JP2015215262A - Method and device for non-destructive inspection - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a non-destructive inspection device capable of simply detecting a state of an inspection object in the case of using Compton scattering γ rays without being affected by fluctuation of a γ ray source, and moreover without causing a problem of restriction of the arrangement position of a detector.SOLUTION: A non-destructive inspection method includes: a γ-ray source 1 for radiating a γ-ray toward an inspection object 3; a collimator for collimating a scattered γ-ray based on Compton scattering obtained as a result of the irradiation; and a detector for generating a scattered γ-ray energy distribution characteristic representing signal strength for scattered γ-ray energy of a scattered γ-ray signal representing the scattered γ-ray incident via the collimator. The detector 2 detects a state of the inspection object 3 when a peak of signal intensity of a scattered γ-ray based on Compton scattering is shifted to a high energy side or a low energy side in the scattered γ-ray energy distribution characteristic as a thickness of the inspection object 3 becomes thin.

Description

  The present invention relates to a nondestructive inspection method and an apparatus therefor, and is particularly useful when applied to a nondestructive inspection utilizing Compton scattering.

  Non-destructive inspection using X-rays or γ-rays (hereinafter collectively referred to as γ-rays in the present specification) is widely used for inspection of piping of nuclear facilities. In this method, γ-rays are irradiated to a pipe or the like that is an inspection object, and a transmission image of the inspection object is analyzed to detect the degree of thinning (for example, see Patent Document 1).

  However, when inspecting the degree of thinning by obtaining a transmission image of the inspection object, the detector for detecting γ rays is placed on the opposite side of the inspection object with respect to the radiation source that irradiates γ rays. Need to be placed in.

  For this reason, the opposite side of the object to be inspected with respect to the radiation source is often a narrow part, or a sufficient space for disposing the detector cannot be secured due to the presence of obstacles such as other pipes.

On the other hand, if scattered gamma rays based on Compton backscattering are used, the radiation source and the detector can be arranged on the same side with respect to the inspection object. As shown in FIG. 5 (a), Compton backscattering shows that when the target T is irradiated with a predetermined γ-ray, the energy changes with recoil electrons E _e that jump out in the direction of the angle Φ with respect to the γ-ray. A phenomenon in which the original γ rays are scattered as scattered γ rays. Here, the scattering angle θ of the scattered γ-ray is uniquely determined by the energy E _{0 of the} γ-ray irradiated to the target T and the scattered γ-ray energy E ₁ of the scattered γ-ray scattered. The case of scattering in a region where the scattering angle θ> 90 ° is particularly referred to as backscattering.

Accordingly, as shown in FIG. 5B, if the γ-ray source 01 and the detector 02 are arranged so as to match the scattering angle θ> 90 °, the γ-ray source 01 and the detector 02 are inspected. It can arrange | position on the same side with respect to the piping 03 which is a thing, and the arrangement | positioning conditions of the detector 02 can be eased. Here, in the detector 02, as shown in FIG. 5C, the scattering uniquely identified by the scattering angle θ (the angle formed by the arrangement position of the γ-ray source 01 and the arrangement position of the detector 02). A scattered γ-ray energy distribution having a peak signal intensity is obtained at the scattered γ-ray energy E ₁ of γ-rays. In FIG. 5C, the horizontal axis represents the energy of the scattered γ-ray, and the vertical axis represents the signal intensity of the scattered γ-ray signal detected by the detector 02. The scattered γ-ray signal is a signal representing the intensity of the scattered γ-ray. Although not shown, a normal collimator is usually provided in front of the γ-ray source 01 and the detector 02.

On the other hand, as shown in FIG. 6A, the scattered γ-ray energy E of the back-scattered γ-ray when the pipe 03 that is the inspection object maintains a normal state without causing thinning on the inner periphery. _As shown in FIG. 6B, ₁ is larger than the case where the thinned portion 03A is formed on the inner periphery of the pipe 03 that is the inspection object. The thick portion of the pipe 03, which is the inspection object, is a high-density material such as iron, whereas the thinned portion 03A is low-density air, so that the γ-ray scattering intensity greatly decreases in the air portion. Because. For example, assuming that the energy E _{0 of} γ-rays emitted from the radioisotope iridium source, which is the γ-ray source 01, is 320 keV, the scattered γ-ray energy E ₁ of the scattered γ-rays when the scattering angle θ = 90 ° is 197 keV. It is uniquely determined. Accordingly, the signal intensity of the scattered γ ray energy E ₁ of the scattered γ ray becomes small when the reduced thickness portion 03A on the pipe 03 which is an inspection object is occurring.

