Non-destructive testing method and device

Abstract

To provide a technique that can evaluate the depth and concentration of a target component existing in an object to be inspected without destroying the object to be inspected.SOLUTION: A non-destructive inspection device 20 irradiates a neutron beam into an object to be inspected 1, detects specific gamma rays generated by the neutron beam that originate from a target component in the object to be inspected 1, and detects the depth at which the target component exists based on the detection results. The non-destructive inspection device 20 includes a neutron source 3 that irradiates a surface 1a of the object to be inspected 1 with a pulsed neutron beam, a gamma ray detection device 5 that detects specific gamma rays generated by the incidence of the pulsed neutron beam on the object to be inspected 1, and a time point determining unit 15 for determining the time point at which the specific gamma ray has been detected relative to a reference time point.SELECTED DRAWING: Figure 7

Description

[Technical Field]

[0001] The present invention relates to a non-destructive inspection method and apparatus for non-destructively determining the depth at which a target component exists within an object to be inspected and the concentration of the target component at that depth. [Background technology]

[0002] Salt damage is one of the causes of deterioration of infrastructure structures such as roads and bridges. For example, salt contained in sea breezes from the coast or salt contained in antifreeze sprayed in cold regions or mountainous areas can penetrate into concrete structures, which are infrastructure structures, and the chloride ion concentration (hereinafter referred to as salt concentration) around the reinforcing bars in the concrete structure can reach a limit value (1.2 to 2.5 kg / m 3 If the temperature exceeds the range (value within this range), corrosion of the reinforcing steel will begin and progress, causing deterioration of the concrete structure.

[0003] In order to maintain the safety of concrete structures, inspections are carried out to understand their deterioration state. In conventional inspections, concrete (called a core) is scraped from the surface to near the rebar at one location of the concrete structure, and the salt concentration is measured by performing fluorescent X-ray analysis, electron beam microanalysis, potentiometric titration, etc. on the scraped core. This allows the salt concentration to be measured at each position from the surface of the concrete structure to a depth near the rebar, and the deterioration state of the concrete structure to be understood. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Laid-Open No. 2004-125570 Summary of the Invention [Problem to be solved by the invention]

[0005] However, collecting cores and measuring their salt concentration has the following problems (1) to (3): (1) Because cores are collected by destroying part of the concrete structure, the locations from which cores can be collected are limited. (2) It takes time to collect cores and to pre-treat them for measurement. (3) After measuring the salt concentration in a core collected from one location in a concrete structure, it is not possible to measure the salt concentration again in the same location. Therefore, it is not possible to grasp the changes in the deterioration state of the same location over time.

[0006] Patent Document 1 describes a technique for determining the salt concentration in concrete using electromagnetic waves, but does not disclose how to determine the depth at which salt is present.

[0007] Therefore, a technique that can nondestructively detect the depth of the location of a target component (for example, salt) present in an object to be inspected is desired.

[0008] Therefore, the object of the present invention is to provide a technology that can detect the depth of a target component present in an object to be tested without destroying the object to be tested, and a technology that can evaluate the concentration of the target component at that depth. [Means for solving the problem]

[0009] In a non-destructive inspection method according to one aspect of the present invention, (A) A neutron beam is incident on the object to be inspected, (B) detecting specific gamma rays originating from a target component in the test object among the gamma rays generated by the neutron beam; (C) generating an index value indicating the depth at which the target component exists based on the result of the detection; In the step (B), the intensities of a plurality of types of specific gamma rays having different energies are detected as detection intensities, In the step (C), the ratio between the detected intensities of the plurality of types of specific gamma rays is calculated as the index value.

[0010] A non-destructive testing device according to one aspect of the present invention is a device for irradiating a neutron beam onto an object to be tested, detecting and identifying specific gamma rays originating from a target component in the object to be tested among gamma rays generated by the neutron beam, and deriving the depth at which the target component exists based on the detection results, comprising: a neutron source that irradiates a surface of an object to be inspected with a neutron beam; a gamma ray detection device that detects the intensities of a plurality of types of specific gamma rays having different energies as detection intensities; and a ratio calculation unit that calculates a ratio between the detection intensities of a plurality of types of specific gamma rays.

[0011] In another aspect of the present invention, a non-destructive inspection method includes: (A) A pulsed neutron beam is irradiated onto the object to be inspected, (B) detecting specific gamma rays originating from a target component in the test object among the gamma rays generated by the pulsed neutron beam; (C) Based on the result of the detection, the time at which the specific gamma ray was detected in (B) is identified relative to a reference time point.

[0012] Further, a non-destructive testing device according to another aspect of the present invention is a device for irradiating a pulsed neutron beam onto an object to be tested, detecting and identifying specific gamma rays originating from a target component in the object to be tested among gamma rays generated by the pulsed neutron beam, and deriving a depth at which the target component exists based on the detection results, comprising: a neutron source that irradiates a pulsed neutron beam onto the surface of the object to be inspected; a gamma ray detection device for detecting specific gamma rays generated by the incidence of pulsed neutron rays on an object to be inspected; and a time point specifying unit that specifies the time point at which the specific gamma ray is detected relative to a reference time point.

[0013] A non-destructive inspection method according to another aspect of the present invention is a non-destructive inspection method for irradiating an inspection object with neutron rays from a neutron source, detecting and identifying specific gamma rays originating from a target component in the inspection object among gamma rays generated by the neutron rays, and obtaining a depth at which the target component exists based on the detection results, comprising: (A) A gamma ray detection device is prepared, the gamma ray detection device comprising a gamma ray detector for detecting specific gamma rays and a gamma ray shielding part, a gamma ray passing hole is formed in the gamma ray shielding part, the gamma ray passing hole has an opening through which gamma rays can enter, the gamma ray detector is disposed at a position in the gamma ray passing hole shifted toward the back side from the opening, and the opening and the gamma ray detector are positioned on a reference straight line, (B) arranging the neutron source, the gamma ray detector, and the gamma ray shielding part so that a path of a neutron ray emitted from the neutron source intersects with an extension of the reference straight line inside the inspection object; (C) in the state of (B), irradiating the inspection object with neutrons from the neutron source and detecting the gamma rays generated thereby with the gamma ray detector; (D) The number of times the gamma ray detector detects a specific gamma ray is calculated based on the detection data obtained in (C).

[0014] Further, according to another aspect of the present invention, there is provided a non-destructive inspection device for irradiating a neutron beam onto an object to be inspected, detecting and identifying specific gamma rays originating from a target component in the object to be inspected among gamma rays generated by the neutron beam, and deriving a depth at which the target component exists based on the detection results, comprising: a neutron source that irradiates a surface of an object to be inspected with a neutron beam; a gamma ray detection device for detecting specific gamma rays generated by the incidence of neutron rays on the inspection object; The gamma ray detection device includes a gamma ray detector for detecting specific gamma rays and a gamma ray shielding unit, A gamma ray passing hole is formed in the gamma ray shielding portion, and the gamma ray passing hole has an opening through which gamma rays can enter. The gamma ray detector is positioned in the gamma ray passing hole at a position shifted toward the back from the opening, and the opening and the gamma ray detector are located on a reference straight line. [Effects of the Invention]

[0015] According to the present invention, it is possible to detect the depth of a target component present in an object to be inspected and to evaluate the concentration of the target component at that depth without destroying the object to be inspected. [Brief explanation of the drawings]

[0016] [Figure 1] 1 shows the configuration of a non-destructive testing device according to a first embodiment of the present invention. [Figure 2] 1 shows an example of the energy spectrum of neutron rays emitted from a neutron source. [Figure 3] The graph shows the relationship between the counting rate Rγ (times / second) of specific gamma rays detected by the gamma ray detector in the experiment and the salinity concentration. [Figure 4] The theoretically calculated values ​​of the transmittance of multiple types of gamma rays through concrete are expressed as a ratio. [Figure 5] FIG. 2 is a schematic diagram for explaining the principle of detecting the depth of a target component according to the first embodiment. [Figure 6] 1 is a flowchart showing a nondestructive inspection method according to a first embodiment. [Figure 7] 3 shows the configuration of a nondestructive testing device according to a second embodiment of the present invention. [Figure 8A] 1 shows a proton beam pulse signal versus time. [Figure 8B] The number of times a specific gamma ray is detected over time is shown. [Figure 9] 10 shows a schematic of an example of time difference versus spectral data. [Figure 10] 10 is a flowchart showing a nondestructive inspection method according to a second embodiment. [Figure 11A] FIG. 10 is a diagram for explaining the detection principle according to the third embodiment. [Figure 11B] FIG. 11B is a partially enlarged view of FIG. 11A. [Figure 12] 10 shows the configuration of a non-destructive testing device according to a third embodiment of the present invention. [Figure 13A] 11B is a view taken along the line XIII-XIII in FIG. 11A, showing a specific example of the shape of the gamma ray shielding portion. [Figure 13B]11B is a view taken along the line XIII-XIII in FIG. 11A, showing another specific example of the shape of the gamma ray shielding portion. [Figure 14] 10 is a flowchart showing a nondestructive inspection method according to a third embodiment. [Figure 15A] 1A and 1B are explanatory diagrams showing variations of non-destructive inspection methods. [Figure 15B] FIG. 10 is an explanatory diagram showing another variation of the non-destructive inspection method. [Figure 15C] FIG. 10 is an explanatory diagram showing yet another variation of the non-destructive inspection method. DETAILED DESCRIPTION OF THE INVENTION

[0017] An embodiment of the present invention will be described with reference to the drawings. Note that common parts in each drawing are designated by the same reference numerals, and duplicate explanations will be omitted. Furthermore, the following description does not limit the invention described in the claims. For example, the present invention is not limited to an apparatus that includes all of the components described below.

[0018] [First embodiment] 1 shows the configuration of a non-destructive inspection device 10 according to a first embodiment of the present invention. The non-destructive inspection device 10 is an apparatus for irradiating a neutron ray (neutron beam) from outside an inspection object 1 onto its surface 1a, detecting and identifying gamma rays (hereinafter simply referred to as specific gamma rays) originating from a target component within the inspection object 1 among the gamma rays thus generated in the inspection object 1, and deriving the depth at which the target component exists based on this detection result. Note that the depth of the target component is the depth from the surface 1a of the inspection object 1.

[0019] In this embodiment, the inspection target 1 is a concrete structure containing reinforcing bars inside, and the target component is salt (chlorine). When the target component is salt, the salt is, for example, an isotope of stably existing chlorine Cl. 35The test object 1 and the target component are not limited to a combination of a concrete structure and salt. That is, according to the first embodiment, the test object 1 is not limited to a concrete structure, and the target component may be any component that emits multiple types of specific gamma rays when neutron rays are incident on the test object 1. For example, the target component may be calcium (mainly 40 Ca), silicon (mainly 28 Si) etc. In addition, hydrogen ( 1 H) emits only one gamma ray and is therefore unsuitable as a target component in the first embodiment, but hydrogen may be used as a target component in the second and third embodiments described below.

