Non-destructive inspection method for synthesis bed plate

Abstract

To detect even a small defect in a synthetic slab, using a neutron beam.SOLUTION: A nondestructive inspection device 10 for a synthetic slab comprises: a neutron irradiation device 2 that irradiates a local irradiation location on a surface 1e of a synthetic slab 1 with a neutron beam; a detection device 3 that detects scattered neutrons returned from the synthetic slab 1 as a result of irradiating the irradiation location with the neutron beam at each detection position facing the surface 1e, and measures the number of detected scattered neutrons at each detection position; and a ratio calculation unit 5 that calculates, for each detection position, a ratio of the number of detected neutrons at the detection position to a reference value of the detection position. The reference value is set for each detection position as the number of detected neutrons when it is assumed that the synthetic slab 1 has no defects.SELECTED DRAWING: Figure 1A

Description

Technical Field

[0001] The present invention relates to an apparatus and method for inspecting a composite floor slab using a neutron beam. More specifically, the present invention relates to an apparatus and method for inspecting the presence or absence and type of defects in a composite floor slab based on scattered neutrons that are scattered back inside the composite floor slab as a result of irradiating the composite floor slab with a neutron beam.

Background Art

[0002] A composite floor slab is composed by integrating a steel plate and concrete. Composite floor slabs are used, for example, as floor slabs of road bridges and railway bridges. Defects may occur in composite floor slabs due to their use and aging deterioration. Such defects include sandification of concrete, layered cracks, water stagnation areas, etc. In addition, at the time of initial construction of a composite floor slab, there may also occur unfilled portions of concrete, etc. Such unfilled portions occur, for example, in the vicinity of the steel plate.

[0003] Note that Patent Document 1 exists in the prior art of the present application. Patent Document 1 discloses a technique for inspecting defects in infrastructure structures, etc. using a neutron beam. In Patent Document 1, a pulsed neutron beam is irradiated onto an inspection object such as an infrastructure structure, scattered neutrons scattered back in the inspection object are detected, detection number data representing the number of detected scattered neutrons with respect to time is generated, and based on this detection number data, the presence or absence of defects inside the inspection object is determined.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] The composite deck plate constitutes, for example, a road bridge or a railway bridge as described above, and is an important member that supports the load of vehicles passing over the road bridge or railway bridge. Therefore, it is necessary to maintain the composite deck plate through regular inspections and the like.

[0006] In order to maintain the composite deck plate, it is desirable to detect defects occurring in the composite deck plate by non-destructively inspecting the composite deck plate while the defects are small. That is, if the defects occurring in the composite deck plate can be detected before they grow significantly, it can greatly contribute to the maintenance of the composite deck plate.

[0007] However, conventionally, it has been impossible to non-destructively detect defects with dimensions of 10 mm or less (for example, a 3-mm gap or a 6-mm water stagnation area, etc.) occurring in locations that are not visible by visual inspection in the composite deck plate.

[0008] Therefore, an object of the present invention is to provide an apparatus and a method capable of non-destructively detecting even small defects (for example, defects with a size of 10 mm or less) occurring in locations that are not visible by visual inspection in the composite deck plate.

Means for Solving the Problems

[0009] To achieve the above object, a non-destructive inspection apparatus for a composite deck plate according to the present invention includes a neutron irradiation device that irradiates a neutron beam to a local irradiation location on the surface of the composite deck plate, a detection device that detects scattered neutrons returning from the composite deck plate at each detection position facing the surface as a result of the irradiation, and measures the number of detected scattered neutrons for each detection position, a ratio calculation unit that obtains and outputs, for each detection position, the ratio of the number of detected neutrons at the detection position to the reference value of the detection position, wherein the reference value is set for each detection position as the number of detected neutrons when it is assumed that there are no defects in the composite deck plate.

[0010] Also, in a non-destructive inspection method for a composite deck plate according to the present invention, (A) Irradiate a neutron beam at a local irradiation location on the surface of the composite bed plate, (B) As a result of (A) above, detect the scattered neutrons returning from the composite bed plate at each detection position facing the surface, and measure the number of detected scattered neutrons for each detection position. (C) For each detection position, a ratio calculation unit obtains and outputs the ratio of the number of detections at the detection position to the reference value at the detection position. The reference value is set for each detection position as the number of detections when it is assumed that there are no defects in the composite bed plate.

Effect of the Invention

[0011] According to the present invention, a neutron beam is irradiated at a local irradiation location on the surface of the composite bed plate. As a result, when scattered neutrons return from the composite bed plate, the scattered neutrons are detected at each detection position facing the surface of the composite bed plate, and the number of detected scattered neutrons is measured for each detection position. Further, for each detection position, the ratio of the number of detections at the detection position to the reference value at the detection position is obtained.

[0012] Even if the defect existing in the composite bed plate is small, in the distribution of the above ratio regarding the detection position, one or both of an increase peak forming part and a decrease peak forming part of the ratio are generated due to the defect. Therefore, even if the defect in the composite bed plate is small, it is possible to detect the presence or absence of the defect based on the above ratio of each detection position.

Brief Description of the Drawings

[0013]

Figure 1A

Figure 1B

Figures 2A - 2B

Figures 2C - 2D

Figure 3

Figure 4

Figure 5A

Figure 5B

Figure 5C

Figure 6A

Figure 6B

Figure 7A

Figure 7B

Figure 8

Figure 9A

Figure 9B

Figure 10

Figure 11

Embodiments for Carrying Out the Invention

[0014] Embodiments of the present invention will be described with reference to the drawings. In the drawings, the same reference numerals are given to the common parts in each figure, and duplicate explanations are omitted.

[0015] FIG. 1A shows a non-destructive inspection apparatus 10 for a composite floor slab according to an embodiment of the present invention and a composite floor slab 1 to be inspected. FIG. 1B is a view taken along the line 1B-1B of FIG. 1A. The non-destructive inspection apparatus 10 irradiates the composite floor slab 1 with a neutron beam, and as a result, detects scattered neutrons returning from the composite floor slab 1, and based on the detection result, detects the presence or absence, type, etc. of defects.

[0016] (Composite floor slab) The composite floor slab 1 may constitute a bridge (road bridge or railway bridge) on which vehicles travel. In FIG. 1, the left-right direction is the direction in which the bridge extends (bridge axis direction), and the direction orthogonal to the plane of the drawing in this figure is the direction orthogonal to the bridge axis direction (horizontal direction) and is the width direction of the bridge. The composite floor slab 1 is configured by integrating a steel plate and concrete 1c. More specifically, the composite floor slab 1 has a bottom steel plate 1a, a section steel 1b, and concrete 1c.

[0017] The bottom steel plate 1a is installed on the upper surface of a main girder (not shown) extending in the bridge axis direction (the direction in which the bridge extends) and is fixed to the main girder.

[0018] The section steel 1b has a function of reinforcing the bottom steel plate 1a. The section steel 1b is coupled to the upper surface of the bottom steel plate 1a so as to rise upward from the upper surface of the bottom steel plate 1a. This coupling may be made by welding, for example. Further, the section steel 1b extends in the width direction of the bridge. A plurality of such section steels 1b are provided. That is, the plurality of section steels 1b are arranged at intervals in the bridge axis direction. In the example of FIG. 1, the cross section of the section steel 1b by a vertical plane parallel to the bridge axis direction is T-shaped. That is, the section steel 1b having a T-shaped cross section has a plate-like portion 1b1 rising upward from the upper surface of the bottom steel plate 1a and a plate-like portion 1b2 coupled to the upper end of the plate-like portion 1b1 and extending in the bridge axis direction. Note that the cross section of the section steel 1b may have a shape other than T-shaped.

