention among methods, devices, systems, etc. are also effective as aspects of the present invention.

According to the present invention, the position of a neutron source can be easily measured.

FIG. 2 is a diagram schematically showing a neutron beam emitted from an accelerator neutron source. FIG. 1 is a side view schematically showing the configuration of a neutron source position measuring device according to a first embodiment. 3 is a table showing characteristics of metal elements used in metal plate converters. FIG. 2 is a rear view schematically showing the configuration of a metal plate converter. FIG. 2 is a front view schematically showing the configuration of a neutron absorber and a support plate. FIG. 3 is a rear view schematically showing the configuration of the neutron source position measuring device of FIG. 2; FIG. 2 is a cross-sectional view schematically showing the configuration of a transfer device. FIG. 3 is a diagram showing an example of a transferred image of a metal plate converter. FIG. 3 is a diagram schematically showing a method of calculating the position of a neutron source. It is a flowchart which shows the flow of a neutron beam source position measurement method. FIG. 2 is a side view schematically showing the configuration of a neutron source position measuring device according to a second embodiment. FIG. 7 is a side view schematically showing the configuration of a neutron source position measuring device according to a third embodiment. FIGS. 13(a) to 13(e) are diagrams showing examples of transferred images of a plurality of metal plate converters. It is a graph showing an example of a three-dimensional profile of a neutron beam. It is a graph showing an example of directivity of a neutron beam.

EMBODIMENT OF THE INVENTION Hereinafter, the form for implementing this invention is demonstrated 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 denoted by the same reference numerals, and redundant description will be omitted as appropriate. Further, 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 actual dimensions or ratios.

This embodiment relates to a technique for measuring the position of a neutral source by measuring the spatial distribution of neutrons emitted from the neutron source. In particular, the location of the neutron source is determined by measuring the spatial distribution of fast neutrons emitted from the accelerator neutron source. The term "fast neutron" as used herein refers to a high-energy neutron with a neutron energy of 1 MeV or more.

FIG. 1 is a diagram schematically showing a neutron beam NB emitted from an accelerator neutron source 90. Accelerator neutron source 90 includes an accelerator 92 and a target 94. The accelerator 92 is a device that accelerates the particle beam PB irradiated onto the target 94, and is a cyclotron or the like. The particle beam PB is a proton beam, an alpha beam, or the like. The accelerator 92 generates a proton beam accelerated to, for example, 10 MeV or more. The target 94 generates fast neutrons through a nuclear reaction caused by irradiation with the particle beam PB. An example of target 94 is beryllium metal, but other materials such as lithium may also be used. A neutron beam source 96, which is a source of the neutron beam NB, is located inside the target 94, and is located at a location where the particle beam PB and the target 94 interact to generate neutrons.

The neutron beam NB emitted from the neutron beam source 96 has directivity depending on the energy of the neutron. FIG. 1 schematically shows directivity angles θ1, θ2, and θ3 of neutron beams NB1, NB2, and NB3 having different energies. The first neutron beam NB1 is a fast neutron with relatively high energy (for example, 10 MeV), and exists within the range of the relatively small first directivity angle θ1. The second neutron beam NB2 is a fast neutron with medium energy (for example, 5 MeV), and exists within the range of a second directivity angle θ2 that is larger than the first directivity angle θ1. The third neutron beam NB3 is a fast neutron with relatively low energy (for example, 1 MeV), and exists within the range of a third directivity angle θ3 that is larger than the second directivity angle θ2.

In this way, the higher the energy of the neutrons emitted from the neutron beam source 96, the smaller the directivity angles θ1 to θ3 tend to be. Although low energy neutrons of less than 1 MeV can also be emitted from the neutron source 96, low energy neutrons tend to be emitted from the neutron source 96 isotropically. The purpose of this embodiment is to measure the position of a neutron beam source 96, which is a source of fast neutrons having directivity as shown in FIG.

(First embodiment)
FIG. 2 is a side view schematically showing the configuration of the neutron source position measuring device 10 according to the first embodiment. The neutron source position measuring device 10 includes a metal plate converter 12, a neutron absorber 14, and a fixing jig 16. The neutron source position measuring device 10 may further include a positioning plate 18.

The neutron source position measuring device 10 includes a reference point 20 and a reference axis 22 that serve as a reference for position measurement. The reference point 20 is set at an arbitrary position on the metal plate converter 12, for example, at the center of the metal plate converter 12. The reference axis 22 is an axis perpendicular to the metal plate converter 12 and extends in the thickness direction of the metal plate converter 12. The reference axis 22 is set to pass through the reference point 20. In the drawings, the direction in which the reference axis 22 extends is defined as the z-axis, and the two directions orthogonal to the reference axis 22 are defined as the x-direction and the y-direction. Further, in the specification, the z direction may be referred to as an axial direction, and the x direction and y direction may be collectively referred to as a radial direction.

The neutron source position measuring device 10 is used to measure the position of the neutron source 96 with respect to the reference point 20 and the reference axis 22. By using the neutron source position measuring device 10, the distance L in the direction along the reference axis 22 (z direction) from the reference point 20 to the neutron source 96 and the radial direction from the reference axis 22 to the neutron source 96 can be determined. The distance r can be specified. The radial distance r can be specified as a distance rx in the x direction and a distance ry in the y direction.

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 of absorbing 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 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 is calculated. can.

FIG. 3 is a diagram showing the characteristics of metal elements used in the metal plate converter 12. As 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. In these metal elements, radioactive isotopes produced by threshold reactions undergo beta decay and emit beta rays, making it easy to measure the two-dimensional intensity distribution of radiation with high precision. Moreover, since the half-life of radioactive isotopes of these metal elements is 0.1 hour or more and 200 hours or less, it is highly convenient in terms of time for measuring radiation.