Therefore, occurrence of thinning can be detected by detecting the scattered γ-ray energy E ₁ of the scattered γ-rays in the scattered γ-ray energy distribution shown in FIG. 5C (see, for example, Non-Patent Document 1).

JP 2006-177841 A

(Japan) Atomic Energy Society of Japan "1995 Autumn Conference" (October 17-20, 1995, JAERI) Inspection technology from the surface of thermal insulation materials using Compton scattering, Toshiba Corporation, Akira Udaka, Takayuki Takashima, Goto Tetsuo

However, as described above, when the thinning is detected based on the signal intensity of the scattered γ-ray energy E ₁ of the scattered γ-rays in the scattered γ-ray energy distribution characteristics shown in FIG. It becomes a problem. For example, when a radioisotope source is used as the γ-ray source, the intensity of the γ-ray irradiated from the γ-ray source 01 may fluctuate with time, and the reference signal intensity changes accordingly. This is because it becomes an impediment to highly accurate measurement.

Note that, as described above, the problem that the reference signal intensity changes is not only when using Compton backscattering as shown in FIG. 6, but also when using Compton scattering. Occur. That is, a problem that fluctuation of the signal intensity of such criteria as long as it utilizes only the magnitude of the signal intensity of the scattered γ ray energy E _1, not limited to backscattering generally occurs.

  In view of the above-described prior art, the present invention, in the case of using Compton scattered γ-rays, the state of the inspection object is not affected by fluctuations in the γ-ray source, and is further referred to as a restriction on the arrangement position of the detector. It is an object of the present invention to provide a nondestructive inspection method and apparatus capable of easily and accurately detecting without causing a problem.

The present invention that achieves the above object is based on the following knowledge. As shown in FIG. 1, γ-rays are irradiated from a γ-ray source 1 toward an iron plate (thickness 10 mm) as an inspection object 3, and backscattered γ-rays in this case are converted into a collimator (for example, inner diameter φ = 10 mm). ) Let us consider a case in which the detector 2 detects via 4. As described above, in this case, a scattered γ-ray energy distribution characteristic as shown in FIG. 5C is obtained. The case shown in the figure, the peak P of the signal intensity in the scattered γ ray energy E ₁ are observed.

  In this case, the scattered γ-ray energy is given by the following equation (1).

In FIG. 2, the thickness of the iron plate that is the inspection object 3 is changed to 10 mm, 7 mm, 6 mm, and 5 mm, and γ-rays are similarly irradiated, scattered by the inspection object 3, and detected through the collimator 4. The scattered γ-ray energy distribution characteristics based on the scattered γ-rays thus obtained are shown. The scattered γ-ray energy distribution characteristics are the results of simulation calculations for each plate thickness. Referring to the figure, as is clear, as the plate thickness decreases from 10 mm (FIG. 2 (a)) to 5mm (FIG. 2 (d)), the position of the peak P of the signal intensity is higher than the theoretical value. You can see that it is shifting to the energy side. In the figure, in the case of the scattered γ-rays in which E ₀ = 468 keV γ-rays are scattered in the θ = 90 ° direction, the case of 10 mm shown in FIG. 2A and the case of 5 mm shown in FIG. A shift of the shift amount ΔE ₁ has occurred. As described above, if the correlation between the shift amount ΔE ₁ and the thickness of the inspection object 3 is used by utilizing the phenomenon that the position of the peak P shifts to the high energy side, It is thought that the state can be detected.

