JP2008014816A - Nondestructive inspecting method and apparatus capable of precisely measuring presence of heterogeneous materials existing inside surface layer of complex structure in short time - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a nondestructive inspecting apparatus or the like capable of measuring specific information such as a size of an iron rod present inside the surface layer of a reinforced concrete with accuracy of a millimeter order for a short time, i.e., about 20 seconds for one iron rod. <P>SOLUTION: The apparatus comprises: a particle accelerator 2 for generating muons μ; a magnetic confinement transport beam transporting system 3 for capturing/transporting the muons generated by the particle accelerator 2 at a prescribed solid angle; a positron detecting means 4 for irradiating the surface of the complex structure 5 which is composed of two kinds of heterogeneous materials, with the transported muons, bringing the muons to rest at a prescribed depth position 6 inside the surface layer of the complex structure 5 in accordance with the energy dissipation of irradiation muons μ, and detecting the amount of positron e+ which is emitted along with extinction of resting muons in a direction reverse to the irradiation direction of the muons μ; and an image processing means for acquiring the presence of the heterogeneous materials 7, 8, present inside the surface layer of the complex structure 5 as a radiography, from the amount of positron e<SP>+</SP>detected by the positron detecting means 4. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a nondestructive inspection method and apparatus capable of accurately measuring in a short time the state of existence of foreign substances located inside the surface layer of a composite structure such as a reinforced concrete building having a cover thickness of 10 to 20 cm.

  As a conventional method for nondestructively inspecting the existence state in the surface layer of a composite structure (for example, a reinforced concrete structure in which a steel bar is embedded in concrete), for example, infrared thermography (Patent Document 1), ultrasonic method (Patent Literature 2), radar method (Patent Literature 3), X-ray method (Patent Literature 4) and the like. However, since all of these conventional methods have limited spatial resolution and searchable depth, specific information such as the shape and size of the iron bar located inside the surface layer of the reinforced concrete with the above-mentioned cover thickness can be accurately obtained. It was difficult to measure.

  Further, in a thick composite structure having a thickness of several meters or more, for example, a reinforced concrete structure, a foreign material reinforcing bar is embedded in the surface layer of 10 to 20 cm from the surface (that is, the cover thickness is 10-20 cm), in the case of measuring the existence state of foreign objects (for example, iron bar and concrete) located inside the surface layer of such a composite structure, the transmission type inspection apparatus measures in principle. Therefore, it is necessary to use a reflection type inspection apparatus.

  For this reason, it is a thick composite structure having a thickness of several meters or more, and it is possible to accurately measure specific information such as the shape and size of the iron bar located inside the surface layer of the composite structure. It is desirable to develop a new method.

JP 2005-249536 A JP 2005-315622 A JP 9-292350 A JP-A-10-197456

  An object of the present invention is to use a high-energy particle muon generated by a particle accelerator, specifically, a composite structure (for example, an iron bar and concrete covering the iron bar) composed of at least two kinds of foreign substances. Muon is irradiated on the surface of a reinforced concrete structure consisting of two different kinds of materials), and the muon is stopped at a predetermined depth position inside the surface layer of the composite structure with the loss of energy of the irradiated muon, and the muon is killed By detecting the amount of positrons emitted in the direction opposite to the irradiation direction, the surface layer of a reinforced concrete building having a thickness of several meters or more and a cover thickness of 10 to 20 cm Specific information such as the shape and size of the iron bar located inside is accurate to the order of millimeters, and in a short time of about 20 seconds per iron bar. It is to provide a nondestructive inspection method and a nondestructive inspection apparatus that can be measured by the above method.

In order to achieve the above object, the gist of the present invention is as follows.
(1) The process of generating muons from elementary particles generated by a particle accelerator, and the generated muons are captured and transported at a predetermined solid angle, and the transported muons are a composite structure composed of at least two kinds of foreign substances. As the muon is irradiated, the muon is stopped at a predetermined depth position inside the surface of the composite structure with the loss of energy of the irradiated muon, and the muon irradiation direction with the death of the muon The process of detecting the amount of positrons emitted in the direction opposite to the above, and measuring the presence of foreign materials located inside the surface of the composite structure with high accuracy in a short time Possible non-destructive inspection method.

