JP2014081209A - Neutron radiographic apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a neutron radiographic apparatus which features reduced device size, improved spatial resolving power, and wider irradiation field.SOLUTION: A neutron radiographic apparatus 1 includes a multi-pinhole collimator 3 having a plurality of neutron guide tubes 9. Each neutron guide tube 9 has a relatively high collimation ratio and relatively high spatial resolving power but has a relatively short guide tube length and a relatively small opening diameter, which makes the multi-pinhole collimator 3 compact. Use of multiple neutron guide tubes 9 makes the irradiation field relatively wide and neutron utilization efficiency relatively high, even though the opening diameter of each neutron guide tube 9 is relatively small.

Description

  The present invention relates to a neutron radiography apparatus.

  Non-Patent Document 1 discloses a small neutron collimator. The neutron collimator of Non-Patent Document 1 has a microchannel plate (MCP). The MCP contains at least one of an additive of Gd (gadolinium) and an additive of B (boron). Gd and B have a relatively high absorption cross section for thermal neutrons.

“Neutron Collimation With Microchannel Plates: Calibration of Existing Technology and Near Future Possibilities”, Tremsin, Anton S .; Hussey, Daniel S .; Downing, R. Gregory; Feller, W. Bruce; Mildner, David FR; Jacobson, David L .; Arif, Muhammad; Siegmund, Oswald HW, IEEE, TRANSACTIONS ON NUCLEAR SCIENCE, VOL.54, NO.2, p362-p366 APRIL 2007

Conventionally, relatively high spatial resolution is required for observation of water behavior in a fuel cell and observation of living cells. A neutron radiography apparatus using thermal neutrons and cold neutrons is suitable for applications requiring such a relatively high spatial resolution. This is because the reaction cross section between neutron and hydrogen is larger than the reaction cross section between neutron and metal. The spatial resolution of the neutron radiography apparatus is influenced by the resolution of the measuring instrument of the neutron radiography apparatus, but is mainly influenced by the parallelism of the neutron beam. The parallelism of the neutron beam is affected by the structure of the neutron collimator of the neutron radiography apparatus. An index indicating the parallelism of the neutron beam is a collimate ratio. The collimating ratio is a value (L / D) obtained by dividing the length (L) of the neutron conduit of the neutron collimator by the diameter (D) of the opening of the neutron conduit. The collimation ratio of the conventional neutron collimator can be about 100 to 1000. The longer the length of the neutron conduit, the greater the collimation ratio. The smaller the diameter of the neutron conduit opening, the greater the collimating ratio. However, the length of the neutron conduit affects the scale of the device (the overall size of the device). The diameter of the neutron conduit opening affects the size of the neutron field. That is, the determination of the collimating ratio affects the overall size of the apparatus and the width of the irradiation field. Therefore, when conditions are set for the scale of the apparatus and the irradiation field of view, the spatial resolution is also limited by these conditions.

  Accordingly, an object of the present invention has been made in view of the above matters, and provides a neutron radiography apparatus capable of reducing the scale of the apparatus, improving the spatial resolution, and improving the irradiation field. That is.

  A neutron radiography apparatus according to the present invention includes a multi-pinhole collimator, and the multi-pinhole collimator includes a plurality of neutron conduits, a casing that holds the plurality of neutron conduits, and a neutron absorption region. The housing includes a first surface and a second surface, and the first surface and the second surface are arranged so as to be orthogonal to a reference axis extending along the incident direction of the neutron beam. The first surface is opposite the second surface, each of the plurality of neutron conduits has a hollow pipe shape, and includes a first opening and a second opening, Extending between the first surface and the second surface and arranged parallel to each other along the reference axis, the first opening is provided in the first surface, and the second surface An opening is provided in the second surface, and the neutron absorption The region occupies between the inner wall surface of the housing and the outer surface of the plurality of neutron conduits, and the neutron absorption region is filled with a neutron absorber, and the neutron absorber is Gd, B, Any of Li is included.

