JP7166121B2 - Neutron detection unit, non-destructive inspection system, neutron collimator - Google Patents

Description

The present invention relates to a neutron detection unit, a nondestructive inspection system, and a neutron collimator for nondestructive inspection of an object to be inspected using neutrons.

Conventionally, by using radiation such as neutrons, which have high penetrability for inspected objects such as concrete, non-destructive inspections that can analyze the internal structure without destroying the inspected objects have been performed. .

In non-destructive inspection, high spatial resolution is required to accurately know information such as the position of defective parts (e.g., water, voids, etc.) of the object to be inspected. It is necessary to ensure the parallelism of the neutrons to be emitted.

Therefore, for example, Patent Document 1 discloses a configuration in which a collimator (multi-pinhole collimator) is provided between a neutron source (volume neutron source) and a detection unit (image detection device) in order to improve spatial resolution. there is The collimator of Patent Document 1 is arranged between the neutron source and the object to be inspected (object to be observed) to regulate the direction of neutrons irradiated to the object to ensure parallelism. .

JP 2014-81209 A

However, in the technique of Patent Document 1, the neutrons before being irradiated to the object to be inspected are regulated, and the parallelism of the neutrons irradiated to the object to be inspected is secured, but the neutrons passing through the object to be inspected are detected. There is a problem that the parallelism of neutrons incident on the device is not always ensured.

In particular, in non-destructive testing, in which the object is irradiated with fast neutrons and the thermal neutrons emitted from the object are detected, the thermal neutrons scatter from the object and are not irradiated onto the object. Parallelism of thermal neutrons cannot be obtained even if the fast neutrons are regulated by a collimator.

If the parallelism of the neutrons incident on the detector cannot be obtained in this way, the S/N ratio (signal-to-noise ratio) and spatial resolution of the detector are lowered, and inspection accuracy cannot be obtained.

The present invention has been made to solve such problems, and its object is to improve the S/N ratio and spatial resolution of neutron detection in non-destructive inspection using neutrons. Another object of the present invention is to provide a neutron detection unit, a non-destructive inspection system, and a neutron collimator capable of realizing more accurate inspection.

In order to achieve the above object, a neutron detection unit according to the present invention has a plurality of through passages extending in the same direction, and a wall material forming the through passages is made of a material that transmits fast neutrons and absorbs thermal neutrons. and a neutron detector capable of detecting thermal neutrons from an object to be inspected. They are arranged in contact with each other or with a distance shorter than the passage length of the through passage from the detection surface.

In the neutron detection unit described above, the wall material may contain at least cadmium or boron.

Further, in the above-described neutron detection unit, the neutron detection section has a plurality of detection elements arranged vertically and horizontally on the detection surface, and the collimator is formed in a plurality vertically and horizontally on the surface facing the detection surface where the through path faces the detection surface. may have been

Further, in the neutron detection unit described above, the wall material of the collimator may be formed so that the through passage has a circular cross section.

Alternatively, in the neutron detection unit described above, the wall material of the collimator may be formed so that the through passages form a honeycomb structure.

Alternatively, in the neutron detection unit described above, the wall material of the collimator is formed such that the cross-sectional shape of the through passage is the same as the detection surfaces of the detection elements of the neutron detection unit, and the arrangement corresponds to the arrangement of the detection elements. may be

In order to achieve the above object, a nondestructive inspection system according to the present invention includes the above-described neutron detection unit and a neutron source capable of irradiating fast neutrons, wherein the neutron detection unit comprises the neutron source and the subject. It is arranged between the object to be inspected and directs the detection surface toward the object to be inspected.

The nondestructive inspection system may further include a support section that supports the neutron detection unit such that the direction of the detection surface can be changed.

In order to achieve the above object, a neutron collimator according to the present invention has a plurality of through passages extending in the same direction, and the wall material forming the through passages is made of a material that transmits fast neutrons and absorbs thermal neutrons. consists of

According to the present invention using the above means, in non-destructive inspection using neutrons, the S/N ratio and spatial resolution of neutron detection can be improved, and more accurate inspection can be realized.

1 is a schematic configuration diagram of a nondestructive inspection system according to this embodiment; FIG. It is an exploded perspective view of a neutron detection unit according to the present embodiment. It is an enlarged view of a neutron detection unit portion. (a) A top view of FIG. 1, (b) A top view of a state in which the neutron detection unit is rotated from the state in FIG. It is an exploded perspective view showing (a) the 1st modification of a neutron detection unit, (b) the 2nd modification, and (c) the 3rd modification.

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, embodiments of the present invention will be described based on the drawings.