[0020] As shown in FIG. 1, the non-destructive inspection device 10 includes a neutron source 3, a gamma ray detection device 5, a ratio calculation unit 7, a depth data storage unit 9a, a depth detection unit 11, and a concentration data storage unit 9b.

[0021] The neutron source 3 irradiates the surface 1a of the inspection object 1 with a neutron beam, causing the neutron beam to enter the inspection object 1. The neutron source 3 may emit a pulsed neutron beam or may emit a neutron beam continuously. In the example of Fig. 1, the neutron source 3 has an ion source 3a, an accelerator 3b, a beam adjuster 3c, a target 3d, a container 3e, and a tubular shielding member 3f.

[0022] The ion source 3a generates, for example, hydrogen ions (protons). The accelerator 3b accelerates the protons generated by the ion source 3a. In one example, the protons accelerated by the accelerator 3b have an energy of, for example, 7 MeV. The beam adjuster 3c has multiple magnetic field coils that adjust the direction and spread of the proton beam accelerated by the accelerator 3b to match the target 3d. The proton beam that has passed through the beam adjuster 3c is incident on the target 3d. As a result, neutrons are generated by a reaction between the protons and the target 3d (e.g., beryllium). The target 3d is placed in a container 3e made of a material that is difficult for neutrons and gamma rays to penetrate. The container 3e has a hole that penetrates from the outer surface to the interior of the container 3e. A tubular shielding member 3f for emitting neutrons is attached to this hole. The tubular shielding member 3f is made of a material that is difficult for neutrons to penetrate. Neutrons generated in the target 3d pass through the inside of the tubular shielding member 3f and are incident on the inspection object 1 as a neutron beam.

[0023] Such a neutron source 3 can be configured to be small enough to be loaded onto a vehicle such as a truck. Therefore, the nondestructive inspection device 10 can be loaded onto a vehicle such as a truck and transported to the location of the inspection object 1 (for example, an infrastructure structure such as a road or bridge).

[0024] In the first embodiment, the neutron beam emitted by the neutron source 3 may include thermal neutrons and fast neutrons. Generally, thermal neutrons refer to neutrons having an energy of around 25 meV or less at room temperature, and fast neutrons refer to neutrons having an energy (several hundred keV or more) that is significantly higher than that of thermal neutrons. Here, there is no strict definition of the threshold for naming neutrons based on energy, so in the definitions herein, thermal neutrons may be neutrons having an energy of several tens of meV (e.g., 50 meV) or less, and fast neutrons may be neutrons having an energy of several hundred keV (e.g., 200 keV) or more. Note that neutrons between thermal and fast neutrons are sometimes referred to as epithermal neutrons, and neutrons of 0.01 eV or less are sometimes referred to as cold neutrons.

[0025] The energy of each neutron emitted from the neutron source 3 is, for example, 1×10 -3 eV~1×10 7 The distribution of electrons in the neutron beam has a value of 1 eV, which may be set to an appropriate value depending on the type of the object 1 to be inspected. FIG. 2 shows an example of the energy spectrum of the neutron beam emitted from the above-mentioned neutron source 3. In FIG. 2, the horizontal axis shows the energy (kinetic energy) of the neutrons, and the vertical axis shows the number of electrons per unit cross section (cm) per unit time (seconds). 2 ) According to the definition of the present application above, in Figure 2, neutrons with energies within range A are thermal neutrons, and neutrons with energies within range B are fast neutrons.

[0026] The neutron beam incident on the inspection object 1 by the neutron source 3 reacts with the target component in the inspection object 1. As a result, specific gamma rays originating from the target component are generated. In the first embodiment, multiple types of specific gamma rays with different energies are generated from the target component.

[0027] The gamma ray detection device 5 detects, as detection intensities, the intensities of multiple types of specific gamma rays generated by the incidence of neutron rays on the inspection object 1. The gamma ray detection device 5 includes a gamma ray detector 5a and an intensity detection unit 5b.

[0028] The gamma ray detector 5a detects gamma rays for each energy (each wavelength) of gamma rays from the inspection object 1 and inputs the detection data to the intensity detection unit 5b. This detection data may be a pulse height value corresponding to the energy of each detected gamma ray.

[0029] The intensity detection unit 5b acquires the energy spectrum of gamma rays based on each pulse height value input from the gamma ray detector 5a. This energy spectrum indicates the number of times gamma rays are detected at each energy of gamma rays. In the present application, the detection intensity of gamma rays may be a value proportional to the number of times gamma rays of the corresponding energy are detected. In the first embodiment, this number of times may be the number of times detections over a predetermined measurement time. The predetermined measurement time is set as the origin at the time when the inspection object 1 is irradiated with neutron rays, and is the time period from the origin until the gamma ray detector 5a detects a sufficient amount of gamma rays due to the neutron rays. The predetermined measurement time may be, for example, a time period of 100 seconds, 200 seconds, or 300 seconds from the origin, but is not limited to these time periods. The detection intensity of gamma rays is also calculated based on a counting rate R (to be described later). γ The gamma ray detector 5a may be, for example, a germanium detector, but is not limited to this.

[0030] The intensity detection unit 5b determines the intensities of multiple types of specific gamma rays (for example, in the energy spectrum) as detection intensities based on the acquired energy spectrum, and inputs these detection intensities to the ratio calculation unit 7. Of the multiple types of specific gamma rays, one specific gamma ray may be designated as a first specific gamma ray and another specific gamma ray may be designated as a second specific gamma ray, and the intensity detection unit 5b may determine the intensities of the first specific gamma ray and the second specific gamma ray as detection intensities, and input these detection intensities to the depth detection unit 11 and the concentration evaluation unit 13.

[0031] In the examples, the target component 35The main types of specific gamma rays derived from Cl include gamma rays with energies of 517 keV, 786 keV, 788 keV, 1165 keV, 1951 keV, and 6111 keV. In this case, for example, the first specific gamma ray may be a gamma ray with an energy of 1951 keV, and the second specific gamma ray may be a gamma ray with an energy of 517 keV. However, the combination of the first specific gamma ray and the second specific gamma ray is not limited to this. Note that the greater the difference in energy between the first specific gamma ray and the second specific gamma ray, the higher the accuracy of depth detection tends to be. However, the detection intensity of a specific gamma ray with a higher energy (e.g., 6111 keV) does not need to be used.

[0032] The ratio calculation unit 7 obtains the ratio between the detection intensities of the multiple types of specific gamma rays input from the intensity detection unit 5 b. In this embodiment, the ratio calculation unit 7 calculates the ratio of the detection intensity of the second specific gamma ray to the detection intensity of the first specific gamma ray.

[0033] The depth data storage unit 9a stores depth data that indicates the relationship between the depth at which the target component exists in the inspection object 1 and the ratio between the detection intensities of multiple types of specific gamma rays. This depth data may be obtained in advance, for example, by experiment.

[0034] In this experiment, multiple specimens made of the same material as the inspection target 1 are prepared. The depths at which the target components exist vary among the multiple specimens. For each specimen, the ratio of the detection intensities of multiple types of specific gamma rays is determined using the neutron source 3 and gamma ray detection device 5 described above. The depth data described above is created based on the depth of the target components in each of the multiple specimens and the above-mentioned ratios for each of the multiple specimens. The depth data created in this manner is stored in advance in the depth data storage unit 9a. In this embodiment, the depth data represents the relationship between the depth at which the target components exist in the inspection target 1 and the ratio of the second specific gamma ray to the first specific gamma ray.

[0035] The above experiment for obtaining depth data and the actual inspection of the object under inspection 1 (step S1 described below) are preferably performed under the same conditions. These conditions include a neutron spectrum condition, a distance condition, and an orientation condition. The neutron spectrum condition is a condition that the energy spectrum of the neutron beam emitted from the neutron source 3 to the object under inspection 1 (the specimen in the above experiment) is a set spectrum. The distance condition is a condition that the distance between the surface of the object under inspection 1 (the specimen in the above experiment) and the detector 5a is a set distance. The orientation condition is a condition that the relationship (incident angle) between the orientation of the neutron beam emission port of the neutron source 3 (the opening at the tip of the tubular shielding member 3f in FIG. 1) and the orientation of the surface 1a of the object under inspection 1 (the specimen in the above experiment) and the relationship (detection angle) between the orientation of the detector 5a and the orientation of the surface 1a of the object under inspection 1 are set (for example, the incident angle is 90 degrees and the detection angle is 45 degrees). The above-mentioned "same condition" may further include other conditions (for example, a measurement time condition). This measurement time condition is a condition that the above-mentioned measurement time is a set time.

[0036] The depth detection unit 11 determines the depth at which the target component exists based on the depth data stored in the depth data storage unit 9a and the ratio calculated by the ratio calculation unit 7. At this time, the depth detection unit 11 may determine the depth at which the target component exists by applying the ratio to the depth data. The depth detection unit 11 outputs the determined depth. The output depth may be stored in an appropriate storage medium, displayed on a display, or printed on paper.

[0037] The concentration data storage unit 9b stores concentration data that indicates the relationship between the detection intensity of the selected gamma ray and the concentration of the target component when either the first specific gamma ray or the second specific gamma ray is set as the selected gamma ray. The concentration data storage unit 9b stores concentration data for each depth in the inspection object 1 in association with the depth. This concentration data may be obtained in advance, for example, by experiment.

[0038] In this experiment, the following steps (1) to (3) are carried out. (1) Prepare a specimen (called a known concentration specimen) that is made of the same material as the test object 1 but has a known concentration of the target component. (2) A zero-concentration specimen is stacked on top of a known-concentration specimen with no gaps in the thickness direction. Here, the zero-concentration specimen is made of the same material as the test object 1 but has zero concentration of the target component. Each specimen has, for example, a rectangular parallelepiped shape. (3) In the state of (2) above, neutrons are emitted from the neutron source 3 so that the neutrons pass through the zero-concentration specimen and the known-concentration specimen in that order, and the detection intensity of the selected gamma rays thus produced is determined by the gamma ray detection device 5.

[0039] The above steps (1) to (3) are performed for each of a plurality of known concentration specimens in which the concentration of the target component differs from one another. As a result, the above-mentioned concentration data is created based on the concentration of the target component in each of the plurality of known concentration specimens and the detection intensity of the selected gamma ray for each of the plurality of known concentration specimens. Here, the detection intensity may be calculated using the following formula (A). Each symbol in formula (A) is the same as in formula (1) described below. Formula (A) is obtained by dividing ε in formula (1) described below by γ If we eliminate ε γ This is the equation when is set to 1. R γ = {(A / t) / I γ} / (I p / 50) ···(A)

[0040] The distance from the surface of the zero-concentration specimen where the neutron beam is incident to the known-concentration specimen corresponds to the depth in the object under test 1 (depth from its surface 1a). Therefore, the concentration data obtained as described above for one zero-concentration specimen (i.e., the thickness of the specimen) is for one depth in the object under test 1. Therefore, concentration data is obtained as described above for each of multiple zero-concentration specimens with different thicknesses. In this way, concentration data is obtained for each depth in the object under test 1. Alternatively, for example, a standard gamma ray source (e.g., 133Ba and 152 Eu) for each depth, the detection efficiency ε γ (described later) may be acquired in advance, and concentration data for each depth may be calculated based on the detection efficiency at that depth. In this case, in (3) above, the detection intensity of the selected gamma ray is calculated by equation (1) described later. Concentration data for depths where no experiments were conducted (thickness of zero-concentration specimen) and selected gamma rays (energy of gamma rays) may be obtained by interpolation based on concentration data and detection efficiency for which experiments were conducted.