  Since the multi-pinhole collimator has a plurality of neutron conduits, the number of neutron conduits can be reduced even if the neutron conduit length is relatively short and the aperture diameter is relatively short in order to achieve a suitable collimation ratio. By increasing, the irradiation field and neutron utilization efficiency can be increased. Therefore, a suitable spatial resolution can be realized by a suitable collimating ratio, and the irradiation field and neutron utilization efficiency can be increased by providing a plurality of neutron conduits. Furthermore, even if the conduit length is shortened, a suitable collimating ratio can be maintained if the opening diameter is shortened, so that the scale of the multi-pinhole collimator can be reduced while maintaining a relatively high spatial resolution, and the cost can be reduced. Become. Furthermore, the neutron absorber includes any of Gd, B, and Li. Each of Gd, B, and Li has a relatively large reaction cross section with thermal neutrons or the like (neutrons having thermal kinetic energy equal to or lower than the thermal kinetic energy of thermal neutrons). Accordingly, in the multi-pinhole collimator, thermal kinetic energy such as thermal neutrons traveling in a different location from the inside of the neutron conduit can be sufficiently reduced by the neutron absorber.

  In the neutron radiography apparatus according to the present invention, neutrons incident from a first opening of one neutron conduit included in the plurality of neutron conduits are adjacent to the one neutron conduit and are included in the plurality of neutron conduits. When exiting from the second opening of the conduit, the shortest distance that the neutron travels from the outer surface of the one neutron conduit to the outer surface of the other neutron conduit is between the plurality of neutron conduits. It is larger than the mean free path of the filled neutron absorber. Therefore, neutrons that enter the neutron conduit from the opening and travel to the neutron absorption region through the outer surface of the neutron conduit can be sufficiently attenuated in the neutron absorption region, and thus are emitted from the openings of other neutron conduits other than the neutron conduit. Can be suppressed.

  In the neutron radiography apparatus of the present invention, the plurality of neutron conduits include a neutron conduit having a first aperture diameter and a neutron conduit having a second aperture diameter, and the first aperture diameter is the first aperture diameter. 2 is different from the opening diameter. Therefore, since it has a plurality of collimating ratios, a plurality of collimating ratios can be used depending on the application.

  In the neutron radiography apparatus according to the present invention, the plurality of neutron conduits include a neutron conduit having a first conduit length and a neutron conduit having a second conduit length, and the first conduit length and the second conduit length. Is the length of the neutron conduit in the direction of the reference axis, and the first conduit length is different from the second conduit length. Therefore, since it has a plurality of collimating ratios, a plurality of collimating ratios can be used depending on the application.

  In the neutron radiography apparatus of the present invention, the plurality of neutron conduits are arranged in a hexagonal lattice shape when viewed from the direction of the reference axis. Accordingly, the plurality of neutron conduits can be densely arranged inside the housing. Therefore, the aperture ratio of the first surface of the multi-pinhole collimator on which the neutron beam is incident is improved.

  The neutron radiography apparatus of the present invention further includes a volume neutron source, the volume neutron source includes an exit surface that emits neutrons, the first surface faces the exit surface, and the reference axis As seen from the incident direction of the neutron beam along, the exit surface overlaps the first surface. Therefore, the observation object can be irradiated with the neutron beam 8 having a large diameter without extending the length of the neutron conduit.

  According to the present invention, it is possible to provide a neutron radiography apparatus capable of both reducing the scale of the apparatus, improving the spatial resolution, and improving the irradiation field.

It is a figure which shows the structure of the neutron radiography apparatus 1 which concerns on embodiment. It is a figure which shows the structure of the multi-pinhole collimator which concerns on embodiment. It is a figure for demonstrating the neutron absorber which concerns on embodiment. It is a figure which shows the cross-sectional structure of the multipin hole collimator which concerns on embodiment. It is a figure which shows two numerical formulas used in order to prescribe | regulate the structure of the multi-pinhole collimator which concerns on embodiment. It is a figure which shows the structure of the modification of the multi-pinhole collimator which concerns on embodiment. It is a figure which shows the structure of the modification of the multi-pinhole collimator which concerns on embodiment. It is a rocking curve showing the result of having simulated the transmittance of an example.

  Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the drawings. In the description of the drawings, if possible, the same elements are denoted by the same reference numerals, and redundant description is omitted. FIG. 1 is a diagram illustrating a configuration of a neutron radiography apparatus 1 according to the embodiment. The neutron radiography apparatus 1 includes a volume neutron source 2, a multi-pinhole collimator 3, an image detection apparatus 4, a metal filter 5, and a shield 6. The volume neutron source 2 includes an emission surface 2a. The multi-pinhole collimator 3 includes a housing 3a. The housing 3a includes a main surface 3b and a surface 3c. The neutron radiography apparatus 1 captures a transmission image of the observation object 7 using the neutron beam 8. The neutrons of the neutron beam 8 are neutrons having a thermal kinetic energy equal to or lower than the thermal kinetic energy of thermal neutrons (approximately 0.025 eV or lower), and are hereinafter referred to as thermal neutrons.

  The volume neutron source 2 emits the neutron beam 8 from the emission surface 2a. The emission surface 2a, the metal filter 5, the main surface 3b, the surface 3c, the observation object 7, and the image detection device 4 are arranged in this order along the reference axis Ax. The emission surface 2a, the main surface 3b, and the surface 3c are orthogonal to the reference axis Ax. The main surface 3b faces the emission surface 2a. The exit surface 2a overlaps the main surface 3b when viewed from the incident direction of the neutron beam 8 along the reference axis Ax. The reference axis Ax extends along the traveling direction of the neutron beam 8 emitted from the emission surface 2a. The volume neutron source 2 includes a pool filled with, for example, heavy water and light water. The volume neutron source 2 decelerates fast neutrons using a pool and generates a neutron beam 8. Fast neutrons enter the volume neutron source 2 from, for example, a nuclear reactor or an accelerator. The multi-pinhole collimator 3 collimates the neutron beam 8. The image detection device 4 receives the collimated neutron beam 8 emitted from the multi-pinhole collimator 3 via the observation object 7. The image detection device 4 captures a transmission image of the observation object 7 as a two-dimensional image with the neutron beam 8. The metal filter 5 is provided between the emission surface 2 a of the volume neutron source 2 and the main surface 3 b of the multi-pinhole collimator 3. The metal filter 5 shields γ rays (for example, γ rays emitted from the volume neutron source 2). The energy of γ rays incident on the multi-pinhole collimator 3 is reduced by the metal filter 5. The shield 6 shields radiation (radiation other than γ rays) emitted from the volume neutron source 2. The shield 6 reduces the energy of radiation incident on the multi-pinhole collimator 3.

  FIG. 2 is a diagram showing a configuration of the multi-pinhole collimator 3. The multi-pinhole collimator 3 is a straight tube type neutron collimator. The multi-pinhole collimator 3 includes a housing 3a. The housing 3a includes a main surface 3b and a surface 3c. The main surface 3b is on the opposite side of the surface 3c. The main surface 3b and the surface 3c are arranged so as to be orthogonal to the reference axis Ax. The reference axis Ax extends along the incident direction of the neutron beam 8. The housing 3a includes a plurality of neutron conduits 9. The housing 3a holds a plurality of neutron conduits 9. The housing 3 a includes a neutron absorption region 10. The plurality of neutron conduits 9 are arranged in a hexagonal lattice shape as viewed from the direction of the reference axis Ax inside the housing 3a.