In the case of zinc (Zn), various natural isotopes exist, and the isotope abundance ratios are: ⁶⁴ Zn 48.63%, ⁶⁶ Zn 27.90%, ⁶⁷ Zn 4.10%, ⁶⁸ Zn 18 .75%, ⁷⁰ Zn is 0.62%. Among these, ⁶⁴ Zn undergoes an (n,p) reaction with a threshold energy of 0.9 MeV to produce ⁶⁴ Cu, which undergoes β ^- decay with a half-life of 12.7 hours. ⁶⁶ Zn undergoes an (n,p) reaction with a threshold energy of 1.887 MeV to produce ⁶⁶ Cu, which undergoes β ^- decay with a half-life of 5.12 minutes. Since the half-life of ⁶⁶ Cu is less than 0.1 hour, the remaining amount of ⁶⁶ Cu sharply decreases during the preparation time from the completion of neutron beam NB irradiation to the start of radiation measurement. Therefore, by waiting approximately 30 minutes to 1 hour after neutron beam NB irradiation and then measuring the radiation, it is possible to substantially measure only the contribution of ⁶⁴ Cu. Therefore, by using a Zn plate for the metal plate converter 12, it is possible to measure the two-dimensional intensity distribution of neutrons having energy of 0.9 MeV or more.

In the case of aluminum (Al), the isotope abundance ratio is 100% for ²⁷ Al. ²⁷ Al undergoes β ^- decay with a half-life of 9.458 min through an (n, p) reaction with a threshold energy of 1.896 MeV, and ²⁷ Mg is produced with a half-life of 14 through an (n, α) reaction with a threshold energy of 3.249 MeV. ²⁴ Na is produced which undergoes β ^- decay in .959 hours. Immediately after neutron beam NB irradiation, a large amount of ²⁷ Mg, which has a short half-life, is produced compared to ²⁴ Na, which has a long half-life. However, after about 1 to 2 hours have passed after neutron beam NB irradiation, the remaining amount of ²⁷ Mg, which has a short half-life, decreases dramatically, and the remaining amount of ²⁴ Na, which has a long half-life, becomes larger. For example, by measuring radiation for a period of about one hour after neutron beam NB irradiation, it is possible to substantially measure only the contribution of ²⁷ Mg, and by measuring radiation in the subsequent period, it is possible to substantially measure the contribution of ²⁴ Mg. Only the contribution of Na can be measured. Therefore, by using an Al plate for the metal plate converter 12, it is possible to measure a two-dimensional intensity distribution of neutrons having an energy of 1.896 MeV or more and a two-dimensional intensity distribution of neutrons having an energy of 3.249 MeV or more.

In the case of magnesium (Mg), the isotope abundance ratios are 78.99% for ²⁴ Mg, 10.00% for ²⁵ Mg, and 11.01% for ²⁶ Mg. Of these, ²⁴ Mg undergoes (n,p) reaction with a threshold energy of 4.931 MeV to generate ²⁴ Na, which undergoes β ^- decay with a half-life of 14.96 hours. 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 energy of 4.931 MeV or more.

In the case of gadolinium (Gd), the isotope abundance ratios are: ¹⁵² Gd 0.20%, ¹⁵⁴ Gd 2.18%, ¹⁵⁵ Gd 14.80%, ¹⁵⁶ Gd 20.47%, ¹⁵⁷ Gd 15. 65%, ¹⁵⁸ Gd 24.84%, and ¹⁶⁰ Gd 21.86%. Of these, ¹⁶⁰ Gd undergoes β ^- decay in 18.479 hours through an (n,2n) reaction with a threshold energy of 7.498 MeV, producing ¹⁵⁹ Gd. Furthermore, from ¹⁵⁸ Gd, ¹⁵⁹ Gd is generated mainly through an (n, γ) reaction in a resonance region of less than 1 MeV. Since the ¹⁵⁹ Gd produced is the same isotope, they cannot be separated based on differences in half-life. However, since low-energy neutrons of less than 1 MeV are emitted isotropically from the target 94, their influence on the relative shape of the two-dimensional intensity distribution of directional fast neutrons is small. Therefore, by using a Gd plate for the metal plate converter 12, it is possible to measure the two-dimensional intensity distribution of neutrons having energy of 7.498 MeV or more.

In the case of molybdenum (Mo), the isotope abundance ratios are 14.84% for ⁹² Mo, 9.25% for ⁹⁴ Mo, 15.92% for ⁹⁵ Mo, 16.68% for ⁹⁶ Mo, and ^9.9 % for 97 Mo. 55%, ⁹⁸ Mo 24.13%, and ¹⁰⁰ Mo 9.63%. Among these, ¹⁰⁰ Mo undergoes (n, 2n) reaction with a threshold energy of 8.373 MeV to produce ⁹⁹ Mo which undergoes β ^- decay with a half-life of 65.94 hours, and (n, γ) mainly in the resonance region below 1 MeV. The reaction produces ¹⁰¹ Mo, which undergoes β ^- decay with a half-life of 14.61 minutes. Since ¹⁰¹ Mo has a shorter half-life than ⁹⁹ Mo, with a half-life of 14.61 minutes, measuring the radiation after one hour or more has passed after irradiation with neutron beam NB can effectively eliminate Only the contribution of ⁹⁹ Mo can be measured. Furthermore, from ⁹⁸ Mo, ⁹⁹ Mo is generated mainly through an (n, γ) reaction in a resonance region of less than 1 MeV. Since the ⁹⁹ Mo produced is the same isotope, it is not possible to separate them based on differences in half-life. However, since low-energy neutrons of less than 1 MeV are emitted isotropically from the target 94, their influence on the relative shape of the two-dimensional intensity distribution of directional fast neutrons is small. Therefore, by using a Mo plate for the metal plate converter 12, it is possible to measure the two-dimensional intensity distribution of neutrons having energy of 8.373 MeV or more.

In the case of gold (Au), the isotope abundance ratio is 100% ¹⁹⁷ Au. ¹⁹⁷ Au undergoes a (n,2n) reaction with a threshold energy of 8.114 MeV to produce ¹⁹⁶ Au which undergoes β ^- decay with a half-life of 6.183 days. Furthermore, ¹⁹⁷ Au undergoes β ^- decay with a half-life of 2.695 days, mainly through an (n, γ) reaction in a resonance region of less than 1 MeV, to produce ¹⁹⁸ Au. In the case of ¹⁹⁷ Au, since the reaction cross section in the resonance region is extremely large, a larger amount of ¹⁹⁸ Au is produced than in ¹⁹⁶ Au. Furthermore, since the half-life of ¹⁹⁸ Au is relatively long, it is difficult to separate only the contribution of ¹⁹⁶ Au in a short period of time. Therefore, when using an Au plate for the metal plate converter 12, a filter made of an Au plate may be added to the front side in the direction of incidence of the neutron beam NB, so that the filter absorbs neutrons in the resonance region. As a result, fast neutrons are mainly incident on the metal plate converter 12, which is an Au plate, and the contribution of the resonance region can be separated. Therefore, when using an Au plate for the metal plate converter 12, by combining it with an Au plate filter, it is possible to measure the two-dimensional intensity distribution of neutrons having energy of 8.114 MeV or more. Note that it is also possible to substantially measure only the contribution of ¹⁹⁶ Au by measuring radiation after a period of time approximately four times the half-life of ¹⁹⁸ Au (for example, 11 days) has elapsed. In this case, it is not necessary to combine the Au plate filter.