FIG. 1 shows a schematic configuration diagram of the non-destructive inspection system according to this embodiment, FIG. 2 shows an exploded perspective view of the neutron detection unit, and FIG. 3 shows an enlarged view of the neutron detection unit. The configuration of the non-destructive inspection system will be described based on the drawings.

A non-destructive inspection system 1 of this embodiment has a compact accelerator neutron source 2 , a neutron detection unit 3 , and a support section 4 that supports the neutron detection unit 3 . Further, the object to be inspected O to be inspected is located on the back side of the neutron detection unit 3 with respect to the compact accelerator neutron source 2 . The object to be inspected O in this embodiment is assumed to be a concrete block.

The compact accelerator neutron source 2 is a neutron source that generates and irradiates neutrons, and has a power source section 10 , a linear accelerator 11 , a target station 12 and an irradiation section 13 .

Specifically, the power supply unit 10 is a high-voltage power supply that supplies power to the accelerator. The high-voltage power supply of the power supply unit 10 preferably has power generation performance capable of accelerating at least protons to the energy necessary for generating neutrons, and has little voltage fluctuation.

The linear accelerator 11 has an ion source 11 a from which a cylindrical accelerator 11 b extends and is connected to the target station 12 .

The target station 12 is covered with a shield and has a neutron generation target (not shown) inside. The shield is made of a material that shields neutrons and gamma rays, such as boron-containing polyethylene or lead. The target is one that collides with protons to generate neutrons, such as beryllium (Be).

The irradiation unit 13 is formed of a shielding material such as polyethylene, for example, and is a portion that irradiates the object O to be inspected with fast neutrons Nf generated from the target.

The neutron detection unit 3 is composed of a neutron detector 20 and a collimator 30 .

As shown in FIG. 2, the neutron detection unit 20 is configured as one detector array 23 in which four square detection modules 22 are arranged on one surface of a rectangular parallelepiped detection unit main body 21 .

The detection module 22 is formed by arranging a plurality of square detection elements vertically and horizontally on the detection surface without gaps. The detection element does not have sensitivity to fast neutrons, but has sensitivity to thermal neutrons. The detection unit body 21 includes a power source, a control unit that controls the exposure time and exposure timing of the detection elements, and a signal processing unit that receives the detection signal of each detection element and calculates the coordinates in the detection plane and the neutron intensity. It is In other words, the neutron detection unit 20 can analyze the internal structure of the object to be inspected from information on thermal neutrons detected by each detection element. Although the neutron detection unit 20 in the present embodiment comprises the detector array 23 from four detection modules 22, the number of detection modules constituting the neutron detection unit is not limited to this, and may be, for example, one.

The collimator 30 has a plurality of through paths P extending in the same direction inside the housing 31 . Specifically, the housing 31 has a cubic shape, and the through passage P has a tubular shape with a circular cross section due to the wall material. In the collimator 30 of the present embodiment shown in FIG. 2, eight through-passages P are arranged in a row on the opening plane where the openings of the through-passages P are arranged. The wall material forming the housing 31 and the through passage P restricts thermal neutrons passing through the through passage P by being made of a material that transmits fast neutrons and absorbs thermal neutrons. Specific examples of materials for the wall material include cadmium (Cd), boron (B), gadolinium (Gd), samarium (Sm), europium (Eu), and dysprosium (Dy).

In order for the through passage P to have at least an opening diameter r shorter than the passage length L and an angle of incidence (acceptance angle) on the detection surface of the neutron detector 20 to be substantially perpendicular, the opening diameter r and the passage length ratio (r:L) is preferably about 1:50.

The collimator 30 is attached to the neutron detection section 20 in contact with the detection surface of the neutron detection section 20 so that the through path P is substantially perpendicular to the detection surface of the neutron detection section 20 . The collimator 30 is desirably in contact with the neutron detector 20, but may be positioned in the vicinity. In that case, the space between the collimator 30 and the neutron detector 20 needs to be shielded with a shielding material. Moreover, the distance between the collimator 30 and the neutron detector 20 may be set to be shorter than the passage length L of the through passage P from the detection surface of the neutron detector 20, for example.

Returning to FIG. 1 , the neutron detection unit 3 is supported by the support portion 4 . The support portion 4 extends from the target station 12 in the irradiation direction of the fast neutron beams Nf, and a rotating portion 4a that rotates in the horizontal direction is provided at the tip thereof. The neutron detection unit 3 is provided on the supporting portion 4 via the rotating portion 4a, and the orientation of the detection surface of the neutron detecting portion 20 can be changed by rotating the rotating portion 4a.

3 and 4, FIG. 3 is an enlarged view showing the neutron detection unit portion, FIG. 4 is (a) a top view of FIG. 1, and (b) the neutron detection unit is rotated from the state of FIG. A top view of the folded state is shown, and the operation and effect of this embodiment will be described below based on these figures.