  The neutron conduit 9 has a hollow pipe shape (cylindrical shape). The neutron conduit 9 includes an opening Ap1a and an opening Ap1b. The shape of the opening Ap1a is the same as the shape of the opening Ap1b. The opening Ap1a is on the opposite side of the opening Ap1b. The opening Ap1a is provided at one end of the neutron conduit 9 in the longitudinal direction. The opening Ap1b is provided at the other end of the neutron conduit 9 in the longitudinal direction. The neutron conduit 9 extends between the main surface 3b and the surface 3c. The plurality of neutron conduits 9 are arranged in parallel to each other along the reference axis Ax inside the housing 3a. Opening Ap1a is provided in main surface 3b. The main surface 3b is provided with a plurality of openings Ap1a. The opening Ap1b is provided in the surface 3c. A plurality of openings Ap1b are provided in the surface 3c. The neutron beam 8 is incident from the aperture Ap1a, travels inside the neutron conduit 9, and is emitted from the aperture Ap1b.

The neutron conduit 9 is made of a material such as SUS and glass. The material of the neutron conduit 9 transmits neutrons and shields charged particles such as electrons (e ⁻ ) and α rays. SUS and glass transmit neutrons and shield charged particles such as electrons and α rays.

  The collimating ratio of the neutron conduit 9 is the collimating ratio of the multi-pinhole collimator 3. The collimating ratio of the neutron conduit 9 is a value obtained by dividing the length of the neutron conduit 9 in the direction of the reference axis Ax (conduit length Va4 shown in FIG. 4) by the opening diameter of the neutron conduit 9 (opening diameter Va2 shown in FIG. 4). It is. The collimating ratio of the neutron conduit 9 is, for example, 50 or more and 2000 or less. The spatial resolution of the multi-pinhole collimator 3 is the spatial resolution of the neutron conduit 9, and the spatial resolution of the neutron conduit 9 is defined by the collimating ratio of the neutron conduit 9.

  The neutron absorption region 10 occupies between the inner wall surface 3d of the housing 3a and the outer surface 9a of the neutron conduit 9. The neutron absorption region 10 is filled with a neutron absorber. The neutron absorber contains any of Gd, B, and Li. The neutron absorber can be any nanopowder of Gd, B, Li (particle powder having a particle size of less than 100 nm). The neutron absorber may be a resin in which any nanopowder of Gd, B, and Li is mixed. The neutron absorbing material is filled without gaps in the neutron absorption region 10 between the inner wall surface 3d and the outer surfaces 9a of the plurality of neutron conduits 9. The distance between two adjacent neutron conduits 9 is sufficiently wider than the particle size of the nanopowder of the neutron absorber.

  As shown in FIG. 3, the reaction cross section of Gd, B, Li and thermal neutrons or the like (neutrons having thermal kinetic energy equal to or lower than that of thermal neutrons, the same applies hereinafter) is relatively large. The reaction cross section shown in FIG. 3 is a reaction cross section with thermal neutrons or the like. FIG. 3 also shows reaction cross sections of Sm and Cd with thermal neutrons and the like. The nuclear reaction between each of Sm and Cd and thermal neutrons generates γ rays. The nuclear reaction between each of Gd, B, Li and thermal neutrons generates charged particles such as electrons and α rays, and does not generate γ rays. The material of the neutron conduit 9 is SUS, glass, and the like. Since SUS, glass, and the like can shield charged particles such as electrons and α rays as compared with γ rays, the neutron absorber is Gd, B , Li is appropriate, and Sm, CD is inappropriate.

FIG. 4 is a diagram showing a main part of a cross section of the multi-pinhole collimator 3 taken along the line II shown in FIG. The length of the outer diameter Va1 of the neutron conduit 9 is “D1”. The length of the opening diameter Va2 of the neutron conduit 9 (the inner diameter of the neutron conduit 9) is “D2”. The neutron absorption region 10 between one neutron conduit 9 (particularly neutron conduit 9_1 in FIG. 4) and another neutron conduit 9 adjacent to the neutron conduit 9_1 (particularly neutron conduit 9_2 in FIG. 4). The size of the thickness V3 (the distance between the outer surface 9a of the neutron conduit 9_1 and the outer surface 9a of the neutron conduit 9_2) is “d”. The length of the neutron conduit 9 with respect to the length Va4 (the length in the longitudinal direction of the neutron conduit 9 and also the length in the direction of the reference axis Ax of the neutron conduit 9) is set to “L”. When neutrons incident from the aperture Ap1a of the neutron conduit 9_1 exit from the aperture Ap1b of the neutron conduit 9_2 along the direction Dir, the neutrons reach from the outer surface 9a of the neutron conduit 9_1 to the outer surface 9a of the neutron conduit 9_2. “X” is the length of the shortest distance Va5 along the direction Dir. The atomic density (cm ⁻³ ) of Gd, B, Li of the neutron absorber filled in the neutron absorption region 10 is “n”. The neutron reaction cross section (barn) of the neutron absorber filled in the neutron absorption region 10 is defined as “σ”.