The material of the metal plate converter 12 is preferably composed of Zn, Al, or Mo in consideration of practicality such as price and ease of handling. The metal plate converter 12 is preferably made of a material containing 95% or more or 99% or more of the metal elements used. For example, when Al is used, 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 neutrons to be measured is extremely small, even if the thickness of the metal plate converter 12 is set to several mm, the intensity of the fast neutrons before and after passing through the metal plate converter 12 will hardly change.

Returning to FIG. 2, the neutron absorber 14 is placed away from the metal plate converter 12 toward the neutron source 96 on the reference axis 22 passing through the reference point 20. The neutron absorber 14 absorbs and blocks the neutron beam NB directed from the neutron beam source 96 toward the metal plate converter 12 so that a projected image of the neutron absorber 14 is formed on the surface of the metal plate converter 12. . The neutron absorber 14 is a plate-like member with a uniform thickness. The neutron absorber 14 has a ring shape with an outer diameter of φ2 and an inner diameter of φ1, and is provided with an opening 42 in the center. The neutron absorber 14 is arranged such that the center 44 of the neutron absorber 14 is located on the reference axis 22. The radial size φ2 of the neutron absorber 14 in the radial direction (x direction and y direction) is smaller than the radial direction (x direction and y direction) size of the metal plate converter 12, for example, the radial size φ2 of the metal plate converter 12. It is 1/2 or less or 1/3 or less.

The neutron absorber 14 is made of a material with a larger neutron absorption coefficient than the metal plate converter 12. It is preferable that the neutron absorber 14 is made of a material having a larger neutron absorption coefficient than the metal plate converter 12 at the energy at which the threshold reaction of the metal element contained in the metal plate converter 12 occurs. As a material for the neutron absorber 14, iron (Fe), copper (Cu), nickel (Ni), or tungsten (W) can be used. The material of the neutron absorber 14 may be a metal material containing at least one of Fe, Cu, Ni, and W, or a compound material containing at least one of these. The thickness of the neutron absorber 14 is not particularly limited, but is, for example, about 0.1 mm to 5 mm.

Fixing jig 16 fixes metal plate converter 12 and neutron absorber 14 so that the arrangement of metal plate converter 12 and neutron absorber 14 with respect to neutron beam source 96 does not change. The fixing jig 16 includes a support plate 24, a spacer 26, and a fastening member 28.

The support plate 24 supports the neutron absorber 14 and fixes the position of the neutron absorber 14. The support plate 24 is a flat metal plate with a uniform thickness similar to the metal plate converter 12, and is made of the same material as the metal plate converter 12. By configuring the support plate 24 from the same material as the metal plate converter 12, the intensity of fast neutrons before and after passing through the support plate 24 can be made to remain almost unchanged. As a result, the influence of the provision of the support plate 24 on the neutron beam intensity distribution projected onto the metal plate converter 12 can be substantially eliminated. The method for fixing the neutron absorber 14 to the support plate 24 is not particularly limited, but the neutron absorber 14 can be attached to the center of the support plate 24 using, for example, a resin adhesive or double-sided tape.

The spacer 26 is arranged between the metal plate converter 12 and the support plate 24 so that the distance L1 from the metal plate converter 12 to the neutron absorber 14 is maintained at a predetermined value. If a positioning plate 18 is provided, a spacer 26 is also arranged between the support plate 24 and the positioning plate 18. Spacers 26 ensure that metal plate converter 12, support plate 24 and positioning plate 18 are parallel to each other.

The fastening member 28 is a bolt, screw, or the like, and fastens and fixes the metal plate converter 12, the support plate 24, the positioning plate 18, and the spacer 26 to each other. The fixing jig 16 is configured such that the metal plate converter 12 can be removed by removing the fastening member 28, for example. By disassembling the neutron source position measuring device 10 after irradiation with the neutron beam NB, the two-dimensional intensity distribution of the radiation emitted from the metal plate converter 12 can be measured with high accuracy.

The positioning plate 18 is a metal plate having a mark used for positioning when installing the neutron source position measuring device 10. The positioning plate 18 is fixed to the metal plate converter 12 and the neutron absorber 14 by a fixing jig 16. The positioning plate 18 is arranged, for example, closer to the neutron beam source 96 than the metal plate converter 12 and the neutron absorber 14 (that is, closer to the front side in the direction of incidence of the neutron beam NB). The positioning plate 18 is a flat metal plate with a uniform thickness similar to the metal plate converter 12, and is made of the same material as the metal plate converter 12 and the support plate 24.

FIG. 4 is a rear view schematically showing the configuration of the metal plate converter 12. The metal plate converter 12 has a center hole 32, notches 34a, 34b, a fixing hole 36, and score lines 38a, 38b.

The center hole 32 is a through hole provided at the reference point 20 of the metal plate converter 12, and is a marker for identifying the position of the reference point 20 in the x direction and the y direction. The notches 34a and 34b are V-shaped or U-shaped cutouts provided at some locations on the outer periphery of the metal plate converter 12. Notches 34a and 34b are marks for identifying the orientation of metal plate converter 12 in the x and y directions. The fixing hole 36 is a through hole provided in the outer peripheral portion of the metal plate converter 12, and is used for fixing with the fixing jig 16. In the illustrated example, the outer shape of the metal plate converter 12 is a square, and fixing holes 36 are provided at each of the four corners of the square. The ruled lines 38a and 38b are marks indicating the center positions in the x direction and the y direction. The first score line 38a is drawn as a straight line extending through the center hole 32 in the y direction, and the second score line 38b is drawn as a straight line extending through the center hole 32 in the x direction.