  The reason why the position of the peak P shifts to the high energy side is considered as follows. As shown in FIG. 5C, generally, Compton scattered γ-rays have a certain energy spread around the peak P of the signal intensity on the scattered γ-ray energy distribution characteristics. One reason for this is that the inner diameter φ of the lead collimator 4 is 10 mm and the observation region is not pinpointed. That is, the cross section of the collimator 4 has a finite extent. In the above simulation, attention is paid to γ-rays scattered at a scattering angle θ = 90 °. As shown in FIG. 1, the intersection of the rotational symmetry axis of the collimator 4 and the γ-ray traveling axis is determined from the inspection object 3. Since the radius of the inner diameter φ of the collimator 4 is 5 mm at a position 10 mm deeper, scattered γ-rays from a position deeper than 10− (5√2) = 6.5 mm from the surface of the inspection object 3 (Scattering angle θ = 90 °) is observed. On the other hand, as shown in FIG. 1, scattered γ-rays (scattering angle θ = 90 °) are not observed from an area shallower than 6.5 mm due to geometric limitations, and scattered γ-rays having a scattering angle θ <90 °. Only observed. The scattered γ-ray energy at a scattering angle θ <90 ° is higher than that of θ = 90 ° from the above equation (1), and this indicates that the peak energy position of the scattered γ-rays becomes smaller as the inspection object 3 becomes thinner. This is considered to be the reason for shifting to the high energy side.

FIG. 3 is a characteristic diagram showing the relationship between the thickness of Fe that is the inspection object detected based on the detection result shown in FIG. 2 and the peak shift. Referring to the figure, the shift amount ΔE ₁ increases rapidly in a region shallower than 6.5 mm where no scattered γ-rays (scattering angle θ = 90 °) are observed due to geometric limitations of the collimator 4. I understand that.

  The first aspect of the present invention based on this knowledge is based on Compton scattering obtained as a result of the irradiation while irradiating the inspection object with X-rays or γ-rays (hereinafter collectively referred to as γ-rays). The scattered γ-rays are detected by collimating with a collimator, and the scattered γ-ray energy distribution characteristic representing the signal intensity with respect to the scattered γ-ray energy of the scattered γ-ray signal representing the detected scattered γ-rays is obtained. As the thickness decreases, the peak of the signal intensity shifts to the high energy side or the low energy side of the scattered γ-ray energy in the scattered γ-ray energy distribution characteristics according to the diameter of the collimator. And a non-destructive inspection method characterized by detecting the state of the inspection object.

  According to this aspect, it is possible to easily and accurately detect the state such as thinning of the inspection object by grasping the shift aspect of the signal intensity peak in the scattered γ-ray energy distribution characteristics.

  According to a second aspect of the present invention, in the nondestructive inspection method according to the first aspect, the detection of the state uses the peak position in a standard inspection object as a reference peak position, and the reference peak position; The nondestructive inspection method is characterized in that the nondestructive inspection method is performed based on a shift amount which is a difference from the actually measured peak position which is the peak position of the actually measured inspection object.

  According to this aspect, it is possible to objectively grasp a predetermined state such as thinning using a shift amount that is a quantitative reference.

  According to a third aspect of the present invention, in the nondestructive inspection method according to the first or second aspect, the Compton scattering is Compton backscattering.

  According to this aspect, even if it is a detection target of a narrow portion where piping and the like are arranged in a complicated manner, the detection position condition is relaxed and good workability is ensured, and a predetermined state is easily detected. be able to.

  According to a fourth aspect of the present invention, there is provided a γ-ray source that irradiates a test object with γ-rays, a collimator that collimates scattered γ-rays based on Compton scattering obtained as a result of the irradiation, and the collimator And a detector that generates a scattered γ-ray energy distribution characteristic that represents a signal intensity with respect to scattered γ-ray energy of a scattered γ-ray signal that represents the scattered γ-rays incident thereon. As the inspection object becomes thinner, the peak of the signal intensity of the scattered γ-rays based on the Compton scattering has a higher energy of the scattered γ-ray energy in the scattered γ-ray energy distribution characteristics according to the diameter of the collimator. The non-destructive inspection apparatus is characterized in that the state of the inspection object is detected based on a shift amount when shifting to a low energy side or a low energy side.

  According to this aspect, it is possible to easily and accurately detect the state such as thinning of the inspection object by grasping the shift aspect of the signal intensity peak in the scattered γ-ray energy distribution characteristics.

  According to a fifth aspect of the present invention, in the nondestructive inspection apparatus according to the fourth aspect, the detector determines that the inspection object is defective when the shift amount exceeds a predetermined threshold value. It is in the nondestructive inspection apparatus characterized by this.

  According to this aspect, whether or not the inspection object is good can be accurately determined by using whether or not the threshold value is exceeded.

  According to a sixth aspect of the present invention, in the nondestructive inspection apparatus according to the fourth or fifth aspect, the Compton scattering is Compton backscattering, and the detector is configured to detect the inspection object. The non-destructive inspection apparatus is arranged on the same side.