  Equation 1 shown in FIG. 5 indicates that when thermal neutrons (neutron beam 8) incident on the neutron conduit 9_1 from the opening Ap1a proceed to the neutron absorption region 10 via the outer surface 9a of the neutron conduit 9_1, Is a condition for sufficient absorption by the neutron absorption region 10. The left side of Formula 1 is the length “x” of the shortest distance Va5, and the right side of Formula 1 is the mean free path of the neutron absorber in the neutron absorption region 10.

  The conditions defined by Equation 1 are described below. That is, when thermal neutrons or the like (neutron beam 8) incident from the aperture Ap1a of the neutron conduit 9_1 exit from the aperture Ap1b of the neutron conduit 9_2 along the direction Dir, the outer surface 9a of the neutron conduit 9_1 exits the neutron conduit 9_2. The shortest distance Va5 in which the thermal neutrons or the like travel along the direction Dir up to the side surface 9a is larger than the mean free path of the neutron absorber filled between the plurality of neutron conduits 9 (the above formula 1).

  If the condition of Formula 1 is satisfied, thermal neutrons that enter the neutron conduit 9_1 from the opening Ap1a and proceed to the neutron absorption region 10 through the outer surface 9a of the neutron conduit 9_1 are other neutron conduits other than the neutron conduit 9_1. 9 can be prevented from being emitted from the aperture Ap1b.

  Equation 2 in FIG. 5 defines the aperture ratio R of the main surface 3b. The aperture ratio R is a ratio (%) of the total value S2 of the areas of the plurality of openings Ap1a provided on the main surface 3b to the entire area S1 of the main surface 3b (R = (S2 / S1) × 100). . By providing a lower limit for the aperture ratio R, an upper limit value of the outer diameter Va1 (in other words, the thickness of the wall of the neutron conduit 9) when the opening diameter Va2 and the thickness V3 are constant is defined. The thickness of the wall of the neutron conduit 9 is a value obtained by subtracting the length of the opening diameter Va2 from the length of the outer diameter Va1 (D1-D2) / 2. The thickness of the wall of the neutron conduit 9 is equal to or less than the upper limit value defined by Equation 2, and is thin enough to sufficiently transmit neutrons. The lower limit of the wall thickness of the neutron conduit 9 is the thickness necessary to ensure straightness and rigidity, and the charged particles incident from the neutron absorption region 10 are shielded to reduce noise, and the S for the image detection device 4 is reduced. In order to improve the / N ratio, it is a value that does not exceed the smallest value among the thicknesses required for the energy of the charged particles incident on the wall of the neutron conduit 9 to sufficiently attenuate within the wall.

  For example, if the lower limit of the aperture ratio R is 40%, the length of the aperture diameter Va2 is 500 μm, and the thickness V3 is 100 μm, the upper limit of the length of the outer diameter Va1 is 653 μm, and the wall of the neutron conduit 9 The upper limit of the thickness is (653-500) /2=76.5 μm.

