JP6567296B2 - Internal substance identification device and internal substance identification method - Google Patents

Description

  Embodiments described herein relate generally to an internal substance specifying device and method for specifying an internal substance of an object using a muon.

  As a method for imaging the inside of a structure, there is a muon tomography technique for measuring muon scattering. For example, a technique for inspecting the inside of a vehicle or a cargo container by observing a Coulomb multiple scattering angle in a cosmic ray muon material reaching the ground surface is known.

  In imaging by muon tomography, muon trajectory detectors are externally provided on the top and bottom or front and back of a structure to be seen through. The detector detects the flight trajectory of muon and analyzes the trajectory before and after scattering, thereby imaging the inside of the structure. Muon's Coulomb multiple scattering depends on the atomic number of the material, so the atomic number of the material can be estimated from the average scattering angle.

C. Morris, et al. , Science and Global Security 16, 37 (2008). C. Morris, et al. , AIP Advances 2, 042128 (2012).

  However, when a structure such as a shield is present and the object to be measured is observed through the structure, the scattering angle of the muon changes compared to the case where there is no shield. That is, the energy of the muon particles decreases as the muon passes through the shielding body. On the other hand, the Coulomb multiple scattering angle of muon is inversely proportional to the energy of muon particles. Therefore, muon multiple scattering at the measurement object changes.

  As a result, a specific error increases when trying to specify a substance by the muon scattering angle. For this reason, it has been difficult to identify substances in the shielding object by the conventional method.

  Embodiments of the present invention have been made in view of such circumstances, and an object of the present invention is to be able to quantitatively specify constituent elements of a substance present inside a target object.

In order to achieve the above-described object, the present embodiment is an internal substance specifying device that specifies a substance existing inside an object using a muon, and is provided on both sides of the object and faces each other. Spreads on a plane, two muon trajectory detectors capable of measuring the incident position and direction of muons on the plane, and a plurality of muon detection signals from the two muon trajectory detectors, and constitutes an internal substance. An analysis computer for identifying an element, and the analysis computer is configured to group the plurality of muon detection signals for each signal generated by the same muon, and to be the same group as a result of the grouping. Using a muon scattering angle calculation unit that calculates a muon scattering angle based on a plurality of signals, and the object containing a known substance And a muon scattering angle calibration unit calculating a calibration data, and the internal substance identification unit that identifies the element constituting the internal material on the basis of the muons scattering angle using the compare positive over data, characterized by comprising .

Further, the present embodiment is an internal substance identification method of identifying an agent that is present in the interior of the object by using the muon, detection of muons by two muon trajectories detector mounted across said object Detecting a plurality of muon detection signals, grouping the plurality of muon detection signals for each signal generated by the same muon, and after the grouping step, the grouping result, A muon scattering angle calculating step for calculating a muon scattering angle based on a plurality of signals in the same group, and a muon scattering angle calibration step for calculating and outputting calibration data using the object containing a known substance ; the muon scattering angle calculated using the calibration data obtained in the muons scattering angle calibration step And having a an internal substance specifying step of specifying an element constituting the internal material for each group based on the muons scattering angle obtained in step.

  According to the embodiment of the present invention, it is possible to quantitatively specify the constituent elements of the substance existing inside the object.

It is a block diagram which shows the structure of the internal substance specific device which concerns on this embodiment. It is a perspective view which shows the structure of the muon locus detector of the internal substance specific device which concerns on this embodiment. It is an elevation sectional view showing the composition of the drift tube of the muon locus detector of the internal substance identification device according to the present embodiment. FIG. 4 is a partial cross-sectional view taken along line IV-IV in FIG. 2. It is a conceptual perspective view explaining how to take a scattering angle. It is a flowchart which shows the procedure of the internal substance identification method which concerns on this embodiment. It is a conceptual perspective view explaining the example at the time of applying the internal substance specific method by the internal substance specific apparatus which concerns on this embodiment to a dry cask.