  According to this aspect, even if the detection target is a narrow portion where piping and the like are arranged in a complicated manner, the condition of the arrangement position of the detector is relaxed. As a result, it is possible to easily detect a predetermined state while ensuring good workability.

  According to the present invention, as the inspection object becomes thinner, the peak of the signal intensity of the scattered γ-ray signal representing the scattered γ-rays irradiated and scattered on the inspection object becomes the scattered γ-ray energy distribution characteristic. The state of the object to be inspected, for example, the thickness or the like can be accurately detected using the shift of the scattered γ-ray energy to the high energy side or the low energy side. Here, the present invention does not compare the signal intensity based on the scattered γ-rays with other objects, but makes a predetermined determination based on only the peak shift. It is not affected by.

It is explanatory drawing which shows notionally the aspect in the case of irradiating a to-be-inspected object with a gamma ray and collimating and detecting the scattered gamma ray accompanying this with a collimator. It is a characteristic view which shows the scattered gamma ray energy distribution characteristic corresponding to each thickness in the case of the detection using the scattered gamma ray shown in FIG. 1 performed by changing the thickness of a test object. It is a characteristic view which shows the relationship between the thickness of Fe which is a test object detected based on the detection result shown in FIG. 2, and a peak shift. It is a block diagram which shows the nondestructive inspection apparatus which concerns on embodiment of this invention. It is explanatory drawing which shows the principle of conventionally well-known Compton backscattering typically. It is explanatory drawing which shows typically the principle of the prior art which carries out nondestructive inspection of the thinning of piping using Compton backscattering.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

  FIG. 4 is a block diagram showing a nondestructive inspection apparatus according to an embodiment of the present invention. As shown in the figure, the nondestructive inspection apparatus according to this embodiment includes a γ-ray source 1 that irradiates γ-rays toward an inspection object 3 that is, for example, a pipe, and scattering based on Compton scattering obtained as a result of the irradiation. and a detector 2 for detecting γ-rays. Here, a collimator 4 (see FIG. 1) formed of a lead cylindrical member having an inner diameter φ of, for example, 10 mm is disposed between the detector 2 and the inspection object 3. As a result, the scattered γ rays are collimated by the collimator 4 and are incident on the detector 2.

  Here, as the γ-ray source 1, for example, a radioisotope iridium radiation source can be suitably applied. In addition, the detector 2 generates a scattered γ-ray energy distribution characteristic (see FIG. 2) indicating the signal intensity of the scattered γ-ray signal representing the scattered γ-rays incident through the collimator 4 with respect to the scattered γ-ray energy. .

  The detector has a signal intensity peak of scattered γ-rays based on the Compton scattering as the thickness of the object to be inspected decreases in the scattered γ-ray energy distribution characteristics according to the diameter of the collimator. The state of the inspection object is detected based on the shift amount when the γ-ray energy is shifted to the high energy side or the low energy side.

More specifically, the detector 2 includes an incident unit 2A that receives Compton backscattered γ rays, a signal processing unit 2B that generates a Compton backscattered γray signal representing Compton backscattered γrays, and a Compton backscattered γray signal. An arithmetic processing unit 2C that processes and detects a thinning state of the inspection object 3, a storage unit 2D that stores reference data for detecting the thinning state, and a detection result detected by the arithmetic processing unit 2C. It has a display section 2E for displaying. The signal processing unit 2B processes the Compton backscattered γ-ray to generate a γ-ray energy distribution characteristic as shown in FIG. 2 that represents the signal intensity of the Compton backscattered γ-ray signal with respect to the scattered γ-ray energy. The storage unit 2D stores in advance a scattered γ-ray energy distribution characteristic (hereinafter referred to as a reference scattered γ-ray energy distribution characteristic) of a healthy inspection object 3 (which does not cause thinning). Here, a peak P of the signal intensity of the scattered γ-ray energy E ₁ exists in the reference scattered γ-ray energy distribution characteristic. In the arithmetic processing unit 2C, the position of the peak P of the signal intensity of the scattered γ-ray energy in the scattered γ-ray energy distribution generated from the actual measurement data is detected, and this position exceeds a predetermined threshold value to the high energy side or the low energy side. When shifting, a warning or data indicating this is displayed on the display unit 2E.