[0019] The concrete 1c is placed on the upper side of the bottom steel plate 1a so as to embed a plurality of profiled steels 1b. In the example of FIG. 1, it is placed on the upper surface of the bottom steel plate 1a. In addition, other structural parts such as reinforcing bars (not shown) may be provided inside the concrete 1c.

[0020] Such a composite floor slab 1 may substantially have a structure that is periodically repeated in the bridge axis direction. In this case, the plurality of profiled steels 1b are arranged at regular intervals in the bridge axis direction, and the said regular intervals correspond to the period of the structure of the composite floor slab 1.

[0021] In addition, the composite floor slab 1 may further have an asphalt layer 1d laid on the upper side of the concrete 1c (for example, the upper surface of the concrete 1c) as shown in FIG. 1. The surface 1e of the composite floor slab 1 (the surface of the asphalt layer 1d in FIG. 1) is the upper surface on the side where the vehicle travels.

[0022] (Configuration of the non-destructive inspection device) The non-destructive inspection device 10 includes a neutron irradiation device 2, a detection device 3, a ratio calculation unit 5, a storage unit 6, a data processing unit 7, a determination value calculation unit 8, and a determination unit 9.

[0023] The neutron irradiation device 2 irradiates a local irradiation location R on the surface 1e of the composite floor slab 1 (substantially only at the irradiation location R) with a neutron beam. The direction of the irradiation may be a direction perpendicular to the surface 1e or an oblique direction with respect to the surface 1e. The irradiation location R may be an irradiation spot. The shape of the irradiation location R may be, for example, circular, elliptical, or rectangular, but is not limited thereto.

[0024] The dimension of the irradiation location R may be 100 mm or less, 70 mm or less, or 50 mm or less. There is no particular lower limit for the dimension of the irradiation location R, but it may be as small as possible (for example, the lower limit may be a value within the range of 0.3 mm or more and 10 mm or less). The dimension of the irradiation location R is the dimension of the cross-section of the neutron beam on the surface 1e. Also, the dimension of the irradiation location R may mean the minimum dimension among the dimensions in each direction of the cross-section of the neutron beam on the surface 1e.

[0025] The neutron irradiation device 2 includes a neutron source 2a that emits neutrons and a collimator 2b.

[0026] The neutron source 2a may, for example, have a target that emits neutrons when irradiated with a charged particle beam. In this case, the target may be lithium, but is not limited thereto. 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 may 252 be Cf, but is not limited thereto.

[0027] 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 the local irradiation location R on the surface 1e.

[0028] The collimator 2b may be formed by partitioning a passage through which the neutron beam passes with a material that is difficult for neutrons to penetrate. The collimator 2b may be, for example, a cylindrical shape with an internal space serving as the above passage.

[0029] The neutron irradiation device 2 emits a neutron beam to the irradiation location R over a set time period. For example, the neutron irradiation device 2 may be configured to emit a pulsed neutron beam to the irradiation location R one or more times over a set time period, or may be configured to emit a temporally continuous neutron beam to the irradiation location R over a set time period as in a modification example described later. In the former case, the pulse time width (duration of the neutron beam) of the pulsed neutron beam is, for example, about 0.1 milliseconds or less than 0.1 milliseconds, and the repetition frequency of the pulsed neutron beam (irradiation frequency of the neutron beam to the composite floor slab 1) is, for example, about 100 Hz, but is not limited thereto as long as it does not prevent the detection of the presence or type of defects. Also, in one example, since the charged particle beam described above is a pulsed charged particle beam, the neutron irradiation device 2 emits a pulsed neutron beam, but the neutron irradiation device 2 may be configured to emit a pulsed neutron beam by other methods.

[0030] Also, the neutron beam emitted by the neutron irradiation device 2 to the irradiation location R may, for example, mainly contain fast neutrons, or may contain fast neutrons and thermal neutrons, or may mainly contain thermal neutrons, but is not limited thereto.

[0031] The detection device 3 detects, at each detection position (each of a plurality of continuously arranged detection positions) facing the surface 1e of the composite floor slab 1, the scattered neutrons that have returned from the composite floor slab 1 as a result of the irradiation of the neutron beam to the irradiation location R, and measures the number of detected scattered neutrons for each detection position. For example, the detection device 3 has a detection surface 3a1 on which the scattered neutrons are incident. Each position on the detection surface 3a1 is each of the above-described detection positions, and the number of detections at each detection position is the number of scattered neutrons incident on that detection position. Also, the detection device 3 may be configured to record, for each detection position, in addition to the number of detections, the energy of the scattered neutrons incident on that detection position and the detection time of the scattered neutrons. The detection device 3 outputs the number of detections measured for each detection position to the ratio calculation unit 5.

[0032] When viewed from the direction facing the surface 1e of the composite floor slab 1, the detection surface 3a1 extends continuously over an area larger than the irradiation location R. In this case, when viewed from the direction facing the surface 1e of the composite floor slab 1, the irradiation location R may be included in the detection surface 3a1. Note that the detection surface 3a1 may be rectangular as shown in FIG. 1B, or may have other shapes. For example, the detection surface 3a1 may be an elongated surface.

[0033] The measurement of the above detection count (detection of scattered neutrons) by the detection device 3 may be performed over a measurement time. This measurement time (hereinafter also simply referred to as the measurement time) may be longer than the pulse time width of the above-described pulsed neutron beam. For example, this measurement time may be a period from immediately after the neutron irradiation device 2 irradiates the neutron beam (immediately after the elapse of the above setting time) until the number of scattered neutrons incident on the detection surface 3a1 per unit time decreases (for example, becomes less than the lower limit value). The length of the measurement time may be, for example, a value within 10 seconds to 10 minutes. However, the measurement time is not limited to this, and it may be set such that at least one of an increasing peak forming portion and a decreasing peak forming portion occurs in the ratio distribution described later when defects such as a water stagnation location or a low-density portion (for example, a void) exist in the composite floor slab 1. Note that hereinafter, the detection count may mean the number of neutrons detected over the above measurement time.

[0034] The water stagnation location may simply be a location where water exists, or may be a location where rust of the metal portion of the composite floor slab 1 (for example, the above reinforcing bars, shape steel 1b, or bottom steel plate 1a) is progressing due to moisture. The low-density portion is a portion having a lower density than the normal portion of the composite floor slab 1. Specifically, the low-density portion may be a portion having a density of 1 / 3 or less, 1 / 5 or less, or 1 / 10 or less of the density of the normal portion of the composite floor slab 1. Such a low-density portion may be a void (for example, a layered crack in the concrete 1c), or may be a portion where a part of the concrete 1c has become sandy soil.

[0035] The detection device 3 includes a detector 3a and a measurement unit 3b. Hereinafter, the inspection time means the time when the neutron beam is irradiated to the irradiation position R on the surface 1e of the composite floor slab 1 to inspect the presence or absence of defects in the composite floor slab 1 (when performing step S3 described later). Further, hereinafter, the inspection means inspecting the presence or absence of defects in the composite floor slab 1 by irradiating the neutron beam in this way (for example, performing steps S3 to S8 described later or beam scanning).

[0036] The detector 3a (detection surface 3a1) is arranged to face the surface 1e of the composite floor slab 1 during inspection. In this arrangement, a part of a large number of detection positions in the detector 3a (for example, the center of the detector 3a (detection surface 3a1)) faces the irradiation position R. In this case, during inspection, the neutron beam from the neutron irradiation device 2 passes through the detector 3a (detection surface 3a1) and irradiates the surface 1e of the composite floor slab 1. In one example, the (for example, virtual) surface having a two-dimensional spread in the detector 3a is the above-mentioned detection surface 3a1. In FIG. 1, an xyz coordinate system having an x-axis, a y-axis, and a z-axis orthogonal to each other is shown. In the example of FIG. 1, the x-axis direction is the bridge axis direction, the y-axis direction is the width direction of the bridge, the z-axis direction is the vertical direction, and the detection surface 3a1 is parallel to the xy plane. Note that the xyz coordinate system in FIG. 1 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).