The non-destructive inspection system 1, for example, collides protons with an energy of about 7 MeV generated by the linear accelerator 11 with beryllium in the target station 12 to generate fast neutrons with a maximum energy of about 5 MeV, and the fast neutrons through the irradiation unit 13. output line Nf.

As shown in FIG. 3, the fast neutron beams Nf pass through the neutron detection unit 3 and irradiate the object O to be inspected. When the fast neutron beams Nf pass through the object to be inspected O, the thermal neutron beams Ns are scattered. In particular, when the defect portion D in the object to be inspected O contains an element lighter than concrete such as water, the energy of the fast neutrons Nf is deprived of energy by the light element so that the defect D in the object to be inspected O is relatively relatively smaller than the other parts of the object to be inspected O. Many thermal neutrons are produced. On the other hand, if the defect portion D is a void, thermal neutrons Ns are not generated in that portion and are not scattered relatively. less.

The collimator 30 regulates the thermal neutrons Ns that have been scattered (so-called backscattering) in the direction opposite to the irradiation direction of the fast neutrons Nf from the object to be inspected O, and directs the thermal neutron beams substantially perpendicularly to the detection surface of the neutron detector 20. Only Ns is selectively passed. For example, in FIG. 3, in the collimator 30, only thermal neutrons Ns1 incident substantially perpendicularly to the detection surface pass through the through-path P among the thermal neutrons backscattered from the defect portion D. As shown in FIG. On the other hand, the thermal neutrons Ns2 and Ns3 that enter the collimator 30 at angles to the passage axis of the through passage are absorbed by the wall material.

As described above, the collimator 30 is provided between the object O to be inspected and the neutron detection unit 20, so that the thermal neutrons Ns scattered from the object to be inspected O are regulated and are substantially perpendicular to the detection surface. Only thermal neutrons directed toward That is, the parallelism of the thermal neutrons Ns is ensured, and the information on the position facing the detection surface can be accurately detected. In particular, the collimator 30 of the present embodiment is attached so that the opening surface where the openings of the through path P are arranged and the detection surface of the neutron detection unit 20 are in contact with each other, so that the thermal neutrons Ns passing through the collimator 30 are detected as they are. The parallelism of the thermal neutrons Ns can be ensured more reliably because they are incident on the plane.

From these, according to the neutron detection unit 3 and the non-destructive inspection system 1 using the neutron detection unit 3 in the present embodiment, the S / N ratio and spatial resolution of neutron detection can be improved, and higher accuracy inspection can be realized.

Moreover, the collimator 30 can easily form a structure that transmits fast neutrons Nf and absorbs thermal neutrons Ns by using cadmium or boron as the material of the wall material.

Further, a plurality of detection elements of the neutron detection unit 20 are arranged vertically and horizontally on the detection surface, and the collimator 30 also has a plurality of through paths P formed vertically and horizontally, so that the internal information of the object to be inspected O can be analyzed at least two-dimensionally. be able to.

In addition, the collimator can be easily formed by making the cross-section of the through passage circular as in the collimator 30 of the present embodiment.

Furthermore, since the neutron detection unit 3 is supported by the rotating portion 4a of the support portion 4, the direction of the detection surface can be changed in the horizontal direction, and the direction according to the shape of the object to be inspected O and the inspection point can be changed. inspection can be carried out.

For example, as shown in FIG. 4(a), when the object to be inspected O is placed in a posture perpendicular to the irradiation axis A of the fast neutrons Nf, the passage axis of the through path P of the collimator 30 is also parallel to the irradiation axis A. The neutron detection unit 3 may be positioned so as to form

On the other hand, as shown in FIG. 4B, when the object to be inspected O is arranged in an oblique posture with respect to the irradiation axis A of the fast neutrons Nf, the neutron detection unit 3 is moved to the right by the rotating portion 4a. It is rotated in the direction (clockwise when viewed in FIG. 4(b)) for positioning. As a result, the surface of the object to be inspected O can face the tip opening surface of the collimator 30 and the detection surface of the neutron detector 20 at a constant interval. Therefore, the detection surface can be oriented in an optimum direction according to the shape and posture of the object to be inspected, and highly accurate inspection can be performed regardless of the shape of the object to be inspected.

Although the description of the embodiment of the present invention is finished above, the aspect of the present invention is not limited to this embodiment.

Further, in the above-described embodiment, the object to be inspected O is described as a concrete block, but the object to be inspected is not limited to this. For example, as long as the neutron source is movable, a bridge pier, a floor plate of a bridge or a road, a wall of a tunnel, a pillar or floor of a building, or the like can be used as an object to be inspected. Moreover, the shape of the object to be inspected O is not limited to a cube, and the present invention can be applied to various shapes of objects to be inspected.

