Non-destructive testing equipment and methods

Abstract

A nondestructive inspecting device (10) is provided with: a neutron radiating device (2) which radiates a neutron beam onto a localized irradiation site on a surface (1a) of an inspection target object (1); a detecting device (3) which detects scattered neutrons arriving back from the inspection target object (1) as a result of the irradiation of the neutron beam onto the irradiation site, at each detecting position facing the surface (1a), and measures the detected number of scattered neutrons at each detecting position; and a ratio calculating unit (5) which, for each detecting position, obtains the ratio of the detected number at each detected position to a reference value for the detecting position. The reference value is set for each detecting position, as the detected number for a case in which it is assumed that there are no defects in the inspection target object (1).

Description

[Technical Field]

[0001] The present invention relates to an apparatus and method for inspecting an object using a neutron beam, and more particularly to an apparatus and method for irradiating a neutron beam onto an object made of, for example, concrete or steel, and inspecting the object for the presence and type of defects based on the scattered neutrons that are scattered inside the object and returned. [Background technology]

[0002] Infrastructure structures (hereinafter referred to as infrastructure structures) such as airport runways, roads (e.g., expressways), tunnels, and bridges may develop defects due to their use and aging. For example, defects may occur inside infrastructure structures, such as water retention, iron rust, and cavities.

[0003] A technology for inspecting for the presence or absence of such defects using a neutron beam is disclosed in Patent Document 1. In Patent Document 1, a pulsed neutron beam is irradiated onto an inspection object such as an infrastructure structure, scattered neutrons that have scattered in the inspection object and returned are detected, detection number data is generated that represents the number of detected scattered neutrons over time, and the presence or absence of defects inside the inspection object is determined based on this detection number data. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] International Publication No. 2017 / 043581 Summary of the Invention [Problem to be solved by the invention]

[0005] Conventionally, it has been difficult to detect the presence or absence of small defects in an object being inspected. For example, it has been difficult to detect defects of a few millimeters in size (such as a 3 mm void or a 6 mm water-logged area) that have occurred inside the object being inspected.

[0006] Therefore, an object of the present invention is to enable detection of even small defects (for example, defects of about 3 mm) in non-destructive testing of an object to be tested. [Means for solving the problem]

[0007] In order to achieve the above object, a non-destructive inspection device according to the present invention comprises: a neutron irradiation device that irradiates a local irradiation spot on the surface of an object to be inspected with a neutron beam; a detection device that detects scattered neutrons returning from the inspection object as a result of irradiating the irradiation point with the neutron beam at each detection position facing the surface and counts the number of scattered neutrons detected at each detection position; a ratio calculation unit that calculates and outputs a ratio of the number of detections at each detection position to a reference value for the detection position, The reference value is set for each detection position as the number of detections that would occur if it were assumed that no defects existed in the object to be inspected.

[0008] In addition, in the non-destructive inspection method according to the present invention, (A) Irradiating a localized irradiation spot on the surface of the object to be inspected with a neutron beam; (B) detecting scattered neutrons returning from the object to be inspected as a result of (A) at each detection position facing the surface, and counting the number of scattered neutrons detected at each detection position; (C) for each detection position, a ratio calculation unit calculates and outputs a ratio of the number of detections at the detection position to a reference value for the detection position; The reference value is set for each detection position as the number of detections that would occur if it were assumed that no defects existed in the object to be inspected. [Effects of the Invention]

[0009] According to the present invention, a neutron beam is irradiated onto a local irradiation spot on the surface of an object to be inspected, and as a result, when scattered neutrons return from the object to be inspected, the scattered neutrons are detected at each detection position facing the surface of the object to count the number of detected scattered neutrons for each detection position. Also, for each detection position, the ratio of the number of detected scattered neutrons at that detection position to a reference value for that detection position is calculated.

[0010] Even if a defect in the inspection object is small, the defect will cause one or both of an increasing peak and a decreasing peak in the ratio in the distribution of the ratios for the detection positions, so that even if the defect in the inspection object is small, it is possible to detect the presence or absence of the defect based on the ratios for each detection position. [Brief explanation of the drawings]

[0011] [Figure 1A] 1 shows the configuration of a non-destructive inspection device according to an embodiment of the present invention. [Figure 1B] FIG. 1B is a view taken along the arrows 1B-1B in FIG. 1A. [Figure 2A-2B] 10A and 10B show a schematic diagram of a ratio distribution obtained when a low-density portion (for example, a void) exists inside the object to be inspected. [Figures 2C-2D] The figure shows a schematic diagram of the ratio distribution obtained when there is a water-stagnation area inside the object to be inspected. [Figure 3] 1 is an explanatory diagram of determining the presence or absence and type of a defect in an inspection object; [Figure 4] 1 is a flowchart illustrating a non-destructive inspection method according to an embodiment of the present invention. [Figure 5A] 2 shows a cross section of an object to be inspected in Example 1. [Figure 5B] FIG. 5B is a view taken along the arrows 5B-5B in FIG. 5A. [Figure 5C] The dimensions of each part in FIG. 5A are shown below. [Figure 6A] 1 shows a two-dimensional distribution of reference values ​​when thermal neutrons are selectively detected in Example 1. [Figure 6B]1 shows a one-dimensional distribution of reference values ​​when thermal neutrons are selectively detected in Example 1. [Figure 7A] 1 shows a two-dimensional distribution of the ratio on the detection surface when thermal neutrons are selectively detected in Example 1. [Figure 7B] 1 shows a two-dimensional distribution of the ratio on the detection surface when intermediate neutrons are selectively detected in Example 1. [Figure 8] 1 shows the test results in Example 1. [Figure 9A] 10 shows a cross section of an object to be inspected in Example 2. [Figure 9B] FIG. 9B is a view taken along the arrows 9B-9B in FIG. 9A. [Figure 10] 10 shows the two-dimensional distribution of the ratio on the detection surface when the defect is a void in Example 2. [Figure 11] 10 shows the distribution of the ratio in the x-axis direction on the detection surface when the defect is a void in Example 2. [Figure 12] 1 shows the value of Sp / Sn obtained by beam scanning when the defect is a void in Example 2. [Figure 13] 10 shows a two-dimensional distribution of the ratio on the detection surface when the defect is water in Example 2. [Figure 14] 10 shows the distribution of the ratio in the x-axis direction on the detection surface when the defect is water in Example 2. [Figure 15] 1 shows the Sn / Sp value obtained by beam scanning when the defect is water in Example 2. DETAILED DESCRIPTION OF THE INVENTION

[0012] An embodiment of the present invention will be described with reference to the drawings. In addition, common parts in each drawing are given the same reference numerals, and duplicated explanations will be omitted.

[0013] (Configuration of non-destructive testing equipment) Fig. 1A shows a schematic diagram of a nondestructive inspection device 10 according to an embodiment of the present invention. Fig. 1B is a view taken along the line 1B-1B in Fig. 1A. The nondestructive inspection device 10 irradiates an inspection object 1 with a neutron beam, detects scattered neutrons returning from the inspection object 1, and detects the presence and type of defects based on the detection results.

[0014] The inspection object 1 may be the above-mentioned infrastructure structure or another structure. For example, the inspection object 1 may be a structure including, as components, one or both of concrete and metal components such as steel members (e.g., multiple or many metal members). In the case of an inspection object 1 including such a component or another component, the inspection object 1 may include an organic material made of polyethylene. One example of this organic material is a waterproof sheet or a sheath for an optical fiber cable provided within the inspection object 1 (e.g., a structure forming the road surface).

[0015] The non-destructive inspection device 10 includes a neutron irradiation device 2, a detection device 3, a ratio calculation unit 5, a data processing unit 7, a judgment value calculation unit 8, and a judgment unit 9.

[0016] The neutron irradiation device 2 irradiates a local irradiation area R on the surface 1a of the inspection object 1 with a neutron beam (substantially only at the irradiation area R). The irradiation area R may be an irradiation spot. The shape of the irradiation area R may be, for example, a circle, an ellipse, or a rectangle, but is not limited to these.