[0037] During inspection, the detector 3a (detection surface 3a1) is arranged at a position close to or in contact with the surface 1e. Here, the position close to the surface 1e may be, for example, a position within 30 mm, 50 mm, 100 mm, or 300 mm from the surface 1e, but is not limited thereto. Further, during inspection, the detection surface 3a1 may be parallel to the surface 1e of the composite floor slab 1.

[0038] The detector 3a may be 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 where the neutron is incident.

[0039] Detector 3a may be configured to selectively detect thermal neutrons and not detect neutrons other than thermal neutrons. In this case, detector 3a may use a helium-3 ( 3 He) proportional counter tube, or may be a detector that combines a scintillator containing lithium-6 ( 6 Li) and an optical sensor.

[0040] Alternatively, detector 3a may be configured to selectively detect intermediate neutrons and not detect neutrons other than intermediate neutrons. In this case, detector 3a may be a detector that combines a scintillator containing at least one of chlorine ( 35 Cl) and bromine ( 79 Br, 81 Br) and an optical sensor. For example, detector 3a may be a detector that combines a scintillator containing CLYC or LaBr 3 and an optical sensor.

[0041] Note that detector 3a is not limited to the above, and for example, 155 Gd, 157 Gd, 10 B, etc., may be a detector that combines a scintillator containing them and an optical sensor. Also, each of the above-described optical sensors may be a photomultiplier tube or a SiPM (Silicon Photomultiplier), but is not limited thereto.

[0042] Thermal neutrons generally refer to neutrons having an energy value of 25 meV or less at room temperature. Intermediate neutrons refer to neutrons having an energy sufficiently higher than that of thermal neutrons (an energy of several keV or more and less than several hundred keV), and fast neutrons refer to neutrons having an energy of several hundred keV or more. Here, since there is no strict definition for the threshold of the neutron name based on energy, in the definition of the present application, thermal neutrons may be neutrons having an energy of several tens of meV (for example, 50 meV) or less, intermediate neutrons are neutrons having an energy of several keV (for example, 5 keV) or more and less than several hundred keV (for example, 500 keV), and fast neutrons may be neutrons having an energy of several hundred keV (for example, 500 keV) or more.

[0043] Based on a large number of detection signals output from the detector 3a, the measurement unit 3b measures the number of detected scattered neutrons incident on each detection position for each detection position. When the above-described optical sensor is used, the measurement unit 3b may be incorporated in the above-described optical sensor such as a SiPM.

[0044] The ratio calculation unit 5 obtains, for each detection position in the detector 3a, the ratio of the number of detections at the detection position to the reference value at the detection position (hereinafter also simply referred to as the ratio). The reference value is set for each detection position as the number of detections when it is assumed that there are no defects in the composite floor slab 1. Such reference values may vary depending on the detection position. That is, the reference values may be different between at least some of the detection positions. That is, the reference value is the number of detections obtained when the composite floor slab 1 without defects is hypothetically inspected. The reference value for each detection position in the detector 3a (detection surface 3a1) is preset according to the positional relationship between the irradiation location R and the detection position, and the neutron scattering characteristics in the composite floor slab 1, etc.

[0045] In this embodiment, the reference value for each detection position is preset as the number of detections when neutron rays are irradiated from the neutron irradiation device 2 toward any one of the steel sections 1b. In the case of the steel section 1b having a T-shaped cross section, the reference value for each detection position may be preset as the number of detections when neutron rays are irradiated from the neutron irradiation device 2 toward the plate-like portion 1b1 included in the T-shaped steel section 1b in the direction (vertical direction) in which the plate-like portion 1b1 rises from the bottom steel plate 1a. Here, "irradiating neutron rays from the neutron irradiation device 2 toward the steel section 1b (or the plate-like portion 1b1)" means that the neutron beam enters the steel section 1b (or the plate-like portion 1b1) assuming that the neutron beam from the neutron irradiation device 2 travels straight without being scattered before reaching the steel section 1b.

[0046] The reference value for each detection position may be set at one irradiation location R where the neutron beam is irradiated during the inspection. Further, for example, when performing an inspection by irradiating the neutron beam to each of a plurality of irradiation locations R as in the beam scan described later, the reference value for each detection position may be set for each of these irradiation locations R.

[0047] <Method for setting reference value> The above-mentioned reference value may be preset for each detection position in the detector 3a as follows. That is, when inspecting the composite floor slab 1 without defects under the same conditions as the actual inspection, the number of neutrons (for example, the estimated number of detections) detected at each detection position of the detector 3a over the measurement time may be set as the reference value for that detection position. Here, "the same conditions as the actual inspection" includes the following detection conditions (a) to (c).

[0048] (a) The positional relationship and the attitude relationship (orientation relationship) between the detector 3a (detection surface 3a1), the composite floor slab 1 (irradiation location R), and the neutron irradiation device 2 are the preset positional relationship and attitude relationship. (b) The spectrum of the neutron beam emitted from the neutron irradiation device 2 to the composite floor slab 1 is defined. The spectrum of the neutron beam when the neutron irradiation device 2 emits the neutron beam is the energy distribution of a large number of neutrons irradiated from the neutron irradiation device 2 to the composite floor slab 1 per unit time (for example, in the case of a pulsed neutron beam, within the pulse time width), and in this distribution, for each energy, the number of neutrons having that energy is represented. (c) The intensity of the neutron beam is defined. The intensity of the neutron beam is the number of neutrons irradiated per unit time to the irradiation location R (or per unit area at the irradiation location R) by the emission when the neutron irradiation device 2 emits the neutron beam.

[0049] In one example, under the above detection conditions (a) to (c), the neutron irradiation device 2 irradiates neutrons to one irradiation location R on the actual composite floor slab 1 (for example, a composite floor slab 1 assumed to have a low probability of defects), and the number of detections at each detection position in the detector 3a is obtained. Then, the irradiation location R is changed on the same composite floor slab 1 and the same process is performed again. By repeating this process, for each of the plurality of irradiation locations R, the number of detections at each detection position in the detector 3a is obtained. And for each detection position in the detector 3a, the average value of the plurality of detection numbers at that detection position obtained for the plurality of irradiation locations R is set as the reference value for that detection position. Note that these plurality of irradiation locations R may be locations shifted from each other in the width direction of the above bridge, or may be locations shifted from each other by the period of the structure of the composite floor slab 1 (the arrangement interval of the H-beams 1b) in the above bridge axis direction. Also, in this case, each of these plurality of irradiation locations R may be located directly above the H-beam 1b.

[0050] In another example, a specimen having the same configuration (such as material) as the actual composite floor slab 1 (for example, the composite floor slab 1 with a high assumed probability of defects) but without defects is prepared. This specimen is used as the composite floor slab 1, and under the above detection conditions (a) to (c), the neutron irradiation device 2 irradiates neutrons at the irradiation position R on the specimen, the number of detections at each detection position in the detector 3a is obtained, and the number of detections is set as the reference value for the detection position.

[0051] In yet another example, under the above detection conditions (a) to (c), when inspecting the composite floor slab 1 without defects, the number of detections obtained for each detection position of the detector 3a is obtained by simulation, and the number of detections is set as the reference value for the detection position.

[0052] When viewed in the direction in which the neutron beam is incident on the surface 1e of the composite floor slab 1 under the above detection conditions (a) to (c), the reference value for each detection position in the detector 3a (detection surface 3a1) tends to decrease as the detection position is farther from the irradiation position R of the neutron beam on the surface 1e.

[0053] The storage unit 6 stores the reference value for each detection position in the detector 3a for one irradiation position R or for each of a plurality of irradiation positions R. The ratio calculation unit 5 calculates a ratio for each detection position in the detector 3a based on the reference value in the storage unit 6 and the above-described number of detections.