Further, although the neutron detection unit 3 of the above-described embodiment can only be horizontally rotated by the rotating portion 4a, the change of the direction of the detection surface of the neutron detection unit is not limited to this. For example, the neutron detection unit may be configured to be rotatable in the vertical direction, or may be configured to be capable of changing the orientation of the detection surface in six axial directions by being supported by a robot arm.

In addition, although the through passages P of the collimator 30 in the above-described embodiment have a circular cross section and are arranged vertically and horizontally on the opening surface, the dimensions, cross-sectional shape, number and arrangement of the through passages are not limited to this. do not have.

FIG. 5 shows exploded perspective views of (a) the first modification, (b) the second modification, and (c) the third modification of the neutron detection unit. A modification of is explained. Since the neutron detector is the same as that of the above-described embodiment, the same reference numerals are used and the description thereof is omitted.

In the neutron detection unit 3a of the first modified example shown in FIG. 5(a), the through passage Pa of the collimator 40 has a circular cross-section like the through passage P of the above embodiment, but has a large diameter. Only four through paths Pa are formed corresponding to the detection modules. If a sufficient length L of the through passage can be secured, the parallelism of thermal neutrons can be improved even with such a configuration. Moreover, since the structure of the collimator 40 is simplified, the processing cost can be reduced.

In the neutron detection unit 3b of the second modification shown in FIG. 5(b), the through passage Pb has a hexagonal cross section due to the wall material of the collimator 50, and the through passages Pb are arranged without gaps to form a so-called honeycomb structure. there is Thereby, the aperture area can be maximized while maintaining the strength of the neutron detection unit 3b.

In the neutron detection unit 3c of the third modification shown in FIG. 5(c), the wall material of the collimator 60 makes the cross-sectional shape of the through path Pc a rectangular shape that is the same shape as the detection surface of the detection element. The arrangement of the through paths Pc and the thickness of the wall material on the opening surface of the collimator 60 are also formed along the arrangement of the detector array 23, and one through path Pc corresponds to one detection element. is doing. With such a configuration, since the wall material of the collimator 60 does not block the detection surface of the detection element, more highly accurate inspection can be realized.

1 non-destructive inspection system 2 compact accelerator neutron source 3 neutron detection unit 10 power supply unit 11 linear accelerator 12 target station 13 irradiation unit 20 neutron detection unit 21 detection unit body 22 detection module 23 detector array 30, 40, 50, 60 collimator O Object to be inspected P Through passage

Claims (8)

A non-destructive inspection system comprising a neutron detection unit and a support that rotatably supports the neutron detection unit,
The neutron detection unit is
a collimator having a plurality of through passages extending in the same direction, and wall materials forming the through passages made of a material that transmits fast neutrons and absorbs thermal neutrons;
A neutron detection unit capable of detecting thermal neutrons from the object to be inspected,
The collimator is placed in contact with the detection surface of the neutron detection unit so that the through path is perpendicular to the detection surface, or is arranged with a distance between the detection surface and the through path that is shorter than the passage length of the through path. and
The collimator is attached to the neutron detector,
The non-destructive inspection system, wherein the support unit integrates the collimator and the neutron detection unit and is rotatable in a direction different from the irradiation direction of the fast neutrons . 2. The non- destructive inspection system according to claim 1, wherein the material of said wall material contains at least cadmium or boron. The neutron detection unit has a plurality of detection elements arranged vertically and horizontally on the detection surface,
3. The non- destructive inspection system according to claim 1, wherein the collimator has a plurality of through paths formed vertically and horizontally on a surface facing the detection surface. 4. The nondestructive inspection system according to any one of claims 1 to 3, wherein the wall material of the collimator is formed so that the through passage has a circular cross section. 4. The nondestructive inspection system according to any one of claims 1 to 3, wherein the wall material of the collimator is formed so that the through passages form a honeycomb structure. 4. The collimator wall material according to any one of claims 1 to 3, wherein the cross-sectional shape of the through passage is the same as the detection surface of the detection element of the neutron detection unit, and the wall material is formed so as to correspond to the arrangement of the detection elements. or the nondestructive inspection system according to item 1. It also has a neutron source that can irradiate fast neutrons,
7. The nondestructive inspection system according to any one of claims 1 to 6 , wherein the neutron detection unit is arranged between the neutron source and the inspection object, and directs the detection surface toward the inspection object. . 8. The nondestructive inspection system according to any one of claims 1 to 7 , wherein the support portion is rotatable so that the direction of the detection surface can be changed.

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