JP2006177841A - Nondestructive inspection device and method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a small-sized nondestructive inspection device having high measurement accuracy. <P>SOLUTION: A pulsed electron beam 22 is allowed to enter a target 18 by an electron accelerator 16, to thereby generate a bremsstrahlung X-ray, and an inspection object 10 is irradiated therewith. The X-ray 28 transmitted through the inspection object 10 is received by a scintillator 30, and generated light is converted into a corresponding electric signal 34 by a photodetector 32. The electric signal 34 is integrated during a period T when the pulsed electron beam is generated, or during a period T' in consideration of a signal delay of the detector. The integration is repeated relative to a plurality of pulses. Thus, the transmission quantity of the X-ray through the inspection object 10 is measured from the integrated value, and a shape characteristic of the inspection object 10 can be inspected. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to an apparatus and method for nondestructive inspection of structures such as factory plants and buildings.

In general, a non-destructive inspection method for a structure such as a factory plant, a power plant, a building, or a building uses a radiation source such as an X-ray. In such a non-destructive inspection method, an inspection object is disposed between a radiation source and a detector, and characteristics such as the thickness and shape of the object are inspected from the radiation transmittance of the inspection object.
When the inspection object is small, the inspection is possible even when the energy of the X-ray is low. However, if the inspection object is large, if the energy of the X-ray is low, the X-ray is almost absorbed by the object. Therefore, in such a case, a high energy X-ray source with high energy is used. In particular, a highly transparent X-ray source of 300 keV or more is suitable for a metal having a thickness of about 5 cm or more and a concrete having a thickness of about 20 cm or more.

In a non-destructive inspection apparatus using portable X-rays or γ-rays, for example, as disclosed in Non-Patent Document 1, the target is a γ-ray or high-energy electron beam emitted from a radioisotope. X-rays that are incident and thereby emitted from the target are used. By irradiating the inspection object with this X-ray and detecting the X-ray transmitted therethrough with a detector, or exposing the X-ray to a film having sensitivity to X-rays, the X-ray transmittance of the inspection object is obtained. Inspect shape characteristics such as the thickness of the object.
Japanese Unexamined Patent Publication No. 2000-243599 <http://hadron.kek.jp/KogataAcc2003/Body/Presentation/09_Ohnishi.pdf>

Non-destructive inspection equipment using radioisotopes can emit highly transparent γ-rays of 300 keV or higher even if the volume of the radioisotope source itself is very small. However, since the radioactive isotope radiation source always emits radiation even when it is not in use, a radiation shielding material is required, which increases the weight of the entire apparatus. Furthermore, strict management is required for radioisotopes.
In a nondestructive inspection system using an X-ray source that uses a high-energy electron beam, an accelerator such as a microwave-driven electron accelerator or a betatron is used to generate highly transparent X-rays of 300 keV or higher. These accelerators require a trade-off between downsizing and increasing the output of the X-ray intensity. For example, if the accelerator is downsized, the X-ray intensity becomes weak. In the case of weak X-ray intensity, a highly sensitive radiation detector such as a scintillation detector must be used. However, such a high-sensitivity detector is greatly affected by background radiation, which may cause an error in measurement results. Such a problem was also the same in the nondestructive inspection apparatus using weak radiation isotopes.

  An object of the present invention is to eliminate such drawbacks of the prior art and to provide a nondestructive inspection apparatus that is small and has high measurement accuracy. Another object of the present invention is to provide a nondestructive inspection method capable of effectively using such a nondestructive inspection apparatus.

  In order to solve the above-described problems, a nondestructive inspection apparatus according to the present invention generates an bremsstrahlung X-ray in response to a drive signal and irradiates the inspection target with an X-ray, and transmits the inspection target. An X-ray detector that receives the generated X-ray and converts the X-ray into a corresponding electric signal, a pulse signal generation circuit that generates a drive signal in a pulse form and supplies the drive signal to the X-ray source, and a pulse signal An integration circuit that integrates the electrical signal only during a period in which the generation circuit generates the drive signal, and the integration circuit integrates the electrical signal in the period. Furthermore, integration is performed for a plurality of pulses, and the sum of the integrated values is used for measurement of the amount of X-ray transmission through the inspection object and inspection of the characteristics of the inspection object.