[0054] The data processing unit 7 performs data processing on the ratios of each detection position of the detector 3a output by the ratio calculation unit 5. The data processing unit 7 identifies an increasing peak forming part and a decreasing peak forming part in the distribution of the ratios (hereinafter also simply referred to as the ratio distribution) regarding the detection positions on the detector 3a. Further, the data processing unit 7 obtains the magnitude of the identified increasing peak forming part and the magnitude of the decreasing peak forming part.

[0055] <Ratio distribution> Figures 2A to 2D schematically show ratio curves C1 to C4 indicating the ratio distribution regarding the detection positions.

[0056] Figures 2A and 2B show the case where there are low-density portions (e.g., voids) as defects inside the composite floor slab 1, and Figures 2C and 2D show the case where there is water as a defect inside the composite floor slab 1. Also, Figures 2A and 2C show the case where the defect in the composite floor slab 1 exists on the extension line of the neutron beam irradiated on the composite floor slab 1, and Figures 2B and 2D show the case where the defect in the composite floor slab 1 exists at a position deviated from the extension line of the neutron beam irradiated on the composite floor slab 1.

[0057] In FIGS. 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 above ratio of the number of detections. The ratio distributions in FIGS. 2A to 2D indicate the distributions at the same constant y coordinate (see FIG. 1B) as the irradiation location R. FIGS. 2A to 2D show the case where the number of detections is the number of thermal neutrons detected. However, even if the number of detections is the number of intermediate neutrons detected, the tendency of the ratio distribution is the same as that in FIGS. 2A to 2D.

[0058] As in each of FIGS. 2A to 2D, due to the influence of the defect existing in the composite floor slab 1, a decrease peak forming portion and an increase peak forming portion are generated in the ratio distribution. The decrease peak forming portion is a portion where the ratio is less than 1 and forms a decrease peak (negative direction peak) of the ratio. The increase peak forming portion is a portion where the ratio is greater than 1 and forms an increase peak (positive direction peak) of the ratio.

[0059] In FIGS. 2A and 2B, the decrease peak forming portion is the portion from point D2 to point D3 on the ratio curves C1 and C2 representing the ratio distribution, and the increase peak forming 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.

[0060] In FIGS. 2C and 2D, the decrease peak forming 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 increase peak forming portion is the portion from point D2 to point D3 on the ratio curves C3 and C4.

[0061] Further, the size of the decreasing peak forming portion may be the area of the region sandwiched between the portion where the ratio is 1 (the straight line L indicated by the broken line in FIGS. 2A to 2D) and the decreasing peak forming portion (the hatched area indicated by the symbol N in FIGS. 2A to 2D). That is, assuming that x is the position coordinate (the x-axis coordinate in FIG. 1A), when the ratio curve is represented by ratio = f(x), ∫{1 - f(x)}dx may be the size of the decreasing peak forming portion. This integration is performed over the x interval of the decreasing peak forming portion.

[0062] Similarly, the size of the increasing peak forming portion may be the area of the region sandwiched between the portion where the ratio is 1 (the straight line L indicated by the broken line in FIGS. 2A to 2D) and the increasing peak forming portion (the hatched area indicated by the symbol P in FIGS. 2A to 2D). That is, assuming that x is the position coordinate (the x-axis coordinate in FIG. 1A), when the ratio curve is represented by ratio = f(x), ∫{f(x) - 1}dx may be the size of the increasing peak forming portion. This integration is performed over the x interval of the increasing peak forming portion.

[0063] · Defects in the low-density portion Hereinafter, voids are assumed as defects in the low-density portion for explanation, but the following content also applies when other defects in the low-density portion are assumed. In this case, hereinafter, each "void" may be read as a low-density portion.

[0064] When the defect existing inside the composite floor slab 1 is a void, as shown in FIG. 2A, in the detector 3a, in the vicinity of the region facing the void (that is, in the vicinity of the same x coordinate as the void), a decreasing peak forming portion of the ratio occurs in the ratio distribution.

[0065] This decrease peak forming part is formed for the following reason. Since neutrons do not scatter in voids, the neutrons irradiated on the composite floor slab 1 do not scatter from the location of the void to the detector 3a when passing through the void to the side away from the surface 1e of the composite floor slab 1. Therefore, correspondingly, in the region near the detector surface 3a1 facing the void, the number of detected scattered neutrons decreases, resulting in the formation of a decrease peak forming part. Also, the fast neutrons incident on the composite floor slab 1 turn into thermal neutrons while passing through the composite floor slab 1 (for example, concrete 1c), but the presence of voids in the composite floor slab 1 means that the generation of thermal neutrons is reduced accordingly. Therefore, in the region near the detector surface 3a1 facing the void, the number of detected scattered thermal neutrons decreases.

[0066] On the other hand, in the region adjacent to the region near the detector 3a facing the void (decrease peak forming part), as shown in FIG. 2A, in the ratio distribution (ratio curve C1), an increase peak forming part (peak in the positive direction) of the ratio occurs.

[0067] This increase peak forming part is formed for the following reason. The scattered neutrons incident on the region adjacent to the region near the detector surface 3a1 facing the void (decrease peak forming part) include scattered neutrons that scatter at a position deeper than the void and pass through the void toward the adjacent region. This "scattered neutron passing through the void" does not scatter in other directions in the void and is less likely to be absorbed by the composite floor slab 1 (for example, concrete 1c) due to the presence of the void. Therefore, correspondingly, in the above adjacent region, the number of detected scattered neutrons increases, resulting in the formation of the above increase peak forming part.

[0068] Also, as shown in FIG. 2B, even if the position of the void is slightly deviated from the extension line of the neutron beam irradiated on the irradiation location R, a ratio distribution similar to that in the case of FIG. 2A can be obtained. In FIG. 2B, a relatively large increase peak forming part occurs on the left side. This is because among the neutron beams incident on the composite floor slab 1 in FIG. 2B, more scattered neutrons pass through the void and are detected at the position corresponding to the increase peak forming part on the left side.

[0069] · Defect of water When the defect existing inside the synthesis bed plate 1 is water (a water stagnation point), as shown in Fig. 2C, in the ratio distribution, in the vicinity of the region facing the water stagnation point (i.e., near the same x coordinate as the water stagnation point), an increasing peak forming part occurs.

[0070] This increasing peak forming part is formed for the following reason. In the detection surface 3a1, the scattered neutrons incident on the region facing the water stagnation point include the scattered neutrons from the water stagnation point. Here, since neutrons easily react with water, many of the scattered neutrons from the water stagnation point are those that have reacted with water and become thermal neutrons. Therefore, correspondingly, in the detection surface 3a1, in the region facing the water stagnation point, the number of detected scattered thermal neutrons increases, so the increasing peak forming part occurs.

[0071] Note that, as shown in Fig. 2C, the depression in the negative direction at the top of the increasing peak forming part is due to the following reason. When neutrons pass through the water stagnation point on the side away from the surface 1e of the synthesis bed plate 1, it is difficult for them to be scattered from the water stagnation point to the detector 3a. Therefore, correspondingly, in the center of the region facing the water stagnation point on the detection surface 3a1, the number of detected thermal neutrons decreases, so the above-mentioned depression occurs.

[0072] The determination value calculation unit 8 receives from the data processing unit 7 the size of the increasing peak forming part and the size of the decreasing peak forming part as Sp and Sn respectively. The determination value calculation unit 8 obtains the sum (Sp + Sn) of the size of the increasing peak forming part and the size of the decreasing peak forming part, and also obtains the value (Sn / Sp) obtained by dividing the size of the decreasing peak forming part by the size of the increasing peak forming part. Further, the determination value calculation unit 8 outputs the obtained Sp + Sn and Sn / Sp.