[0041] The depth data storage unit 9a, the concentration data storage unit 9b, and the detection efficiency storage unit 8 described below may be different storage areas in the same storage device such as a semiconductor memory, a hard disk, or a USB memory as shown in Figure 1, or may be separate storage devices.

[0042] The concentration evaluation unit 13 calculates the concentration of the target component at a depth based on the depth calculated by the depth detection unit 11, the concentration data corresponding to that depth stored in the concentration data storage unit 9b, and the detection intensity of the selected gamma rays that was input. At this time, the concentration evaluation unit 13 may calculate the concentration of the target component at that depth by applying the detection intensity of the selected gamma rays to the concentration data corresponding to the depth calculated by the depth detection unit 11, among the concentration data corresponding to each depth in the concentration data storage unit 9b. The concentration evaluation unit 13 outputs the calculated concentration. The output concentration may be input to the concentration evaluation unit 13, stored in an appropriate storage medium, displayed on a display, or printed on paper.

[0043] The above experiment for obtaining concentration data and the actual inspection of the concentration of the target component in the inspection object 1 (the actual inspection when obtaining the detection intensity of the selected gamma rays used in step S5 described below (steps S105 and S205 described below in the second and third embodiments, respectively)) are performed under the same conditions. These conditions include the neutron spectrum conditions, the distance conditions, and the orientation conditions described above. The "same conditions" may also include other conditions (for example, the measurement time conditions described above). The beam diameter of the neutron beam emitted by the neutron source 3 is the same in the above experiment and the actual inspection of the inspection object 1, for example, due to the configuration of the neutron source 3 (for example, the tubular shielding member 3f).

[0044] (Principle of detecting the depth of the target component) <Gamma rays originating from elements> The principle of detecting the depth of a target component according to the first embodiment will be described in detail. When a neutron beam is incident on the inspection target 1, various elements present in the inspection target 1 undergo a reaction of capturing neutrons, resulting in excited compound nuclei. The compound nuclei immediately transition from the excited state to the ground state, at which time they emit gamma rays. The energy and intensity of the gamma rays are derived from the elements (atomic nuclei) that emit the gamma rays.

[0045] <Detection depth range for thermal and fast neutrons> Of the neutrons contained in the neutron beam from the neutron source 3, thermal neutrons are captured by elements, but fast neutrons are not easily captured by elements. Therefore, the thermal neutrons incident on the inspection object 1 are highly likely to react with target components present in the inspection object 1 within a range close to the surface 1a. If the inspection object 1 is a concrete structure, this range is, for example, up to several centimeters from the surface 1a. Therefore, thermal neutrons are used to detect target components within a range close to the surface 1a.

[0046] On the other hand, fast neutrons incident on the inspection object 1 hardly react with target components in the range close to the surface 1a within the inspection object 1, but are repeatedly scattered within the inspection object 1 and become thermal neutrons. In this way, there is a high probability that fast neutrons will become thermal neutrons and react with target components present in the range deep from the surface 1a within the inspection object 1. If the inspection object 1 is a concrete structure, this range is, for example, from 10 cm to 30 cm from the surface 1a. Therefore, thermal neutrons are used to detect target components in the range deep from the surface 1a.

[0047] Therefore, by irradiating the inspection target 1 with neutron rays containing both thermal neutrons and fast neutrons, it is possible to detect target components both in a range close to the surface 1a and in a range deep from the surface 1a.

[0048] <Experiment> The experiment was carried out using several mortar specimens. The chloride ion concentration (hereinafter referred to as salt concentration) of the target component in these mortar specimens was set at 0.3 kg / m 3 , 0.5 kg / m 3 , 1 kg / m 3 , 3 kg / m 3 , 5 kg / m 3 Each mortar specimen was cubic in shape, with each side measuring 40 mm.

[0049] For each mortar specimen, a neutron beam was incident on the mortar specimen using the neutron source 3, and the energy spectrum of the gamma rays generated within the mortar specimen was measured. The experiment was carried out for each mortar specimen under the same conditions, i.e., the conditions included the above-mentioned neutron spectrum conditions, distance conditions, and orientation conditions.

[0050] FIG. 3 shows the counting rate R, which is the intensity of a specific gamma ray detected by the gamma ray detector 5a in the experiment. γThe relationship between the count rate (counts / second) and the salinity is shown in Figure 3. The measurement results for specific gamma rays with energies of 517 keV, 786 keV, 788 keV, 1165 keV, and 1951 keV are shown. Note that since the values ​​of 786 keV and 788 keV are close, in Figure 3 the detection intensities of gamma rays with these two energies are combined and treated as a single energy of 787 keV, and the count rate R of specific gamma rays is calculated. γ It states that:

[0051] Counting rate R γ indicates the total gamma ray dose (gamma ray intensity) calculated from the number of gamma rays of each energy detected in a unit time. This total gamma ray dose is 35 The total amount of gamma rays emitted by Cl capturing neutrons. Specifically, the counting rate R γ (times / second) was calculated using the following formula (1). R γ = [{(A / t) / ε γ} / I γ ] / (I p / 50) ···(1)

[0052] Here, A indicates the number of times a specific gamma ray of each energy was detected. ε γ indicates the gamma ray detection efficiency (% / 100), and is a value that is determined in advance using a standard gamma ray source or the like. The gamma ray detection efficiency is the ratio of the number of times that gamma rays are detected by the gamma ray detector 5a to the amount of gamma rays from the gamma ray source (the location where the gamma rays are emitted), and is a value that is inversely proportional to the energy of the gamma rays and inversely proportional to the distance between the gamma ray source and the gamma ray detector 5a. In order to determine the depth of the target component, the gamma ray detection device 5 is provided with a gamma ray detection efficiency ε for each energy, assuming that the distance between the gamma ray source and the gamma ray detector 5a in the inspection object 1 is a predetermined constant value. γ is set (the ε γ In the following, ε γS and ε γd The same applies to the second and third embodiments.) The gamma ray detection device 5 detects ε γBased on the count rate R over the measurement time γ The integrated value of is calculated as the detection intensity of the specific gamma ray of that type.

[0053] In the first embodiment, the gamma ray detection efficiency (i.e., the gamma ray detection efficiency used in step S2 described below) for determining the ratio between the detection intensities of multiple types of specific gamma rays is a value when there is nothing but air between the gamma ray source and the gamma ray detector 5a. On the other hand, the gamma ray detection efficiency for determining the concentration of the target component (for example, the gamma ray detection efficiency used when determining the concentration data described above or in step S5 described below) should be a value that corresponds to the material of the object to be inspected 1 and the test specimen.

[0054] I γ teeth, 35 The intensity ratio (% / 100) of specific gamma rays in the neutron capture of Cl is shown. γ teeth, 35 It is a ratio of the number of times each type of specific gamma ray originating from Cl was detected. For example, if 100 neutrons 35 This shows how many of each type of specific gamma ray is emitted when captured by Cl. 35 When Cl captures 100 neutrons, 26.82 and 19.05 neutrons of 1165 keV and 1951 keV are emitted, respectively (specifically, I γ Enter =0.2682, 0.1905.) t indicates the measurement time (seconds). I p is the average current (μA) of the proton beam incident on the target 3d during measurement, and 50 is the count rate R at 50 μA. γ This value does not have to be 50, but can be 10 or 100. γ indicates the intensity of gamma rays.

[0055] Furthermore, as can be seen from Figure 3, for each salinity concentration, the higher the energy of the specific gamma ray, the greater the counting rate R γis higher. This indicates that the higher the energy of the gamma rays, the higher the transmittance of the gamma rays. Here, transmittance means the proportion of gamma rays generated within the mortar specimen or the object under test 1 that can pass through the surface of the mortar specimen or the object under test 1. In other words, when a predetermined amount of gamma rays passes through the surface of the total amount of gamma rays generated at a predetermined depth from the surface of the mortar specimen or the object under test 1, the transmittance is the proportion of the predetermined amount to the total amount (the same applies hereinafter).

[0056] Furthermore, as can be seen from Figure 3, the higher the salt concentration in the mortar specimen, the higher the detected intensity of each specific gamma ray. In Figure 3, the salt concentration and the detected intensity of the specific gamma ray are in an approximately proportional relationship. Therefore, it can be said that the intensity ratio between multiple types of specific gamma rays does not depend on the concentration of the target component (salt).

[0057] By utilizing the difference in transmittance of multiple types of specific gamma rays and the difference in intensity ratio of multiple types of specific gamma rays in combination, the depth of the target component can be determined as described below.

[0058] In addition, from Figure 3, the salt concentration is 0.3 kg / m 3 Therefore, the lower limit of the salt concentration that causes corrosion of rebar in concrete is 1.2 to 2.5 kg / m 3 Therefore, it is clear that the concentration evaluation unit 13 can detect whether or not there is a salt content at a concentration that causes corrosion of the reinforcing bars.

[0059] <Theoretical calculation of transmittance> Figure 4 shows the theoretically calculated values ​​of the transmittance of several types of gamma rays through concrete, expressed as a ratio. In Figure 4, the horizontal axis shows the energy of the gamma rays, and the vertical axis shows the transmittance, which indicates the proportion of gamma rays generated within the concrete that pass through its surface. In other words, the transmittance of gamma rays with an energy of 2000 keV is set to 1, and the ratio of the transmittance of each gamma ray to this transmittance is shown. The energies of the gamma rays are 500 keV and 1250 keV.

[0060] In Figure 4, the circles represent calculated values ​​for gamma rays generated at a depth of 1 cm from the surface of the concrete, the squares represent calculated values ​​for gamma rays generated at a depth of 5 cm from the surface of the concrete, and the triangles represent calculated values ​​for gamma rays generated at a depth of 10 cm from the surface of the concrete. As can be seen from Figure 4, for each depth, the higher the energy of the gamma rays, the higher their transmittance.

[0061] <Detection principle> Fig. 5 is a schematic diagram for explaining the principle of depth detection of a target component according to the first embodiment. Fig. 5 shows a case where a neutron beam is incident on the surface of concrete as an inspection target 1, and the neutron reacts with salt in the concrete to generate specific gamma rays.