The notches 34a and 34b are also marks for identifying the front surface (for example, the neutron beam NB incident side) and the back surface (for example, the neutron beam NB output side) of the metal plate converter 12. The notches 34a, 34b are provided at a plurality of positions asymmetrical with respect to the center hole 32. In the illustrated example, if the U-shaped second notch 34b is on the left side of the V-shaped first notch 34a in the transfer result, the transfer on the surface of the converter (the surface on the incident side of the neutron beam NB) It is shown that the result is

Note that 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 cutout or a through hole different from the notches 34a and 34b as a mark for identifying the position and orientation in the x direction and the y direction. For example, instead of providing two notches 34a and 34b, only one of the first notch 34a and the second notch 34b may be provided. In addition, cutouts or through holes may be provided at a plurality of positions asymmetrical with respect to the center hole 32 in order to identify the front and back sides of the metal plate converter 12. The fixing hole 36 may be used as a mark for identifying the position and orientation in the x direction and the y direction. For example, the plurality of fixing holes 36 may be provided at asymmetrical positions with respect to the center hole 32.

FIG. 5 is a front view schematically showing the structure of the neutron absorber 14 and the support plate 24, and shows the structure when viewed from the neutron beam NB incidence side. Support plate 24 has a similar shape and size as metal plate converter 12 . In the illustrated example, the outer shape of the support plate 24 is a square, and fixing holes 40 are provided at each of the four corners of the square. The neutron absorber 14 is attached to the center of the support plate 24. The neutron absorber 14 is formed so that the outer diameter φ2 and the inner diameter φ1 are concentric circles, and is attached to the support plate 24 so that the center 44 of the neutron absorber 14 coincides with the reference axis 22. Since the neutron absorber 14 has a characteristic shape having an outer diameter φ2 and an inner diameter φ1, it becomes easy to specify the size and position of the projected image of the neutron absorber 14 formed on the metal plate converter 12.

Note that the shape of the support plate 24 is not limited to that shown in FIG. 5, and may be any other shape such as a rectangle or a circle. Further, the shape of the neutron absorber 14 is not limited to that shown in FIG. 5, and may be any other shape such as a rectangle, hexagon, or octagon. The neutron absorber 14 may have a frame shape such as a rectangle, hexagon, or octagon with an opening 42 provided in the center. The neutron absorber 14 may have a shape in which the opening 42 is not provided in the center.

FIG. 6 is a rear view schematically showing the configuration of the neutron source position measuring device 10 of FIG. 2, and shows the configuration when viewed from the side opposite to the incident direction of the neutron beam NB. The positioning plate 18 has ruled lines 38c and 38d that are marks indicating the center position in the x direction and the y direction. The third score line 38c is drawn as a straight line extending in the y direction through the center hole 32, and is provided at a position overlapping with the first score line 38a. The fourth score line 38d is drawn as a straight line extending in the x direction through the center hole 32, and is provided at a position overlapping the second score line 38b.

The positioning plate 18 is larger in size in the x and y directions than the metal plate converter 12 and the support plate 24, and has scored lines 38c and 38d at locations that do not overlap with the metal plate converter 12 and the support plate 24 in the axial direction. There is. This can prevent the ruled lines 38c and 38d from being hidden behind the metal plate converter 12 and becoming invisible. In the example of FIG. 6, the outer shape of the positioning plate 18 is an octagon, but the outer shape of the positioning plate 18 may be any other shape such as a circle or a rhombus. Further, a positioning mark different from the ruled lines 38c and 38d may be provided on the positioning plate 18.

As shown in FIG. 2, when the neutron source position measuring device 10 is installed in front of the accelerator neutron source 90, the marked lines 38a and 38b are attached to the metal plate converter 12, and the scored lines are attached to the positioning plate 18. The installation position is adjusted using lines 38c and 38d. The installation position of the neutron source position measuring device 10 is assumed to be, for example, an exit on an extension line in the radial direction of the neutron beam NB emitted from the target 94 of the accelerator neutron source 90. Normally, the neutron beam NB cannot be seen directly, so a cross laser is irradiated from a laser marker to match the designed position of the neutron beam source and the designed radiation direction of the radiation NB, and the reference coordinate axes are set. do. Next, the neutron source position measuring device 10 is arranged so that the cross laser and the marked lines 38a to 38d are aligned. For example, by using a pedestal (not shown) that supports the neutron source position measuring device 10, the three-dimensional position can be adjusted using the cross laser as a reference. Thereby, the neutron source position measuring device 10 can be installed on the designed extension line of the radial direction of the neutron beam NB.

Next, a method for measuring radiation emitted from the activated metal plate converter 12 will be explained. FIG. 7 is a cross-sectional view schematically showing the configuration of the transfer device 50. The transfer device 50 is a cassette that transfers the two-dimensional intensity distribution of radiation emitted from the metal plate converter 12 onto a transfer plate 52 to form an image. The transfer device 50 includes a transfer plate 52, a buffer material 54, and a shielding container 56.

The transfer plate 52 is an imaging plate (IP) for generating an image corresponding to the radiation intensity distribution in response to radiation. As the transfer plate 52, for example, one using a stimulable phosphor can be used. Stimulable phosphors emit fluorescence mainly in response to beta rays, and have a memory function (optical memory function) in which areas that have reacted to radiation emit light again when irradiated with readout light afterwards. As a result, it is possible to obtain a highly sensitive image and obtain image data with a large dynamic range compared to the case of using a general phosphor that does not have photostimulability. Furthermore, by using the transfer device 50, the neutron beam NB irradiation environment and the transfer environment to the transfer plate 52 can be separated, and the high-dose gamma rays generated in the neutron beam NB irradiation environment are transferred to the transfer process. It is possible to prevent adverse effects.

The activated metal plate converter 12 is housed inside the shielding container 56 with one side of the metal plate converter 12 in close contact with the transfer plate 52 . For example, one side of both surfaces of the metal plate converter 12, which is the incident side of the neutron beam NB, is brought into close contact with the transfer plate 52. The buffer material 34 is a sponge-like resin member or rubber member, and is configured to press the transfer plate 52 against the metal plate converter 12. This prevents a gap from forming between the transfer plate 52 and the metal plate converter 12, and prevents the relative positions of the transfer plate 52 and the metal plate converter 12 from changing during the transfer process. The shielding container 56 shields light from the outside so that the inside of the container is in a dark room state during the transfer process. The radiation intensity distribution transferred to the transfer plate 52 is read using a dedicated reading device (reader or scanner), and image data corresponding to the radiation intensity distribution is generated.