[0073] Note that when a plurality of increasing peak forming parts occur in the ratio distribution, Sp may be the sum of the sizes of the plurality of increasing peak forming parts. Similarly, when a plurality of decreasing peak forming parts occur in the ratio distribution, Sn may be the sum of the sizes of the plurality of decreasing peak forming parts.

[0074] Based on Sp+Sn and Sn / Sp output by the data processing unit 7, the determination unit 9 determines the presence or absence of defects and the types of defects in the composite floor slab 1. 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.

[0075] When there are no defects in the composite floor slab 1, in the ratio distribution, no increasing peak forming part or decreasing peak forming part occurs, or even if an increasing peak and a decreasing peak occur, these peak forming parts are small, so Sp+Sn becomes a value of 0 or close to 0. Therefore, assuming that the first threshold value T1 is a positive value of 0 or close to 0, when there are no defects, as shown in FIG. 3, Sp+Sn is less than or equal to the first threshold value T1.

[0076] When there are voids as defects in the composite floor slab 1, in the ratio distribution, as shown in FIG. 2A, a relatively large decreasing peak forming part occurs, and an increasing peak forming part also occurs. Therefore, when there are voids, as shown in FIG. 3, Sp+Sn becomes larger than the above-mentioned first threshold value T1, and Sn / Sp becomes greater than or equal to the second threshold value T2 which is a positive value.

[0077] When there is water (a water stagnant area) as a defect in the composite floor slab 1, in the ratio distribution, as shown in FIG. 2C, a considerably large increasing peak forming part occurs, and the decreasing peak forming part hardly appears. Therefore, when there is water, as shown in FIG. 3, Sp+Sn becomes larger than the above-mentioned first threshold value T1, and Sn / Sp becomes less than the above-mentioned second threshold value T2.

[0078] According to the above, the determination unit 9 makes a determination as follows. When Sp+Sn is less than or equal to the first threshold value, the determination unit 9 determines that there are no defects in the composite floor slab 1 and outputs a signal indicating the absence of defects. Based on this output, for example, it may be displayed on the display that there are no defects.

[0079] When Sp + Sn is greater than the first threshold value, the determination unit 9 determines that there is a defect in the composite floor slab 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. When Sp + Sn is greater than the first threshold value T1 and Sn / Sp is greater than or equal to the second threshold value T2, the determination unit 9 determines that there is a void in the composite floor slab 1 and outputs a first defect signal to that effect. When 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 there is water (a water stagnant area) in the composite floor slab 1 and outputs a second defect signal to that effect.

[0080] (Non-destructive inspection method) FIG. 4 is a flowchart showing a non-destructive inspection method for a composite floor slab according to an embodiment of the present invention. This non-destructive inspection method is performed using the above-described non-destructive inspection apparatus 10 and includes steps S1 to S8.

[0081] In step S1, the reference values at each detection position of the detector 3a are set as described above.

[0082] In step S2, the neutron irradiation device 2 and the detector 3a are arranged with respect to the composite floor slab 1. In the present embodiment, the neutron irradiation device 2 and the detector 3a are arranged on the surface 1e side of the composite floor slab 1 as viewed from the inside of the composite floor slab 1.

[0083] In step S3, a neutron beam is incident on a local irradiation location R on the surface 1e of the composite floor slab 1 by the neutron irradiation device 2. Such steps S2 and S3 are performed under the above-described detection conditions (a) to (c).

[0084] Note that in step S3, the irradiation direction of the neutron beam to the irradiation location R may be perpendicular to the flat surface 1e of the composite floor slab 1 or may be an oblique direction with respect to the direction perpendicular to the surface 1e.

[0085] In step S4, based on the result of step S3, the scattered neutrons that have returned from the composite floor slab 1 are detected at each detection position on the detection surface 3a1 facing the surface 1e, and the number of detected scattered neutrons is measured for each detection position. Step S4 is performed by the detection device 3.

[0086] In step S5, based on the reference value of each detection position set in step S1 and the number of detections of each detection position measured in step S4, the ratio calculation unit 5 obtains and outputs, for each detection position on the detection surface 3a1, the ratio of the number of detections at the detection position to the reference value of the detection position.

[0087] In step S6, the data processing unit 7 identifies the increasing peak forming part and the decreasing peak forming part in the distribution of the ratios calculated in step S5 with respect to the detection positions, and obtains the size Sp of the increasing peak forming part and the size Sn of the decreasing peak forming part.

[0088] In step S7, the determination value calculation unit 8 obtains Sp + Sn, and the determination unit 9 determines whether there is a defect inside the composite floor slab 1 based on Sp + Sn. In step S7, when Sp + Sn is less than or equal to the first threshold value T1, the determination unit 9 determines that there is no defect inside the composite floor slab 1 and outputs a signal indicating that no defect exists. On the other hand, in step S7, when Sp + Sn is greater than the first threshold value T1, the determination unit 9 determines that there is a defect inside the composite floor slab 1 and proceeds to step S8.

[0089] In step S8, the determination value calculation unit 8 obtains Sn / Sp, and the determination unit 9 determines the type of defect based on Sn / Sp. In step S8, when Sn / Sp is greater than or equal to the second threshold value T2, the determination unit 9 determines that there is a low-density part (for example, a void) as a defect inside the composite floor slab 1 and outputs a first defect signal to that effect. On the other hand, in step S8, when Sn / Sp is less than the second threshold value T2, the determination unit 9 determines that there is water (a water stagnant area) as a defect inside the composite floor slab 1 and outputs a second defect signal to that effect.

[0090] <Beam scanning> Next to step S8, steps S3 to S6 may be repeated by changing the irradiation position R in step S3. That is, the irradiation position R where the neutron beam is incident on the surface 1e of the composite floor slab 1 in step S3 is made different from each other during a plurality of repeated steps S3. In this case, a plurality of steps S3 may be performed so as to scan the composite floor slab 1 with the neutron beam.

[0091] Also, taking one cycle of steps S3 to S6, for each cycle, Sp / Sn or Sn / Sp is obtained from Sp and Sn obtained in step S6 of the cycle. At this time, when it is determined in step S8 described above that there is a low-density portion as a defect, Sp / Sn may be obtained, and when it is determined in step S8 described above that there is water as a defect, Sn / Sp may be obtained.

[0092] Among the plurality of Sp / Sn or Sn / Sp obtained for each of the plurality of cycles, the minimum Sp / Sn or Sn / Sp is specified. The irradiation position R corresponding to the specified minimum Sp / Sn or Sn / Sp (that is, the irradiation position R in the cycle in which this Sp / Sn or Sn / Sp was obtained) is specified as the position closest to the above-mentioned low-density portion (void) or the above-mentioned water among the plurality of irradiation positions R corresponding to these Sp / Sn or Sn / Sp respectively.

[0093] That is, when a plurality of Sp / Sn are obtained for each of the plurality of cycles, the irradiation position R corresponding to the minimum Sp / Sn among these Sp / Sn is specified as the position closest to the above-mentioned low-density portion (void). Similarly, when a plurality of Sn / Sp are obtained for each of the plurality of cycles, the irradiation position R corresponding to the minimum Sn / Sp among these Sn / Sp is specified as the position closest to the above-mentioned water. Such beam scanning will be described in more detail in Example 2 below.

[0094] (Example 1: When detecting thermal neutrons and when detecting intermediate neutrons) The nondestructive inspection apparatus 10 was used to inspect the composite floor slab 1 (specimen) with known positions and dimensions of voids as defects. Fig. 5A shows a cross-section of the inspected composite floor slab 1, and Fig. 5B is a view taken along the arrow 5B-5B in Fig. 5A. Fig. 5C is a diagram showing the dimensions of each part in Fig. 5A.