[0062] As shown in Figure 5, it is assumed that salt is present in concrete at a first, second, or third depth from the surface. When salt is present at the first depth, neutrons incident on the concrete surface react with the salt in the concrete, generating multiple types of specific gamma rays with energies E1, E2, and E3, which are emitted from the surface. Similarly, when salt is present at the second and third depths, it is assumed that multiple types of specific gamma rays with energies E1, E2, and E3 are generated and emitted from the surface.

[0063] In Figure 5, when salt is present at the first depth, specific gamma rays with energies E1, E2, and E3 are generated at the first depth with intensities A1, A2, and A3, respectively, pass through the surface with transmittances P1, P2, and P3, respectively, and are detected with intensities A1 x P1, A2 x P2, and A3 x P3, respectively. Similarly, if salt is present at the second depth, specific gamma rays with energies E1, E2, and E3 will be generated at the second depth with intensities B1, B2, and B3, respectively, will pass through the surface with transmittances Q1, Q2, and Q3, respectively, and will be detected with intensities B1×Q1, B2×Q2, and B3×Q3, respectively. Similarly, if salt is present at the third depth, specific gamma rays with energies E1, E2, and E3 will be generated at the third depth with intensities C1, C2, and C3, respectively, pass through the surface with transmittances R1, R2, and R3, respectively, and be detected with intensities C1×R1, C2×R2, and C3×R3, respectively.

[0064] For the first depth, the ratio of the detection intensities of multiple types of specific gamma rays that have passed through the surface is calculated. For example, the ratio (A1×P1) / (A3×P3) of the detection intensity A1×P1 to the detection intensity A3×P3 is calculated. This ratio is independent of the salinity concentration at the first depth. A1 and A3 are both proportional to the salinity concentration at the first depth. As a result, in A1 / A3, the variations in A1 and A3 due to salinity cancel each other out. Furthermore, A1 / A3 is independent of the first depth. The intensity of neutron rays (thermal neutrons) reaching a certain depth (e.g., the first depth) is proportional to the depth, and the intensity of gamma rays generated at that depth is proportional to the intensity of neutron rays (thermal neutrons) reaching that depth. As a result, the variations in A1 and A3 due to depth cancel each other out in A1 / A3. Therefore, in the ratio (A1 x P1) / (A3 x P3), A1 / A3 does not change depending on the salt concentration or depth, and is a value derived from the target component. On the other hand, the transmittances P1 and P3 are not proportional to the first depth, but are values ​​corresponding to the first depth. Therefore, the intensity ratio (A1 x P1) / (A3 x P3) is a value corresponding to the first depth.

[0065] Similarly, for the second depth, the ratio of the detection intensities (B1×Q1) / (B3×Q3) corresponds to the second depth. For the third depth, the ratio of the detection intensities (C1×R1) / (C3×R3) corresponds to the third depth.

[0066] Therefore, the above-mentioned depth data representing the relationship between such a ratio and the depth at which the target component (here, salt) exists can be obtained in advance, and the depth at which the target component exists can be determined based on the ratio of the detection intensities measured during the inspection and the depth data.

[0067] In addition, when salt is present from the surface to a third depth, the depth determined by the depth detection unit 11 described above is a rough value (e.g., average depth) of the depth at which the salt is present. Even in this case, the rough value of the depth at which the salt is present can be known from the depth output by the depth detection unit 11. For example, if the depth output by the depth detection unit 11 is close to the position of rebars in a concrete structure as the inspection object 1, it can be determined that the rebars may be corroded by salt. Furthermore, by repeatedly determining the salt depth for the same inspection object 1 at predetermined inspection date intervals (e.g., monthly or yearly), it is possible to know the change over time in the penetration depth of salt in the inspection object 1.

[0068] (Non-destructive testing method) 6 is a flowchart showing a non-destructive inspection method according to the first embodiment. This method may be performed using the above-described non-destructive inspection device 10. This method includes steps S1 to S5.

[0069] In step S1, the neutron source 3 irradiates the surface 1a of the inspection object 1 with neutron rays. As a result, the neutron rays incident on the inspection object 1 react with the target components in the inspection object 1, generating multiple types of specific gamma rays derived from the target components.

[0070] In step S2, the gamma ray detection device 5 detects the intensities of the multiple types of specific gamma rays generated in step S1 as respective detection intensities. Step S2 includes steps S21 and S22. In step S21, the gamma ray detector 5a detects gamma rays of each energy. In step S22, the intensity detection unit 5b acquires the energy spectrum of the gamma rays based on the detection data obtained in step S21 (peak values ​​corresponding to the energy of each detected gamma ray), and based on this energy spectrum, detects the intensities of the multiple types of specific gamma rays as respective detection intensities according to the above-mentioned formula (1). The gamma ray detection efficiency ε used in step S2 γ is the above-mentioned ε γS is.

[0071] In step S3, an index value indicating the depth at which the target component exists is generated based on the detection result in step S2. That is, the ratio calculation unit 7 calculates the ratio between the detection intensities of the multiple types of specific gamma rays detected in step S2 as the index value. In this embodiment, this ratio is the ratio of the detection intensity of the second specific gamma ray to the detection intensity of the first specific gamma ray.

[0072] In step S4, the depth detector 11 determines the depth at which the target component exists based on the ratio determined in step S3 and the depth data in the depth data storage unit 9a.

[0073] In step S5, the concentration evaluation unit 13 determines the concentration of the target component at the depth based on the depth determined in step S4, the concentration data for that depth stored in the concentration data memory unit 9b, and the detection intensity of the selected gamma ray.

[0074] When the concentration data acquired for each depth using the above formula (A) is used, step S5 is performed as follows. The concentration evaluation unit 13 calculates the concentration of the target component at that depth based on the depth calculated in step S4, the concentration data for that depth stored in the concentration data storage unit 9b, and the detection intensity of the selected gamma ray. In this case, the gamma ray detection device 5 (intensity detection unit 5b) calculates the number of times A the selected gamma ray is detected based on the energy spectrum of the gamma ray acquired in the above step S2, and calculates the detection intensity of the selected gamma ray based on this number of times A and the above formula (A). This detection intensity is input to the concentration evaluation unit 13 and used by the concentration evaluation unit 13 in step S5. The detection intensity of the selected gamma ray used at this time may be newly selected and acquired from the energy spectrum of the gamma ray acquired in the above step S2.

[0075] On the other hand, the concentration data for each depth is used to calculate the gamma ray detection efficiency ε γ If the data has been acquired using the above, step S5 is performed as follows. First, the gamma-ray detection efficiency ε γ ε γS and the gamma ray detection efficiency ε corresponding to the depth calculated in step S4 γ ε γd The intensity detector 5b calculates ε γS ε γd and the number of times A of detection of the selected gamma ray (acquired by the intensity detection unit 5b based on the energy spectrum of the gamma ray obtained in the above step S2 or newly selected and acquired). In this case, the gamma ray detection efficiency ε corresponding to each depth in the inspection object 1 is calculated. γ (That is, the gamma ray detection efficiency ε corresponding to each depth used to obtain the concentration data for each depth γ ) is stored in the detection efficiency storage unit 8 as shown in FIG. 1, and the intensity detection unit 5b calculates the above-mentioned ε based on the detection efficiency data in the detection efficiency storage unit 8 and the depth calculated in step S4 (the depth input from the depth detection unit 11). γdand then, as described above, γS ε γd The above formula (1) is used, where Next, the concentration evaluation unit 13 calculates the concentration of the target component at the depth based on the detection intensity calculated by the intensity detection unit 5b, the depth calculated in step S4, and the concentration data for that depth stored in the concentration data storage unit 9b.

[0076] (Effects of the first embodiment) The intensities of multiple types of specific gamma rays generated by the reaction between neutrons incident on the inspection object 1 and the target component are each detected. As described above, the ratio between the detected intensities of the multiple types of specific gamma rays corresponds to the depth at which the target component is present. In other words, this ratio indicates the depth at which the target component is present. Therefore, by calculating this ratio, the depth at which the target component is present can be detected. Thus, the depth at which the target component is present in the inspection object 1 can be detected non-destructively. For example, it is possible to detect the depth at which the target component is present in the inspection object 1 and evaluate the concentration of the target component at that depth without taking a core from the inspection object 1, which is a concrete structure.

[0077] In addition, the gamma ray detection efficiency (the above counting rate R γ ε in the calculation formula (1) γ ) through experiments in advance (i.e., by acquiring detection efficiency data in advance, as described above regarding the acquisition of concentration data), it is also possible to derive the amount of salt present at the depth of the target component previously determined.

[0078] For example, the salt concentration at which corrosion of steel materials inside concrete begins is 1 kg / m3 as specified in the Standard Specifications for Concrete. 3 or 1 kg / m 3 The lower limit is a concentration lower than the lower limit, and the higher concentration (for example, 10 kg / m 3), the above concentration data can be obtained (i.e., a calibration curve can be drawn) and the concentration can be evaluated by comparing the data obtained during actual measurements with the calibration curve (concentration data). The salt concentration at which corrosion of steel inside concrete begins varies depending on the type of cement and the water-concrete ratio, and is between 1.2 and 2.5 kg / m 3 The range is.

[0079] In the first embodiment, the neutron source 3 may be configured so that the angle between the direction in which the proton beam is incident on the target 3d and the direction of the neutron beam emission port in the neutron source 3 is 90 degrees. The neutron source 3 configured in this manner irradiates the inspection object 1 with a neutron beam that is mainly composed of thermal neutrons, with the fast neutron component being significantly reduced, out of thermal neutrons and fast neutrons. This makes it possible to accurately determine the depth of the target component within a range close to the surface 1a of the inspection object 1.

[0080] On the other hand, in the first embodiment, when the moderator 3g described later is not provided, or when a thermal neutron shielding material is provided on the surface 1a of the inspection object 1 even in a configuration with the moderator 3g provided and the inspection object 1 is irradiated with neutron rays through the thermal neutron shielding material, it is possible to irradiate the inspection object 1 with substantially only fast neutrons out of thermal neutrons and fast neutrons by the neutron source 3. This makes it possible to accurately determine the depth of the target component within a deep range from the surface 1a of the inspection object 1.

[0081] [Second embodiment] 7 shows the configuration of a non-destructive inspection device 30 according to a second embodiment of the present invention. The configuration of the non-destructive inspection device 30 according to the second embodiment differs from the configuration of the non-destructive inspection device 10 according to the first embodiment in the points that will be explained below. Regarding the second embodiment, points that will not be explained below may be the same as in the case of the first embodiment. In the example of the second embodiment, the inspection object 1 is a concrete structure and the target component is salt, but the inspection object 1 and the target component are not limited to this combination.

[0082] The non-destructive inspection device 20 according to the second embodiment includes a neutron source 3, a gamma ray detection device 5, a time point identification unit 15, a depth data storage unit 9c, a depth detection unit 19, a concentration data storage unit 9b, and a concentration evaluation unit 14.