  Hereinafter, an internal substance identification device and method based on muon tomography according to an embodiment of the present invention will be described with reference to the drawings. Here, the same or similar parts are denoted by common reference numerals, and redundant description is omitted.

  FIG. 1 is a block diagram showing the configuration of the internal substance identification device according to this embodiment. The internal substance specifying device 100 specifies a constituent element of a substance inside a target object, and includes a muon locus detector 10, an analysis computer 20, and an output unit 30.

  The muon locus detector 10 includes a first muon locus detector 11 and a second muon locus detector 12. Each of the first muon trajectory detector 11 and the second muon trajectory detector 12 is provided so as to sandwich the object, and the surfaces facing each other are spread on a plane, and each muon passing through each surface is To detect. The muon locus detector 10 can measure the incident position and the incident direction of the muon in the passing portion of the muon that has passed.

  FIG. 2 is a perspective view showing the configuration of the muon locus detector. Each of the first muon trajectory detector 11 and the second muon trajectory detector 12 has a plurality of position-sensitive drift tubes 15 that are cylindrical and extend in the axial direction. Each of the units 16a, 16b, and 16c has a drift tube 15 that is arranged in two stages parallel to each other in a plane. Each of the units 16a, 16b, and 16c is arranged in a direction perpendicular to the plane in which the drift tube 15 extends.

FIG. 3 is an elevational sectional view showing the configuration of the drift tube. The drift tube 15 is
It has a cylindrical portion 15a, a core wire 15b, an end plate 15c, and an end plate 15d. The end plate 15c and the end plate 15d close both ends of the cylindrical portion 15a. The end plate 15c and the end plate 15d have an electrical insulating function. The cylindrical portion 15a, the end plate 15c, and the end plate 15d form a sealed space, and a gas 15e that is ionized by muon is sealed in the sealed space.

  The core wire 15b is provided substantially at the axial center of the cylindrical portion 15a, and both ends are supported by the end plate 15c and the end plate 15d. The core wire 15b penetrates the end plate 15d. The portion where the core wire 15b is exposed to the outside of the end plate 15d is connected to one polarity of the DC power supply 15f. The cylindrical portion 15a is also connected to the other polarity of the DC power supply 15f.

  When the muon passes through the inside of the drift tube 15 and ionizes the atoms of the gas 15e to generate ions, the ions move to either the core wire 15b or the cylindrical portion 15a, and the current flows in a pulsed manner to cause the muon to flow. To detect. In addition, since the current flows through the shortest distance, it is possible to measure at which position in the axial direction ionization has occurred, that is, whether the muon has passed.

  4 is a partial cross-sectional view taken along line IV-IV in FIG. When a muon enters the muon trajectory detector 10 with a trajectory M, ionization occurs in the drift tube 15 through which the trajectory M passes, and ions move, for example, to the respective core wires.

  Here, the ion movement time depends on the distance from the ionized portion to the core wire. In fact, even if signals from the respective drift tubes 15 are simultaneously generated, the movement time differs from the drift tubes 15 by a very small amount of time. The point where a certain movement time occurs is some point on the concentric cylinder with the core line as the center. In the cross-sectional view of FIG. 4, each point is on a circle indicated by a broken line. Therefore, the muon trajectory can be specified based on the circle in each drift tube 15 that has emitted the signal.

  As described above, the incident position and the incident direction can be specified. Therefore, the first muon locus detector 11 and the second muon locus detector 12 can specify the incident position and the incident direction, respectively.

  The analysis computer 20 includes a grouping unit 21, a muon scattering angle calculation unit 22, a muon scattering angle calibration unit 23, and an internal substance specifying unit 24.

  The grouping unit 21 receives a plurality of muon detection signals from the first muon trajectory detector 11 and the second muon trajectory detector 12 as inputs. When the muon detection signal from the first muon trajectory detector 11 and the muon detection signal from the second muon trajectory detector 12 are generated at the same time, it can be determined that the muon detection signal is generated by the same muon. Therefore, by comparing the generation times of the respective muon detection signals, a plurality of muon detection signals can be grouped for each signal generated by the same muon.