[0095] As shown in Figs. 5A and 5B, voids exist as defects inside the composite floor slab 1. In Fig. 5A, x, y, and z represent the x-axis, y-axis, and z-axis that are orthogonal to each other in the xyz coordinate system.

[0096] Steps S2 to S7 described above were performed using the detector 3a that selectively detects thermal neutrons in step S4 described above. At this time, in step S3, the neutron beam was irradiated to the irradiation location R shown in Fig. 5B. This irradiation location R is a square with a side length of 50 mm (the area surrounded by the broken line indicated by the symbol R in Fig. 5B). In step S5, the reference value for the case of selectively detecting thermal neutrons was used.

[0097] The above experiment was conducted under the same conditions for each case where the dimensions of the void in the x-axis direction and y-axis direction were fixed at 50 mm and 300 mm respectively, and the dimension of the void in the z-axis direction was 3 mm, 10 mm, and 30 mm.

[0098] In addition, the above experiment was conducted using the detector 3a that selectively detects intermediate neutrons with other conditions being the same. The reference value used was the value for the case of selectively detecting intermediate neutrons.

[0099] Figs. 6A and 6B 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 30 mm. Fig. 6A shows the case using the detector 3a that selectively detects thermal neutrons, and Fig. 6B shows the case using the detector 3a that selectively detects intermediate neutrons. In Figs. 6A and 6B, the horizontal axis and the vertical axis represent the coordinates of the x-axis and y-axis shown in Fig. 5A, and the origin of each coordinate is the center of the irradiation location R. Also, in Figs. 6A and 6B, the broken line indicates the range where the void exists when viewed in the z-axis direction.

[0100] In Fig. 6A, the approximate ratio distributions on the detection surface 3a1 are shown in sections A to E surrounded by a solid line. The ratio is less than 0.85 in section A, not less than 0.85 and less than 0.90 in section B, not less than 0.90 and less than 1.00 in section C, and not less than 1.00 and less than 1.10 in section D. Note that section E is a section with a large error.

[0101] Similarly, in Fig. 6B, the approximate ratio distributions on the detection surface 3a1 are shown in sections A to D surrounded by a solid line. The ratio is less than 0.90 in section A, not less than 0.90 and less than 0.95 in section B, not less than 0.95 and less than 1.00 in section C, and not less than 1.00 and less than 1.10 in section D. Note that section E is a section with a large error.

[0102] As can be seen from Fig. 6A and Fig. 6B, whether the neutrons to be detected are thermal neutrons or epithermal neutrons, the presence of voids can be detected. For example, in Fig. 6A and Fig. 6B, since there are regions where the ratio decreases below 1 and regions where the ratio increases above 1 (and the ratio is the smallest near directly above the void), it can be determined that voids are present.

[0103] Fig. 7A shows the x-axis direction distribution of the ratio obtained when the detector 3a that selectively detects thermal neutrons is used in the above experiment. Fig. 7B shows the x-axis direction distribution of the ratio obtained when the detector 3a that selectively detects epithermal neutrons is used in the above experiment. In Fig. 7A and Fig. 7B, each triangular mark indicates the case where the dimension of the void in the z-axis direction is 3 mm, each square mark indicates the case where the dimension of the void in the z-axis direction is 10 mm, and each circular mark indicates the case where the dimension of the void in the z-axis direction is 30 mm.

[0104] In FIGS. 7A and 7B, the curves approximate the ratio distributions when the z-axis dimension of the void is 30 mm. In FIGS. 7A and 7B, as the absolute value of the position coordinate in the x-axis direction increases (exceeding about 400 mm in the case of FIG. 7B), the obtained ratio has a large error. Therefore, Sn and Sp may be obtained within the range of position coordinates where the error does not exceed the tolerance limit. For example, in FIG. 7B, Sn and Sp may be obtained within the range where the x-coordinate is from -200 mm to 400 mm or about 600 mm. Note that the coordinate range for obtaining Sn and Sp may be appropriately set according to the size and type of the defect. In FIGS. 7A and 7B, the ratio tends to approach 1 as it moves away from the center of the irradiation location R on both ends of the position coordinate in the x-axis direction.

[0105] As can be seen from the comparison between FIGS. 6A and 6B, or between FIGS. 7A and 7B, When detecting intermediate neutrons, the ratio rises more sharply above 1 with respect to the position of the void. Therefore, when Sn and Sp are obtained within the range of position coordinates with a relatively small error (in FIGS. 7A and 7B, for example, the range where the x-coordinate is from -200 mm to 400 mm), the value of Sp + Sn is larger when detecting intermediate neutrons. Thus, by detecting intermediate neutrons, the sensitivity of the value of Sp + Sn to the presence of the void can be increased.

[0106] FIG. 8 shows the values of Sp + Sn for each case in the above experiment. In FIG. 8, the horizontal axis represents the z-axis dimension of the void, and the vertical axis represents the obtained value of Sp + Sn. Also, in FIG. 8, the circles indicate the case of selectively detecting thermal neutrons, and the squares indicate the case of selectively detecting intermediate neutrons.

[0107] As shown in FIG. 8, even when the z-axis dimension of the void is 3 mm, Sp + Sn becomes significantly larger than the first threshold value 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 detected amount of thermal neutrons, as shown in FIG. 8, the sensitivity of the value of Sp + Sn to the presence of the void is higher when intermediate neutrons are detected. Therefore, when a sufficient amount of intermediate neutrons is detected, the presence of the void can be detected with high sensitivity by detecting intermediate neutrons in the inspection.

[0108] (Example 2: Beam Scan) (When the defect is a void) The above-described beam scan was performed using the non-destructive inspection apparatus 10. In this Example 2, the detector 3a that selectively detects thermal neutrons was used. FIG. 9A shows a cross-section of the composite floor slab 1 on which the beam scan was performed, and FIG. 9B is a view taken along the arrow 9B-9B in FIG. 9A. The composite floor slab 1 in FIG. 9A is the same as that in the case of FIG. 5A, and the dimensions of each part are also the same as those in the case of FIG. 5C.

[0109] In FIGS. 9A and 9B, the dimensions of the void existing as a defect inside the composite floor slab 1 in the x-axis direction, y-axis direction, and z-axis direction are 50 mm, 300 mm, and 10 mm, respectively.

[0110] Taking the above-described steps S3 to S6 as one cycle of the beam scan, in each of the three cycles (step S3), the neutron beam was irradiated onto the surface 1e of the composite floor slab 1. Also, the neutron beams irradiated in the three cycles are respectively indicated by B1 to B3 in FIG. 9A. Also, the irradiation locations in the three cycles are squares with a side length of 50 mm. FIG. 9B shows the irradiation location R1 and its center r1 in the first cycle, the center r2 of the irradiation location in the second cycle, and the center r3 of the irradiation location in the third cycle. r1, r2, and r3 are shifted from each other by 29 mm in the x-axis direction.

[0111] FIG. 10 shows the result of performing the beam scan in three cycles as described above, and shows the x-axis direction distribution of the ratio on the detection surface 3a1. In FIG. 10, the horizontal axis represents the position coordinate in the x-axis direction, and the vertical axis represents the ratio (number of detections / reference value). In FIG. 10, each triangular mark indicates the case where the center of the neutron beam irradiation position on the surface 1e of the composite floor slab 1 is r1 in FIG. 9B, each square mark indicates the case where the center is r2 in FIG. 9B, and each circular mark indicates the case where the center is r3 in FIG. 9B. Note that in FIG. 10, the ratio at each position coordinate indicates the ratio at the same y-axis coordinate as the center of the neutron beam irradiation position R1 on the surface 1e. In FIG. 10, as the absolute value of the position coordinate in the x-axis direction increases, the obtained ratio has a larger error. Therefore, Sn and Sp may be obtained within the range of the position coordinates where the error does not exceed the tolerance limit. Note that in FIG. 10, at both ends of the position coordinate in the x-axis direction, there is a tendency to approach zero as the distance from the center of the irradiation position increases.