FIG. 8 is a diagram showing an example of a transferred image of the metal plate converter 12. In the example of FIG. 8, a 100 mm x 100 mm Al plate is used as the metal plate converter 12, a 2.3 mm thick Cu ring is used as the neutron absorber 14, and the distance from the neutron absorber 14 to the metal plate converter 12 is The case where L1 is 41.3 mm is shown. A center hole 32 with a diameter of 3 mm is provided in the center of the Al plate converter. Since the transfer to the transfer plate 52 was started 1.5 hours after irradiation with the neutron beam NB, radiation emitted mainly from ²⁴ Na was transferred, and neutrons with energy of 3.249 MeV or more were measured. has been done. The darker (darker) the transfer image is, the higher the intensity of the radiation and the larger the amount of neutrons, and the whiter (thinner) it is, the lower the intensity of the radiation and the smaller the amount of neutrons.

At the center of the transferred image in FIG. 8, there is a circular reference area 60 that is relatively white (thinner) than the surrounding area. The reference region 60 corresponds to the center hole 32 of the metal plate converter 12, and since the through hole is provided, the radiation intensity is locally reduced. The reference area 60 corresponds to a marker indicating the position of the reference point 20.

Outside the reference area 60, there is a circular first edge 62 that defines the outer edge of a relatively black (dark) area, and outside the first edge 62, there is a circular first edge 62 that defines the outer edge of a relatively thin (white) area. There is a defining circular second edge 64 . The region between the first edge 62 and the second edge 64 corresponds to a projected image of the neutron absorber 14, and the radiation intensity is locally reduced because neutrons are partially shielded by the neutron absorber 14. ing. Note that the neutron absorber 14 does not completely block neutron beams. In other words, when the neutron beam from the neutron beam source 96 is irradiated onto the metal plate converter 12 through the neutron absorber 14, a part of the neutron beam incident on the neutron absorber 14 passes through the neutron absorber 14 and is converted into the metal plate converter. Reach 12. Inside the first edge 62 and outside the second edge 64, the radiation intensity is locally high because neutrons are not shielded by the neutron absorber 14. Moreover, a circular distribution 66 that gradually becomes whiter (thinner) toward the outside in the radial direction can be seen over almost the entire transferred image in FIG. A circular distribution 66 shows a two-dimensional intensity distribution of the neutron beam NB directed from the neutron beam source 96 toward the metal plate converter 12.

FIG. 9 is a diagram schematically showing a method for calculating the neutron source position, in which the reference area 60, the first edge 62, and the second edge 64 are extracted from the transferred image of FIG. The size D1 of the first edge 62 or the size D2 of the second edge 64 in FIG. 8 is used to calculate the axial distance L from the metal plate converter 12 to the neutron source 96 shown in FIG. 2. The first edge 62 is a projected image obtained by enlarging and projecting the inner diameter φ1 of the neutron absorber 14 by the neutron beam NB from the neutron beam source 96, which is a point light source. Similarly, the second edge 64 is a projected image obtained by enlarging and projecting the outer diameter φ2 of the neutron absorber 14 by the neutron beam NB from the neutron beam source 96, which is a point light source.

The magnification factor α of the first edge 62 and the second edge 64 is α=L/L2 from the geometrical arrangement shown in FIG. Here, the distance L2 is the distance from the neutron absorber 14 to the neutron source 96, and L2=L−L1. Therefore, regarding the first edge 62, D1=α·φ1=φ1/(1−L1/L) holds, and can be expressed as L=L1×D1/(D1−φ1). Similarly, regarding the second edge 64, D2=α·φ2 holds true and can be expressed as L=L1·D2 (D2−φ2). The distance L1, the inner diameter φ1, and the outer diameter φ2 are known, and the sizes D1 and D2 of the first edge 62 and the second edge 64 can be obtained from the transferred image, so using these values, the distance to the neutron source 96 can be determined. L can be calculated.

Since the distance L can be calculated from only one of the inner diameter φ1 and the outer diameter φ2, it is not essential that the neutron absorber 14 has a ring shape, and the neutron absorber 14 may have a disk shape without an opening 42. However, since there are both the inner diameter φ1 and the outer diameter φ2, even if one of the first edge 62 and the second edge 64 included in the transferred image is unclear, the distance L can be calculated using the size of the other. It can be calculated.

Furthermore, the radial distances rx and ry from the reference axis 22 to the neutron source 96 can be calculated using the coordinates of the center position 68 of the first edge 62 and second edge 64 in the transferred image of FIG. . The center position 68 of the first edge 62 and the second edge 64 can be determined mathematically from the positions of any three points on the arc of the first edge 62 or the second edge 64. The center position 68 can be defined as coordinates with the reference area 60 (reference point 20) as the origin, and can be expressed as (dx, dy).

The center position 68 lies on a straight line passing through the neutron source 96 and the center 44 of the neutron absorber 14 in FIG. Therefore, from the geometrical arrangement shown in FIG. Using the distance L2 to the neutron source 96 and the distance L1 from the neutron absorber 14 to the metal plate converter 12, it can be expressed as L2 (=L−L1):L1. Further, the neutron beam source 96 and the center position 68 are in a point-symmetric positional relationship with respect to the reference axis 22. Therefore, using the xy coordinates (dx, dy) of the center position 68, the xy coordinates (rx, ry) of the neutron source 96 are calculated as (rx, ry)=-(L-L1)/L1(dx, dy). It can be expressed as. That is, rx=(1-L/L1)dx, and ry=(1-L/L1)dy.

In this way, the distance L, the x coordinate rx, and the y coordinate ry for specifying the three-dimensional position of the neutron beam source 96 can be determined from the transferred image of the metal plate converter 12.

FIG. 10 is a flowchart showing the flow of the neutron source position measurement method. First, the neutron source position measuring device 10 is positioned with respect to the neutron beam NB to be measured (S10). For example, the origin of the x-direction and the y-direction is 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 irradiating the target 94. Specifically, the reference coordinate axes can be determined using a surveying instrument such as a laser marker (laser theodolite). Next, the neutron source position measuring device 10 is installed based on the determined coordinate axes. For example, the neutron beam source is set so that the cross laser irradiated from the laser marker, the scored lines 38a, 38b attached to the metal plate converter 12, and the scored lines 38c, 38d attached to the positioning plate 18 match. Adjust the installation position of the position measuring device 10.