  The muon scattering angle calculation unit 22 calculates the muon scattering angle based on a plurality of signals that are grouped as a result of grouping by the grouping unit 21. FIG. 5 is a conceptual perspective view for explaining how to determine the scattering angle. Now, the muon detection signal from the first muon trajectory detector 11 and the muon detection signal from the second muon trajectory detector 12 are simultaneously generated and grouped by the grouping unit 21 as a muon detection signal group from the same muon. Take as an example the case.

  The muon detection signal from the first muon trajectory detector 11 has information on the passing position and direction of the muon in the first muon trajectory detector 11. Similarly, the muon detection signal from the second muon trajectory detector 12 has information on the muon passage position and direction in the second muon trajectory detector 12.

  When the same muon occurs, the straight line L10 extending the trajectory direction at the muon passage position in the first muon trajectory detector 11 and the muon passage position in the second muon trajectory detector 12 extend in the direction opposite to the trajectory direction. The straight line L20 is a saddle that intersects at the point A as shown in FIG. 5, and the position of the point A that is the scattering occurrence point where the muon is scattered can be calculated in this way.

  Since the straight line L10 and the straight line L20 intersect at a point A, a plane S including the straight line L10 and the straight line L20 exists. In the plane S, an angle formed by the straight line L10 and the straight line L20 is defined as θ. The angle θ is an angle at which the muon travel direction changes. This angle θ is the scattering angle. In addition, the direction of the plane S does not matter about the muon scattering angle. That is, the plane S may be rotated with the straight line L10 as the center of rotation. In other words, when the light is incident in the direction of the straight line L10 in FIG. 5 and scattered at the point A, the scattering angle is equal to any straight direction connecting the point A to the point on the circle C similarly to the straight line L20. It is assumed that θ. Here, the circle C is a locus when the point P is rotated about the straight line L10.

  The muon scattering angle calculation unit 22 calculates this scattering angle. In addition, in this way, a plurality of muon scattering angle results for each coordinate position (point A in FIG. 5) are accumulated and stored, and a value obtained by averaging the accumulated results in terms of time is obtained for each scattering occurrence location. Output as muon scattering angle at.

  Note that the output from the muon scattering angle calculation unit 22 may be performed by batch-wise collecting the scattering angle calculation results for the respective coordinate positions, and intermittently outputting the results of statistical processing such as the average value. Good. Or you may always output the average value after an integration | stacking start. Or you may always output the moving average by a predetermined time width.

When the substance is composed of a plurality of types of elements, the value of the scattering angle corresponding to each element is calculated for the same location. The frequency distribution for each coordinate position is obtained by accumulating the data for each coordinate position in the object at the scattering occurrence positions calculated in this way. The shape of the substance is derived from this frequency distribution. As will be described later, the composition of the constituent elements at each position is derived by the internal substance specifying unit 24. That is, muon tomography is possible .

  The distribution of muon scattering angles is approximately Gaussian around 0 degrees. The standard deviation σ is obtained from the frequency distribution of the muon scattering angle. The average value θ of the muon scattering angle is about the standard deviation σ. The scattering angle of a substance is given by the following equation (1).

ただし、θ（ｒａｄ）は散乱角、１３．６は１３．６ＭｅＶ、Ｖ（ｍ／ｓｅｃ）は速度、ｐ（ｋｇ・ｍ／ｓｅｃ）は運動量、Ｘ_０（ｍ）は放射長であり物質に固有の値、ｔ（ｍ）は物質の厚さである。ｔは、ミュオントモグラフィで導出された物質の形状から求められる。

Where θ (rad) is the scattering angle, 13.6 is 13.6 MeV, V (m / sec) is the velocity, p (kg · m / sec) is the momentum, and X ₀ (m) is the radiation length. The intrinsic value t (m) is the thickness of the material. t is obtained from the shape of the substance derived by muon tomography.

  Further, the following expression (2) obtained by modifying expression (1) and simplifying it gives a sufficiently good approximation in practice.

