JP4106445B2 - Method for obtaining internal structure information of large structures by horizontal cosmic ray muon multiple division type detection means - Google Patents

Description

  The present invention relates to a method for obtaining internal structure information of a large structure such as a steel blast furnace, a power generation dam, a bridge pier, an elevated road, a ship, a vehicle or the like by using a horizontal cosmic ray muon multiple division type detection means.

Large structures, such as large structures such as blast furnaces, are difficult to obtain internal structure information unless they are once dismantled once installed and in steady operation.
It is extremely useful if such internal structure information can be obtained while maintaining the form of a large structure and in operation.

As a conventional method for obtaining internal structure information while maintaining the form of a large structure, for example, there is a method of Patent Document 1 proposed by one of the present inventors. As shown in FIG. 1, this method uses muons that pass through the atmosphere from space and pour onto the surface of the earth, and based on a change in the strength of the muons that penetrate the blast furnace 201, It is a method for measuring the thickness nondestructively, more specifically, three position sensitive detectors (scintillators) 211 to 213 having a square measurement surface are arranged in parallel with each other at intervals, In the position sensitive detectors 211, 212, and 213, photomultiplier tubes are installed at the four corners. When the muon penetrates the measurement surface of the position detectors 211 to 213, light is emitted at the penetration position. The emitted light is detected by photomultiplier tubes installed at the four corners of the measurement surface, the detected optical information is converted into pulse signals, and the position difference is detected from the difference in time until these photomultiplier tubes detect the position. The position where the muon penetrates the measurement surface of the detectors 211 to 213 can be specified. By calculating the penetration position on each measurement surface of the three position detectors 211 to 213 arranged in parallel, the path H when the muon penetrates the blast furnace 201 can be calculated, and the attenuation of the muon intensity for each path is calculated. It is a method to obtain the internal structure information of the blast furnace by knowing.
JP-A-8-261741

  However, when the present inventors examined the above-mentioned conventional method (analog method) in more detail, the pulse waveform from each photomultiplier tube changes depending on the ambient temperature to be measured, etc., and long-term stability cannot be obtained. In such cases, it has been found that the internal structure information of structures such as blast furnaces cannot be obtained with high accuracy.

  Also, in the atmosphere, soft cosmic ray background components such as light and electrons are several tens of times larger than the horizontal muon, so the internal structure information of large structures can be accurately obtained using muons. In order to obtain this, it was not sufficient to use three analog detectors 211 to 213, and it was necessary to take measures to distinguish between such soft background components and muons.

  Furthermore, when obtaining the internal structure information of a large structure using a muon, the internal structure information of the large structure is obtained from the intensity change of the muon that passes through the measurement target part of the large structure and reaches the position sensitive detection means. However, it was found that the internal structure information of large structures could not be obtained accurately because long-term stable low background measurement was not possible.

  Furthermore, the muon's penetration through the atmosphere from space through the atmosphere depends on the angle at which it falls on the surface, i.e., the zenith angle, which is the angle with respect to the vertical direction, and in particular in the range of 50-90 ° zenith angle. Although the horizontal muon that pours in is weak in strength, it has high permeability to penetrate the material, that is, high permeability. Therefore, if there is a means that can remove the soft background component, it is necessary to obtain information on the internal structure of large structures. It is extremely useful, and by using a nearly horizontal cosmic ray muon, it is easy to install a detector on the object, and it is not necessary to construct a tunnel or the like necessary when using a vertical muon.

  An object of the present invention is to provide a method of obtaining the internal structure information of a large structure with high accuracy using a horizontal muon having a high penetrability, that is, a penetrating material, although its strength is weak.