The thickness required for the energy of charged particles incident on the wall of the neutron conduit 9 to sufficiently attenuate within the wall is defined by the average range in the wall of the neutron conduit 9. For example, when the material of the wall of the neutron conduit 9 is SUS, the average energy of α particles and Li ions generated by the nuclear reaction of ¹⁰ B (n, α) ⁷ Li is about 0.8 MeV and 2,74 MeV, respectively. The average ranges of α particles and Li ions generated in this nuclear reaction in SUS are about 1.4 μm and 2.8 μm, respectively.
¹⁵⁷ Gd (n, e ⁻ ) The average energy of electrons (e ⁻ ) generated by the nuclear reaction of ¹⁵⁸ Gd is about 70 keV, and the average range of electrons (e−) generated by this nuclear reaction in SUS Is on the order of 10 μm.

  Since the surface of SUS or glass has relatively little unevenness (because it is smooth), when SUS or glass is used as the material of the neutron conduit 9, the reflectance of thermal neutrons incident on the neutron conduit 9 is relatively high. Very expensive.

  As described above, since the multi-pinhole collimator 3 includes a plurality of neutron conduits 9, in order to realize a suitable collimation ratio, the conduit length Va4 of the neutron conduit 9 is made relatively short and the opening diameter Va2 is made relatively. Even if it is shortened, the irradiation field and neutron utilization efficiency can be increased by increasing the number of neutron conduits 9. Therefore, a suitable spatial resolution can be realized by a suitable collimating ratio, and the irradiation field and neutron utilization efficiency can be increased by providing a plurality of neutron conduits 9. Furthermore, even if the conduit length Va4 is shortened, if the opening diameter Va2 is also shortened, a suitable collimating ratio can be maintained, so that the scale of the multi-pinhole collimator 3 can be reduced while maintaining a relatively high spatial resolution, thereby reducing cost. Is also possible. Furthermore, the neutron absorber includes any of Gd, B, and Li. Each of Gd, B, and Li has a relatively large reaction cross section with thermal neutrons or the like (neutrons with thermal kinetic energy of 0.025 eV or less). Therefore, in the multi-pinhole collimator 3, the thermal kinetic energy such as thermal neutrons traveling in a location different from the inside of the neutron conduit 9 can be sufficiently reduced by the neutron absorber. Further, the plurality of neutron conduits 9 are arranged in a hexagonal lattice shape when viewed from the direction of the reference axis Ax. Accordingly, the plurality of neutron conduits 9 can be densely arranged inside the housing 3a. Therefore, the aperture ratio R of the main surface 3b of the multi-pinhole collimator 3 on which the neutron beam 8 is incident is improved. Further, the main surface 3b faces the emission surface 2a, and the main surface 3b overlaps the emission surface 2a when viewed from the incident direction of the neutron beam 8 along the reference axis Ax. Accordingly, the metal filter 5 can be irradiated with the large-diameter neutron beam 8 without extending the conduit length Va4 of the neutron conduit 9.

  An example of a specific configuration of the multi-pinhole collimator 3 is shown. If the thickness of the observation object is “k”, the geometric blur of the image due to the spread of the neutron beam 8 is expressed by k / (L / D) using the collimate ratio. That is, when it is desired to observe an object having a thickness of 1 cm with a spatial resolution of 10 μm, a collimation ratio L / D = 1000 is required. In order to satisfy such a condition, for example, the neutron conduit 9 having the opening diameter Va2 having a length D2 of 50 μm, the outer diameter Va1 having a length D1 of 100 μm, and a conduit length Va4 having a length of 5 cm is spaced at an interval of 2 mm. Arranged in a hexagonal close-packed structure and filled with neutron absorbers of gadolinium oxide between the neutron conduits 9 (for example, this can be realized by applying a gadolinium oxide coating with a thickness of about 1 mm to each neutron conduit 9 and then bundling it. .) In the multi-pinhole collimator 3 having this configuration, the aperture ratio R = 31% and the collimating ratio L / D = 1000.