したがって、較正は、実質的には、式（２）の定数Ｃを求めることである。ミュオン散乱角較正部２３は、式（２）を算出し、その結果得られた定数Ｃを較正データとして出力する。定数Ｃを求めるいくつかの方法を以下に示す。

Therefore, the calibration is substantially to obtain the constant C of Equation (2). The muon scattering angle calibration unit 23 calculates Equation (2) and outputs the constant C obtained as a result as calibration data. Several methods for determining the constant C are shown below.

In order to specify a substance, an object having a known shape and material is placed in the container in advance. C is determined by equation (2) using the muon scattering angle measured for the known object and the known parameters specific to the known object, ie, the radiation length X ₀ (m) and the material thickness t (m). Using this C, the material of the unknown substance can be obtained from the muon scattering angle of the unknown substance and the thickness t (m) of the unknown substance. This is effective, for example, when a standard known substance is put in a standard object such as a dry cask.

  Alternatively, if a calibration substance is put in the object in advance and data for calibration is taken, it is not always necessary to put the calibration substance in the object at the time of this measurement. Calibration data can be obtained by simulation, or muon scattering on the wall of a dry cask can be used as calibration data.

The internal substance specifying unit 24 uses the constant C calculated by the muon scattering angle calibration unit 23 and specifies the element of the substance using the above-described formula (1) or formula (2) based on the scattering angle θ .

  In order to specify the constituent elements of a substance, an object with a known shape and material is placed in the container in advance for calibration, and C is determined from the measured muon scattering angle. It is also possible to obtain the material of an unknown substance.

  The output unit 30 displays an image of the element configuration of the internal substance of the target object specified by the analysis computer 20. That is, the output unit 30 includes an imaging unit and a display unit. The display unit may be a separate screen or a display unit such as a liquid crystal attached to the analysis computer.

  FIG. 6 is a flowchart showing the procedure of the internal substance specifying method according to this embodiment. First, a muon detection signal is acquired by the muon locus detector 10 (step S01). That is, each of the first muon locus detector 11 and the second muon locus detector 12 detects the muon and generates a muon detection signal.

  Next, the grouping unit 21 receives a plurality of muon detection signals generated by the first muon locus detector 11 and the second muon locus detector 12, and the first muon locus detector 11 and the second muon at the same timing. The trajectory detector 12 signals are grouped (step S02). That is, the muon detection signals from the first muon trajectory detector 11 and the second muon trajectory detector 12 generated at the same time are grouped as signals generated by the same muon.

Next, the muon scattering angle calculation unit 22 calculates the muon scattering angle based on a plurality of signals in the same group (step S03). Also, the muon scattering angle calculation unit 22 stores and accumulates muon scattering angle data for each coordinate position inside the object (step S04). Next, the muon scattering angle calibration unit 23 outputs the constant C, which is calibration data calculated based on the calibration result, to the internal substance specifying unit 24 (step S05). Next, the internal substance specifying unit 24 uses the constant C given by the muon scattering angle calibration unit 23, and based on the scattering angle θ calculated by the muon scattering angle calculation unit 22 , each coordinate position in the object. The element configuration and the element amount of the substance are specified (step S06). Next, the output unit 30 displays this result (step S07).

  FIG. 7 is a conceptual perspective view for explaining an example when the internal substance specifying method by the internal substance specifying apparatus according to the present embodiment is applied to a dry cask. In this example, an unknown substance 53 and a calibration substance 52 whose substance is known are incorporated in a dry cask 51 as an object.

  The first muon locus detector 11 measures the (X, Y) coordinates and direction of the muon passage position. Similarly, the second muon locus detector 12 measures the (X, Y) coordinates and direction of the muon passage position.

The muon scattering angle calculation unit 22 calculates the scattering angle for the calibration substance 52 as θ1 and the scattering angle for the unknown substance 53 as θ2. As a result, for example, since the radiation length X ₀ (m) and the thickness t (m) for the calibration substance 52 in the above-described equation (2) are known, the count C in the equation (2) is obtained. It is done. Further, the scattering angle θ2 for the unknown substance 53 is obtained, and the thickness t of the unknown substance 53 is also obtained by muon tomography.