[0017] The dimension of the irradiation area R may be 100 mm or less, 70 mm or less, or 50 mm or less. There is no particular lower limit to the dimension of the irradiation area R, but it may be as small as possible (for example, the lower limit may be a value in the range of 0.3 mm or more and 10 mm or less). The dimension of the irradiation area R is the dimension of the cross section of the neutron beam on the surface 1a. Furthermore, the dimension of the irradiation area R may mean the smallest dimension of the cross section of the neutron beam on the surface 1a in each direction.

[0018] The neutron irradiation device 2 has a neutron source 2a that emits neutrons and a collimator 2b.

[0019] In one example, the neutron source 2a may have a target that emits neutrons when irradiated with a charged particle beam. In this case, the target may be, but is not limited to, lithium. In another example, the neutron source 2a may be a portable DD nuclear fusion reaction neutron source (DD tube). In yet another example, the neutron source 2a may be a radioactive source (RI (radioactive isotope) source) that emits neutrons. In this case, the radioactive source is , 252 It may be, but is not limited to, Cf.

[0020] The collimator 2b shapes the neutrons from the neutron source 2a into a neutron beam with a narrowed cross section. By narrowing the cross section of the neutron beam in this way, the neutron beam is irradiated onto a local irradiation spot R on the surface 1a.

[0021] The collimator 2b may be a neutron beam passage formed by partitioning a passageway through the collimator 2b with a material that is difficult for neutrons to transmit. The collimator 2b may be, for example, a cylindrical one whose internal space serves as the passageway.

[0022] The neutron irradiation device 2 may be configured to emit a pulsed neutron beam to the irradiation location R, or may be configured to emit a time-continuous neutron beam to the irradiation location R, as described below. In the former case, the pulse time width of the pulsed neutron beam (duration of the neutron beam) is, for example, about 0.1 milliseconds or less, and the repetition frequency of the pulsed neutron beam (irradiation frequency of the neutron beam to the inspection object 1) is, for example, about 100 Hz, but is not limited thereto as long as it does not interfere with the detection of the presence or absence and type of defects. In one example, the neutron irradiation device 2 emits a pulsed neutron beam because the above-mentioned charged particle beam is a pulsed charged particle beam, but the neutron irradiation device 2 may be configured to emit a pulsed neutron beam by other methods.

[0023] Furthermore, the neutron beam emitted by the neutron irradiation device 2 to the irradiation location R may, for example, contain mainly fast neutrons, or may contain fast neutrons and thermal neutrons, or may contain mainly thermal neutrons, but is not limited to these.

[0024] The detection device 3 detects scattered neutrons returning from the inspection object as a result of irradiating the irradiation point R with a neutron beam at each detection position (each of a plurality of detection positions arranged consecutively) facing the surface 1a of the inspection object 1, and measures the number of scattered neutrons detected at each detection position. For example, the detection device 3 has a detection surface 3a1 on which scattered neutrons are incident. Each position on the detection surface 3a1 is the above-mentioned each detection position, and the number of detections at each detection position is the number of scattered neutrons incident on that detection position. The detection device 3 outputs the number of detections measured for each detection position to the ratio calculation unit 5. The detection surface 3a1 may be rectangular as shown in FIG. 1B or may have another shape. For example, the detection surface 3a1 may be an elongated surface.

[0025] The detection number may be measured by the detection device 3 over a predetermined time period. This predetermined time period may be, for example, the period from immediately after the neutron irradiation device 2 irradiates the neutron beam until the number of scattered neutrons incident on the detection surface 3a1 per unit time decreases (for example, falls below a lower limit value). This predetermined time period may be, for example, a value of 10 seconds or more and 10 minutes or less. However, the predetermined time period is not limited to this, and may be set so that at least one of an increasing peak portion and a decreasing peak portion appears in the ratio distribution described below when defects such as water-stagnation areas or low-density areas (for example, voids) exist in the inspection object 1. In the following description, the detection number may refer to the number of neutrons detected over the predetermined time period.

[0026] The water-saturated area may simply be an area where water is present, or in the case of an inspection object 1 containing metal, it may be an area where metal rust (e.g., iron rust) is progressing due to moisture. The low-density area is an area with a lower density than normal areas of the inspection object (in the case of an inspection object being concrete, the low-density area is an area with a lower density than normal concrete areas). Specifically, the low-density area may be an area with a density of 1 / 3 or less, 1 / 5 or less, or 1 / 10 or less than that of normal areas of the inspection object. For example, a void may be considered as the low-density area. However, without being limited thereto, the low-density area may be low-density wood mixed in the inspection object (e.g., concrete), or other materials.

[0027] The detection device 3 has a detector 3a and a measurement unit 3b. In the following, "during inspection" means when a neutron beam is irradiated onto an irradiation point R on the surface 1a of the inspection object 1 in order to inspect the presence or absence of defects in the inspection object 1 (when performing step S3, which will be described later). In the following, "inspection" means irradiating the neutron beam in this way to inspect the presence or absence of defects in the inspection object 1 (performing steps S3 to S8, which will be described later, or beam scanning).

[0028] The detector 3a (detection surface 3a1) is disposed so as to face the surface 1a of the inspection object 1 during inspection. In this arrangement, some of the many detection positions on the detector 3a (for example, the center of the detector 3a (detection surface 3a1)) face the irradiation point R. In this case, during inspection, the neutron beam from the neutron irradiation device 2 passes through the detector 3a (detection surface 3a1) and is irradiated onto the surface 1a of the inspection object 1. In one example, a (for example, imaginary) surface having a two-dimensional extent on the detector 3a is the above-mentioned detection surface 3a1. FIG. 1A shows an xyz coordinate system having x-, y-, and z-axes that are orthogonal to each other, and in the example of FIG. 1A, the detection surface 3a1 is parallel to the xy plane. Note that the xyz coordinate system in FIG. 1A is for convenience of explanation, and in actual operation, any coordinate axis may indicate any direction (the same applies to the xyz coordinate systems in other figures).

[0029] During inspection, the detector 3a (detection surface 3a1) is placed in a position close to or in contact with the surface 1a. Here, a position close to the surface 1a may be, for example, but is not limited to, a position within 30 mm, 50 mm, 100 mm, or 300 mm of the surface 1a. Furthermore, during inspection, the detection surface 3a1 may be parallel to the surface 1a of the inspection target 1.

[0030] The detector 3a is a position sensitive detector (PSD). Each time a neutron is incident on the detection surface 3a1, the detector 3a outputs a detection signal corresponding to the detection position on the detection surface 3a1 at which the neutron is incident.

[0031] The detector 3a may be configured to selectively detect thermal neutrons and not detect neutrons other than thermal neutrons. In this case, the detector 3a is configured to selectively detect thermal neutrons and not detect neutrons other than thermal neutrons. 3 He) proportional coefficient tube may be used, or lithium 6( 6 The detector may be a combination of a scintillator containing Li) and a photosensor.

[0032] Alternatively, the detector 3a may be configured to selectively detect intermediate neutrons and not detect neutrons other than intermediate neutrons. In this case, the detector 3a detects chlorine ( 35 Cl) and bromine ( 79 Br, 81 For example, the detector 3a may be a detector that combines a scintillator containing at least one of CLYC or LaBr3 with a photosensor.

[0033] The detector 3a is not limited to the above, and may be, for example: 155 Gd, 157 Gd, 10 The detector may be a combination of a scintillator containing B or the like and a photosensor. Each of the photosensors may be a photomultiplier tube or a SiPM (Silicon Photomultiplier). However, the present invention is not limited to these.

[0034] A thermal neutron generally refers to a neutron having an energy value of around 25 meV or less at room temperature, a medium neutron refers to a neutron having an energy sufficiently higher than that of a thermal neutron (an energy of several keV or more and less than several hundred keV), and a fast neutron refers to a neutron having an energy of several hundred keV or more. Here, since there is no strict definition of the threshold for naming neutrons based on energy, in the definitions herein, a thermal neutron may be a neutron having an energy of several tens of meV (e.g., 50 meV) or less, a medium neutron may be a neutron having an energy of several keV (e.g., 5 keV) or more and less than several hundred keV (e.g., 500 keV), and a fast neutron may be a neutron having an energy of several hundred keV (e.g., 500 keV) or more.