  As described above, in the detector 2 according to the present embodiment, as the inspection object 3 becomes thinner, the peak P of the scattered γ-ray signal intensity based on Compton scattering becomes the scattered γ-ray energy in the scattered γ-ray energy distribution characteristics. The shift amount when shifting to the high energy side or the low energy side is detected, and the state of the inspection object 3 such as the thinning amount of the inspection object 3 is detected based on the shift amount. Here, in this embodiment, the signal intensity is not compared with other objects, but a predetermined determination is made based only on the shift of the peak, so that it is affected by fluctuations of the γ-ray source 1 and the like. There is nothing.

  In the above embodiment, the case of using Compton backscattered γ rays has been described. However, the present invention is not limited to backscattering. However, when using backscattering, since the γ-ray source 1 and the detector 2 can be arranged on the same side with respect to the pipe that is the inspection object 3, the degree of freedom in equipment arrangement is improved. Further, the inspection object 3 does not need to be a pipe, and does not necessarily need to detect thinning. It is useful as a nondestructive inspection apparatus that widely detects the dimensions of each part of an inspection object. Furthermore, it is not always necessary to detect the shift amount in comparison with a standard sample that provides standard data. In short, as the thickness of the inspection object 3 becomes thinner, the peak P of the signal intensity becomes the scattered γ-ray energy distribution characteristic. In the case of detecting the state of the inspection object 3 by utilizing the shift of the scattered γ-ray energy to the high energy side or the low energy side, all are included in the technical idea of the present invention.

  Further, the data of the scattered γ-ray energy distribution characteristics for each thickness of the inspection object 3 shown in FIGS. 2A to 2D is stored in the storage unit 2D one by one, and the arithmetic processing unit is read by reading each data. By performing a predetermined calculation at 2C, for example, a peak shift characteristic diagram shown in FIG. 3 can be created and displayed on the display unit 2E.

  INDUSTRIAL APPLICABILITY The present invention can be effectively used in an industrial field where non-destructive inspection is performed for maintenance, inspection, etc. of a power plant where inspection objects such as piping are arranged in a complicated manner.

1 Gamma ray source 2 Detector 3 Inspection object 4 Collimator

Claims (6)

X-rays or γ-rays (hereinafter collectively referred to as γ-rays) are irradiated onto the inspection object, and scattered γ-rays based on Compton scattering obtained as a result of the irradiation are collimated and detected by a collimator. While obtaining the scattered γ-ray energy distribution characteristics representing the signal intensity relative to the scattered γ-ray energy of the scattered γ-ray signal representing the scattered γ-ray,
As the thickness of the inspection object decreases, the peak of the signal intensity shifts to the high energy side or the low energy side of the scattered γ-ray energy in the scattered γ-ray energy distribution characteristics according to the diameter of the collimator. A non-destructive inspection method characterized by detecting the state of the inspection object by using. In the nondestructive inspection method according to claim 1,
The detection of the state uses the peak position in a standard inspection object as a reference peak position, and a shift amount that is a difference between the reference peak position and the actual measurement peak position that is the actual peak position of the inspection object A non-destructive inspection method characterized by In the nondestructive inspection method according to claim 1 or 2,
The non-destructive inspection method, wherein the Compton scattering is Compton backscattering. A γ-ray source that irradiates γ-rays toward an inspection object, a collimator that collimates scattered γ-rays based on Compton scattering obtained as a result of the irradiation, and the scattered γ-rays incident through the collimator In a nondestructive inspection apparatus having a detector that generates a scattered γ-ray energy distribution characteristic that represents a signal intensity with respect to scattered γ-ray energy of a scattered γ-ray signal that represents
The detector has a signal intensity peak of scattered γ-rays based on the Compton scattering as the thickness of the object to be inspected decreases in the scattered γ-ray energy distribution characteristics according to the diameter of the collimator. A nondestructive inspection apparatus for detecting a state of the inspection object based on a shift amount when shifting to a high energy side or a low energy side of γ-ray energy. In the nondestructive inspection device according to claim 4,
The non-destructive inspection apparatus, wherein the detector determines that the inspection object is defective when the shift amount exceeds a predetermined threshold. In the nondestructive inspection device according to any one of claims 4 and 5,
The Compton scattering is Compton backscattering, and the detector is disposed on the same side with respect to the inspection object.