In order to achieve the above object, the gist of the present invention is as follows.
(I) Position sensitive detection means as a measurement system at a finite distance on the side facing the measurement target part of a large structure, and a particle muon created in the atmosphere by primary cosmic rays from the universe and falling on the ground Measures the muon intensity at a predetermined time interval when it reaches the measurement system that constitutes the position sensitive detection means through the measurement target part of the large structure, and knows the distribution of the muon intensity for each passing path. The position sensitive detection means includes a square-shaped first detection plate partitioned into a plurality of horizontally long members of a plastic scintillator with a predetermined width in the horizontal direction, and a vertical detection method. Two position sensitive detector complexes having a square second detector plate divided into a number of vertically long members with a predetermined width along the direction, and the two position sensitive detector complexes at predetermined intervals Arranged The sensitive detector complex is arranged so that the horizontally long member and the vertically long member are orthogonal to each other so as to specify the horizontal and vertical xy coordinates by simultaneously measuring the muons reaching the first and second detection plates. A metal member made of iron or a metal heavier than iron is placed between the vessel complex, and among the muons, a large structure using a high-energy horizontal muon that falls on the ground surface in the range of zenith angle 50 to 90 ° When a forward horizontal muon that reaches the first position-sensitive detector complex through the object's measurement target part and subsequently reaches the second position-sensitive detector complex, a straight line connecting the respective arrival positions is obtained. By tracing in reverse, the path in the measurement target portion through which the front horizontal muon penetrates is specified, and the second position sensitivity is sequentially passed through the measurement target portion of the large structure, the first position sensitive detector complex, and the metal member. To the detector complex The strength of the front horizontal muon and the second position sensitive detector complex and the metal member are sequentially penetrated from the opposite side of the large structure across the position sensitive detection means to reach the first position sensitive detector complex. When both the horizontal horizontal muon intensity measured by the same position sensitive detection means and the internal structure of the large structure changes with time, the absolute time is recorded in the computer when recording all measured data. The internal structure information of the large structure is obtained by using the multi-division horizontal muon detection means characterized in that the internal structure information of the large structure is obtained from the measured intensity ratio of the front and rear horizontal muons. How to get.

(II) The position sensitive detection means is located on the side of the large structure, and a plurality of units are arranged at different angular intervals around the large structure. How to get.

According to the present invention, it is possible to accurately obtain the internal structure information of a large structure in a non-destructive manner.
In addition, in the present invention, there are few spatial restrictions such as arranging the position sensitive detection means by digging a hole, as in the case of detecting a vertical muon pouring from directly above, and the finite interval positions on the side of the large structure are reduced. Can be arranged. For this reason, it is possible to arrange a plurality of units at different angular intervals around the position sensitive detection means, and if a plurality of units are arranged in this way, it is possible to observe the density length on the cut surface at a plurality of different angles. Thus, it is possible to obtain a three-dimensional tomographic image of a large structure as a measurement object (tomographic observation).

  Furthermore, the measurement system (measurement circuit system) constituting the position sensitive detection means penetrates a large structure as an object by using a high-speed electronic circuit of nanosecond or less with respect to a high-speed pulse from a scintillator. Separate the front horizontal muon signal (F) and the rear horizontal muon signal (B) that passes through the “sky” part with the observation angle just opposite (in other words, it reaches directly without passing through the object). It can be measured separately. In addition, other means for distinguishing the front horizontal muon signal (F) from the rear horizontal muon signal (B) are limited to those where the muon pours into the ground from above, and there are no muons coming from below. The method of distinguishing both signals (F and B) from the vertical relationship of the y-coordinate (vertical coordinate) position through which the horizontal muon penetrates the second detection plate constituting each position-sensitive detector complex using the phenomenon Can also be used. This method has the advantage that a high-speed electronic circuit is not required. By capturing the F / B intensity ratio thus obtained as data, extremely stable data acquisition can be achieved. In addition, by acquiring data by adding absolute time with sub-microsecond accuracy, it is possible to track numerous real-time changes and perform stroboscopic analysis in synchronization with periodic internal structure time fluctuations. .

Embodiments according to the present invention will be described below with reference to the drawings.
FIG. 2 is a diagram showing an arrangement configuration of position sensitive detection means optimum for use in the method for obtaining the internal structure information of a large structure according to the present invention.
The position sensitive detection means 1 shown in FIG. 2 includes two position sensitive detector complexes 2 and 3 and a metal member made of heavy metal such as iron or iron. In FIG. And is mainly composed.

Each position sensitive detector complex 2, 3 is composed of a first detection plate 5 and a second detection plate 6.
The first detection plate 5 is divided into a large number of horizontally long members 7 having a predetermined width W1 along the horizontal direction H, and in FIG. 2, 10 horizontally long members 7 having a length of 1 m and a width of 10 cm have a square shape as a whole.
The second detection plate 6 is divided into a number of vertically long members 8 having a predetermined width W2 along the vertical direction V, and in FIG. 2, 10 vertically long members 8 having a length of 1 m and a width of 10 cm have a square shape as a whole.