(2) The nondestructive inspection method according to (1), wherein the predetermined depth position is a position within a depth of 20 cm from the surface of the composite structure.

(3) The nondestructive inspection method according to the above (1) or (2), wherein the composite structure is reinforced concrete made of two kinds of foreign materials, namely, an iron bar and a concrete covering the iron bar.

(4) A particle accelerator for generating muons, a magnetic field confining and transporting means for capturing and transporting muons generated by an electron accelerator at a predetermined solid angle, and at least two kinds of foreign materials for transported muons. When the surface of the composite structure is irradiated, the muon is stopped at a predetermined depth position inside the surface layer of the composite structure in accordance with the loss of energy of the irradiated muon, and the muon is killed as the stationary muon is killed. The positron detection means for detecting the amount of positrons emitted in the direction opposite to the irradiation direction of the positron, and the presence state of foreign substances located inside the surface layer of the composite structure are determined from the amount of positrons detected by the positron detection means. It is possible to accurately measure the presence of foreign materials located inside the surface layer of a composite structure in a short time. Non-destructive inspection equipment.

(5) The nondestructive inspection apparatus according to (4), wherein the particle accelerator is a high energy small electron accelerator of 300 MeV or higher.

(6) The nondestructive inspection apparatus according to (4) or (5), wherein the magnetic field confinement transport means is a superconducting solenoid.

(7) The non-destructive inspection apparatus according to (4), (5), or (6), wherein the positron detection means is two pieces of plastic scintillators that are divided into multiple pieces.

(8) The nondestructive inspection apparatus according to any one of (4) to (7), wherein the nondestructive inspection apparatus is movable to a place where the composite structure is located.

   According to this invention, a high-energy elementary particle muon generated by a particle accelerator is used, and specifically, a composite structure (for example, an iron bar and concrete covering the iron bar) composed of at least two kinds of foreign substances. The muon is irradiated to the surface of a reinforced concrete structure consisting of two kinds of foreign materials), and the muon is stopped at a predetermined depth inside the surface of the composite structure with the loss of energy of the irradiated muon. By detecting the amount of positrons emitted in the direction opposite to the irradiation direction upon death, the reinforced concrete building having a thickness of several meters or more and a cover thickness of 10 to 20 cm Specific information such as the shape and size of the iron bar located inside the surface layer is accurate to the order of millimeters, and it takes about 20 seconds per iron bar. It is now possible to provide a nondestructive inspection method and a nondestructive inspection device that can measure between the two.

  In particular, the present invention is suitable for measuring the presence inside a surface layer of a large composite structure such as a reinforced concrete structure, an elevated road, a bridge, a dam, etc. The present invention can be applied to a wide variety of fields, such as when observing the brain function of an animal in a deep microscopic region by measuring muesuar (μSR).

Embodiments according to the present invention will be described below with reference to the drawings.
FIG. 1 is a perspective view schematically showing a main configuration of a nondestructive inspection apparatus according to the present invention.

  A nondestructive inspection apparatus 1 shown in FIG. 1 is mainly composed of a particle accelerator 2, a magnetic field confinement transport means 3, a positron detection means 4, and an image processing means (not shown).

A particle accelerator is a device for generating muons from particles such as electrons, protons, and heavy ions. Specifically, pions π ⁺ and π ⁻ are generated by the reaction between the particles and nuclei. Muon μ ⁺ and μ ⁻ can be generated by the decay of pion. In particular, when it is necessary to downsize and make the entire nondestructive inspection apparatus 1 movable, it is preferable to use a high-energy small electron accelerator of 300 MeV or higher as the particle accelerator 2.