[0035] The measuring unit 3b counts the number of scattered neutrons detected at each detection position based on the multiple detection signals output from the detector 3a. When the optical sensor described above is used, the measuring unit 3b may be incorporated into the optical sensor such as a SiPM.

[0036] The ratio calculation unit 5 calculates the ratio (hereinafter simply referred to as ratio) of the number of detections at each detection position on the detector 3a to a reference value for that detection position. The reference value is set for each detection position as the number of detections that would occur if no defects were present in the inspection object 1. That is, the reference value is the number of detections that would be obtained if an inspection were performed on an inspection object 1 that does not have any defects. Such a reference value may vary depending on the detection position. That is, the reference value may differ between at least some of the detection positions. The reference value for each detection position on the detector 3a (detection surface 3a1) is set in advance depending on the positional relationship between the irradiation point R and the detection position, the neutron scattering characteristics of the inspection object 1, and the like. Such a reference value for each detection position may be set for each irradiation point on the inspection object 1, or may be common to different irradiation points when the inspection object 1 has a uniform configuration (material), for example.

[0037] <How to set the reference value> The above-mentioned reference value may be set in advance for each detection position on the detector 3a as follows: That is, when an inspection is performed on an inspection object 1 that does not contain defects under the following detection conditions (a) to (c), the number of neutrons detected at each detection position on the detector 3a over a predetermined time (for example, an estimated number of detections) may be set as the reference value for that detection position.

[0038] (a) The positional relationship and attitude relationship (orientation relationship) between the detector 3a (detection surface 3a1), the inspection object 1 (irradiation location R), and the neutron irradiation device 2 are set in advance. (b) The spectrum of the neutron beam emitted from the neutron irradiation device 2 to the inspection object 1 is determined. The neutron beam spectrum is the energy distribution of the many neutrons irradiated from the neutron irradiation device 2 to the inspection object 1 per unit time (for example, in the pulse time width in the case of a pulsed neutron beam), and in this distribution, the number of neutrons having each energy is expressed. (c) The intensity of the neutron beam is determined. The intensity of the neutron beam is the number of neutrons irradiated per unit time from the neutron irradiation device 2 to the irradiation point R (or unit area at the irradiation point R) on the inspection object 1.

[0039] In one example, under the above detection conditions (a) to (c), the neutron irradiation device 2 irradiates neutrons to one irradiation point R on the actual inspection object 1 (for example, the inspection object 1 where the probability of defects being present is assumed to be low), and the number of detections at each detection position on the detector 3a is determined. Thereafter, the same process is performed again for a different irradiation point R on the same inspection object 1. By repeating this process, the number of detections at each detection position on the detector 3a is determined for each of the multiple irradiation points R. Then, for each detection position on the detector 3a, the average value of the multiple detection numbers at that detection position determined for the multiple irradiation points R is set as the reference value for that detection position.

[0040] In another example, a specimen is prepared that has the same configuration (material, etc.) as the actual inspection object 1 (for example, an inspection object 1 that is assumed to have a high probability of having defects) but does not have any defects, and using this specimen as the inspection object 1, the neutron irradiation device 2 irradiates neutrons to the irradiation point R on the specimen under the above detection conditions (a) to (c), and the number of detections at each detection position on the detector 3a is determined, and this number of detections is set as the reference value for that detection position.

[0041] In yet another example, the number of detections obtained at each detection position of the detector 3a when an inspection is performed on an inspection object 1 that does not contain defects under the above detection conditions (a) to (c) is determined by simulation, and the number of detections is set as the reference value for the detection position. Such a simulation may be performed, for example, on an inspection object 1 that is assumed to have a high probability of containing defects.

[0042] When viewed in the direction in which the neutron beam is incident on the surface 1a of the object 1 to be inspected under the above-mentioned detection conditions (a) to (c), the reference value of each detection position on the detector 3a (detection surface 3a1) becomes smaller as the detection position moves away from the point on the surface 1a where the neutron beam is irradiated (see, for example, Figures 6A and 6B described below).

[0043] The reference value for each detection position in the detector 3a may be stored in the memory unit 6 of the nondestructive testing device 10. In this case, the ratio calculation unit 5 calculates the ratio for each detection position in the detector 3a based on the reference value in the memory unit 6 and the above-mentioned number of detections.

[0044] The data processing unit 7 performs data processing on the ratios at each detection position on the detector 3a output by the ratio calculation unit 5. The data processing unit 7 identifies an increase peak forming portion and a decrease peak forming portion of the ratio in the distribution of the ratios (hereinafter simply referred to as a ratio distribution) for the detection positions on the detector 3a. The data processing unit 7 also calculates the size of the identified increase peak forming portion and decrease peak forming portion.

[0045] <Ratio distribution> 2A to 2D schematically show ratio curves C1 to C4 that indicate ratio distributions related to the detection positions.

[0046] 2A and 2B show a case where a low-density portion (e.g., a void) exists as a defect inside the inspection object 1, and Fig. 2C and 2D show a case where water exists as a defect inside the inspection object 1. Also, Fig. 2A and 2C show a case where a defect inside the inspection object 1 exists on the extension line of the neutron beam irradiated onto the inspection object 1, and Fig. 2B and 2D show a case where a defect inside the inspection object 1 exists at a position shifted from the extension line of the neutron beam irradiated onto the inspection object 1.

[0047] 2A to 2D, the horizontal axis indicates the detection position (x coordinate) on the detector 3a in the x-axis direction (left-right direction) of FIG. 1A, and the vertical axis indicates the ratio of the number of detections. The ratio distributions in FIGS. 2A to 2D show distributions at the same constant y coordinate (see FIG. 1B) as the irradiation location R. FIGS. 2A to 2D show cases where the number of detections is the number of thermal neutrons. However, even if the number of detections is the number of intermediate neutrons, the tendency of the ratio distribution is the same as in FIGS. 2A to 2D.

[0048] As shown in each of Figures 2A to 2D, due to the influence of defects present in the inspection object 1, a decreasing peak forming portion and an increasing peak forming portion occur in the ratio distribution. A decreasing peak forming portion is a portion where the ratio is smaller than 1 and forms a decreasing peak of the ratio (a peak in the negative direction). An increasing peak forming portion is a portion where the ratio is larger than 1 and forms an increasing peak of the ratio (a peak in the positive direction).

[0049] In Figures 2A and 2B, the decreasing peak formation portion is the portion from point D2 to point D3 on the ratio curves C1 and C2 representing the ratio distribution, and the increasing peak formation portion is the portion from point D1 to point D2 on the ratio curves C1 and C2 and the portion from point D3 to point D4 on the ratio curves C1 and C2.

[0050] In Figures 2C and 2D, the decreasing peak formation portion is the portion from point D1 to point D2 on the ratio curves C3 and C4 and the portion from point D3 to point D4 on the ratio curves C3 and C4, and the increasing peak formation portion is the portion from point D2 to point D3 on the ratio curves C3 and C4.

[0051] Furthermore, the size of the decrease peak forming portion may be the area of ​​the region sandwiched between the portion where the ratio is 1 (the dashed line L in FIGS. 2A to 2D) and the decrease peak forming portion (the area of ​​the diagonally shaded portion indicated by the symbol N in FIGS. 2A to 2D). That is, when the ratio curve is expressed as ratio=f(x), where x is the position coordinate (x-axis coordinate in FIG. 1A), ∫{1-f(x)}dx may be the size of the decrease peak forming portion. This integration is performed over the x section of the decrease peak forming portion.

[0052] Similarly, the size of the increased peak forming portion may be the area of ​​the region sandwiched between the portion where the ratio is 1 (the dashed line L in FIGS. 2A to 2D) and the increased peak forming portion (the area of ​​the diagonally shaded portion indicated by the symbol P in FIGS. 2A to 2D). That is, when the ratio curve is expressed as ratio=f(x), where x is the position coordinate (x-axis coordinate in FIG. 1A), ∫{f(x)-1}dx may be the size of the increased peak forming portion. This integration is performed over the x section of the increased peak forming portion.

[0053] Defects in low density areas In the following description, a void is assumed as a defect in a low-density portion, but the following content also applies to cases where other defects in a low-density portion are assumed. In this case, in the following description, each "void" may be read as a low-density portion.