Next, the installed neutron source position measuring device 10 is irradiated with a neutron beam NB to be measured (S12). By irradiation with the neutron beam NB, the metal plate converter 12 included in the neutron source position measuring device 10 is activated. As the neutron beam NB is partially absorbed by the neutron absorber 14, a projected image of the neutron absorber 14 is formed on the metal plate converter 12. After irradiation with the neutron beam NB, the radiation emitted from the metal plate converter 12 is transferred to the transfer plate 52 (S14). For example, the two-dimensional intensity distribution of radiation is transferred to the transfer plate 52 by disassembling the neutron source position measuring device 10 and placing the metal plate converter 12 in the transfer device 50 . After the transfer is completed, the image of the two-dimensional intensity distribution of the radiation transferred to the transfer plate 52 is read to generate image data (S16).

Next, the sizes D1 and D2 of the projected images of the neutron absorber 14 included in the image data are measured (S18), and the distance L1 from the metal plate converter 12 to the neutron absorber 14, the size φ1 of the neutron absorber 14, Using φ2 and the sizes D1 and D2 of the projected image of the neutron absorber 14, the distance L from the metal plate converter 12 to the neutron source 96 is calculated (S20). Next, the position (dx, dy) of the projected image of the neutron absorber 14 with respect to the position of the marker (reference area 60) included in the image data is measured (S22), and the position (dx, dy) of the projected image is used. , the position (rx, ry) of the neutron source 96 with respect to the reference axis 22 is calculated (S24).

According to this embodiment, the three-dimensional position of the neutron source 96 can be specified using the neutron source position measuring device 10. When using an Al plate for the metal plate converter 12, the material is inexpensive and the time required for the transfer step S14 is about one day, so the three-dimensional position of the neutron beam source 96 can be quickly and easily obtained. .

(Second embodiment)
FIG. 11 is a side view schematically showing the configuration of a neutron source position measuring device 70 according to the second embodiment. The second embodiment differs from the above-described embodiments in that a second neutron absorber 76 is used as a marker indicating the position of the reference point 20. The second embodiment will be described below, focusing on the differences from the first embodiment, and common features will be omitted as appropriate.

The neutron source position measuring device 70 includes a metal plate converter 72, a first neutron absorber 74, a second neutron absorber 76, and a fixing jig 78. The neutron source position measuring device 70 includes a reference point 20 and a reference axis 22 similarly to the first embodiment. Each of the metal plate converter 72 and the first neutron absorber 74 is configured similarly to the metal plate converter 12 and the neutron absorber 14 according to the first implementation. The first neutron absorber 74 has, for example, a ring shape with an opening 42 in the center, and is arranged so that the center 44 of the first neutron absorber 74 is located on the reference axis 22 . The first neutron absorber 74 is provided at a distance L1 from the metal plate converter 72.

The second neutron absorber 76 is arranged closer to the neutron source 96 than the metal plate converter 72 on the reference axis 22 passing through the reference point 20 . The second neutron absorber 76 is preferably arranged closer to the metal plate converter 72 than the first neutron absorber 74, and is preferably arranged closer to the surface 80 of the metal plate converter 72 on the neutron source 96 side. The second neutron absorber 76 absorbs and blocks the neutron beam NB directed from the neutron source 96 toward the metal plate converter 72 , so that a projected image of the second neutron absorber 76 is formed on the surface of the metal plate converter 72 . so that The projected image of the second neutron absorber 76 is used to identify the position of the reference point 20. Therefore, the second neutron absorber 76 is a marker for identifying the position of the reference point 20 in the metal plate converter 72 in the x direction and the y direction.

The second neutron absorber 76 is a plate-like member with a uniform thickness. The size φ3 in the radial direction (x direction and y direction) of the second neutron absorber 76 is smaller than the radial direction (x direction and y direction) size of the metal plate converter 72. It is smaller than the diameter φ2. The radial size φ3 of the second neutron absorber 76 may be approximately the same as the inner diameter φ1 of the first neutron absorber 74, or may be smaller than the inner diameter φ1 of the first neutron absorber 74. By making the radial size φ3 of the second neutron absorber 76 equal to or smaller than the inner diameter φ1 of the first neutron absorber 74, the first neutron absorber 74 and the second neutron absorber 76 are They can be arranged so that they are unlikely to overlap in the axial direction.

The second neutron absorber 76, like the first neutron absorber 74, is made of a material having a larger neutron absorption coefficient than the metal plate converter 12. The second neutron absorber 76 is preferably made of a material that has a larger neutron absorption coefficient than the metal plate converter 12 at an energy that causes a threshold reaction of the metal element contained in the metal plate converter 12 . As a material for the second neutron absorber 76, iron (Fe), copper (Cu), nickel (Ni), or tungsten (W) can be used. The material of the second neutron absorber 76 may be a metal material containing at least one of Fe, Cu, Ni, and W, or may be a compound material containing at least one of these. The material of the second neutron absorber 76 may be the same as the material of the first neutron absorber 74. The thickness of the second neutron absorber 76 is not particularly limited, but is, for example, about 0.1 mm to 5 mm. The shape of the second neutron absorber 76 is not particularly limited either, and may be any shape such as a circle, a rectangle, a hexagon, an octagon, or a cross.

The fixing jig 78 fixes the metal plate converter 72 , the first neutron absorber 74 , and the second neutron absorber 76 , and connects the metal plate converter 72 , the first neutron absorber 74 , and the second neutron absorber 76 to the neutron source 96 . Make sure that the arrangement of 76 does not change. The fixing jig 78 includes a base 82 extending in the axial direction, a first support member 84 extending radially from the base 82 and supporting the first neutron absorber 74, and a second neutron absorber extending radially from the base 82. A second support member 86 that supports the body 76 is provided. Note that the specific configuration of the fixing jig 78 is not particularly limited, and any fixture that can fix the relative positions of the metal plate converter 72, the first neutron absorber 74, and the second neutron absorber 76 can be used as the fixing jig 78. Any structure can be adopted.