By the way, muons are elementary particles whose mass is about 1/9 times the proton mass and about 207 times the electron mass, and there are two types, μ ⁺ and μ ⁻ , which have positive and negative charges. The muon dies with a lifetime of 2.2 μs, and at that time, positrons e ⁺ , electrons e ⁻ and neutrinos having an energy of 50 megaelectron volts (MeV) are generated. Muons fly to the surface as cosmic rays, but in order to obtain high intensity, high energy (300 MeV or higher) protons and electrons are obtained using an accelerator and reacted with nuclei to produce pions (Pion and Yukawa mesons). ^{+ And} π ⁻ can be generated, and the pions π ⁺ and π ⁻ can be collapsed to generate a large amount of muons μ ⁺ and μ ⁻ . In the material, muons mainly work only by electromagnetic interaction. Various applied scientific researches are possible by utilizing such properties of elementary particle muons.

  On the other hand, the most familiar example of radiography is “X-ray photography” in which a transmission image of a human body is taken using X-rays. Further, as light / particle beam radiography, there are generally two methods, a “transmission attenuation method” using a single detector system and a “transmission perturbation method” using two detector systems.

  The transmission attenuation method is a method that uses a light source / particle source with relatively well-known properties to obtain information on the internal density distribution from the intensity change of each light / particle path that passes through the target object. Yes, the transmission perturbation method places an object in the middle of the two detectors, and how the properties of the light and particles obtained by the previous detector "changed" when passing through the substance. This is a method for performing an internal search for an object, which is known by a later detector, and the multiple scattering angle, the generation of secondary particles, the degree of polarization, and the like can be “variations”.

  In order to obtain some kind of transmission image, as X-rays use light (X-rays) to obtain a transmission image of the human body, the range for the energy of light and particles (distance that passes through the substance before stopping) It must be longer than or equal to the thickness of the object, and it should be easy to detect light and particles and easily identify the path.

  2 (a) and 2 (b) show the change of the average range in the substance with respect to the incident energy using proton p, electron e and muon μ, and FIG. 2 (a) shows the substance. 2 is carbon (graphite), FIG. 2B shows an example in which the substance is water.

  As is clear from these figures, the range of particles in various materials generally increases as the energy of the particles increases, but the electrons are also "protons converted to light due to their light mass" and also protons. Because of the “increase in nuclear reaction due to strong interaction”, no matter how much the energy is increased, the range cannot be raised beyond a certain thickness. In contrast, muons can increase the incident energy even in an object with a thickness of several meters or more, making the range longer than the thickness of the object. Since it becomes possible to make it stand still in a predetermined position, it is a very effective elementary particle.

  In any case, measuring the internal state of a composite structure having a thickness of several meters or more by the above-described transmission method requires high energy and is not easy.

In general, there are two methods for creating the pion (pion, Yukawa meson) that is the parent of muon, that is, hadron nuclear reaction by proton or heavy ion accelerator: p (n) + A → π ^± , electron Photonuclear reaction by an accelerator: e ⁻ + A → e ⁻ + B + γ, γ + C → D + π ^± .

  Furthermore, accelerator types are roughly classified into linear accelerators and circular accelerators such as cyclotrons, synchrotrons, and fixed field strong focusing synchrotrons (also referred to as FFAG for short).

  From the consideration of the pion production cross-sectional area and the necessary muon intensity described later, the proton requires an intensity of 0.1 μA or more, and the electron requires an intensity of 10 μA or more. In either case, radiation shielding is required. It is preferred to use a localized circular accelerator.

  On the other hand, for protons and electrons, for the same energy, the magnetic field curvature radius of protons is several hundred times larger than the magnetic field curvature radius of electricity, so that it is impossible to make the proton circular accelerator small and movable. For this reason, it is preferable to use an electron accelerator from the viewpoint of miniaturization of the apparatus. In particular, in an electron circular accelerator, it is preferable to use FFAG or microtron for reasons such as low radiation loss, easy control, and commercialization.

  The beam transport system 3, which is a magnetic confinement transport means, captures muons generated by the particle accelerator 2, a high-energy small electron accelerator of 300 MeV or higher in FIG. 1 at a predetermined solid angle, and the captured muons are measured. Is disposed between the accelerator 2 and the measurement object in order to transport it to the irradiation target surface position of the composite structure. Specifically, it is preferable to use a superconducting solenoid as the magnetic field confinement transport means. In FIG. 1, in order to show the internal structure of the nondestructive inspection apparatus 1, the members that cover the internal structure in a sealed state are shown in a removed state.