When the horizontally long member 7 and the vertically long member 8 have the same measurement surface of the first detection plate 5 and the second detection plate 6, respectively, the measurement accuracy of the penetrating position of the muon increases as the width becomes narrower and the number of arrangements increases. Although it is preferable, specifically, there are limitations due to the cost of the detection circuit and the occupied space ratio. For this reason, the number of members 7 and 8 constituting each detection plate 5 and 6 is as follows.
A range of 5 to 20 is more preferable.

  Each horizontally long member 7 and each vertically long member 8 has one plastic scintillator 9 and a photomultiplier tube 10 provided at one end of the plastic scintillator 9, and these plastic scintillators are shown in FIG. 9 and the photomultiplier tube 10 are housed in an aluminum case.

Metal member 4 is disposed between position sensitive detector complexes 2 and 3 to remove soft background components such as light and electrons.
The metal member 4 is not particularly limited as long as it is a metal member that removes a soft material background component, and examples thereof include a metal member made of iron or a metal heavier than iron. However, it is particularly preferable to use an iron member in terms of cost. In addition, when using an iron member, it is preferable that the thickness of an iron member shall be 20-200 mm. When the thickness of the iron member is less than 20 mm, the effect of removing the soft background component is not recognized, and when it exceeds 200 mm, the strength of the horizontal muon changes.

  FIG. 2 shows a case where information from the photomultiplier tube 10 is sequentially sent to the NIM high-speed circuit, the CAMAC high-speed circuit, and the computer through the wiring and processed, but the front horizontal muon signal (F ) And the rear horizontal muon signal (B) as a means for distinguishing the y-coordinate (vertical coordinate) through which the horizontal muon penetrates the second detection plate 6 constituting each position sensitive detector complex 2, 3. In the case of using a method for distinguishing both signals (F and B) from the positional relationship of the position, the time resolution of information from the photomultiplier tube 10 is relatively low (for example, 0.1 to 1 microsecond) via the wiring. The data may be sent to a computer via the electronic circuit and processed.

  By the way, muons are a kind of cosmic rays that are generated when primary cosmic rays mainly composed of protons flying from space pass through the Burn-Allen belt and the atmosphere and fall on the surface of the earth. Muons are long-lived next to neutrons, are approximately 207 times the weight of electrons, are elementary particles with + and-charges, and interact only with electromagnetic forces with other particles, and have strong interactions. There is no (nuclear power). Therefore, it has a higher material penetrating force and easier to analyze the interaction than those having both electromagnetic and nuclear strength attenuation such as pion, proton and neutron. In addition, because of the charge, detectors such as scintillators have 100% detection efficiency. Electrons have the same properties but light mass, so they quickly turn into light in the material and cannot be used with thick objects.

  Among the cosmic ray muons, the present inventors show that the intensity after transmission of a horizontal muon that falls on the ground surface in the range of zenith angle 50 to 90 ° is higher than that of other zenith angle muons as shown in FIG. Found it expensive.

  However, soft air background components such as light and electrons are present in the atmosphere about several tens of times that of muons, and horizontal muons use a horizontal muon because the amount that falls on the ground is small. Measurement requires a means to remove the soft background component.

  For this reason, when a means for removing the soft background component was examined, when a metal member 4 made of a heavy metal such as iron is disposed between the position sensitive detector complexes 2 and 3, one piece is provided. The fact that when the soft component passes through the metal member 4 after passing through the first (second) detector complex 2, a plurality of signals are generated in the second (first) detector complex 3. As a result, the present invention has made it possible to effectively remove the soft background component, and as a result, in the present invention, although the amount is small and the background is large, it is possible to use a horizontal muon having high intensity after transmission.

Next, a method for obtaining the internal structure information of the large structure 11 according to the present invention will be described below.
First, as shown in FIG. 4, the position sensitive detection means 1 is arrange | positioned in the finite space | interval position of the side facing the measurement object part 12 of large sized structures 11, such as a blast furnace.

Position-sensitive detector 1 is out of the muons falling on the ground through the air from space, using the horizontal muons, this forward horizontal muon M _F is, the position detected through the target portion 12 of the large structure 11 The position sensitive detection complex 2, the two iron members 4, 4 and the position detection complex 3 constituting the means 1 are arranged so as to pass through sequentially. In the figure, the dashed line is the flying trajectory of the front horizontal muon M _F.