[0083] In the second embodiment, the neutron source 3 emits a pulsed neutron beam. The pulse duration of the proton beam for emitting the pulsed neutron beam is, for example, about 0.1 milliseconds or less, but is not limited thereto, as long as it does not interfere with the detection of the depth of the target component. Similarly, the repetition frequency of the proton beam pulse is, for example, about 100 Hz, but is not limited thereto, as long as it does not interfere with the detection of the depth of the target component. FIG. 8A is a schematic diagram illustrating the pulse duration and repetition period (the reciprocal of the repetition frequency) of the proton beam in the neutron source 3. In FIG. 8A, the horizontal axis represents time, the vertical axis represents the magnitude of the proton beam pulse signal (the synchronization signal described above), and the repetition period is equal to the repetition period of the proton beam described above.

[0084] The emission of this pulsed neutron beam is performed under a distance condition. The distance condition is a condition that the distance between the surface 1a of the inspection object 1 (or a specimen when obtaining depth data, which will be described later) and the emission position of the pulsed neutron beam in the neutron source 3 is a set distance. This emission position may be, for example, the surface of the target 3d on the side of the inspection object 1. When a deceleration unit 3g, which will be described later, is provided, the emission position may be the surface of the deceleration unit 3g on the side of the inspection object 1.

[0085] The neutron source 3 further includes a moderator section 3g through which neutrons generated in the target 3d pass. The moderator section 3g is made of a material (e.g., polyethylene) that moderates the fast neutrons passing through it and converts them into thermal neutrons. Therefore, as the neutrons generated in the target 3d pass through the moderator section 3g, some of the neutrons become thermal neutrons and are incident on the inspection object 1. Therefore, the neutron source 3 can cause thermal neutrons and fast neutrons to be incident on the inspection object 1.

[0086] The pulsed neutron beam incident on the inspection object 1 by the neutron source 3 reacts with the target component in the inspection object 1. As a result, gamma rays (specific gamma rays) originating from the target component are generated.

[0087] The gamma ray detection device 5 detects specific gamma rays generated by the pulsed neutron beam incident on the inspection object 1. More specifically, the gamma ray detection device 5 detects the energy spectrum of gamma rays at each time point after the time point when the neutron source 3 incidents the pulsed proton beam on the target 3d (i.e., the time point when neutrons are generated as a reference time point), and generates time difference vs. spectrum data that correlates each time point with the reference time point (i.e., the time difference from the reference time point) with the energy spectrum of the gamma ray detected at that time point. The gamma ray detection device 5 includes a gamma ray detector 5a, a data acquisition unit 5c, and an intensity detection unit 5b.

[0088] At each time point, the gamma ray detector 5a detects the intensity of gamma rays for each energy (each wavelength) of gamma rays from the inspection object 1. That is, the gamma ray detector 5a detects the energy spectrum of the gamma rays at each time point, and outputs the energy spectrum to the data acquisition unit 5c for each time point.

[0089] The data acquisition unit 5c generates the above-mentioned time difference vs. spectrum data representing the energy spectrum at each time point based on the energy spectrum input from the gamma ray detector 5a at each time point. The energy spectrum at each time point indicates the number of gamma ray detections at each energy of gamma rays detected at that time point. In the second embodiment, each time point at which the energy spectrum is detected means the time difference between the neutron generation time point (reference time point) and the gamma ray detection time point. The gamma ray detection time point may be the time point at which the gamma ray detector 5a detects each gamma ray corresponding to the energy spectrum.

[0090] Fig. 9 shows an outline of an example of time difference versus spectrum data generated by the data acquisition unit 5c. In Fig. 9, the horizontal axis indicates TOF (Time of Flight), which is the time difference between the time of neutron generation and the time of gamma ray detection, and the vertical axis indicates the energy of the detected gamma ray. Also, in Fig. 9, A indicates the number of times that gamma rays of the corresponding energy were detected at the corresponding time, which is approximately 1 x 10 3 B indicates the area where the number of gamma rays of the corresponding energy detected at the corresponding time is approximately 4 × 10 2 That's more than 9 x 10 2 C indicates the area where the number of gamma rays of the corresponding energy detected at the corresponding time is approximately 3 × 10 1 is equal to or greater than 2 x 10 2 D indicates the area where the number of gamma rays of the corresponding energy detected at the corresponding time is approximately 1 × 10 1 That's more than 3 x 10 1 E indicates the area where the number of gamma rays of the corresponding energy detected at the corresponding time is approximately 1 × 10 1 The following shows the area:

[0091] The data acquiring unit 5c receives a synchronization signal indicating the time point of proton beam injection (time point of neutron generation) from the neutron source 3, and generates the above-mentioned time difference vs. spectrum data based on this synchronization signal. For example, the data acquiring unit 5c measures time using the time point at which the synchronization signal is received as the origin of time, and generates time difference vs. spectrum data that correlates each time point relative to the origin with the energy spectrum detected by the gamma ray detector 5a at that time point.

[0092] The intensity detection unit 5b determines the detection intensity of the specific gamma ray based on the time difference vs. spectrum data acquired and generated by the data acquisition unit 5c. Here, the specific gamma ray is a selected gamma ray related to the concentration data described below, and the detection intensity is a value proportional to the number of times the specific gamma ray is detected over the predetermined measurement time described above in the first embodiment.

[0093] The time point identifying unit 15 identifies the time point at which a specific gamma ray was detected based on the time difference versus spectrum data acquired and generated by the gamma ray detection device 5 (data acquiring unit 5c). For example, the time point identifying unit 15 identifies the time point at which the energy of a specific gamma ray was detected from the energy spectrum at each time point detected by the gamma ray detector 5a based on the time difference versus spectrum data. In one example, the time point identifying unit 15 extracts data indicating the number of times a specific gamma ray was detected at each time point from the above-mentioned time difference versus spectrum data, and identifies the time point at which a specific gamma ray was detected (i.e., the specific time point) as the time point at which the energy of the specific gamma ray was detected based on the extracted data.

[0094] When multiple types of specific gamma rays are emitted from the target component upon incidence of a pulsed neutron beam on the object to be inspected 1, the time point determination unit 15 preferably determines the time point at which a pre-specified type of specific gamma ray (hereinafter also referred to as a specified gamma ray) is detected.

[0095] The depth data storage unit 9c stores depth data that indicates the relationship between the depth at which the target component exists in the inspection object 1 and the specific time point (time point relative to a reference time point) at which a specific gamma ray (specified gamma ray) originating from the target component is detected when a pulsed neutron beam is incident on the inspection object 1. This depth data may be obtained, for example, by experiment.

[0096] In this experiment, multiple specimens made of the same material as the object to be inspected 1 are prepared. The depths at which the target components exist vary among the multiple specimens. For each specimen, pulsed neutrons are incident on the surface of the specimen from the neutron source 3, and the time point at which the energy of a specific gamma ray (designated gamma ray) is detected from the energy spectrum of the gamma ray detected at each time point by the gamma ray detector 5a is identified by the time point identification unit 15. The depth of the target component in one specimen and the above-mentioned detection time point (specific time point) identified for that specimen are considered as one set of data, and the above-mentioned depth data is created based on multiple sets of data obtained for each of the multiple specimens. The depth data created in this way is pre-stored in the depth data storage unit 9c.

[0097] The above experiment for obtaining depth data and the actual inspection of the inspection object 1 (step S101 described later) are performed under the distance conditions described above. Furthermore, the above experiment for obtaining depth data and the actual inspection of the inspection object 1 (step S101 described later) are preferably performed under the neutron spectrum conditions and orientation conditions described above.

[0098] The depth detection unit 19 determines the depth at which the target component exists based on the depth data stored in the depth data storage unit 9c and the time point identified by the time point identification unit 15. At this time, the depth detection unit 19 may determine the depth at which the target component exists by applying the time point to the depth data. The depth detection unit 19 outputs the determined depth. The output depth may be input to the concentration evaluation unit 14, stored in an appropriate storage medium, displayed on a display, or printed on paper.

[0099] For example, when the neutron source 3 is provided with the moderator 3g as described above and both fast neutrons and thermal neutrons are irradiated onto the surface 1a of the inspection object 1, one or both of the depth data for fast neutrons and the depth data for thermal neutrons are obtained in advance as described above. This will be explained with reference to FIG. 8B. In FIG. 8B, the horizontal axis indicates time, and the vertical axis indicates the number of times a specific gamma ray is detected. Note that at time t in FIG. 8B a ,t b ,t c ,t d are the time points t in FIG. 8A. a ,t b ,t c ,t d is equivalent to

[0100] When data indicating the number of times a specific gamma ray is detected at each time point is extracted from the above-mentioned time difference versus spectrum data as described above, the distance between the emission position of the neutron source 3 and the surface 1a of the object 1 to be inspected, as well as the pulse width and repetition frequency of the proton beam, are set in advance by simulation or experiment so that, with respect to the time points (specific time points) at which a specific gamma ray is detected in the extracted data (for example, the data of FIG. 8B), the specific time point (time point t1 in FIG. 8B) caused by fast neutrons irradiating the surface 1a of the object 1 to be inspected and the specific time point (time point t2 in FIG. 8B) caused by thermal neutrons irradiating the surface 1a of the object 1 to be inspected are distinguishably shifted from each other. This is possible because fast neutrons and thermal neutrons travel at different speeds. That is, gamma rays caused by irradiated fast neutrons are detected at an earlier time point, and gamma rays caused by irradiated thermal neutrons are detected at a later time point. If the pulse width of the proton beam is large in Fig. 8A, the width (time width) of the waveform of the number of detections in Fig. 8B will be wide, and if the distance between the emission position of the neutron source 3 and the surface 1a of the inspection target 1 is short, the time t1 and the time t2 in Fig. 8B will be close to each other. Taking this into consideration, the distance, pulse width, and repetition frequency are set in advance. In this embodiment, the specific point in time is a specific point in time within a time range in which a specific number of detections of a gamma ray occurs, and may be, for example, the point in time at which the number of detections reaches a peak, or the start point at which the number of detections begins to occur.

[0101] When obtaining both depth data for fast neutrons and depth data for thermal neutrons, for example, the depth detection unit 19 may extract data indicating the number of times a specific gamma ray is detected at each time point from the above-mentioned time difference versus spectrum data, and determine the depth at which the target component exists based on the earlier of two specific time points (e.g., t1 and t2 in Figure 8B) of the detection count in the extracted data and the depth data for fast neutrons, or based on the later of the two specific time points (t2) and the depth data for thermal neutrons.

[0102] In the above description, the neutron source 3 is configured to irradiate thermal neutrons and fast neutrons onto the inspection target 1. In this case, target components present in the inspection target 1 in a range close to the surface 1a and in a deep range can be detected. On the other hand, if the moderator 3g is omitted, or if a thermal neutron shielding material 4 (FIG. 7) is installed on the surface 1a of the inspection object 1 even in a configuration with the moderator 3g, the neutron source 3 will irradiate the inspection object 1 with substantially only fast neutrons out of thermal neutrons and fast neutrons. In this case, it is possible to detect the depth of the target component present in a range deep from the surface 1a within the inspection object 1. In this case, it is not necessary to obtain depth data for thermal neutrons.