[0054] When a defect present inside the object to be inspected 1 is a low-density portion, as shown in Figure 2A, a peak of decreasing ratio occurs in the ratio distribution near the region facing the void in detector 3a (i.e., near the same x-coordinate as the void).

[0055] This decrease peak forming portion is formed for the following reason. Neutrons are not scattered by voids, so when neutrons irradiated onto the inspection object 1 pass through the void away from the surface 1a of the inspection object 1, they are not scattered from the void to the detector 3a. Therefore, the number of scattered neutrons detected decreases in the vicinity of the area facing the void on the detection surface 3a1, resulting in the decrease peak forming portion. Furthermore, fast neutrons incident on the inspection object are converted into thermal neutrons while passing through the inspection object (e.g., concrete), but the presence of voids in the inspection object 1 means that thermal neutrons are not generated accordingly. Therefore, the number of scattered thermal neutrons detected decreases in the vicinity of the area facing the void on the detection surface 3a1.

[0056] On the other hand, in the region of detector 3a adjacent to the region facing the gap (decreasing peak forming portion), an increasing peak forming portion of the ratio (positive peak) occurs in the ratio distribution (ratio curve C1) as shown in FIG. 2A.

[0057] This increased peak forming portion is formed for the following reason. The scattered neutrons incident on the detection surface 3a1 in a region adjacent to the region facing the void (decreased peak forming portion) include scattered neutrons that are scattered at a position deeper than the void and pass through the void toward the adjacent region. These "scattered neutrons that pass through the void" are not scattered in other directions by the void, and are less likely to be absorbed by the object being inspected (e.g., concrete) due to the presence of the void. Therefore, the number of scattered neutrons detected in the adjacent region increases accordingly, resulting in the increased peak forming portion.

[0058] Furthermore, as shown in Figure 2B, even if the position of the void is slightly shifted from the extension line of the neutron beam irradiated to the irradiation point R, a ratio distribution similar to that in Figure 2A can be obtained. Note that in Figure 2B, a relatively large increased peak formation portion occurs on the left side. This is because in Figure 2B, of the neutron beam incident on the inspection object 1, more scattered neutrons pass through the void and are detected at the position corresponding to the increased peak formation portion on the left side.

[0059] Water defects When the defect inside the object to be inspected 1 is water (a water-stagnation area), as shown in Figure 2C, a peak of increased ratio occurs in the ratio distribution near the area opposite the water-stagnation area (i.e., near the same x-coordinate as the water-stagnation area).

[0060] This increased peak formation portion is formed for the following reason. The scattered neutrons incident on the detection surface 3a1 in the region facing the water-stagnation area include scattered neutrons from the water-stagnation area. Here, neutrons easily react with water, so the scattered neutrons from the water-stagnation area include many that have reacted with water and become thermal neutrons. Therefore, the number of detected scattered thermal neutrons increases in the region of the detection surface 3a1 facing the water-stagnation area, and an increased peak formation portion occurs.

[0061] 2C, a depression in the negative direction occurs at the top of the increased peak formation portion for the following reason: When neutrons pass through a water-stagnation area away from the surface 1a of the object 1 under inspection, they are less likely to scatter from the water-stagnation area to the detector 3a. Therefore, the number of detected thermal neutrons decreases in the center of the area facing the water-stagnation area on the detection surface 3a1, causing the depression.

[0062] The judgment value calculation unit 8 receives the magnitude of the increase peak formation portion and the magnitude of the decrease peak formation portion as Sp and Sn, respectively, from the data processing unit 7. The judgment value calculation unit 8 calculates the sum (Sp+Sn) of the magnitude of the increase peak formation portion and the magnitude of the decrease peak formation portion, and also calculates the value (Sn / Sp) obtained by dividing the magnitude of the decrease peak formation portion by the magnitude of the increase peak formation portion. The judgment value calculation unit 8 also outputs the calculated Sp+Sn and Sn / Sp.

[0063] In addition, when a plurality of increasing peak forming portions occur in the ratio distribution, Sp may be the sum of the sizes of the plurality of increasing peak forming portions. Similarly, when a plurality of decreasing peak forming portions occur in the ratio distribution, Sn may be the sum of the sizes of the plurality of decreasing peak forming portions.

[0064] The determination unit 9 determines the presence or absence of defects and the type of defects in the inspection object 1 based on Sp+Sn and Sn / Sp output by the data processing unit 7. Fig. 3 shows a two-dimensional coordinate system related to this determination. In Fig. 3, the horizontal axis represents Sp+Sn, and the vertical axis represents Sn / Sp.

[0065] If there is no defect in the inspection object 1, there will be no increase peak forming portion or decrease peak forming portion in the ratio distribution, or even if there is an increase peak or a decrease peak, these peak forming portions will be small, so Sp+Sn will be 0 or a value close to 0. Therefore, assuming that the first threshold value T1 is 0 or a positive value close to 0, if there is no defect, Sp+Sn will be equal to or less than the first threshold value T1, as shown in FIG.

[0066] If the inspection object 1 has a void as a defect, the ratio distribution will have a relatively large decrease peak forming portion and an increase peak forming portion, as shown in Fig. 2A. Therefore, if a void is present, Sp+Sn will be greater than the first threshold value T1 described above, and Sn / Sp will be equal to or greater than the second threshold value T2, which is a positive value, as shown in Fig. 3.

[0067] If water (a water-stagnation portion) exists as a defect in the inspection object 1, a fairly large increase peak appears in the ratio distribution as shown in Fig. 2C, and a decrease peak hardly appears. Therefore, if water exists, Sp + Sn becomes larger than the first threshold value T1, and Sn / Sp becomes smaller than the second threshold value T2, as shown in Fig. 3.

[0068] In accordance with the above, the judgment unit 9 makes a judgment as follows: If Sp+Sn is equal to or less than the first threshold value, the judgment unit 9 judges that no defect exists in the inspection object 1, and outputs a defect-absence signal to that effect.

[0069] If Sp+Sn is greater than the first threshold value, the determination unit 9 determines that a defect exists in the inspection object 1 and outputs a defect presence signal to that effect. In this case, the signal may include information indicating the type of defect as follows: If Sp+Sn is greater than the first threshold value T1 and Sn / Sp is equal to or greater than the second threshold value T2, the determination unit 9 determines that a void exists in the inspection object 1 and outputs a first defect signal to that effect. If Sp+Sn is greater than the first threshold value T1 and Sn / Sp is less than the second threshold value T2, the determination unit 9 determines that water (a water-stagnation area) exists in the inspection object 1 and outputs a second defect signal to that effect.

[0070] (Non-destructive testing method) 4 is a flowchart showing a nondestructive inspection method according to an embodiment of the present invention. This nondestructive inspection method is performed using the nondestructive inspection device 10 described above, and includes steps S1 to S8.

[0071] In step S1, the reference values ​​for each detection position of the detector 3a are set as described above.

[0072] In step S2, the neutron irradiation device 2 and the detector 3a are placed relative to the inspection object 1.

[0073] In step S3, the neutron irradiation device 2 irradiates a neutron beam onto a local irradiation spot R on the surface 1a of the inspection object 1. Steps S2 and S3 are performed under the above-mentioned detection conditions (a) to (c).

[0074] In step S3, the traveling direction of the neutron beam irradiated onto the irradiation spot R may be perpendicular to the surface 1a, or may be oblique to the direction perpendicular to the surface 1a.

[0075] In step S4, as a result of step S3, the scattered neutrons returning from the object to be inspected 1 are detected by the detection device 3 at each detection position on the detection surface 3a1 opposite the surface 1a, and the number of scattered neutrons detected by the detection device 3 is counted at each detection position.

[0076] In step S5, based on the reference value for each detection position set in step S1 and the number of detections at each detection position measured in step S4, the ratio calculation unit 5 calculates and outputs the ratio of the number of detections at each detection position on the detection surface 3a1 to the reference value for that detection position.

[0077] In step S6, the data processing unit 7 identifies the increase peak formation part and decrease peak formation part of the ratio in the distribution of the ratio calculated in step S5 with respect to the detection position, and calculates the size Sp of the increase peak formation part and the size Sn of the decrease peak formation part.