  FIG. 6 shows the configuration of the multi-pinhole collimator 31. The multi-pinhole collimator 31 is a modification of the multi-pinhole collimator 3. The multi-pinhole collimator 31 has two different collimating ratios. The multi-pinhole collimator 31 includes a housing 3a1, a neutron conduit 91, a neutron conduit 92, and a neutron absorption region 10. The housing 3a1 includes a main surface 3b1. Main surface 3b1 corresponds to main surface 3b. Main surface 3b1 includes first region 3b1a and second region 3b1b. The neutron absorption region 10 of the multi-pinhole collimator 31 is the same as the neutron absorption region 10 of the multi-pinhole collimator 3. The materials of the housing 3a1, the neutron conduit 91, and the neutron conduit 92 are the same as the materials of the housing 3a and the neutron conduit 9, respectively. The neutron conduit 91 has an aperture Ap2, and the neutron conduit 92 has an aperture Ap3. The inner diameter of the opening Ap2 is different from the inner diameter of the opening Ap3. The outer diameter of the opening Ap2 is different from the outer diameter of the opening Ap3. That is, the housing 3a1 holds a plurality of types of neutron conduits having different opening shapes. In the first region 3b1a, an opening Ap2 of the neutron conduit 91 is provided. In the second region 3b1b, an opening Ap3 of the neutron conduit 92 is provided. The length of the neutron conduit 91 is the same as the length of the neutron conduit 92. The conduit length of the neutron conduit 91 and the conduit length of the neutron conduit 92 may be different as shown in FIG. Since the multi-pinhole collimator 31 has a plurality of collimating ratios, a plurality of collimating ratios can be used depending on the application.

  FIG. 7 shows the configuration of the multi-pinhole collimator 32. FIG. 7 shows a configuration viewed from a cross section of the multi-pinhole collimator 32 along the reference axis Ax. The multi-pinhole collimator 32 is another modification of the multi-pinhole collimator 3. Multi-pinhole collimator 32 has two different collimating ratios. The multi-pinhole collimator 32 includes a housing 3 a 2, a neutron conduit 93, a neutron conduit 94, and a neutron absorption region 10. The housing 3a2 includes a main surface 3b1 and a surface 3c1. Main surface 3b1 corresponds to main surface 3b. The surface 3c1 corresponds to the surface 3c. Main surface 3b1 includes first region 3b1a and second region 3b1b. The surface 3c1 includes a first region 3c1a and a second region 3c1b. The surface 3c1 has a step. The first region 3c1a and the second region 3c1b are not arranged on the same plane. The first region 3c1a is parallel to the second region 3c1b. The neutron absorption region 10 of the multi-pinhole collimator 32 is the same as the neutron absorption region 10 of the multi-pinhole collimator 3. The materials of the housing 3a2, the neutron conduit 93, and the neutron conduit 94 are the same as the materials of the housing 3a and the neutron conduit 9, respectively. The length of the neutron conduit 93 is longer than the length of the neutron conduit 94. That is, the housing 3a2 holds a plurality of types of neutron conduits having different conduit lengths. In the first region 3b1a and the first region 3c1a, an opening of a neutron conduit 93 is provided. In the second region 3b1b and the second region 3c1b, an opening of the neutron conduit 94 is provided. The opening diameter of the neutron conduit 93 is the same as the opening diameter of the neutron conduit 94. The opening diameter of the neutron conduit 93 and the opening diameter of the neutron conduit 94 may be different as shown in FIG. Since the multi-pinhole collimator 31 has a plurality of collimating ratios, a plurality of collimating ratios can be used depending on the application.

(Example) FIG. 8 shows a simulation result (rocking curve) of the transmittance (number of transmitted neutrons / number of incident neutrons) of an example of the multi-pinhole collimator 3. In the embodiment, the length D1 of the outer diameter Va1 is 500 μm, the length D2 of the opening diameter Va2 is 400 mm, the length L of the conduit length Va4 is 50 mm, and the thickness d of the thickness V3 is 130 μm. . In the embodiment, the neutron absorber is a material in which Gd is mixed with a resin at a volume ratio of 1:10. The horizontal axis shown in FIG. 8 represents the angle (deg) between the neutron beam 8 and the main surface 3b of the example. The vertical axis shown in FIG. 8 represents the transmittance of the embodiment with respect to the neutron beam 8. According to the rocking curve shown in FIG. 8, the transmittance is highest when the incident angle of the neutron beam 8 on the main surface 3b of the embodiment is vertical (90 degrees). The transmittance decreases as the incident angle of the neutron beam 8 with respect to 3b of the example shifts from the vertical.