[0112] The above-described experiment was performed under the same conditions for each case where the z-axis dimension of the gap was 3 mm and 30 mm, with the beam scan in three cycles as described above. FIG. 11 shows the Sp / Sn values obtained by such a beam scan. In FIG. 11, the horizontal axis represents the x-axis direction distance between the center of the irradiation position R and the center of the gap, and the vertical axis represents the Sp / Sn values obtained in each cycle of the beam scan. Here, Sn and Sp are obtained in a range where the error is relatively small. Also, in FIG. 11, 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.

[0113] As shown in Fig. 11, the irradiation location R in the cycle where the minimum Sp / Sn is obtained is closest to the void in the composite floor slab 1. Therefore, the irradiation location R corresponding to the minimum Sp / Sn can be specified as the location closest to the void. For example, when irradiating the surface 1e of the composite floor slab 1 with a neutron beam directly above the void in the composite floor slab 1, many neutrons pass through the void in the direction away from the surface 1e. At this time, these neutrons do not scatter toward the detector 3a side in the void. As a result, it is considered that the number of detected neutrons significantly decreases in the region directly above the void on the detection surface 3a1. Also, thermal neutrons are not generated in the void. Therefore, it is considered that the closer the irradiation location R is to the void (directly above the void), the larger Sn becomes and the smaller Sp / Sn becomes.

[0114] (Effect of the Embodiment) As described above, irradiate a neutron beam at the local irradiation location R on the surface 1e of the composite floor slab 1. As a result, measure the number of scattered neutrons incident on each detection position on the detector 3a as the detected number, and for each detection position, obtain the ratio of the detected number at the detection position to the reference value at the detection position. The ratio distribution regarding the detection position obtained in this way contains information indicating the presence or absence and type of defects. Therefore, based on the ratio (ratio distribution) of each detection position in the detector 3a, the presence or absence and type of defects can be detected.

[0115] For example, when taking the sizes of the increasing peak formation part and the decreasing peak formation part of the ratio in the ratio distribution as Sp and Sn respectively, and when Sp + Sn is greater than the first threshold value T1, it can be determined that there are defects in water or low-density parts (such as voids).

[0116] Also, when Sp + Sn is greater than the first threshold value T1 and Sn / Sp is greater than or equal to the second threshold value T2, it can be determined that there is a low-density part as a defect in the composite floor slab 1.

[0117] When 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 there is water as a defect in the composite floor slab 1.

[0118] Also, by making the irradiation position R a local position (e.g., a spot), when there are defects in the composite floor slab 1, the above-described increasing peak forming part and decreasing peak forming part are more likely to occur significantly in the ratio distribution.

[0119] When detecting the presence or absence of a low-density part (e.g., voids), by the detector 3a selectively detecting intermediate neutrons, Sp+Sn with high sensitivity to the low-density part can be obtained.

[0120] By the above-described beam scan, Sp / Sn or Sn / Sp is obtained for each irradiation position R, and it can be determined that the irradiation position R corresponding to the minimum Sp / Sn or Sn / Sp is closest to the low-density part or the water stagnation part.

[0121] Also, by the beam scan method, for each of at least two or three irradiation positions R, by obtaining Sp / Sn or Sn / Sp, it can be found that there is a low-density part or a water stagnation part on the side of the irradiation position R where the value of Sp / Sn or Sn / Sp is smaller.

[0122] Each neutron of the neutron beam incident on the composite floor slab 1 can enter to a deeper position by passing through the section of the steel shape 1b rather than passing through the section of the concrete 1c. Therefore, at the time of inspection, the neutron irradiation device can highly sensitively detect small defects (e.g., defects near the steel shape 1b) in the composite floor slab 1 by irradiating neutron rays toward the steel shape 1b in the composite floor slab 1. In this case, correspondingly, the reference value of each detection position used for calculating the ratio is preset as the number of detections when the neutron irradiation device 2 irradiates neutron rays toward the steel shape 1b in the composite floor slab 1.

[0123] In the inspection of this embodiment, since the composite floor slab 1 is irradiated with a neutron beam and the scattered neutrons that return are detected, all inspection devices (neutron irradiation device 2 and detection device 3) can be arranged only on the upper surface side, which is the surface 1e of the composite floor slab 1. Therefore, it is not necessary to arrange inspection devices on the lower surface side of the composite floor slab 1, and the cost and time required for inspection can be reduced.

[0124] The present invention is not limited to the above-described embodiments, and it goes without saying that various modifications can be made within the scope of the technical idea of the present invention. For example, the non-destructive inspection device 10 according to the embodiment of the present invention does not necessarily exhibit all of the above-described effects. Further, the non-destructive inspection device 10 according to the embodiment of the present invention does not necessarily have all of the above-described plurality of components, and may have only some of the above-described plurality of components.

[0125] Further, according to the present invention, any one of the following modification examples 1 to 7 may be adopted alone, or two or more of the modification examples 1 to 7 may be arbitrarily combined and adopted. In this case, the points not described below are the same as above.

[0126] (Modification example 1) In the above description, the neutron irradiation device 2 irradiates the irradiation location R with a pulsed neutron beam, but the irradiation location R may be irradiated with a continuous neutron beam that is temporally continuous. In this case, when there are defects such as a water stagnation location or a low-density portion in the composite floor slab 1, the detection device 3 may measure the number of detections at each detection position in the detector 3a over a time period (measurement time) in which an increase peak formation portion and a decrease peak formation portion occur in the above-described ratio distribution.

[0127] (Modification example 2) When the type of defect is not determined, the determination value calculation unit 8 does not necessarily calculate Sn / Sp.

[0128] (Modification example 3) Although not described above, as shown in FIG. 1A, the non-destructive inspection device 10 may further include a display 11.

[0129] 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 view the displayed ratio distribution to determine the presence or absence and type of defects. In such a modification example 3, when the display 11 is provided, the data processing unit 7, the determination value calculation unit 8, and the determination unit 9 may be omitted.

[0130] The ratio distribution displayed on the display 11 may be represented in a two-dimensional coordinate system having a coordinate axis indicating each detection position (for example, the x-axis in FIG. 1A) and a coordinate axis indicating the ratio, as shown in FIGS. 2A to 2D, for example. Alternatively, the ratio distribution displayed on the display 11 may be represented in a three-dimensional coordinate system having two coordinate axes (for example, the x-axis and the y-axis in FIG. 1A) indicating each detection position and orthogonal to each other and a coordinate axis indicating the ratio. Or, the ratio distribution displayed on the display 11 may be represented by expressing the magnitude of the ratio at each detection position within a two-dimensional plane (detection plane 3a1) displayed on the display 11, such as in FIGS. 6A and 6B, by a plurality of sections (for example, sections A to E in FIG. 6A), colors, or shades. Note that the ranges of the ratio values are different from each other among the plurality of sections, and the upper and lower limits of the ratio ranges of each section may also be displayed on the display 11.

[0131] Alternatively, when the display 11 is provided, only the determination unit 9 among the data processing unit 7, the determination value calculation unit 8, and the determination unit 9 may be omitted. In this case, the determination value calculation unit 8 may output Sp+Sn and Sn / Sp as the obtained determination values to the display 11. In this case, each of the output determination values is displayed on the display 11, and a person may view the displayed determination values to determine the presence or absence and type of defects. In this case, the ratio distribution may further be displayed on the display 11 as described above.