At this time, the forward horizontal muon M _F, and calculates the incident angle alpha from a position of the first detection plate 5 and the second detection plate 6 penetrates, the flying trajectory of the front horizontal muon M _F identified from this angle alpha, which , even passing position in the target portion of the front horizontal muons M _F are identified.

  The muon intensity when reaching the first detection plate 5 and the second detection plate 6 is measured for various α in a predetermined time, for example, 500 hours.

In the present invention, at the same time to measure the intensity (F) of the front horizontal muon M _F, from the opposite side of the large structure 11 across the position-sensitive detector 1, second position sensitive detector complex 3 and strength of the rear horizontal muons M _B arriving from through the metal member 4 in the first position sensitive detector complex 2 (B) was also measured for various α similar, for the same α of these front and rear horizontal muons The internal structure information of the large structure 11 was calculated from the intensity ratio (F / B). Thereby, highly accurate internal structure information can be obtained stably.

  Further, the position sensitive detection means 1 including the two position sensitive detector complexes 2 and 3 is a finite interval position on the side of the large-sized structure 11, and a plurality of units are preferably arranged at different angular intervals around it. If two are arranged at intervals of 90 °, tomographic observation is possible, and a three-dimensional tomographic image of a large structure as a measurement object can be obtained.

Next, since the internal structure of the blast furnace which is a large structure was investigated using the method according to the present invention, the situation will be described below.
As shown in FIG. 4, as a measurement system, the first and second position sensitive detector complexes 2, 3 are arranged between the first and second position sensitive detector complexes 2, 3 at the side position opposite to the hearth part which is the measurement target part of the blast furnace. Position sensitive detection means 1 composed of two disposed iron members 4 and 4 is disposed. Each position sensitive detector complex 2, 3 is a 1 m square first detector plate in which 10 horizontally long members 1 m long and 10 cm wide are arranged along the horizontal direction, and 10 pieces of 1 m long 10 cm wide. And a 1 m square second detection plate arranged along the vertical direction. Each horizontally long member and each vertically long member are composed of one plastic scintillator (Bikelon, product number BC-408) and a photomultiplier tube provided at one end of the plastic scintillator 9 (manufactured by Hamamatsu Photonics, product number H7195). Were housed in an aluminum case. As each iron member, a steel plate having a total thickness of 10 cm was obtained by stacking 20 iron plates each having a thickness of 5 mm. In the present invention, the iron members 4 and 4 disposed between the position sensitive detector composites 2 and 3 may be composed of a single sheet. Since it is bad, it is preferable to configure with two iron members formed by stacking a plurality of iron plates as described above. The arrangement interval between the first position sensitive detector complex 2 and the second position sensitive detector complex 3 was set to 1500 mm. From the intensity ratio (F / B) of the front and rear horizontal muons, the intensity change for each path of the transmitted muon is indicated by the F / B ratio. The ordinate and abscissa are expressed by the angle α (mrad) of the cosmic ray path, and the internal structure information of the blast furnace shown in FIGS. 5A to 5C is obtained.
FIGS. 5A to 5C show the horizontal muon intensity simulated by the position sensitive detection means 1 when the furnace bottom height is changed from the reference position to the vertical position 0 cm, −50 cm and −100 cm. Corresponding to changes in the internal structure of the blast furnace with the vertical angle as the vertical axis and the horizontal angle as the horizontal axis, as calculated and viewed in the right-angle cross section (cross section perpendicular to the paper surface) on the center line of the blast furnace shown in FIG. It shows the intensity distribution per muon path of the F / B ratio. FIG. 5D is a plot of the results of calculating the relationship between the average F / B ratio and the furnace bottom height. In addition, the black square mark in FIG.5 (d) plots the measured value of the actual furnace bottom thickness of a blast furnace.

  From the results shown in FIG. 5, the thickness of the bottom of the blast furnace measured by the method of the present invention is the same as the thickness of the actual bottom of the blast furnace, and the internal structure of the blast furnace is obtained non-destructively and accurately. .

  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 blast furnace has been described as an example of a large structure. However, the present invention is not limited to the blast furnace, and the internal structure of various large structures such as a power generation dam, a bridge pier, an elevated road, a ship, and a vehicle. Needless to say, you can get information.