  The term “solid angle” as used herein refers to an effective angle for capturing pion muons from a target that collides accelerated particles from an accelerator to generate pion muons, and the predetermined solid angle is, specifically, It means a large angle in the range of 0.1 to 1 steradian.

  The generation of pion from the electron accelerator has a cross-sectional area of 1/100 or less compared to that from the proton accelerator, and the efficiency is poor. Therefore, in the present invention, the muon generated by the particle accelerator 2 is captured and transported at a large solid angle by the magnetic field confined beam transport system 3 such as a superconducting solenoid to efficiently capture the muon, The composite structure can be effectively irradiated with almost no reduction in the amount of captured muons.

  In addition, an optical system has been developed that collects and transports “pions” and “muons produced by the death of pions” as much as possible from particle accelerators. It can be set to have energy (momentum) acceptance. A typical example of this optical system is “large omega (large solid angle superconducting axis converging surface muon channel)” in KEK-MSL developed by the group of the present inventors.

  The electrons generated by the accelerator do not have high original electron intensity. For this reason, as shown in FIG. 1, the superconducting coil system magnetic field confinement transport means 3 is arranged on the electron beam, that is, in a form covering the pion / muon generation target and the beam dump, so that a muon with a wide momentum width can be obtained. It can be captured by a large solid angle and transported to the irradiation target surface position of the composite structure as a secondary target.

Captured and transported muons are born with an angle and energy distribution determined by the decay of pions caused by the photonuclear reaction of carbon, and can be used in reflection radiography with the following limitations:
(I) The upper limit of the momentum in the lateral direction is determined from the limit of the magnetic field of the superconducting coil to be captured.
(Ii) As will be described later, in the present invention, since the back positron from the muon stopped in the object is captured and detected as a reflection type signal, the available muon energy is 50 MeV or less.
(Iii) Muons that remain in the object and are used are spin-polarized by 50% or more.

  The positron detection means 4 is a reinforced concrete composed of at least two kinds of foreign matter transported muons, that is, two kinds of foreign matter, such as iron bars arranged at predetermined intervals in FIG. 1 and concrete covering the circumference of these iron bars. ), The surface of the composite structure is irradiated, and with the loss of the energy of the irradiated muon, the muon is stopped at a predetermined depth position inside the surface of the composite structure, and the muon is killed, It is provided to detect the amount of (posterior) positrons emitted in the direction opposite to the direction of muon irradiation. Examples of the positron detection means 4 include a pair of multiple finely divided plastic counters, a fiber scintillation counter, a drift chamber, a semiconductor microchip detector, etc., which are spaced at intervals of ± 5 mm or less. In particular, it is preferable to use a multiple finely divided plastic counter. Thus, by performing multiple subdivision (division subdivision), directivity can be provided, and the accuracy of determining the positron light source, that is, the stationary position of the muon can be improved.

  FIG. 3 shows that the transported muon irradiates the surface part of reinforced concrete where one iron bar embedded in the surface layer of reinforced concrete (within 20 cm from the surface) exists, and with the loss of energy of the irradiated muon, The state when the muon is stopped at the position of the iron bar and the amount of positrons emitted in the direction opposite to the irradiation direction of the muon (backward) is detected by the positron detection means 4 with the death of the stopped muon. It is a conceptual illustration.