According to the present invention, the nondestructive inspection method also corresponds to an X-ray irradiation process of generating bremsstrahlung X-rays in a pulsed manner and irradiating the inspection object with X-rays transmitted through the inspection object. It includes a signal conversion step for converting into an electric signal and an integration step for integrating the electric signal only during a period in which X-rays are generated in a pulse form, whereby the electric signal is integrated in the period. Further, this integration step is performed for a plurality of pulses, the amount of X-ray transmission through the inspection object is measured from the sum of the integrated values, and the characteristics of the inspection object are inspected.
More specifically, for example, a pulse composed of a small electron accelerator that generates a high-energy electron beam pulse of 300 keV or higher and a target that generates a pulsed braking X-ray by making an electron beam generated from this accelerator incident. A scintillation detector comprising an X-ray source, a scintillator and a photo detector, a signal integrating device, and a pulse generator, and the X-ray source and the detector are arranged on both sides of the object to be inspected. The amount of scintillation light from the detector is integrated in synchronization with the time at which the pulse X-ray is generated, and the amount of signal is integrated for a plurality of pulses, thereby measuring the amount of X-ray transmission. Inspect shape such as thickness. This realizes a small and easily portable nondestructive inspection apparatus using high energy X-rays while minimizing the influence of background radiation.

According to the present invention, since the signals are not integrated during the time when no X-ray pulse is generated, the influence of background radiation can be minimized. In addition, the total amount of X-rays generated can be minimized by combination with a highly efficient scintillation detector.
If the interval between X-ray pulses is increased, the X-ray dose per unit time can be reduced. If the X-ray dose per unit time is reduced, the cooling mechanism of the electron accelerator for generating X-rays and the shielding material for leaked X-rays can be simplified, and the entire apparatus can be miniaturized. Such a small, non-destructive inspection device with little X-ray dose per unit time and almost no influence of background radiation can be used not only as a portable device but also as a device installed in a structure operating in a plant or power plant. Are also advantageously applied. In the latter case, it can be used as a monitor device that monitors changes in the thickness of these structures, and the range of use is broader than that of conventional nondestructive inspection devices.

Embodiments of a nondestructive inspection apparatus according to the present invention will now be described in detail with reference to the accompanying drawings. Referring to FIG. 1, in an embodiment of a nondestructive inspection apparatus according to the present invention, a pulse X-ray source 12 is disposed on one side of an inspection object 10, and a scintillation detector 14 is disposed on the other side. . The inspection object 10 is, for example, a structure such as a factory plant, a power plant, a building, or a building, and generally includes metal, concrete, or the like.
The pulse X-ray source 12 includes an electron accelerator 16 and a target 18, and is a radiation source that generates X-rays 20 and irradiates the inspection object 10. The electron accelerator 16 may be a small electron accelerator that generates an accelerating electron beam 22 by microwave driving. For this, for example, a high electric field small standing wave linear accelerator described in Japanese Patent Laid-Open No. 2000-243599 (Patent Document 1) is applied. For example, if the average current of the electron beam 22 is 10 microamperes or less, the acceleration tube volume can be designed to 200 cm ³ or less even with acceleration energy of 500 keV or more, and the apparatus can be miniaturized. The target 18 is a target plate made of an element having a large atomic number, such as tungsten, tantalum, or lead, and generates a bremsstrahlung X-ray 20 when a high-energy accelerated electron beam 22 is incident from the electron accelerator 16.

  The electron accelerator 16 has a drive input 24, to which the output of a pulse signal generator 26 is connected. In the following description, a signal is designated by the reference number of the connecting line that appears. The pulse signal generator 26 is a pulse signal generation circuit that generates a drive pulse 24 having a pulse width set to this. In response to the drive pulse 24, the electron accelerator 16 causes the acceleration electron beam 22 to be incident on the target 18 in a pulsed manner, thereby generating a pulsed bremsstrahlung X-ray 20 from the target 18.