[0132] Alternatively, when providing the display 11, only the determination value calculation unit 8 and the determination unit 9 among the data processing unit 7, the determination value calculation unit 8, and the determination unit 9 may be omitted. In this case, the data processing unit 7 may output Sp and Sn to the display 11. In this case, each value of the output Sp and Sn may be displayed on the display 11, and a person may determine the presence or absence and type of defects by looking at the respective displayed values. In this case, the ratio distribution may be further displayed on the display 11 as described above.

[0133] (Modification Example 4) In the above, the size of the increasing peak forming part in the ratio distribution was represented by area, but it may be the maximum value of the ratio (peak value in the positive direction) in the increasing peak forming part. In this case, the size of the decreasing peak forming part in the ratio distribution may be the minimum value of the ratio (peak value in the negative direction) in the decreasing peak forming part.

[0134] (Modification Example 5) The ratio distribution (ratio at each detection position in the detector 3a) output by the ratio calculation unit 5 may be a distribution represented with respect to a one-dimensional coordinate (x coordinate) as shown in FIGS. 2A to 2D, that is, a distribution represented in a two-dimensional coordinate system having an x-axis and a ratio axis, or a distribution represented with respect to two-dimensional coordinates (x-axis coordinate and y-axis coordinate), that is, a distribution represented in a three-dimensional coordinate system having an x-axis, a y-axis, and a ratio axis.

[0135] In the latter case, the size of the increasing peak forming part may be the volume of the region sandwiched between the part where the ratio is 1 and the increasing peak forming part. That is, assuming that x and y are position coordinates representing two-dimensional coordinates on the detection surface 3a1, when the ratio surface representing the ratio distribution is represented by ratio = f(x, y), ∫{f(x, y) - 1}dxdy may be the size of the increasing peak forming part. This integration is performed over the x interval and y interval of the increasing peak forming part. In this case, the size of the decreasing peak forming part may also be, similarly, the volume of the region sandwiched between the part where the ratio is 1 and the decreasing peak forming part. That is, similar to the case of the increasing peak forming part, ∫{1 - f(x, y)}dxdy may be the size of the decreasing peak forming part.

[0136] Also, when the ratio distribution is represented in a two-dimensional coordinate system as described above, the data processing unit 7 may generate a curve (for example, the ratio curve C1 in FIG. 2A) that approximates the ratio distribution in the two-dimensional coordinate system, and obtain the above-mentioned Sp and Sn based on the curve. When the ratio distribution is represented in a three-dimensional coordinate system as described above, the data processing unit 7 may generate a surface (for example, the above-mentioned f(x, y)) that approximates the ratio distribution in the three-dimensional space, and obtain the above-mentioned Sp and Sn based on the surface.

[0137] (Modification Example 6) In the above description, the detector 3a had a detection surface 3a1 having a two-dimensional spread, 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 a large number of detection positions over a range having a one-dimensional (rod-shaped) spread is obtained.

[0138] Steps S2 to S4 may be performed multiple times using the rod-shaped detector 3a. In this case, between multiple times, the position of the detector 3a is made different while other conditions are the same. Thereby, the number of detections at a large number of detection positions over a range having a two-dimensional spread is obtained, and the ratio at each of these detection positions may be obtained 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. Note that the position and orientation of the detector 3a for each of steps S2 to S4 are input to the detection device 3 by an appropriate means (for example, by a person operating an input device), and based on this input, the detection device 3 may grasp the correspondence between each detection position and the number of detections.

[0139] Note that the detector 3a may be a dot-shaped detector having one detection position. In this case, steps S2 to S4 are performed multiple times. In this case, during multiple times, the position of the detector 3a is varied while other conditions are made the same. Thereby, the number of detections at a large number of detection positions over a range having a one-dimensional or two-dimensional spread may be obtained, and the ratio at each of these detection positions may be determined. In this case, other points are the same as those when steps S2 to S4 are performed multiple times using the bar-shaped detector 3a.

[0140] (Modification Example 7) The ratio calculation unit 5 may obtain the above-described ratio using the normalized reference value and the normalized number of detections as follows.

[0141] The reference value at each detection position i (where i is an identifier of the detection position; the same applies hereinafter) may be a value obtained by normalizing the number αi of emitted neutrons detected at the detection position i by Na as a result of irradiating the composite floor slab 1 in a state where no defect exists inside with Na neutrons (i is an identifier of the detection position). That is, the reference value Ri at each detection position i may be Ri = αi / Na.

[0142] 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 the composite floor slab 1 with Nb neutrons in step S3 described above. That is, the number of detections Di at each detection position i may be Di = βi / Nb.

[0143] The ratio calculation unit 5 calculates the ratio at each detection position i by Di / Ri. Note that the ratio calculation unit 5 may calculate the number of detections Di = βi / Nb from the known Nb and the βi measured by the measurement unit 3b when calculating the ratio. Also, the normalized reference value Ri may be stored in the storage unit 6.

[0144] In such a modification example 7, the above-mentioned Na and Nb may be different from each other, and the time for irradiating the neutron beam onto the composite floor slab 1 (irradiation location R) in step S3 may also be different from the corresponding time (neutron beam irradiation time) in the setting of the reference value. In addition, in modification example 7, the time for measuring the number of detected neutrons in step S4 and the corresponding measurement time in the setting of the reference value may both be the time until the number of neutrons emitted from the composite floor slab 1 per unit time becomes sufficiently small (for example, substantially zero).

Explanation of Signs

[0145] 1 Composite floor slab 1a Bottom steel plate 1b Section steel 1c Concrete 1d Asphalt layer 1e Surface 2 Neutron irradiation device 2a Neutron source 2b Collimator 3 Detection device 3a Detector 3a1 Detection surface 3b Measurement unit 5 Ratio calculation unit 6 Storage unit 7 Data processing unit 8 Judgment value calculation unit 9 Judgment unit 10 Non-destructive inspection device 11 Display R Irradiation location

Claims

1. (A)On the surface of a composite floor slab having a bottom steel plate, a plurality of steel shapes provided at intervals from each other so as to rise from the upper surface of the bottom steel plate, and concrete placed on the upper side of the bottom steel plate so as to embed the plurality of steel shapes, irradiate the steel shapes with a neutron beam from a neutron irradiation device toward a local irradiation location, (B)As a result of (A) above, detect scattered neutrons that have returned from the composite floor slab at each detection position facing the surface, and measure the number of detected scattered neutrons for each detection position, (C)For each detection position, a ratio calculation unit obtains and outputs the ratio of the number of detected neutrons at the detection position to the reference value of the detection position, (D)In the distribution of the ratio regarding the detection position, identify an increasing peak forming portion and a decreasing peak forming portion of the ratio, and obtain and output the size of the increasing peak forming portion and the size of the decreasing peak forming portion as Sp and Sn, respectively, The reference value is the number of detected neutrons when irradiating the steel shapes with a neutron beam from the neutron irradiation device, and is set for each detection position as the number of detected neutrons when there are no defects in the composite floor slab. A non-destructive inspection method for a composite floor slab.

2. The surface of the composite floor slab is the upper surface, In (A) above, irradiate the upper surface with the neutron beam from the neutron irradiation device disposed on the upper surface side when viewed from the inside of the composite floor slab, In (B) above, measure the number of detected scattered neutrons for each detection position by a detection device disposed on the upper surface side when viewed from the inside of the composite floor slab. The non-destructive inspection method for a composite floor slab according to Claim 1.

3. In (D) above, obtain Sp / Sn or Sn / Sp, Change the irradiation location where the neutron beam is incident in (A) above, and repeat (A) to (D), Identify the irradiation location corresponding to the smallest value among the plurality of Sp / Sn or Sn / Sp obtained respectively in a plurality of (D) above as the location closest to a low-density portion or a water stagnation location as a defect among the plurality of irradiation locations, The low-density portion is a portion having a lower density than a normal portion of the composite floor slab. The non-destructive inspection method for a composite floor slab according to Claim 1 or 2.

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