の反応によって生まれる。これらの素粒子反応の性質から、μ^＋は進行方向にスピンを揃えて（偏極して）得られ、そして、μ^＋が死滅して生まれる陽電子は、揃ったスピンの方向に放出され、その陽電子を捕らえることで複合構造物のもつ微視的な磁気的性質をプローブすることができる。この原理は、ミュエスアール（μＳＲ、ミュオン・スピン・ローテーション／リラクゼーション／レゾナンス法ともいう。）法と呼ばれる。図４（ａ）は、パイオン崩壊でスピン偏極したミュオンが生成される様子を概念的に示したものであり、図４（ｂ）は、スピン偏極したミュオンから空間非対称性をもって陽電子が発生する様子を概念的に示したものである。 Muon obtains protons and electrons of high energy (preferably 300 MeV or more) using an accelerator, generates pions (Yukawa mesons) π ⁺ , π ⁻ by reaction with nuclei, which decay,

Born by the reaction of Due to the nature of these elementary particle reactions, μ ⁺ is obtained by aligning (polarizing) the spins in the direction of travel, and the positrons born by the death of μ ⁺ are emitted in the direction of the aligned spins. By capturing positrons, the microscopic magnetic properties of composite structures can be probed. This principle is called the Muesuar (μSR, also called muon spin rotation / relaxation / resonance method) method. Fig. 4 (a) conceptually shows how spin-polarized muons are generated by pion decay, and Fig. 4 (b) generates positrons with spatial asymmetry from spin-polarized muons. This is a conceptual illustration of how this is done.

  In the present invention, by applying such a principle, it is possible to make use of muon's large magnetic efficiency (3.2 times that of protons) and lifetime of 2 microseconds, and at the atomic level, the static and dynamic values are as weak as milligauss. Highly sensitive observation of magnetic field. At this time, no strong magnetic field such as NMR is required. By using this Muesuar method, the existence state of the iron bar in the concrete can be easily and clearly captured.

  The muon spin stopped on the concrete has a weak relaxation phenomenon due to magnetic impurities, etc., while the muon spin stopped at a certain position of the iron bar causes a rapid spin rotation due to the magnetic internal field, and the rotation frequency is 50 MHz. Therefore, when the time resolution of the measurement system is set to 20 nanoseconds or more, rotation cannot be seen, and the detected positron intensity becomes one third.

  Therefore, as shown in FIG. 1, the non-destructive inspection apparatus 1 is installed at a position facing the measurement target surface of the composite structure, and the muon beam is irradiated to thereby measure the measurement target surface in which the iron rod is embedded. When the muon beam stops (stops) at the horizontal bar position, the positron intensity decreases. By preparing a beam deflector that changes the position where the muon beam stops in a large composite structure, and measuring the positron intensity as a function of the position of the muon beam, the size and size of the iron bars in the reinforced concrete can be clearly shortened. It can be measured in time.

  Furthermore, the corrosion state of iron can be monitored by analyzing the Muesuar signal by the time interval spectrum of the muon pulse and the positron pulse. This is because there is a difference in the magnetic internal field between pure iron and iron oxide, and the time spectrum of the positron intensity changes accordingly.

  In addition, the nondestructive inspection apparatus 1 of the present invention is an image processing means (not shown) that extracts, as radiography, the presence state of foreign substances located inside the surface layer of the composite structure from the amount of positrons detected by the positron detection means 4. )).

  Examples of the image processing means include a method by measuring the positron intensity in synchronization with the vertical and horizontal scanning of the muon beam.

  Further, the nondestructive inspection apparatus 1 of the present invention is a reflection type inspection apparatus in which the positron detector 4 is arranged on the same side as the particle accelerator 2 that generates muons with respect to a composite structure that is an object to be measured. In addition, it is possible to measure the existence state of foreign materials (for example, iron bar and concrete) located inside the surface layer (within a depth of 20 cm from the surface) of a thick composite structure having a thickness of several meters or more. .

  In addition, by using a high-energy small electron accelerator of 300 MeV or higher as the particle accelerator, the nondestructive inspection device can be made compact. As a result, all the components from the accelerator to the positron detector, its power supply and A helium cooling source or the like can be mounted on a transporter such as a movable trailer having a floor area of 2.5 m in width and 12 m in length, for example, so that any building can be measured. Can do.

  The above description only shows an example of the embodiment of the present invention, and various modifications can be made within the scope of the claims. In particular, in the present invention, a reinforced concrete structure has been described as an example of a composite structure. However, internal structure information of various composite structures such as a nuclear reactor, a bridge pier, an elevated road, a ship, and a vehicle can be obtained. Needless to say.