  The scintillation detector 14 is an X-ray detector that detects X-rays 28 transmitted through the inspection object 10 out of the X-rays 20 irradiated from the pulse X-ray source 12. The scintillation detector 14 includes a scintillator 30 and a photodetector 32. The scintillator 30 is a radiation-sensitive luminescent material containing an inorganic material or a polymer material that emits light when X-rays 28 are incident thereon. The photodetector 32 is a photoelectric conversion device such as a photoelectron amplifier tube or a high-sensitivity photodiode, and generates an electric signal corresponding to incident light at its output 34. An X-ray collimator (not shown) is inserted between the inspection object 10 and the X-ray source 12 and / or between the inspection object 10 and the scintillation detector 14, and the position resolution of the apparatus May be improved.

The output 34 of the scintillation detector 14 is connected to a signal integrating device 36. The signal integrator 36 also has a control input 38 that is connected to the other output of the pulse signal generator 26. The pulse signal generator 26 makes the control output 28 significant only during a period T (FIG. 2) during which a pulse signal is generated at the drive input 24 of the electron accelerator 16. The accumulator 36 includes an accumulator circuit (not shown) that accumulates the signal of the input 34 only during the period T ′ in which the control input 38 is in a significant state. T ′ may be slightly delayed from T because of the light emission decay time of the scintillator and the signal delay of the photodetector. The integrating device 36 may also include an output function unit (not shown) that outputs the integrated value in some form (soft copy or hard copy) that can be perceived by a human.
This output function unit includes, for example, an analog integration circuit that integrates an integrated value and an analog / digital converter that converts the integrated value into a corresponding digital value, and is configured to display, that is, output the integrated value as a numerical value. Good. Or a high-speed analog-to-digital converter or digital oscilloscope (not shown) that samples the electrical signal 34 at a time interval that is sufficiently shorter than the pulse width T of the pulse signal 24, and the intensity of the output signal of the scintillation detector 14 is The integrated value may be obtained by converting to a digital numerical value and taking the sum of the sampling numerical sequence.
In the operating state, the pulse X-ray source 12 is arranged on one side of the inspection object 10 and the scintillation detector 14 is arranged on the other side. When the pulse X-ray source 12 is driven in a pulse shape by operating the pulse signal generator 26, the X-ray 22 is emitted from the electron accelerator 16 toward the target 18 in a pulse shape. As a result, the bremsstrahlung X-ray 20 is radiated from the target 18 toward the inspection object 10.

In the inspection object 10, a part 28 of the X-ray 20 is transmitted, and the transmitted X-ray 28 enters the scintillation detector 14. In the scintillation detector 14, the photodetector 30 converts this incident X-ray 28 into light, and this light is converted into a corresponding electrical signal 34 by the photodetector 32. The electrical signal 34 is integrated by the integrating device 36 and used for output such as display, printing, and transmission as an integrated value of the digital value as described above.
The electron accelerator 16 is driven by a drive pulse 24 from a pulse signal generator, and the drive waveform is generally a simple rectangular wave as shown in FIG. Therefore, the emitted X-ray 20 also has a duration T corresponding to this. Such an X-ray 20 is irradiated on the inspection object 10, and the X-ray 28 that has passed through the X-ray 20 is detected by the scintillation detector 14 and outputted. A waveform as shown by 50 is exhibited. This waveform may be slightly delayed from T due to the light emission decay time of the scintillator or the signal delay of the photodetector. Actually, the output signal 34 from the scintillation detector 14 is also mixed with a puncture signal as indicated by reference numeral 52 in FIG.

Therefore, in this embodiment, the integrating device 36 performs an integrating operation during the period T ′ in which the control signal 38 is in a significant state. The pulse signal 38 of the pulse signal generator 26 may be a signal having the same time structure as the pulse signal 24 as long as the signal delay is negligible, but if the signal delay cannot be ignored, the duration considering the delay. Take T '. That is, the accumulator 36 is only in the period when the pulse signal 24 of the pulse signal generator 26 is in a significant state (ON), that is, the time T ′ in which the X-ray 20 is generated or the time T ′ in consideration of the signal delay. The integration operation is performed. During other periods, the integration operation is not performed.
When the size of the X-ray source 12 is reduced, the generated X-ray intensity is weak, and if the drive signal 24 is only one pulse, the accuracy of the X-ray transmittance sufficient for the integrated value in the integrating device 36 cannot be obtained. Therefore, by operating the pulse signal generator 26 to generate the drive pulse signal 24 a plurality of times, the electric signal 34 by the X-rays 28 detected by the scintillation detector 14 is integrated and summed up, Improve transmission accuracy.