Also in this embodiment, the three-dimensional position of the neutron source 96 can be measured using the same measurement method and measurement principle as in the first embodiment. In this embodiment, the center position of the projected image of the second neutron absorber 76 can be used as the marker indicating the reference point 20 instead of the reference area 60 corresponding to the center hole 32 of the metal plate converter 12. Since the second neutron absorber 76 is arranged close to the metal plate converter 72, the projected image of the second neutron absorber 76 can be formed at a position that substantially coincides with the reference point 20 of the metal plate converter 72.

(Third embodiment)
FIG. 12 is a side view schematically showing the configuration of a neutron source position measuring device 110 according to the third embodiment. The third embodiment differs from the first embodiment described above in that it further includes a plurality of metal plate converters 112a, 112b, 112c, 112d, and 112e. The third embodiment will be described below, focusing on the differences from the first embodiment, and common features will be omitted as appropriate.

The neutron source position measuring device 110 includes a metal plate converter 12, a neutron absorber 14, a plurality of metal plate converters 112a to 112e, and a fixing jig 116. The neutron source position measuring device 110 may further include a positioning plate 18.

The plurality of metal plate converters 112a to 112e are arranged closer to the neutron source 96 than the neutron absorber 14. The plurality of metal plate converters 112a to 112e are arranged between the positioning plate 18 and the neutron absorber 14, if the positioning plate 18 is provided. The plurality of metal plate converters 112a to 112e are used to measure the two-dimensional intensity distribution of the incident neutron beam NB.

The plurality of metal plate converters 112a to 112e are arranged perpendicular to the reference axis 22, and the thickness direction of the plurality of metal plate converters 112a to 112e coincides with the axial direction. The plurality of metal plate converters 112a to 112e are arranged to overlap each other in the axial direction. The plurality of metal plate converters 112a to 112e are arranged at intervals such that their positions in the axial direction (z direction) are different from each other, for example, they are arranged at equal intervals in the axial direction.

The plurality of metal plate converters 112a-112e are made of the same material. The plurality of metal plate converters 112a-112e may be constructed of the same material as metal plate converter 12. As the metal element used in the plurality of metal plate converters 112a to 112e, for example, zinc (Zn), aluminum (Al), magnesium (Mg), gadolinium (Gd), molybdenum (Mo), or gold (Au) can be used. . By making the plurality of metal plate converters 112a to 112e the same material, the measurement conditions of the plurality of metal plate converters 112a to 112e can be made the same, and only the measurement position 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 a plurality of different positions 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 112a to 112e are added, but the number of additional metal plate converters is not limited to five, and may be at least two or more, and may be three or four. The number of sheets may be six or more. In other words, at least two or more metal plate converters using the same material are sufficient.

The plurality of metal plate converters 112a to 112e can be configured similarly to metal plate converter 12 shown in FIG. Each of the plurality of metal plate converters 112a to 112e may have a center hole 32, notches 34a, 34b, a fixing hole 36, and score lines 38a, 38b.

The fixing jig 116 fixes the metal plate converter 12, the neutron absorber 14, and the plurality of metal plate converters 112a to 112e, and connects the metal plate converter 12, the neutron absorber 14, and the plurality of metal plate converters 112a to 112e to the neutron source 96. The arrangement of 112e should not change. Fixture jig 116 includes support plate 24 , spacer 26 , fastening member 28 , and additional spacer 126 . Additional spacers 126 are positioned between the plurality of metal plate converters 112a-112e to maintain the spacing of the plurality of metal plate converters 112a-112e.

The fixing jig 116 is configured such that the metal plate converter 12 and the plurality of metal plate converters 112a to 112e can be disassembled and removed by, for example, removing the fastening member 28. After irradiation with the neutron beam NB, by disassembling the neutron source position measuring device 110, the two-dimensional intensity distribution of the radiation emitted from the metal plate converter 12 and each of the plurality of metal plate converters 112a to 112e can be measured with high precision. can.

The two-dimensional intensity distribution emitted from the plurality of metal plate converters 112a to 112e can be read using the transfer device 50 of FIG. The radiation intensity distributions of the metal plate converter 12 and the plurality of metal plate converters 112a to 112e may be transferred simultaneously using one transfer device 50. Thereby, the transfer conditions of the metal plate converter 12 and the plurality of metal plate converters 112a to 112e can be made the same. Note that a plurality of transfer devices 50 may be used, and the radiation intensity distributions of the metal plate converter 12 and the plurality of metal plate converters 12a to 12e may be imaged using separate transfer devices 50.

FIGS. 13A to 13E are diagrams showing examples of transferred images of a plurality of metal plate converters 112a to 112e. In the example of FIG. 13, like the metal plate converter 12, 100 mm x 100 mm Al plates are used as the plurality of metal plate converters 112a to 112e, and the axial positions of the plurality of metal plate converters 122a to 212e are changed by 20 mm. Indicate the case. 13A to 13E are arranged in order of distance from the neutron source 96 to the metal plate converters 112a to 112e. 13(a) is a transferred image of the metal plate converter 112a placed closest to the neutron source 96, and FIG. 13(e) is a transferred image of the metal plate converter 112a placed farthest from the neutron source 96. This is a transferred image of the converter 112e. As shown in FIGS. 13(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.

FIG. 14 is a graph showing a three-dimensional profile of the neutron beam NB. Curves A to E shown in FIG. 14 indicate intensity distributions on the diagonal lines of the transferred images shown in FIGS. 13(a) to (e). In FIG. 14, the position of the center hole 32 is set as the origin, and the strength value at the position of the fixing hole 36 is standardized as 1. Further, the peak value is calculated by calculating the intensity distribution (dotted line) assuming that there is no center hole 32 by curve fitting, and the full width (FWHM) of the intensity distribution at half the peak value is shown by the broken line. From FIG. 14, it can be seen that a three-dimensional profile in which the peak value of the neutron amount decreases and the full widths at half maximum Wa and Wb widen as the distance from the neutron beam source 96 increases.

FIG. 15 is a graph showing the directivity of the neutron beam NB, in which the full width at half maximum of the curves A to E shown in FIG. 14 are plotted against the axial positions of the plurality of metal plate converters 112a to 112e. . As shown in the figure, the full width at half maximum of the neutron intensity distribution calculated using each of the plurality of metal plate converters 112a to 112e is lined up on a straight line, and the directivity of the neutron beam NB as shown in FIG. It can be seen that the measurement is successful. Since the slope of the approximate straight line shown in FIG. 15 is about 0.9, it can be seen that the directivity angle based on the full width at half maximum is about 43 degrees.