[0078] In step S7, the judgment value calculation unit 8 calculates Sp+Sn, and the judgment unit 9 judges whether or not a defect exists inside the inspection object 1 based on Sp+Sn. In step S7, if Sp+Sn is equal to or smaller than the first threshold value T1, the judgment unit 9 judges that no defect exists inside the inspection object 1 and outputs a defect-absence signal to that effect. On the other hand, in step S7, if Sp+Sn is greater than the first threshold value T1, the judgment unit 9 judges that a defect exists inside the inspection object 1, and the process proceeds to step S8.

[0079] In step S8, the judgment value calculation unit 8 calculates Sn / Sp, and the judgment unit 9 judges the type of defect based on Sn / Sp. In step S8, if Sn / Sp is equal to or greater than the second threshold value T2, the judgment unit 9 judges that a low-density portion (e.g., a void) exists as a defect inside the inspection object 1, and outputs a first defect signal to that effect. On the other hand, in step S8, if Sn / Sp is less than the second threshold value T2, the judgment unit 9 judges that water (a water-stagnation portion) exists as a defect inside the inspection object 1, and outputs a second defect signal to that effect.

[0080] <Beam scan> After step S8, steps S3 to S6 may be repeated by changing the irradiation location R in step S3. That is, the irradiation location R on the surface 1a of the inspection object 1 where the neutron beam is incident in step S3 is made different among the multiple repeated steps of step S3. In this case, step S3 may be performed multiple times so as to scan the inspection object 1 with the neutron beam.

[0081] Furthermore, one cycle consisting of steps S3 to S6 is used to calculate Sp / Sn or Sn / Sp from Sp and Sn calculated in step S6 of the cycle. At this time, if it is determined in step S8 that a low-density portion exists as a defect, Sp / Sn may be calculated, and if it is determined in step S8 that water exists as a defect, Sn / Sp may be calculated.

[0082] Among the multiple Sp / Sn or Sn / Sp ratios obtained for each of the multiple cycles, the smallest Sp / Sn or Sn / Sp ratio is identified. The irradiation point R corresponding to the identified smallest Sp / Sn or Sn / Sp ratio (i.e., the irradiation point R in the cycle in which this Sp / Sn or Sn / Sp ratio was obtained) is identified as the low-density portion (void) or the point closest to the water. Such beam scanning will be described in more detail in Example 2 below.

[0083] (Example 1: When detecting thermal neutrons and when detecting intermediate neutrons) An inspection object 1 (specimen) in which the position and dimensions of a void as a defect are known was inspected using a non-destructive inspection device 10. FIG. 5A shows a cross section of the inspected inspection object 1, and FIG. 5B is a view taken along the arrows 5B-5B in FIG. 5A. The inspection object 1 in FIG. 5A has concrete 1b and H-beam 1c embedded in the concrete 1b. FIG. 5C is a diagram showing the dimensions of each part in FIG. 5A.

[0084] 5A and 5B, a void exists as a defect inside the inspection object 1. In Fig. 5A, x, y, and z represent the x-axis, y-axis, and z-axis that are orthogonal to each other in an xyz coordinate system.

[0085] The above steps S2 to S7 were carried out using the detector 3a that selectively detects thermal neutrons in the above step S4. At this time, in step S3, 10 8 The neutron beam consisting of neutrons was irradiated at the irradiation point R, which was a square with sides of 50 mm (the area surrounded by a dashed line and indicated by the symbol R in FIG. 5B).

[0086] The above experiment was conducted under the same conditions for each case in which the dimensions of the gap in the x-axis and y-axis directions were fixed at 50 mm and 300 mm, respectively, and the dimensions of the gap in the z-axis direction were set to 3 mm, 10 mm, and 30 mm.

[0087] 6A and 6B show the reference values ​​used in step S5 when selectively detecting thermal neutrons. That is, FIGS. 6A and 6B are specific examples of the number of detections (i.e., reference values) at each detection position in the detector 3a when there are no defects such as voids in the inspection object 1 of FIG. 5A. FIGS. 6A and 6B show the number of detections (i.e., reference values) at each detection position in the detector 3a when the detector 3a detects helium 3( 3 Fig. 6A shows the distribution of reference values ​​set using a test specimen as described above for a neutron beam (He) proportional coefficient tube. Fig. 6A shows the irradiation point R surrounded by a dashed line and the distribution of reference values ​​on a surface having a two-dimensional spread (detection surface 3a1), and Fig. 6B shows the reference values ​​(detection count) for each x-axis coordinate relative to the same y-axis coordinate as the center of the neutron beam irradiation point R on surface 1a.

[0088] In FIG. 6A, the reference value decreases in the order of regions A to H. In FIG. 6A, the reference value is roughly 2.7×10 3 / cm 2 or more, and in region B it is 1.9 × 10 3 / cm 2 Over 2.7 x 10 3 / cm 2 in region C is less than 1.4 × 10 3 / cm 2 Over 1.9 x 10 3 / cm 2 In region D, it is less than 1.0 × 103 / cm 2 Over 1.4 x 10 3 / cm 2 In region E, it is less than 5.2 × 10 2 / cm 2 Over 1.0 x 10 3 / cm 2 in region F is less than 2.8 × 10 2 / cm 2 Over 5.2 x 10 2 / cm 2 and in area G, it is less than 8.0 × 10 / cm 2 Over 2.8 x 10 2 / cm 2 and in region H, it is less than 8.0 × 10 / cm 2 is less than.

[0089] In Figure 6B, crosses (x) indicate reference values, while circles, squares, and triangles indicate the number of detections when the voids described above in Figure 5A are present. These circles, squares, and triangles represent cases where the void dimensions in the z-axis direction are 3 mm, 10 mm, and 30 mm, respectively. Note that in Figure 6B, the marks of each type almost overlap each other at positions more than about 200 mm away from the origin of the x-axis coordinate, and the difference between them decreases as the distance from the origin increases.

[0090] The same experiment was also carried out using the detector 3a that selectively detects intermediate neutrons, with the other conditions remaining the same. The reference values ​​were those obtained when intermediate neutrons were selectively detected.

[0091] 7A and 7B show the two-dimensional distribution of the ratio on the detection surface 3a1 when the dimension of the void in the z-axis direction is 10 mm. FIG. 7A shows the case where a detector 3a that selectively detects thermal neutrons is used, and FIG. 7B shows the case where a detector 3a that selectively detects intermediate neutrons is used. In FIGS. 7A and 7B, the horizontal and vertical axes represent the x- and y-coordinates shown in FIG. 5A, and the origin of each coordinate is the center of the irradiation point R. In addition, in FIGS. 7A and 7B, the dashed lines indicate the range in which the void exists when viewed in the z-axis direction.

[0092] 7A, the distribution of the rough ratios on the detection surface 3a1 is shown by regions A to E surrounded by solid lines. The ratios are less than 0.93 in region A, 0.93 or more and less than 0.97 in region B, 0.97 or more and less than 1.00 in region C, and 1.00 or more and less than 1.13 in region D. Region E is a region with a large error.

[0093] Similarly, in Fig. 7B, the distribution of the rough ratios on the detection surface 3a1 is shown by regions A to D surrounded by solid lines. The ratios are less than 0.97 in region A, 0.97 or more and less than 1.00 in region B, 1.00 or more and less than 1.09 in region C, and 1.09 or more and less than 1.19 in region D. Region E is a region with a large error.

[0094] As can be seen from Figures 7A and 7B, the presence of voids can be detected whether the neutrons being detected are thermal neutrons or intermediate neutrons. For example, in Figures 7A and 7B, there are regions where the ratio is less than 1 and regions where the ratio is greater than 1 (and the ratio is smallest near the irradiation point R), so it can be determined that voids exist.

[0095] In addition, the area where the ratio is greater than 1 is larger when intermediate neutrons are detected, so the value of Sp+Sn is larger when intermediate neutrons are detected. That is, by detecting intermediate neutrons, the sensitivity of the Sp+Sn value to the presence of voids can be Can be made higher

[0096] Figure 8 shows the Sp+Sn values ​​for each case in the above-mentioned experiment. In Figure 8, the horizontal axis represents the z-axis dimension of the gap, and the vertical axis represents the determined Sp+Sn value. Also in Figure 8, circles represent cases where thermal neutrons were selectively detected, and squares represent cases where intermediate neutrons were selectively detected.