According to the present invention, it is possible to accurately obtain the internal structure information of a large structure in a non-destructive manner.
In addition, in the present invention, there are few spatial restrictions such as arranging the position sensitive detection means by digging a hole, as in the case of detecting a vertical muon pouring from directly above, and the finite interval positions on the side of the large structure are reduced. Can be arranged. For this reason, it is easy to arrange a plurality of units at different angular intervals around one position sensitive detection means. If a plurality of units are arranged in this way, density length observation on a cut surface at a plurality of different angles is possible. It is possible to obtain a three-dimensional tomographic image of a large structure as a measurement object (tomographic observation).

  Furthermore, the measurement system (measurement circuit system) constituting the position sensitive detection means penetrates a large structure as an object by using a high-speed electronic circuit of nanosecond or less with respect to a high-speed pulse from a scintillator. Separate the front horizontal muon signal (F) and the rear horizontal muon signal (B) that passes through the “sky” part with the observation angle just opposite (in other words, it reaches directly without passing through the object). It can be measured separately. By capturing the F / B intensity ratio thus obtained as data, extremely stable data acquisition can be achieved. In addition, by acquiring data by adding absolute time with sub-microsecond accuracy, it is possible to track numerous real-time changes and perform stroboscopic analysis in synchronization with periodic internal structure time fluctuations. .

It is a figure for demonstrating the conventional method of patent document 1. FIG. It is a perspective view which shows the example of schematic structure of the position detection means suitable for using for the method according to this invention. It is a graph which shows the muon intensity | strength after permeation | transmission thickness of an object and permeation | transmission using various muons. It is the figure which showed the relative positional relationship of the blast furnace which is a measurement object, and a position detection means. It is a figure which shows the simulation of a measurement of the internal structure of a blast furnace in the measurement condition of FIG. 4 by the method according to this invention. Simulation results for various furnace bottom heights, which are determined from comparison with experimental results.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Position sensitive detection means 2 1st position sensitive detector complex 3 2nd position sensitive detector complex 4 Metal member 5 1st detection plate 6 2nd detection plate 7 Horizontal member 8 Vertical member 9 Plastic scintillator 10 Photomultiplier tube 11 Large structure 12 Measurement target part of large structure

Claims (2)

Position sensitive detection means as a measurement system is placed at a finite distance on the side facing the measurement target part of a large structure, and a large particle muon that is created in the atmosphere by primary cosmic rays from the space and falls on the ground surface Large structure by measuring the muon intensity at a predetermined time interval when it reaches the measurement system that constitutes the position sensitive detection means through the measurement target part of the structure, and knowing the distribution of the muon intensity for each passing path A method for obtaining internal structure information of an object,
The position sensitive detection means is divided into a first detection plate having a square shape and a plurality of horizontally long members of a plastic scintillator with a predetermined width along the horizontal direction, and a plurality of vertically long members with a predetermined width along the vertical direction. Two position sensitive detector complexes with a square second detector plate;
Two position sensitive detector complexes are arranged at predetermined intervals,
Each position sensitive detector complex is arranged so that the horizontally long member and the vertically long member are orthogonal to each other to simultaneously measure the muons that have reached the first and second detection plates to identify the horizontal and vertical xy coordinates.
A metal member made of iron or a metal heavier than iron is disposed between the position sensitive detector complexes,
Among the muons, using a high-energy horizontal muon that falls on the surface of the earth with a zenith angle of 50 to 90 °,
When the forward horizontal muon that reaches the first position-sensitive detector complex through the measurement target part of the large structure and subsequently reaches the second position-sensitive detector complex, the respective arrival positions are connected. By following the straight line, the path in the measurement target part through which the front horizontal muon penetrates is specified,
The strength of the front horizontal muon that reaches the second position sensitive detector complex by sequentially passing through the measurement target portion of the large structure, the first position sensitive detector complex and the metal member, and sandwiching the position sensitive detection means Measure both the strength of the rear horizontal muon that reaches the first position sensitive detector complex through the second position sensitive detector complex and the metal member sequentially from the opposite side of the large structure with the same position sensitive detection means. However, when the internal structure of a large structure changes with time, the absolute time is added with an accuracy of microseconds or less when all the measured data is recorded by a computer . A method for obtaining internal structure information of a large structure by using a multi-division horizontal muon detection means characterized by obtaining dynamic internal structure information of the large structure from an intensity ratio.   2. The method for obtaining internal structure information of a large structure according to claim 1, wherein a plurality of the position sensitive detection means are arranged on the side of the large structure at different angular intervals.