[0103] The concentration data storage unit 9b in the second embodiment is the same as the concentration data storage unit 9b in the first embodiment. That is, this concentration data storage unit 9b stores concentration data that represents the relationship between the detection intensity of selected gamma rays and the concentration of the target component. Here, the selected gamma rays may be the above-mentioned designated gamma rays or may be another type of specific gamma rays.

[0104] The concentration evaluation unit 14 calculates the concentration of the target component at the depth based on the depth calculated by the depth detection unit 19, the concentration data corresponding to that depth stored in the concentration data storage unit 9b, and the input detection intensity of the selected gamma ray. The concentration evaluation unit 14 outputs the calculated concentration. The output concentration may be stored in an appropriate storage medium, displayed on a display, or printed on paper.

[0105] (Non-destructive testing method) 10 is a flowchart showing a nondestructive inspection method according to the second embodiment. This method may be performed using the above-described nondestructive inspection device 20. This method includes steps S101 to S105.

[0106] In step S101, a pulsed neutron beam is irradiated onto the surface 1a of the inspection object 1 by the neutron source 3. As a result, the pulsed neutron beam incident on the inspection object 1 reacts with a target component in the inspection object 1, generating specific gamma rays derived from the target component.

[0107] In step S102, of the gamma rays generated in step S101, specific gamma rays originating from a target component in the object to be inspected are detected, and the time point at which the specific gamma rays (specified gamma rays) were detected is identified. In this embodiment, step S102 may include steps S121 and S122. In step S121, the gamma ray detector 5a detects the energy spectrum of the gamma ray at each time point. In step S122, while measuring time with the time point at which the synchronization signal was received as the origin, time difference versus spectrum data is generated in which the energy spectrum detected by the gamma ray detector 5a at each measured time point corresponds to the time point.

[0108] In step S103, based on the detection result in step S102, the time identifying unit 15 identifies the time point at which a specific gamma ray (designated gamma ray) was detected after the time point at which the pulsed neutron beam was irradiated in step S101. At this time, the time identifying unit 15 may identify the time point at which the specific gamma ray was detected based on the time difference versus spectrum data generated in step S122.

[0109] In step S104, the depth detection unit 19 determines the depth at which the target component exists based on the time point identified in step S103 and the depth data in the depth data storage unit 9c.

[0110] In step S105, the concentration evaluation unit 14 determines the concentration of the target component at the depth based on the depth determined in step S104, the concentration data for that depth stored in the concentration data storage unit 9b, and the detection intensity of the selected gamma ray.

[0111] When the concentration data obtained for each depth using the above formula (A) is used, step 105 is performed as follows. First, the intensity detection unit 5b calculates the detection intensity of the selected gamma ray based on the number of times A of detection of the selected gamma ray and the above formula (A). The number of times A of detection used at this time is based on the result of detection of the selected gamma ray obtained (for example, in step S102 or newly selected in step S102) for the inspection object 1 by the neutron source 3 and the gamma ray detection device 5. Next, the concentration evaluation unit 14 calculates the concentration of the target component at the depth based on the detection intensity of the selected gamma ray calculated by the intensity detection unit 5b, the depth calculated in step S104, and the concentration data for that depth stored in the concentration data storage unit 9b.

[0112] On the other hand, the concentration data for each depth is used to calculate the gamma ray detection efficiency ε γ If the information has been acquired using the above, step S105 is performed as follows. First, the gamma ray detection efficiency ε corresponding to the depth calculated in step S104 is calculated. γ ε γd The intensity detection unit 5b calculates the detection intensity of the selected gamma ray based on the above formula (1) and the number of times A of detection of the selected gamma ray. The number of times A of detection used at this time is based on the result of detection of the selected gamma ray obtained for the inspection object 1 (for example, in step S102 or newly selected in step S102) by the neutron source 3 and the gamma ray detection device 5. The detection efficiency data, which is the same as that in the first embodiment, is stored in the detection efficiency storage unit 8 as shown in FIG. 7, and the intensity detection unit 5b calculates the detection intensity of the selected gamma ray based on the detection efficiency data in the detection efficiency storage unit 8 and the depth calculated in step S104. γd is specified and the above formula (1) is used as described above. Next, the concentration evaluation unit 14 determines the concentration of the target component at the depth based on the detection intensity of the selected gamma ray determined by the intensity detection unit 5b, the depth determined in step S104 (the depth input from the depth detection unit 19), and the concentration data for the depth stored in the concentration data memory unit 9b.

[0113] (Effects of the second embodiment) Specific gamma rays generated by the reaction between neutrons incident on the inspection object 1 and the target component are detected, and the time when the specific gamma rays are detected is identified. The identified time indicates the depth at which the target component is present. Therefore, by determining such a time, the depth at which the target component is present can be detected. Thus, the depth of the target component in the inspection object 1 can be detected non-destructively. For example, it is possible to detect the depth of the position of the target component present in the inspection object 1 and evaluate the concentration of the target component at that depth without taking a core from the inspection object 1, which is a concrete structure.

[0114] [Third embodiment] (Principle of the third embodiment) 11A is a diagram illustrating the detection principle according to the third embodiment. In the third embodiment, the gamma ray detection device 5 collimates the gamma rays to be detected. That is, the gamma ray detection device 5 detects gamma rays that have traveled in a direction within a specific range among gamma rays generated at a specific depth within the inspection object 1. More specifically, a neutron beam with a narrowed cross-sectional dimension is incident on the inspection object 1, and among gamma rays generated at a position Pc (hereinafter simply referred to as the intersection position Pc) where the reference line L of the gamma ray detector 5a intersects with the linear path of the neutron beam, gamma rays that have traveled along the reference line L are selectively incident on the gamma ray detector 5a, and gamma rays traveling in other directions are prevented from entering the gamma ray detector 5a by a gamma ray shielding portion 5d, which will be described later.

[0115] Therefore, when the gamma ray detection device 5 detects a specific gamma ray originating from the target component, it is known that the target component is present at the above-mentioned intersection position Pc (depth). In addition, by changing the geometric relationship (relationships related to position and orientation) between the reference line L and the path of the neutron beam, the intersection position Pc changes, so it is possible to check whether the target component is present at each intersection position Pc.

[0116] However, the neutron beam is incident on the inspection object 1 with the cross-sectional dimension of the neutron beam narrowed to an upper limit value or less. Here, the upper limit value may be several tens of millimeters or less, for example, 50 millimeters or less or 30 millimeters or less. The degree to which the neutron beam is narrowed may be set in the neutron source 3 according to the required resolution of the intersection position Pc. If the cross-section of the neutron beam is large, the number of gamma ray detections increases, but the resolution of the intersection position Pc decreases. If the cross-section of the neutron beam is small, the number of gamma ray detections decreases, but the resolution of the intersection position Pc increases. The cross-sectional shape of the neutron beam may be, for example, circular or a shape close to circular, but is not limited thereto and may be elliptical, rectangular, etc.

[0117] Furthermore, the degree of gamma ray collimation (the area of ​​the opening 21a of the gamma ray shielding portion 5d, described later) is set depending on the extent of the area (intersection position Pc) from which gamma rays are to be detected. If the area of ​​the opening 21a is large, the number of gamma ray detections increases, but the resolution at the intersection position Pc decreases. If the area of ​​the opening 21a is small, the number of gamma ray detections decreases, but the resolution at the intersection position Pc increases. FIG. 11B is a partially enlarged view of FIG. 11A, showing an example of the shape of the gamma ray detector 5a and the gamma ray shielding portion 5d. As shown in FIG. 11B, the gamma ray detector 5a has a detection surface 5a1 and detects gamma rays incident on the detection surface 5a1. The area D1 of this detection surface 5a1 is larger than the cross-sectional area D2 of the gamma ray passage hole 21 in the gamma ray shielding portion 5d and is larger than the area D3 of the opening 21a. That is, when viewed from the direction of the center line L of the gamma ray passing hole 21, the gamma ray detector 5a and the gamma ray shielding portion 5d may be formed so that the gamma ray passing hole 21 and the opening 21a are smaller than the detection surface 5a1, as shown in, for example, Figure 11B.

[0118] (Configuration of the third embodiment) 12 shows the configuration of a non-destructive inspection device 30 according to a third embodiment of the present invention. The non-destructive inspection device 30 includes the neutron source 3 described in the first or second embodiment, and a gamma ray detection device 5. In the third embodiment, the gamma ray detection device 5 has the configuration described below. In the third embodiment, the gamma ray detection device 5 may be the same as in the first or second embodiment described above, except for the points not described below.

[0119] In the third embodiment, the gamma ray detection device 5 includes a gamma ray detector 5a, an intensity detection unit 5b, and a gamma ray shielding unit 5d.

[0120] The gamma ray detector 5a detects gamma rays for each energy of gamma rays generated in the inspection object 1 by the incidence of neutron rays, and inputs the detection data to the intensity detection unit 5b. This detection data may be a peak value corresponding to the energy of each detected gamma ray. The gamma ray detector 5a may be, for example, a germanium detector, but is not limited to this.

[0121] The intensity detection unit 5b acquires the energy spectrum of the gamma rays based on each pulse height value input from the gamma ray detector 5a. The intensity detection unit 5b determines the intensity of the specific gamma rays as the detection intensity based on this energy spectrum. Here, if multiple types of specific gamma rays are emitted from the target component due to the incidence of neutron rays on the inspection target 1, the intensity detection unit 5b determines the intensity of a pre-specified type of specific gamma ray as the detection intensity. The intensity detection unit 5b outputs the determined detection intensity of the specific gamma ray. The output detection intensity may be displayed on a display.

[0122] The gamma ray shielding portion 5d is formed using a material with high gamma ray shielding ability (for example, lead, tungsten, tantalum, or iron) so as to substantially block the passage of gamma rays. The gamma ray shielding portion 5d forms a gamma ray passing hole 21. The gamma ray passing hole 21 has an opening 21a through which gamma rays can enter. The gamma ray detector 5a is disposed in the gamma ray passing hole 21 at a position shifted toward the back from the opening 21a. The opening 21a and the gamma ray detector 5a are located on a reference line L. With such a gamma ray shielding portion 5d, the gamma ray detector 5a substantially detects only gamma rays that enter from the opening 21a along the reference line L. Note that the reference line L may be the center line of the gamma ray passing hole 21.

[0123] When the gamma ray detector 5a is a germanium detector 5a, a cooling device 17 (not shown in FIG. 12 but shown in FIGS. 11A and 11B) for cooling the germanium detector 5a is provided. The cooling device 17 may be provided outside the gamma ray shielding portion 5d. In this case, the cooling device 17 may cool the germanium detector 5a through a hole 18 provided on the gamma ray shielding portion 5d on the opposite side to the opening 21a.