[0097] As shown in Fig. 8, even if the z-axis dimension of the void is 3 mm, Sp+Sn will be significantly larger than the first threshold T1, which is zero or close to zero, even if it is smaller than the actual value due to the error. Also, although the number of detected intermediate neutrons tends to be smaller than the number of detected thermal neutrons, as shown in Fig. 8, the sensitivity of the value of Sp+Sn to the presence of a void is higher when intermediate neutrons are detected. Therefore, when a sufficient number of intermediate neutrons are detected, In such cases, the presence of voids can be detected with high sensitivity by detecting intermediate neutrons during inspection.

[0098] (Example 2: Beam Scanning) <If the defect is a void> The above-mentioned beam scan was performed using a non-destructive inspection device 10. In this Example 2, a detector 3a that selectively detects thermal neutrons was used. FIG. 9A shows a cross section of the inspection object 1 that was subjected to the beam scan, and FIG. 9B is a view taken along the arrows 9B-9B in FIG. 9A. The inspection object 1 in FIG. 9A is the same as that in FIG. 5A, and the dimensions of each part are also the same as those in FIG. 5C.

[0099] In FIGS. 9A and 9B, the dimensions of a void present as a defect inside inspection object 1 in the x-axis direction, y-axis direction, and z-axis direction are 50 mm, 300 mm, and 3 mm, respectively.

[0100] The above-described steps S3 to S6 constitute one cycle of beam scanning, and in each of the three cycles (step S3), the neutron beam was irradiated onto the surface 1a of the object to be inspected 1. The neutron beams irradiated in the three cycles are indicated by B1 to B3 in FIG. 9A, respectively. The irradiation area in the three cycles was a circle with a diameter of 40 mm. FIG. 9B shows the irradiation area R1 and its center r1 in the first cycle, the center r2 of the irradiation area in the second cycle, and the center r3 of the irradiation area in the third cycle.

[0101] Furthermore, the z-axis dimension of the gap was changed to 10 mm, and the other conditions were kept the same, and three cycles of the beam scan described above were performed.Furthermore, the z-axis dimension of the gap was changed to 30 mm, and the other conditions were kept the same, and three cycles of the beam scan described above were performed.

[0102] Figure 10 shows the results of the second cycle when the z-axis dimension of the void is 10 mm, and shows the two-dimensional distribution of the ratio on the detection surface 3a1. In Figure 10, the horizontal and vertical axes represent the x- and y-axis coordinates shown in Figure 9A, and the origin of each coordinate is the center r2 (see Figure 9B) mentioned above. Also, in Figure 10, the ellipse R shown by the dashed line is the irradiation point, and another dashed line indicates the range in which the void exists when viewed in the z-axis direction.

[0103] 10, the distribution of the ratios on the detection surface 3a1 is roughly shown by regions A to D surrounded by solid lines. In region A, the ratio is less than 0.95, in region B, the ratio is 0.95 or more and less than 1.00, in region C, the ratio is 1.00 or more and less than 1.10, and region D is a region with a large error.

[0104] FIG. 11 shows the results for a gap with a z-axis dimension of 10 mm, showing the distribution of the ratio in the x-axis direction on the detection surface 3a1. In FIG. 11, the horizontal axis represents the position coordinate in the x-axis direction, and the vertical axis represents the ratio (detection count / reference value). In FIG. 11, triangles indicate the case where the center of the neutron beam irradiation point on the surface 1a of the inspection object 1 is r1 in FIG. 9B, squares indicate the case where the center is r2 in FIG. 9B, and circles indicate the case where the center is r3 in FIG. 9B. Note that in FIG. 11, the ratio at each position coordinate represents the ratio at the y-axis coordinate, which is the same as the center of the neutron beam irradiation point R1 on the surface 1a. In FIG. 11, when the absolute value of the position coordinate in the x-axis direction exceeds approximately 400 mm, the obtained ratio has a large error, but tends to approach 1 at both ends of the position coordinate in the x-axis direction as it moves away from the center of the irradiation point. Therefore, Sn and Sp may be calculated within a range of position coordinates in which the error does not exceed the allowable limit.

[0105] Figure 12 shows the Sp / Sn values obtained by beam scanning. In Figure 12, the horizontal axis represents the x-axis distance between the center of the irradiation location R and the center of the gap, and the vertical axis represents the Sp / Sn values obtained in each cycle of the beam scanning. Here, Sn and Sp were obtained in the range of -300 mm < x < 500 mm considering the error. Also, in Figure 12, the circular marks indicate the case where the z-axis dimension of the gap is 3 mm, the square marks indicate the case where the z-axis dimension of the gap is 10 mm, and the triangular marks indicate the case where the z-axis dimension of the gap is 30 mm.

[0106] As shown in Figure 12, the irradiation location R in the cycle where the minimum Sp / Sn is obtained is the closest to the gap within the inspection object 1. Therefore, the irradiation location R corresponding to the minimum Sp / Sn can be specified as the location closest to the gap. For example, when irradiating the surface 1a of the inspection object 1 with a neutron beam from directly above the gap within the inspection object 1, many neutrons pass through the gap in the direction away from the surface 1a. At this time, these neutrons do not scatter toward the detector 3a within the gap. As a result, it is considered that the detection count significantly decreases in the region directly above the gap on the detection surface 3a1. Also, no thermal neutrons are generated in the gap. Therefore, it is considered that the closer the irradiation location R is to the gap (directly above the gap), the larger Sn becomes and the smaller Sp / Sn becomes.

[0107] <When the defect is water> In Figure 9A, the above-described beam scanning was performed for the case where the defect is a water accumulation location instead of a gap. In this beam scanning, the water accumulation location is at the same position as in the case of the above-described gap, and its dimensions in the x-axis direction, y-axis direction, and z-axis direction are 50 mm, 300 mm, and 10 mm, respectively. Also, in this beam scanning, the detector 3a that selectively detects thermal neutrons was used. Other points are the same as in the case of the above-described beam scanning where the defect was a gap.

[0108] Figure 13 shows the two-dimensional distribution of ratios on the detection surface 3a1 obtained in the second cycle of such beam scanning. In Figure 13, the horizontal and vertical axes represent the x- and y-axis coordinates shown in Figure 9A, where the voids are replaced with water-stained areas, and the origin of each coordinate is the center of the irradiation area R in the second cycle. In Figure 13, the ellipse R shown by the dashed line is the irradiation area, and another dashed line indicates the range where the water-stained areas exist when viewed in the z-axis direction.

[0109] 13, the distribution of ratios on detection surface 3a1 is shown by regions A to D surrounded by solid lines. Roughly speaking, the ratios are 1.20 or more in region A, 1.15 or more and less than 1.20 in region B, 1.10 or more and less than 1.15 in region C, 1.05 or more and less than 1.10 in region D, 1.00 or more and less than 1.05 in region E, 0.90 or more and less than 1.00 in region F, and region G is a region with a large error.

[0110] FIG. 14 shows the distribution of ratios in the x-axis direction on detection surface 3a1. In FIG. 14, the horizontal axis indicates the position coordinate in the x-axis direction, and the vertical axis indicates the ratio (detection count / reference value). In FIG. 14, triangles indicate the case where the center of the neutron beam irradiation point on surface 1a of inspection object 1 is r1 in FIG. 9B, squares indicate the case where the center is r2 in FIG. 9B, and circles indicate the case where the center is r3 in FIG. 9B. Note that in FIG. 14, the ratio at each position coordinate indicates the ratio at the y-axis coordinate, which is the same as the center of neutron beam irradiation point R. In FIG. 14, when the absolute value of the position coordinate in the x-axis direction exceeds 400 mm, the obtained ratio has a large error, but tends to approach 1 at both ends of the position coordinate in the x-axis direction as it moves away from the center of the irradiation point.

[0111] In Fig. 15, the Sn / Sp values ​​obtained by beam scanning when the z-axis dimension is 10 mm are shown by square marks. In Fig. 15, the horizontal axis represents the distance in the x-axis direction between the center of the irradiation point R and the center of the water-logged area, and the vertical axis represents the Sn / Sp values ​​obtained in each cycle of the beam scan.