  While the principles of the invention have been illustrated and described in the preferred embodiments, it will be appreciated by those skilled in the art that the invention can be modified in arrangement and detail without departing from such principles. The present invention is not limited to the specific configuration disclosed in the present embodiment. We therefore claim all modifications and changes that come within the scope and spirit of the following claims.

DESCRIPTION OF SYMBOLS 1 ... Neutron radiography apparatus, 10 ... Neutron absorption area, 2 ... Volume neutron source, 2a ... Outgoing surface, 3, 31, 32 ... Multi-pinhole collimator, 3a, 3a1, 3a2 ... Housing, 3b, 3b1 ... Main surface 3b1a, 3c1a ... first region, 3b1b, 3c1b ... second region, 3c, 3c1 ... surface, 3d ... inner wall surface, 4 ... image detection device, 5 ... metal filter, 6 ... shield, 7 ... observation object, 8 ... Neutron beam, 9, 91, 92, 93, 94, 9_1, 9_2 ... Neutron conduit, 9a ... Outer surface, Ap1a, Ap1b, Ap2, Ap3 ... Opening, Ax ... Reference axis, Dir ... Direction, Va1 ... Outer diameter Va2 ... opening diameter, V3 ... thickness, Va4 ... conduit length, Va5 ... shortest distance.

Claims (6)

A neutron radiography device,
Equipped with multi-pinhole collimator,
The multi-pinhole collimator is
A plurality of neutron conduits;
A housing holding the plurality of neutron conduits;
A neutron absorption region,
With
The housing includes a first surface and a second surface,
The first surface and the second surface are arranged so as to be orthogonal to a reference axis extending along the incident direction of the neutron beam,
The first surface is opposite the second surface;
Each of the plurality of neutron conduits has a hollow pipe shape, includes a first opening and a second opening, extends between the first surface and the second surface, and the reference Arranged parallel to each other along the axis,
The first opening is provided in the first surface;
The second opening is provided in the second surface;
The neutron absorption region occupies between the inner wall surface of the housing and the outer surface of the plurality of neutron conduits,
The neutron absorption region is filled with a neutron absorber,
The neutron absorber includes any of Gd, B, and Li.
Neutron radiography equipment. Neutrons incident from a first opening of one neutron conduit included in the plurality of neutron conduits exit from a second opening of another neutron conduit adjacent to the one neutron conduit and included in the plurality of neutron conduits. In this case, the shortest distance that the neutron travels from the outer surface of the one neutron conduit to the outer surface of the other neutron conduit is that of the neutron absorber filled between the plurality of neutron conduits. Greater than the mean free path,
The neutron radiography apparatus according to claim 1. The plurality of neutron conduits includes a neutron conduit having a first aperture diameter and a neutron conduit having a second aperture diameter,
The first opening diameter is different from the second opening diameter.
The neutron radiography apparatus according to claim 1 or 2, characterized in that The plurality of neutron conduits comprises a neutron conduit having a first conduit length and a neutron conduit having a second conduit length;
The first conduit length and the second conduit length are neutron conduit lengths in the direction of the reference axis;
The first conduit length is different from the second conduit length;
The neutron radiography apparatus according to any one of claims 1 to 3. The plurality of neutron conduits are arranged in a hexagonal lattice as viewed from the direction of the reference axis.
The neutron radiography apparatus according to any one of claims 1 to 4, wherein A volume neutron source;
The volume neutron source includes an exit surface for emitting neutrons,
The first surface faces the exit surface;
When viewed from the incident direction of the neutron beam along the reference axis, the emission surface overlaps the first surface.
The neutron radiography apparatus according to any one of claims 1 to 5, wherein

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