[0124] The gamma ray shielding portion 5d has a tip surface 22 in which an opening 21a is formed. The reference line L may extend obliquely with respect to the tip surface 22. That is, the tip surface 22 is formed so that the reference line L extends obliquely with respect to the tip surface 22. With this configuration, by performing an inspection with the tip surface 22 facing the surface 1a of the inspection object 1 as shown in FIG. 12, it is possible to more reliably prevent gamma rays from positions other than on the extension of the reference line L from reaching the gamma ray detector 5a. As a result, the resolution of the intersection position Pc is improved. The tip surface 22 may be, but is not limited to, a flat surface.

[0125] Figures 13A and 13B show specific examples of the shape of the gamma ray shielding portion 5d. Figures 13A and 13B are both views taken along the XIII-XIII arrows in Figure 11A, but show different specific examples.

[0126] In the case of Fig. 13A, the gamma ray shielding portion 5d is formed so as to surround the entire periphery of the gamma ray passing hole 21. In this case, the cross-sectional shape of the gamma ray passing hole 21 may be circular as in Fig. 13A, or may be another shape.

[0127] In the case of Fig. 13B, the gamma ray shielding portion 5d has two shielding blocks 23, 24 formed of the above-mentioned material so as to substantially block gamma rays and spaced apart by a gap, the gap being a gamma ray passing hole 21. This gap 21 extends along the reference line L. The dimension of the gap 21 in a first direction perpendicular to the reference line L is smaller than the dimension of the gap 21 in a second direction perpendicular to both the reference line L and the first direction. For example, the dimension of the gap 21 in the first direction is 1 / 2 or less, 1 / 3 or less, or 1 / 5 or less of the dimension of the gap 21 in the second direction.

[0128] In the case of FIG. 13B, the dimension of the cross section of the neutron beam is set to be equal to or less than the above-mentioned upper limit value in at least the first direction out of the first and second directions.

[0129] The gamma ray detection device 5 may include one or more sets of a gamma ray detector 5a, an intensity detection unit 5b, and a gamma ray shielding unit 5d that correspond to each other. Two sets are shown in Fig. 12. The gamma ray shielding unit 5d corresponding to each gamma ray detector 5a in Fig. 12 may have the shape described based on Fig. 13A or 13B.

[0130] The concentration data storage unit 9b in the third embodiment is the same as the concentration data storage unit 9b in the first embodiment. That is, the concentration data storage unit 9b stores concentration data that represents the relationship between the detection intensity of the selected gamma ray and the concentration of the target component.

[0131] The concentration evaluation unit 16 calculates the concentration of the target component at the depth based on the calculated depth, as described below, the concentration data corresponding to the depth stored in the concentration data storage unit 9b, and the input detection intensity of the selected gamma ray. The concentration evaluation unit 16 outputs the calculated concentration. The output concentration may be stored in an appropriate storage medium, displayed on a display, or printed on paper.

[0132] (Non-destructive testing method) 14 is a flowchart showing a non-destructive inspection method according to the third embodiment. This method may be performed using the above-described non-destructive inspection device 30. This method includes steps S201 to S205.

[0133] In step S201, the neutron source 3 and the gamma ray detection device 5 are arranged so that the path of the neutron beam emitted from the neutron source 3 intersects with an extension of the reference line L of the gamma ray shielding portion 5d inside the inspection object 1. In this arrangement, the gamma ray shielding portion 5d and the gamma ray detector 5a may be arranged so that the tip surface 22 of the gamma ray shielding portion 5d faces the surface 1a of the inspection object 1 (for example, so that the flat tip surface 22 is parallel to the flat surface 1a). In this case, the tip surface 22 may be in contact with the surface 1a or a small gap may be provided between the tip surface 22 and the surface 1a. Furthermore, the incident neutron beam does not need to be perpendicular to the surface 1a of the inspection object 1, and the neutron beam may be incident at an angle. The arrangement of the gamma ray detector 5a may be changed depending on the angle between the incident neutron beam and the surface 1.

[0134] Step S202 is performed in the state of arrangement performed in step S201. In step S202, a neutron beam is incident on the surface 1a of the inspection object 1 by the neutron source 3. Also in step S202, the gamma ray detector 5a detects gamma rays of each energy level generated by the incidence of the neutron beam, and the detection data is input to the intensity detection unit 5b. The neutron beam incident on the surface 1a in step S202 may be a pulsed neutron beam as in the second embodiment, or may be a time-continuous neutron beam.

[0135] In step S203, the intensity detection unit 5b acquires the energy spectrum of the gamma rays based on the detection data (peak values ​​corresponding to the energy of each detected gamma ray) obtained in step S202, and calculates the intensity of the specific gamma ray (i.e., the selected gamma ray) as the detection intensity (for example, by formula (A)) based on this energy spectrum. Also, in step S203, the detection intensity is output from the intensity detection unit 5b.

[0136] In step S204, based on the detection intensity of the specific gamma ray output in step S203, it is determined whether or not the target component is present at a depth (hereinafter also referred to as the corresponding depth) within the inspection object 1 corresponding to the reference line L in step S201. This corresponding depth is the depth of the intersection position Pc surrounded by a dashed circle in Figures 11A and 12. In other words, the corresponding depth is the depth of the position of the intersection between the above-mentioned path of the neutron beam emitted from the neutron source 3 and an extension of the above-mentioned reference line L.

[0137] The intersection position Pc (corresponding depth) can be determined in step S204 based on the geometric relationship between the neutron source 3, the gamma ray detection device 5, and the object 1 to be inspected, which were arranged in step S201. For example, the geometric relationship may be detected using an appropriate sensor or measuring device, and the detection results may be input into an appropriate computing device, which then determines the intersection position Pc. Alternatively, the intersection position Pc may be calculated manually based on the detection results. The intersection position Pc determined in this manner consists of the corresponding depth and a position in a direction along the surface 1a. Note that the geometric relationship may be, for example, a relationship regarding the positions and orientations of the path of the neutron beam, the reference straight line L, and the surface 1a of the object 1 to be inspected.

[0138] The determination in step S204 may be made by a person. For example, the detection intensity of the specific gamma ray output in step S203 is displayed on a display, and a person looks at the displayed detection intensity and determines that the target component is present at the corresponding depth if the detection intensity is equal to or greater than a set lower limit. Note that the corresponding depth calculated by the calculation device as described above may be displayed on a display together with the detection intensity.

[0139] In step S205, the concentration of the target component at the corresponding depth (intersection position Pc) determined in step S204 is determined. In this case, the concentration evaluation unit 16 determines the concentration of the target component at the corresponding depth based on the concentration data described above, the corresponding depth, and the detection intensity determined in step S203. The corresponding depth used in this case may be determined in step S204 as described above, and input to the concentration evaluation unit 16 or the intensity detection unit 5b by the calculation device or by a person operating an appropriate operation unit.

[0140] When the concentration data obtained for each depth using the above formula (A) is used, step 205 is performed as follows. First, the intensity detection unit 5b calculates the detection intensity of the selected gamma ray based on the above formula (A) and the number of times A that the selected gamma ray has been detected. The number of times A that is used at this time is based on the result of the detection of the selected gamma ray acquired (for example, in the above step S202 or newly selected in step S202) by the neutron source 3 and the gamma ray detection device 5 for the inspection object 1 under the same conditions (including the above orientation conditions) as those when the concentration data was acquired. Next, the concentration evaluation unit 16 determines the concentration of the target component at the depth based on the detection intensity of the selected gamma ray determined by the intensity detection unit 5b, the corresponding depth determined in step S204, and the concentration data for that depth stored in the concentration data storage unit 9b. Such concentration evaluation may be performed by a person. For example, the detection intensity, the concentration data for each depth, and the corresponding depth may be displayed on a display, and a person may look at the displayed data to determine the concentration of the target component at the corresponding depth.

[0141] On the other hand, the concentration data for each depth is used to calculate the gamma ray detection efficiency ε γ If the data has been acquired using the above, step S205 is performed as follows. The gamma ray detection efficiency ε corresponding to the corresponding depth obtained in step S204 γ ε γd The intensity detection unit 5b calculates the detection intensity of the selected gamma ray based on the above formula (1) and the number A of times of detection of the selected gamma ray. The number A of times of detection used at this time is based on the result of detection of the selected gamma ray acquired (for example, in the above step S202 or newly selected in step S202) by the neutron source 3 and the gamma ray detection device 5 for the inspection object 1 under the same conditions (including the above direction conditions) as those when the concentration data was acquired. In addition, the same detection efficiency data as in the first embodiment is stored in the detection efficiency storage unit 8 as shown in FIG. 12, and the intensity detection unit 5b calculates the detection intensity of the selected gamma ray based on the detection efficiency data in the detection efficiency storage unit 8 and the corresponding depth calculated in step S204. γd is specified and the above formula (1) is used as described above. Next, the concentration evaluation unit 16 calculates the concentration of the target component at the depth based on the detection intensity of the selected gamma ray calculated by the intensity detection unit 5b, the depth calculated in step S204, and the concentration data for that depth stored in the concentration data storage unit 9b. Such concentration evaluation may be performed by a person. For example, the detection intensity, concentration data for each depth, corresponding depth, and detection efficiency data may be displayed on a display, and a person may look at the displayed data to determine the concentration of the target component at the corresponding depth.

[0142] <Variations in testing methods> The following first to third examples will be described as variations of the non-destructive inspection method described above. Points that will not be described below are the same as the non-destructive inspection method described above.

[0143] In the first example, multiple sets of gamma ray detectors 5a, intensity detection units 5b, and gamma ray shielding units 5d are used. That is, in step S201, as shown in FIG. 15A, the multiple gamma ray detectors 5a and the neutron source 3 (not shown) are arranged so that the intersection positions Pc for the multiple gamma ray detectors 5a belonging to each of the multiple sets are different from one another. Thereafter, in step S202, steps S203 to S205 are performed for the detection data obtained by each gamma ray detector 5a. Each time steps S201 to S205 are performed in this manner, steps S201 to S205 are performed again, whereby the positions of the multiple gamma ray detectors 5a are shifted in a direction along the surface 1a (for example, the direction of arrow X in FIG. 15A), and steps S202 to S205 are performed again, thereby repeating steps S201 to S205.

[0144] In this repetition, the path of the neutron beam may be fixed. In this case, in this repetition, the orientation of the reference line L of each gamma ray detector 5a relative to the path of the neutron beam may be fixed or may be changed.