[0112] As shown in Figure 15, it can be determined that the irradiation point R in the cycle in which the smallest Sn / Sp was obtained is closest to the water-stagnation point in the inspection object 1. This is based on the following reason: Neutrons tend to react with water in the water-stagnation point and become thermal neutrons. Therefore, it is thought that the closer the irradiation point R is to the water-stagnation point (directly above the water-stagnation point), the more thermal neutrons are detected, and as a result, Sp becomes larger and Sn / Sp becomes smaller.

[0113] (Effects of the embodiment) As described above, a neutron beam is irradiated onto a local irradiation spot R on the surface 1a of the object 1 to be inspected, and as a result, the number of scattered neutrons incident on each detection position on the detector 3a is measured as the detection number, and for each detection position, the ratio of the detection number at that detection position to the reference value for that detection position is calculated. The ratio distribution for the detection positions obtained in this way contains information indicating the presence or absence and type of defect. Therefore, the presence or absence and type of defect can be detected based on the ratio (ratio distribution) of each detection position on the detector 3a.

[0114] For example, if the sizes of the increasing and decreasing peaks in the ratio distribution are Sp and Sn, respectively, and Sp+Sn is greater than a first threshold T1, it can be determined that there is a defect in the water or low-density portion (e.g., void).

[0115] Furthermore, if Sp+Sn is greater than the first threshold value T1 and Sn / Sp is equal to or greater than the second threshold value T2, it can be determined that the inspection object 1 has a low-density portion as a defect.

[0116] If Sp+Sn is greater than the first threshold value T1 and Sn / Sp is less than the second threshold value T2, it can be determined that water exists as a defect in the inspection object 1.

[0117] Furthermore, by making the irradiation location R a localized location (for example, a spot), if a defect exists in the inspection object 1, the above-mentioned increase peak forming portion and decrease peak forming portion are more likely to occur in the ratio distribution.

[0118] When detecting the presence or absence of a low density portion (for example, a void), the detector 3a selectively detects medium speed neutrons, thereby making it possible to obtain Sp+Sn with high sensitivity for the low density portion.

[0119] By performing the beam scanning described above, Sp / Sn or Sn / Sp is determined for each irradiation point R, and the irradiation point R corresponding to the smallest Sp / Sn or Sn / Sp can be determined to be closest to the low-density area or stagnant water area.

[0120] The present invention is not limited to the above-described embodiment, and various modifications can be made within the scope of the technical concept of the present invention. For example, the nondestructive inspection device 10 according to the embodiment of the present invention does not necessarily have to achieve all of the above-described effects. Furthermore, the nondestructive inspection device 10 according to the embodiment of the present invention does not necessarily have to have all of the above-described multiple components, and may have only some of the above-described multiple components.

[0121] According to the present invention, any one of the following modified examples 1 to 8 may be adopted alone, or any combination of two or more of modified examples 1 to 8 may be adopted. In this case, the points not described below are the same as those described above.

[0122] (Change example 1) In the above description, the neutron irradiation device 2 irradiates the irradiation point R with a pulsed neutron beam, but it may also irradiate the irradiation point R with a continuous neutron beam that is continuous in time. In this case, the detection device 3 may measure the number of detections at each detection position in the detector 3a over a time period (a predetermined time) in which an increasing peak forming portion and a decreasing peak forming portion appear in the above-mentioned ratio distribution when a defect such as a water-stagnation portion or a low-density portion exists in the inspection object 1.

[0123] (Change example 2) When the type of defect is not judged, the judgment value calculation section 8 does not need to calculate Sn / Sp.

[0124] (Change example 3) Although not described above, the non-destructive inspection device 10 may further include a display 11 as shown in FIG. 1A.

[0125] When the display 11 is provided, the data processing unit 7, the judgment value calculation unit 8, and the judgment unit 9 may be omitted. In this case, the ratio calculation unit 5 may output the ratio of each detection position in the detector 3a to the display 11 as a ratio distribution regarding the detection positions. In this case, the output ratio distribution is displayed on the display 11, and a person may look at the displayed ratio distribution to judge the presence or absence and type of defect.

[0126] The ratio distribution displayed on display 11 may be represented by a two-dimensional coordinate system having a coordinate axis indicating each detection position (e.g., the x-axis in FIG. 1A) and a coordinate axis indicating the ratio, as shown in FIGS. 2A to 2D. Alternatively, the ratio distribution displayed on display 11 may be represented by a three-dimensional coordinate system having two mutually orthogonal coordinate axes indicating each detection position (e.g., the x-axis and y-axis in FIG. 1A) and a coordinate axis indicating the ratio. Alternatively, the ratio distribution displayed on display 11 may be represented by a two-dimensional plane (detection plane 3a1) displayed on display 11, as shown in FIGS. 7A and 7B, in which the magnitude of the ratio at each detection position is represented by multiple sections (e.g., sections A to E in FIG. 7A), colors, or shading. Note that the ranges of ratio values ​​differ among the multiple sections, and the upper and lower limits of the ratio range for each section may also be displayed on display 11.

[0127] Alternatively, when the display 11 is provided, only the judgment unit 9 may be omitted from the data processing unit 7, the judgment value calculation unit 8, and the judgment unit 9. In this case, the judgment value calculation unit 8 may output the obtained judgment values ​​Sp+Sn and Sn / Sp to the display 11. In this case, the output judgment values ​​may be displayed on the display 11, and a person may judge the presence or absence and type of a defect by looking at the displayed judgment values. In this case, the display 11 may further display a ratio distribution as described above.

[0128] Alternatively, when the display 11 is provided, only the judgment value calculation unit 8 and the judgment unit 9 may be omitted from the data processing unit 7, the judgment value calculation unit 8, and the judgment unit 9. In this case, the data processing unit 7 may output Sp and Sn to the display 11. In this case, the output values ​​of Sp and Sn may be displayed on the display 11, and a person may determine the presence or absence and type of defect by looking at the displayed values. In this case, the display 11 may further display a ratio distribution as described above.

[0129] (Change example 4) In the above description, the size of the increasing peak portion in the ratio distribution is expressed as an area, but it may also be the maximum value of the ratio in the increasing peak portion (the peak value in the positive direction). In this case, the size of the decreasing peak portion in the ratio distribution may also be the minimum value of the ratio in the decreasing peak portion (the peak value in the negative direction).

[0130] (Change example 5) The ratio distribution (ratio of each detection position in detector 3a) output by ratio calculation unit 5 may be a distribution expressed relative to one-dimensional coordinates (x-coordinate) as shown in Figures 2A to 2D, i.e., a distribution expressed in a two-dimensional coordinate system having an x-axis and a ratio axis, or a distribution expressed relative to two-dimensional coordinates (x-axis coordinate and y-axis coordinate), i.e., a distribution expressed in a three-dimensional coordinate system having an x-axis, a y-axis, and a ratio axis.

[0131] In the latter case, the size of the increase peak forming portion may be the volume of a region sandwiched between the portion where the ratio is 1 and the increase peak forming portion. That is, when x and y are position coordinates representing two-dimensional coordinates on the detection surface 3a1 and a ratio surface representing the ratio distribution is expressed as ratio = f(x, y), ∫{f(x, y)-1}dxdy may be the size of the increase peak forming portion. This integration is performed over the x section and the y section of the increase peak forming portion. In this case, the size of the decrease peak forming portion may also be the volume of a region sandwiched between the portion where the ratio is 1 and the decrease peak forming portion. That is, similar to the case of the increase peak forming portion, ∫{1-f(x, y)}dxdy may be the size of the decrease peak forming portion.

[0132] Furthermore, when the ratio distribution is expressed in a two-dimensional coordinate system as described above, the data processing unit 7 may generate a curve that approximates the ratio distribution in the two-dimensional coordinate system (for example, the ratio curve C1 in FIG. 2A) and determine the above-mentioned Sp and Sn based on the curve. When the ratio distribution is expressed in a three-dimensional coordinate system as described above, the data processing unit 7 may generate a curved surface that approximates the ratio distribution in the three-dimensional space (for example, the above-mentioned f(x, y)) and determine the above-mentioned Sp and Sn based on the curved surface.