According to this embodiment, the three-dimensional position of the neutron source 96 is measured using the metal plate converter 12 and the neutron absorber 14, and the neutron source 96 is measured using the plurality of metal plate converters 112a to 112e. The three-dimensional profile of the output neutron beam NB can be specified with high spatial resolution. Furthermore, by using the positioning plate 18, it is possible to improve the positioning accuracy when installing the neutron source position measuring device 110 with respect to the neutron source 96. As a result, the neutron profile, which is the spatial distribution of neutrons emitted from the neutron beam source 96, can be easily and accurately measured.

When using Al plates for the plurality of metal plate converters 112a to 112e, three-dimensional profile data for each energy can be obtained by dividing the transfer process into two steps. For example, the two-dimensional intensity distribution of radiation emitted from each of the plurality of Al plate converters activated by irradiation with the neutron beam NB is transferred to the first transfer plate to generate the first image data. Subsequently, after being transferred to the first transfer plate, the two-dimensional intensity distribution of radiation emitted from each of the plurality of Al plate converters is transferred to a second transfer plate to generate second image data. Based on the first image data, three-dimensional profile data of neutrons having energy of 1.896 MeV or more can be generated. Moreover, three-dimensional profile data of neutrons having energy of 3.249 MeV or more can be generated based on the second image data.

Instead of the plurality of metal plate converters 112a to 112e, a combination of a plurality of types of metal plate converters may be used. A plurality of first metal plate converters containing a first metal element (for example, Al), a plurality of second metal plate converters containing a second metal element (for example, Zn), and a third metal element (for example, Mo). A plurality of third metal plate converters may also be used. For example, a converter set in which a first metal plate converter, a second metal plate converter, and a third metal plate converter are stacked may be prepared, and the plurality of converter sets may be arranged at intervals using spacers. A plurality of types of metal plate converters included in one converter set may be arranged adjacent to each other, or may be arranged at intervals using spacers. In this case, by combining multiple types of metal plate converters, three-dimensional profile data of the neutron beam NB can be obtained for each of multiple energy regions.

For example, three-dimensional profile data of neutrons having energy of 8.373 MeV or more can be obtained from a plurality of Mo plate converters. Three-dimensional profile data of neutrons having energy of 3.249 MeV or more and three-dimensional profile data of neutrons having energy of 1.896 MeV or more are obtained from the plurality of Al plate converters. Moreover, three-dimensional profile data of neutrons having 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.

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 embodiments described above, and that various design changes and modifications are possible, and that such modifications are also within the scope of the present invention. It is a place where

In the above-described embodiment, a case is shown in which a photostimulable phosphor is used as the transfer plate 52, but other types of phosphor may be used, or a combination of a lead intensifying screen and a photosensitive film may be used. Good too.

In the embodiments described above, a case was described in which a neutron profile was measured for neutron imaging. The measurement method according to this embodiment is not limited to application to neutron imaging, but may be applied to various fields where neutron beams are used. For example, it may be used to evaluate a neutron beam source used in a neutron doping (NTD) method in which silicon (Si) is converted into phosphorus (P) and doped by irradiating a silicon wafer with a neutron beam. It may also be used to evaluate medical neutron sources, such as boron neutron supplementation therapy, which selectively destroys cancer tissue by irradiating boron (B) incorporated into cancer tissue with neutron beams. It may also be used to evaluate neutron sources used in (BNCT).

DESCRIPTION OF SYMBOLS 10, 70, 110... Neutron source position measuring device, 12, 72... Metal plate converter, 14... Neutron absorber, 20... Reference point, 22... Reference axis, 42... Opening, 74... First neutron absorber, 76 ...Second neutron absorber, 90...Accelerator neutron source, 92...Accelerator, 94...Target, 96...Neutron beam source.

Claims (9)

a metal plate converter containing a metal element that is converted into another radioactive isotope that undergoes beta decay by a threshold reaction that absorbs neutrons;
a marker for identifying the position of a reference point of the metal plate converter;
A first element disposed away from the metal plate converter toward the neutron source on a reference axis passing through the reference point, and made of a material having a larger neutron absorption coefficient of energy at which the threshold reaction occurs than the metal plate converter. A neutron source position measuring device comprising: a neutron absorber; The neutron beam source according to claim 1, wherein the metal element is zinc (Zn), aluminum (Al), magnesium (Mg), gadolinium (Gd), molybdenum (Mo), or gold (Au). Position measuring device. Neutron source position measurement according to claim 2, wherein the first neutron absorber contains at least one of iron (Fe), copper (Cu), nickel (Ni), and tungsten (W). Device. The neutron source position measuring device according to claim 1, wherein the first neutron absorber has a ring shape or a frame shape with an opening provided on the reference axis. The neutron source position measuring device according to claim 1, wherein the marker is a through hole provided in the metal plate converter. The marker is disposed close to the neutron source side surface of the metal plate converter on the reference axis, and is made of a material that has a larger neutron absorption coefficient of energy at which the threshold reaction occurs than the metal plate converter. The neutron source position measuring device according to any one of claims 1 to 3, wherein the neutron source position measuring device is a second neutron absorber. The neutron source position measurement according to claim 6, wherein the second neutron absorber contains at least one of iron (Fe), copper (Cu), nickel (Ni), and tungsten (W). Device. Claim 1, further comprising a plurality of metal plate converters that are arranged closer to the neutron source than the first neutron absorber on the reference axis and that contain the same metal element as the metal plate converter. The neutron source position measuring device according to any one of 3 to 3. A neutron source position measuring method using the neutron source position measuring device according to any one of claims 1 to 3,
irradiating the metal plate converter with a neutron beam from the neutron beam source through the first neutron absorber;
Generating image data by imaging a two-dimensional intensity distribution of radiation emitted from the metal plate converter activated by irradiation with the neutron beam;
a distance from the metal plate converter to the first neutron absorber on the reference axis, a size of the first neutron absorber, and a size of a projected image of the first neutron absorber included in the image data. calculating the distance to the neutron source on the reference axis using
calculating the position of the neutron source with respect to the reference axis based on the position of the projected image of the first neutron absorber with respect to the position of the marker included in the image data. Source position measurement method.

Images