   According to this invention, a high-energy elementary particle muon generated by a particle accelerator is used, and specifically, a composite structure (for example, an iron bar and concrete covering the iron bar) composed of at least two kinds of foreign substances. By irradiating muon on the surface of a reinforced concrete structure consisting of two kinds of foreign materials), and displaying the amount of positrons with the characteristic of being emitted in the direction opposite to the irradiation direction when muon dies, Specific information such as the shape and size of the iron bar located inside the surface layer of a reinforced concrete building with a cover thickness of 10 to 20 cm, with a precision of millimeter order, It has become possible to provide a nondestructive inspection method and a nondestructive inspection device that can measure in a short time of about 20 seconds per iron bar.

  In particular, the present invention is suitable for measuring the presence inside a surface layer of a large composite structure such as a reinforced concrete structure, an elevated road, a bridge, a dam, etc. The present invention can be applied to a wide variety of fields, such as when observing the brain function of an animal in a deep micro-flow region by Muesuar (μSR) measurement.

It is a perspective view which shows roughly the principal part structure of the nondestructive inspection apparatus according to this invention. (A) and (b) show the change of the average range in the material with respect to the incident energy using proton p, electron e and muon μ. FIG. 2 (a) shows that the material is carbon (graphite). 2), FIG. 2B shows an example in which the substance is water. Fig. 2 conceptually shows a state from muon irradiation to detection by a positron detection means. (A) conceptually shows how spin-polarized muons are generated by pion decay, and (b) conceptually shows how positrons are generated with spatial asymmetry from spin-polarized muons. It is shown as an example.

Explanation of symbols

1 Nondestructive inspection equipment 2 Particle accelerator 3 Magnetic confinement means (or magnetic confinement beam transport system)
4 Positron detection means 5 Composite structure 6 Placed at predetermined depth 7 Concrete 8 Iron bar

Claims (8)

The process of generating muons from elementary particles generated by a particle accelerator,
The generated muon is captured and transported at a predetermined solid angle, and the transported muon is irradiated onto the surface of a composite structure composed of at least two kinds of foreign materials. The process of stopping the muon at a predetermined depth position inside the surface of the structure,
The process of detecting the amount of positrons with the characteristic of being emitted in the direction opposite to the irradiation direction of the muon as the stationary muon is killed,
A non-destructive inspection method capable of accurately measuring the existence state of foreign substances located inside the surface layer of a composite structure in a short time.   The nondestructive inspection method according to claim 1, wherein the predetermined depth position is a position within a depth of 20 cm from the surface of the composite structure.   The non-destructive inspection method according to claim 1 or 2, wherein the composite structure is reinforced concrete made of two kinds of heterogeneous materials, an iron bar and a concrete covering the iron bar. A particle accelerator to generate muons,
A magnetic confinement transport means for capturing and transporting muons generated by the particle accelerator at a predetermined solid angle;
The transported muon is irradiated onto the surface of the composite structure composed of at least two kinds of foreign materials, and the muon is stopped at a predetermined depth position inside the surface of the composite structure with the loss of energy of the irradiated muon. Positron detection means for detecting the amount of positrons emitted in the direction opposite to the irradiation direction of the muon as the stationary muon is killed,
An image processing means for extracting, as radiography, the presence state of foreign substances located inside the surface layer of the composite structure from the amount of positrons detected by the positron detection means, the inside of the surface layer of the composite structure Non-destructive inspection equipment that can accurately measure the presence of foreign objects located in a short time.   The nondestructive inspection apparatus according to claim 4, wherein the particle accelerator is a high-energy small electron accelerator of 300 MeV or higher.   6. The nondestructive inspection apparatus according to claim 4, wherein the magnetic field confinement transport means is a superconducting solenoid.   7. The nondestructive inspection apparatus according to claim 4, 5 or 6, wherein the positron detection means is two plastic scintillators divided into multiple pieces.   The nondestructive inspection apparatus according to any one of claims 4 to 7, wherein the nondestructive inspection apparatus is movable to a place where a composite structure is located.

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