[0133] (Change example 6) The above-described step S8 was performed under the assumption that the defects in the inspection object 1 were either low-density portions (e.g., voids) or water-stagnation portions (or iron rust). However, if this assumption is not made and the determination in step S7 is negative, it may be determined that other possible defects exist. For example, if an object for which deterioration determination is to be performed (e.g., the waterproof sheet or optical fiber cable described above) exists in the inspection object 1, and if the determination in step S7 is negative, it may be determined that the deterioration of the object for deterioration determination (e.g., the waterproof sheet or the covering (sheath) of the optical fiber cable) is the defect and that such a defect exists. In other words, it may be assumed that the negative determination result in step S7 indicates such deterioration.

[0134] (Change example 7) In the above description, the detector 3a has a detection surface 3a1 that extends two-dimensionally, but the present invention is not limited to this. For example, the detector 3a may extend in a rod shape (for example, in the x-axis direction in FIG. 1A). In this case, such a rod-shaped detector 3a has a plurality (for example, a large number) of detection positions arranged in a rod shape. By performing steps S2 to S4 using the rod-shaped detector 3a, the number of detections at the large number of detection positions over a range that extends one-dimensionally (rod-shaped) is obtained.

[0135] Steps S2 to S4 may be performed multiple times using a rod-shaped detector 3a. In this case, the position of the detector 3a may be changed for each iteration, while other conditions remain the same. This allows the number of detections at multiple detection positions across a two-dimensional range to be obtained, and the ratio at each of these detection positions may be calculated as in step S5 above. Then, based on the ratios (ratio distribution) at these detection positions, the presence or absence and type of defects may be determined as in steps S7 and S8 above, or this ratio distribution may be displayed on the display 11. The position and orientation of the detector 3a for each iteration of steps S2 to S4 may be input to the detection device 3 by appropriate means (for example, by a person operating an input device), and the detection device 3 may determine the correspondence between each detection position and the number of detections based on this input.

[0136] The detector 3a may be a point-like detector with one detection position. In this case, steps S2 to S4 are performed multiple times. In this case, the position of the detector 3a is changed for each of the multiple times, while other conditions are kept the same. This allows the number of detections at multiple detection positions over a range having a one-dimensional or two-dimensional spread to be obtained, and the ratio at each of these detection positions to be calculated. In this case, the other points are the same as when steps S2 to S4 are performed multiple times using a rod-shaped detector 3a.

[0137] (Change example 8) The ratio calculation unit 5 may calculate the above ratio using the normalized reference value and the normalized number of detections as follows.

[0138] The reference value of each detection position i (i is an identifier of the detection position, and the same applies below) may be a value obtained by normalizing the number αi of emitted neutrons detected at the detection position i when Na neutrons are incident on the inspection object 1 in a state where no defects exist inside it, by Na. In other words, the reference value Ri of each detection position i may be Ri=αi / Na.

[0139] Similarly, the number of detections at each detection position i may be a value obtained by normalizing the number βi of emitted neutrons detected at the detection position i by Nb as a result of the neutron irradiation device 2 irradiating Nb neutrons onto the inspection object 1 in the above-mentioned step S3. That is, the number of detections Di at each detection position i may be Di=βi / Nb.

[0140] The ratio calculation unit 5 calculates the ratio at each detection position i using Di / Ri. When calculating the ratio, the ratio calculation unit 5 may calculate the number of detections Di=βi / Nb from the known Nb and βi measured by the measurement unit 3b. The normalized reference value Ri may be stored in the storage unit 6.

[0141] In such modified example 8, the above-mentioned Na and Nb may be different from each other, and the time for irradiating the neutron beam to the inspection object 1 (irradiation point R) in step S3 may be different from the corresponding time (neutron beam irradiation time) in setting the reference value. Note that in modified example 8, the time for measuring the number of detected emitted neutrons in step S4 and the corresponding measurement time in setting the reference value may both be the time until the number of neutrons emitted from the inspection object 1 per unit time becomes sufficiently small (for example, becomes substantially zero). [Explanation of symbols]

[0142] 1. Inspection object 1a surface 1b Concrete 1c H steel 2 Neutron irradiation device 2a neutron source 2b Collimator 3. Detection equipment 3a Detector 3a1 Detection surface 3b Measuring section 5 Ratio calculation section 6 Memory section 7 Data Processing Section 8. Judgment value calculation section 9 Judgment section 10 Non-destructive testing equipment 11 Display R Irradiation point

Claims

1. a neutron irradiation device that irradiates a local irradiation spot on the surface of an object to be inspected with a neutron beam; a detection device that detects scattered neutrons returning from the inspection object as a result of irradiating the irradiation point with the neutron beam at each detection position facing the surface and counts the number of scattered neutrons detected at each detection position; a ratio calculation unit that calculates, for each detection position, a ratio of the number of detections at the detection position to a reference value for the detection position; a data processing unit that identifies a portion in the distribution of the ratio related to the detection position where the ratio is greater than 1 and forms an increase peak of the ratio as an increase peak forming portion of the ratio, and a portion in the distribution where the ratio is less than 1 and forms a decrease peak of the ratio as a decrease peak forming portion of the ratio, and determines a size Sp of the increase peak forming portion and a size Sn of the decrease peak forming portion; a determination unit that determines defects in the object to be inspected based on Sp and Sn.

2. A judgment value calculation unit is provided which calculates and outputs Sp+Sn and Sn / Sp as judgment values, 2. The non-destructive inspection device according to claim 1, wherein the determination unit determines the presence or absence of a defect in the inspection object and the type of the defect based on Sp+Sn and Sn / Sp.

3. The determination unit If Sp+Sn is equal to or less than the first threshold, output a defect-free signal; outputting a first defect signal when Sp+Sn is greater than the first threshold value and Sn / Sp is equal to or greater than a second threshold value; outputting a second defect signal when Sp+Sn is greater than the first threshold value and Sn / Sp is less than the second threshold value; 3. The non-destructive inspection device according to claim 2, wherein the first defect signal and the second defect signal are signals that identify the presence or absence of a defect and the type of the defect.

4. A non-destructive testing device described in any one of claims 1 to 3, wherein the reference value is set for each detection position.

5. 5. The non-destructive testing device according to claim 1, wherein the detection device selectively detects either thermal neutrons or intermediate neutrons as scattered neutrons at each detection position, and counts the number of detections of either type at each detection position.

6. 6. The non-destructive inspection device according to claim 1, wherein the irradiated portion is an irradiation spot.

7. 7. The non-destructive testing device according to claim 1, wherein the neutron irradiation device comprises a neutron source that emits neutrons, and a collimator that shapes the neutrons from the neutron source into a neutron beam with a narrowed cross section.

8. 8. The non-destructive inspection device according to claim 1, further comprising a display for displaying a distribution of the ratios with respect to the detection positions.

9. (A) Irradiating a local irradiation spot on the surface of the object to be inspected with a neutron beam; (B) detecting scattered neutrons returning from the object to be inspected as a result of (A) at each detection position facing the surface, and counting the number of scattered neutrons detected at each detection position; (C) for each detection position, a ratio calculation unit calculates and outputs a ratio of the number of detections at the detection position to a reference value for the detection position; (D) a portion in the distribution of the ratios relating to the detection position where the ratio is greater than 1 and forms an increase peak of the ratio is defined as an increase peak forming portion of the ratio, and a portion in the distribution where the ratio is less than 1 and forms a decrease peak of the ratio is defined as a decrease peak forming portion of the ratio, and the increase peak forming portion and the decrease peak forming portion are identified, and a size Sp of the increase peak forming portion and a size Sn of the decrease peak forming portion are respectively calculated; A non-destructive inspection method for determining defects in an object to be inspected based on Sp and Sn.

10. (E) Calculating Sp / Sn or Sn / Sp, In the step (A), the irradiation position where the neutron beam is injected is changed, and the steps (A) to (E) are repeated; 10. The non-destructive testing method according to claim 9, wherein the irradiated location corresponding to the smallest value of a plurality of Sp / Sn or Sn / Sp values ​​obtained in each of the plurality of runs of (E) is identified as the location closest to a low-density portion or a water-stagnation portion.

11. A non-destructive testing method as described in claim 9 or 10, wherein the reference value is set for each detection position.

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