[0145] In the second example, similarly to the first example, in step S201, the gamma ray detectors 5a and the neutron source 3 (not shown) are arranged so that the intersection positions Pc for the gamma ray detectors 5a belonging to each of the plurality of sets are different from one another, as shown in FIG. 15B. Thereafter, steps S203 to S205 are performed on the detection data obtained by each gamma ray detector 5a in step S202. Each time steps S201 to S205 are performed in this manner, the path of the neutron beam is changed again in step S201 (for example, in FIG. 15B, the path of the neutron beam is shifted in the direction of arrow X or the angle of incidence θ of the neutron beam with respect to the surface 1a is changed), and steps S202 to S205 are performed again, thereby repeating steps S201 to S205. In this repetition, the positions and orientations of the gamma ray detectors 5a with respect to the surface 1a may be fixed.

[0146] In the third example, in step S201, as shown in Fig. 15C, multiple gamma ray detectors 5a and a neutron source 3 (not shown) are arranged so that the intersection positions Pc for the gamma ray detectors 5a belonging to each of the multiple groups are different from one another. Thereafter, in step S202, steps S203 to S205 are performed on the detection data obtained by each gamma ray detector 5a. Each time steps S201 to S205 are performed in this manner, the inclination of the reference line L of each gamma ray detector 5a relative to the surface 1a is changed in step S201 again, and steps S202 to S205 are performed again, thereby repeating steps S201 to S205. In this repetition, the path of the neutron beam may be fixed.

[0147] 15C, the reference line L may be perpendicular to the tip surface 22. In such a case, the shape of the gamma ray shielding portion 5d described above with reference to FIG. 13A or 13B may be adopted. In the third example, a single set of gamma ray detectors 5a may be used instead of multiple sets, and in this case, other points are the same as those described above.

[0148] By the inspections according to the first to third examples, it is possible to inspect the presence or absence of a target component and its concentration over a wide range within the inspection object 1.

[0149] The above-described third embodiment may be implemented in combination with the first embodiment or the second embodiment, or may be implemented independently of the first embodiment and the second embodiment.

[0150] (Effects of the third embodiment) Since the gamma ray detector 5a is disposed in the gamma ray passage hole 21 of the gamma ray shielding portion 5d, the gamma ray detector 5a essentially detects only gamma rays from a depth corresponding to the reference line L of the gamma ray shielding portion 5d. Therefore, by changing the direction of the reference line L and obtaining the detection intensity of a specific gamma ray for each direction, it is possible to determine that the target component is present at a depth corresponding to the direction of the reference line L where the detection intensity exceeds a set lower limit value. In this way, the depth of the target component can be identified. Furthermore, if concentration data for concentration evaluation has been obtained in advance through experiments, the concentration of the target component can also be obtained and evaluated along with the depth.

[0151] The present invention is not limited to the above-described embodiment, and various modifications may be made within the scope of the technical concept of the present invention. For example, the above-described effects do not necessarily limit the present invention. Furthermore, the present invention may achieve any of the effects shown in this specification, or other effects that can be understood from this specification. Furthermore, any of the following modified examples 1 to 3 may be adopted, or any combination of two or more of modified examples 1 to 3 may be adopted. In this case, points not described below may be the same as those described above.

[0152] (Change example 1) In the first embodiment, the depth detection unit 11 may be omitted. In this case, a person may determine the depth of the target component based on the ratio and depth data determined in step S3 described above. For example, the ratio and depth data determined in step S3 may be displayed on a display or printed on paper, and a person may determine the depth of the target component by looking at the displayed or printed ratio and depth data.

[0153] Similarly, in the second embodiment, the depth detection unit 19 may be omitted. In this case, a person may determine the depth of the target component based on the time point and depth data identified in the above-described step S103. For example, the time point and depth data identified in step S103 may be displayed on a display or printed on paper, and a person may determine the depth of the target component by looking at the displayed or printed time point and depth data.

[0154] (Change example 2) In the first embodiment, the concentration evaluation unit 13 may be omitted. In this case, the depth calculated in step S4 and the gamma ray detection efficiency ε γ A person may determine the concentration of the target component at the depth based on the detection intensity of the selected gamma rays based on the above and the concentration data. That is, each piece of data used in the above step S5 (e.g., the detection intensity of the selected gamma rays detected in step S2, the above detection efficiency data, the depth determined in step S4, and the above concentration data) may be displayed on a display or printed on paper, and a person may determine the concentration of the target component at the depth by looking at the displayed or printed data.

[0155] Similarly, the concentration evaluation unit 14 may be omitted in the second embodiment. In this case, the depth calculated in step S104 and the gamma ray detection efficiency ε corresponding to the depth are calculated. γ A person may determine the concentration of the target component at the depth based on the detection intensity of the selected gamma ray based on (1) and the concentration data described above. That is, each piece of data used in the above step S105 may be displayed on a display or printed on paper, and a person may determine the concentration of the target component at the depth by looking at the displayed or printed data.

[0156] (Change example 3) In the first and third embodiments described above, the neutron source 3 may be any neutron source that can irradiate a neutron beam onto the inspection object 1, and is not limited to a neutron source that uses an accelerator including a pulse type. For example, the neutron source 3 may be an RI ray source ( 252 1 and 12, for example, the RI radiation source is placed at the position of the target 3d, a container 3e is provided surrounding the RI radiation source, and a tubular shielding member 3f for the RI radiation source is provided in the container 3e.

[0157] The present invention is not limited to the embodiments, examples, and modifications described above, and may be widely applied as long as they do not deviate from the spirit of the invention. For example, the selected gamma rays described above are not limited to the examples described above, and may be specific gamma rays. [Explanation of symbols]

[0158] 1 inspection object, 1a surface, 3 neutron source, 3a ion source, 3b accelerator, 3c beam adjuster, 3d target, 3e container, 3f tubular shielding member, 3g deceleration section, 5 gamma ray detection device, 5a gamma ray detector, 5b intensity detection section, 5c data acquisition section, 5d gamma ray shielding section, 7 ratio calculation section, 8 detection efficiency memory section, 9a, 9c depth data memory section, 9b concentration data memory section, 10, 20 non-destructive inspection device, 11 depth detection section, 13, 14, 16 concentration evaluation section, 15 time point identification section, 17 cooling device, 18 hole, 19 depth detection section, 21 gamma ray passage hole, 21a opening 22 tip surface, 23, 24 shielding block, L reference line, Pc intersection position,

Claims

1. A non-destructive testing device for irradiating a pulsed neutron beam including fast neutrons into a concrete structure containing reinforcing steel bars therein, detecting and identifying specific gamma rays generated by the reaction of the pulsed neutron beam with chlorine Cl in the concrete structure, and deriving the depth of existence of chlorine Cl as salt that causes corrosion of the reinforcing steel bars within the concrete structure based on the detection results, a neutron source that irradiates the surface of the concrete structure with the pulsed neutron beam; a gamma ray detection device that detects the energy spectrum of gamma rays generated based on the pulsed neutron beam at each time point relative to a reference time point, and generates time difference vs. spectrum data that correlates the time difference between the time point and the reference time point with the energy spectrum of the gamma rays detected at the time point; a time point identifying unit that identifies a time point at which the specific gamma ray was detected relative to the reference time point based on the time difference versus spectrum data; a depth data storage unit that stores depth data for fast neutrons, the depth data representing the relationship between the depth at which chlorine Cl exists in the concrete structure and the time at which the specific gamma ray is detected when the fast neutron is incident on the concrete structure; a depth detection unit that determines the depth at which the chlorine Cl exists based on the depth data for the fast neutrons and the time point identified by the time point identification unit.

2. 2. The non-destructive inspection device according to claim 1, wherein the neutron source irradiates the concrete structure with only fast neutrons out of thermal neutrons and fast neutrons.

3. The neutron source irradiates the concrete structure with thermal neutrons and fast neutrons, the depth data storage unit stores depth data for thermal neutrons, which indicates a relationship between a depth at which the chlorine Cl exists in the concrete structure and a time point at which the specific gamma ray is detected when the thermal neutron is incident on the concrete structure; 2. The non-destructive inspection device according to claim 1, wherein the depth detection unit determines the depth at which the chlorine Cl exists based on an earlier point in time among the points in time specified by the time point specifying unit and the depth data for fast neutrons, and determines the depth at which the chlorine Cl exists based on a later point in time among the points in time specified by the time point specifying unit and the depth data for thermal neutrons.

4. The gamma ray detection device determines the detection intensity of the specific gamma ray based on the time difference vs. spectrum data, a concentration data storage unit that stores concentration data representing a relationship between the detection intensity of the specific gamma ray and the concentration of chlorine Cl for each depth in the concrete structure; 3. The non-destructive testing device according to claim 2, further comprising: a concentration evaluation unit that calculates the concentration of chlorine Cl at the depth based on the calculated depth, concentration data stored in the concentration data storage unit, and the detection intensity calculated by the gamma ray detection device.

5. A non-destructive testing method for deriving the depth of existence of chlorine Cl as salt that causes corrosion of the reinforcing steel within the concrete structure based on a result of the detection, comprising: irradiating a pulsed neutron beam including fast neutrons onto a concrete structure containing reinforcing steel; detecting and identifying specific gamma rays generated by the reaction of the pulsed neutron beam with chlorine Cl within the concrete structure; and an irradiation step of irradiating the surface of the concrete structure with the pulsed neutron beam; a gamma ray detection process for detecting the energy spectrum of gamma rays generated based on the pulsed neutron beam at each time point relative to a reference time point, and generating time difference vs. spectrum data in which the time difference between the time point and the reference time point corresponds to the energy spectrum of the gamma rays detected at the time point; a time point identifying step of identifying a time point at which the specific gamma ray was detected relative to the reference time point based on the time difference versus spectrum data; a depth detection step of determining the depth at which chlorine Cl exists based on the time point specified in the time point specifying step, and fast neutron depth data representing the relationship between the depth at which chlorine Cl exists in the concrete structure and the time point at which the specific gamma ray is detected when fast neutrons are incident on the concrete structure.

6. 6. The non-destructive inspection method according to claim 5, wherein in the irradiation step, only fast neutrons out of thermal neutrons and fast neutrons are irradiated onto the concrete structure.

7. In the irradiation step, thermal neutrons and fast neutrons are irradiated onto the concrete structure, depth data for thermal neutrons and depth data for fast neutrons are obtained in advance, the depth data representing the relationship between the depth at which chlorine Cl exists in the concrete structure and the time at which the specific gamma ray is detected when the thermal neutrons are incident on the concrete structure; 7. The non-destructive testing method according to claim 6, wherein the depth detecting step determines the depth at which the chlorine Cl exists based on an earlier one of the time points specified in the time point specifying step and the depth data for fast neutrons, and determines the depth at which the chlorine Cl exists based on a later one of the time points specified in the time point specifying step and the depth data for thermal neutrons.

8. determining the detection intensity of the specific gamma ray based on the time difference versus spectrum data; 7. The non-destructive inspection method according to claim 6, further comprising a concentration evaluation step of determining the concentration of chlorine Cl at each depth in the concrete structure based on concentration data representing a relationship between the detection intensity of the specific gamma ray and the concentration of chlorine Cl, the determined depth, and the detection intensity determined based on the time difference vs. spectrum data.

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