  As a result, the radiation length X (m) of the unknown substance 53 can be calculated from the equation (2). Since the radiation length X is a value inherent to a substance, that is, an element, the element can be specified. Further, the amount of the element of the unknown substance 53 can be quantitatively specified based on the intensity ratio of each measurement value and the intensity of the calibration substance 52 whose amount of the element is known.

  As described above, according to the present embodiment, the constituent elements of the substance existing inside the object can be quantitatively specified.

[Other Embodiments]
As mentioned above, although embodiment of this invention was described, embodiment is shown as an example and is not intending limiting the range of invention. For example, the muon locus detector is not limited to that shown in the embodiment. As long as the incident position and the incident direction can be measured, for example, a method in which a plurality of muon locus detectors and a simultaneous measurement circuit are combined may be used.

  Further, the analysis computer need not be a single computer. What is necessary is just to have the part which has each function of the grouping part 21 thru | or the internal substance specific part 24. FIG.

  The embodiments can be implemented in various other forms, and various omissions, replacements, and changes can be made without departing from the scope of the invention.

  The embodiments and the modifications thereof are included in the scope of the invention and the scope of the invention, and are also included in the invention described in the claims and the equivalents thereof.

  DESCRIPTION OF SYMBOLS 10 ... Muon locus detector, 11 ... 1st muon locus detector, 12 ... 2nd muon locus detector, 15 ... Drift tube, 15a ... Cylindrical part, 15b ... Core wire, 15c, 15d ... End plate, 15e ... Gas, 15 f ... DC power supply, 20 ... analysis computer, 21 ... grouping unit, 22 ... muon scattering angle calculation unit, 23 ... muon scattering angle calibration unit, 24 ... internal substance specifying unit, 30 ... output unit, 51 ... dry cask, 52 ... Calibration substance, 53 ... Unknown substance, 100 ... Internal substance identification device

Claims (4)

An internal substance identification device that uses muons to identify substances existing inside an object,
Two muon trajectory detectors provided on both sides of the object and having mutually facing surfaces spread on a plane and capable of measuring the incident position and the incident direction of the muon in the plane;
An analysis computer that receives a plurality of muon detection signals from each of the two muon trajectory detectors and identifies an element constituting the internal substance;
With
The analysis computer
A grouping unit that groups the plurality of muon detection signals for each signal generated by the same muon;
As a result of the grouping, a muon scattering angle calculation unit that calculates a muon scattering angle based on a plurality of signals that are the same group, and
A muon scattering angle calibration unit for calculating calibration data using the object containing a known substance,
An internal substance identification unit that identifies the element constituting the internal material on the basis of the muons scattering angle using the compare positive over data,
An internal substance identification device comprising:   2. The internal substance specifying device according to claim 1, wherein the calibration data is a value of a coefficient C in the following equation (1).
        θ = C · √ (t / X ₀ (1)
    Where θ is the muon scattering angle and X ₀ Is the radiation length and t is the thickness of the material. An internal substance identification method for identifying a substance existing inside an object using a muon,
A detection step of detecting a muon by two muon trajectory detectors provided across the object and obtaining a plurality of muon detection signals;
A grouping step of grouping the plurality of muon detection signals for each signal generated by the same muon;
After the grouping step, a muon scattering angle calculation step for calculating a muon scattering angle based on a plurality of signals made into the same group as a result of the grouping;
A muon scattering angle calibration step of calculating and outputting calibration data using the object containing a known substance ; and
Using the calibration data obtained in the muon scattering angle calibration step, based on the muon scattering angle obtained in the muon scattering angle calculation step, an internal substance identification step for identifying an element constituting an internal substance for each group When,
Internal substance identification how to, comprising a. The internal substance identification method according to claim 3 , wherein the calibration data is a value of a coefficient C in the following equation (2) .
θ = C · √ (t / X ₀ ) (2)
Where θ is the muon scattering angle, X ₀ is the radiation length, and t is the thickness of the substance.

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