The X-ray transmittance can be obtained from the integrated value thus obtained, and compared with the transmittance obtained by measurement or simulation of the reference sample, and the thickness of the inspection object 10 can be calculated. If the relationship between the integrated value and the thickness is known in advance, the thickness can be obtained directly from the integrated value.
Furthermore, if the same measurement is performed by changing the positions of the X-ray source 12 and the scintillation detector 14 with respect to the inspection object 10, the thickness distribution and the overall shape of the inspection object 10 can be grasped.

It is a functional block diagram which shows the Example of the nondestructive inspection apparatus by this invention. It is a figure which shows the signal waveform which appears in a part of Example shown in FIG. FIG. 3 is a waveform diagram similar to FIG. 2, showing signal waveforms appearing in a part of the embodiment.

Explanation of symbols

12 Pulse X-ray source
14 Scintillation detector
16 Small electron accelerator
18 Target
26 Pulse signal generator
30 Scintillator
32 photodetectors
36 Signal integrator

Claims (7)

An X-ray source that generates bremsstrahlung X-rays in response to a drive signal and irradiates the inspection target with the X-rays;
An X-ray detector that receives X-rays transmitted through the inspection object and converts the X-rays into corresponding electrical signals;
A pulse signal generation circuit for generating the drive signal in a pulse form and supplying the drive signal to the X-ray source;
An integration circuit that integrates the electrical signal only during a period in which the pulse signal generation circuit generates the drive signal,
The integration circuit integrates the electrical signal in the period, and the pulse signal generation circuit generates the drive signal in a pulsed manner over a plurality of periods, and the integration circuit performs the electrical signal for the plurality of periods. Is accumulated,
A non-destructive inspection apparatus characterized in that the integrated value thus obtained is used for measurement of the amount of X-ray transmission in the inspection object and inspection of characteristics of the inspection object. The apparatus of claim 1, wherein the X-ray source is
An electron accelerator that generates an electron beam in response to the drive signal;
A nondestructive inspection apparatus comprising: a target body that receives the electron beam and generates bremsstrahlung X-rays to irradiate the inspection target with the X-rays.   The apparatus according to claim 1, wherein the X-ray detector is a scintillator that receives X-rays transmitted through the inspection object and converts the X-rays into light, and light that converts the light into a corresponding electrical signal. A non-destructive inspection apparatus characterized by being a scintillation detector including a detector.   3. The nondestructive inspection apparatus according to claim 2, wherein the electron accelerator is a small electron accelerator that generates a high energy electron beam of 300 keV or more. An X-ray irradiation step of generating a bremsstrahlung X-ray in a pulse shape and irradiating the inspection object with the X-ray;
A signal conversion step of converting X-rays transmitted through the inspection object into corresponding electrical signals;
An integration step of integrating the electrical signal only during a period in which the X-rays are generated in a pulse form,
Accordingly, the electrical signal is integrated in the period, and the pulse generation process is repeated a plurality of times, and the integration process is performed over a plurality of periods in response to the repetition, and the X value in the inspection object is calculated from the integrated value. A non-destructive inspection method characterized by measuring a transmission amount of a line and inspecting a characteristic of the inspection object. The method according to claim 5, wherein the X-ray irradiation step includes:
An electron beam generating step of generating an electron beam in a pulse form by an electron accelerator; and a step of receiving the electron beam by a target body, generating the bremsstrahlung X-ray by the target body and irradiating the inspection object A non-destructive inspection method characterized by that. 6. The method of claim 5, wherein the signal conversion step comprises
Receiving X-rays transmitted through the inspection object with a scintillator and converting the X-rays into light;
And a step of converting the light into a corresponding electrical signal.

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