JPH0616102B2 - Method and apparatus for measuring the depthwise distribution of gamma ray emitting nuclides existing inside a wall such as concrete - Google Patents

Description

The present invention relates to a method and apparatus for measuring the depthwise distribution of γ-ray emitting nuclides existing inside concrete or the like in nuclear facilities and the like.

[Conventional technology]

When dismantling nuclear facilities such as nuclear reactors, it is important to investigate the abundance and distribution of radionuclides such as γ-ray emitting nuclides in concrete before dismantling to reduce exposure during dismantling work. That's right. As the estimation method, conventionally, a large-scale computer was used to perform large-scale calculation, or concrete type core boring was actually performed on site to confirm the calculation accuracy, and samples were taken and measured. Was there.

[Problems to be solved by the invention]

However, the method of large-scale calculation using a large-scale computer is expensive and its accuracy is not clear. In addition, the method of measuring each sample by core boring is
The accuracy is high, but it has a drawback that it takes a long time because core boring is performed at several places.

The present invention is to solve the above problems, and provides a method and an apparatus capable of simply and accurately measuring the distribution of γ-ray emitting nuclides in the depth direction inside a wall such as concrete. With the goal.

[Means for solving problems]

Therefore, the method and apparatus for measuring the distribution in the depth direction of the γ-ray emitting nuclide existing inside the wall body such as concrete of the present invention, the distance from the surface of the wall body in which the γ-ray emitting nuclide exists inside. Instead, one radionuclide is focused on and measured n times, and from the n measured values C ₁ , C ₂ ... C _{n at} that time, the abundance N of the γ-ray emitting radionuclides in the depth direction of the wall is determined. ₁ , N ₂ ...
... N _n However ε: Detection efficiency of the detector for γ-ray energy of a certain γ-ray emitting nuclide λ: Linear attenuation coefficient of the wall for γ-ray energy of the γ-ray emitting nuclide t _n : Transmission distance in the wall B _n : Transmission distance t build-up factor Karadasuru in the wall of the _n r _n: be determined from multiple simultaneous linear equations of the distance from the wall to the detector, and a radiation measuring instrument, a radiation measuring instrument, there are γ-ray emitting nuclide inside A measuring device driving device that moves in a direction perpendicular to the surface of the wall body, and a computing device to which the nuclear measurement values obtained at measurement positions with different distances from the wall surface are input, and the computing device is , Calculate the abundance of γ-ray emitting nuclides distributed in the wall depth direction by solving a multi-dimensional simultaneous linear equation between each measured value and the abundance of γ-ray emitting nuclides distributed in the wall depth direction It is characterized by

[Action]

The method and apparatus for measuring the distribution in the depth direction of the γ-ray emitting nuclide existing inside the wall body such as concrete of the present invention focuses on only the nuclide that emits γ-rays, from the outside of the wall body such as concrete, the wall By measuring the radiation multiple times by changing the distance from the body surface, and solving the multi-dimensional simultaneous linear equation that holds between each measured value and the abundance of γ-ray emitting nuclides distributed in the wall depth direction The existing amount of γ-ray emitting nuclides distributed in the depth direction can be obtained very easily and accurately.

〔Example〕

 Hereinafter, embodiments will be described with reference to the drawings.

FIG. 1 is a diagram for explaining the principle of measuring the amount of γ-ray emitting nuclides according to the present invention, in which 1 is a measuring instrument, 2 is a shield, 3 is a concrete surface, and 4 is a measurement target region. .

In the figure, a γ-ray measuring device 1 provided with a sufficient shield 2 around the γ-ray from other than the measurement target, for example, G
e The detector is measured at a distance r _i from the concrete surface 3. Γ-ray emitting nuclides (eg ⁶⁰ C ₀ ) present in concrete are present in all parts,
When the mesh is divided into meshes having a finite volume in the depth direction of the concrete, the center positions of the meshes t ₁ , t _2, ... T
It is assumed that _n exists and exists. Now, ⁶⁰ C ₀
The amount at the position t ₁ of N ₁ , the amount at the position t ₂ of N ₂ , ...
Assuming that the quantity at the position t _n is N _n , the measured value C _i at a position distant from the concrete surface by r _i can be expressed by the following equation.

Here, epsilon: ⁶⁰ detection efficiency of the detector to γ-ray energy of C ₀ lambda: ⁶⁰ linear attenuation coefficient of the concrete for the γ-ray energy of C ₀ B _n: the build-up factor similar measurement for concrete transmission distance t _n If the distance r _i from the concrete surface 3 is changed and the measurement is performed n times, n measurement values C _i can be obtained. This measurement And the amount of ⁶⁰ C ₀ The relationship between and is expressed by the matrix expression and the following expression.

Where the matrix R is Is. Therefore, if the matrix R is obtained in advance, the measured value To ⁶⁰ C ₀ amount Is required.

FIG. 2 is a diagram showing an embodiment of a measuring device based on the measuring principle shown in FIG. 1, the same reference numerals as those in FIG. 1 indicate the same contents, 5 is a measuring device driving device, and 6 is a calculation. It is a device.

In the figure, the measuring instrument driving device 5 moves the position of the measuring instrument 1 to change the distance r _i from the concrete surface 3 to perform the measurement value n times, and the n measurement values C _i at that time are compared to the minicomputer etc. Is input to the arithmetic unit 6. The above-mentioned matrix R is stored in the arithmetic unit 6, and the amount of ⁶⁰ C _{0 at} each position in the concrete depth direction is calculated by solving the above-mentioned multi-dimensional simultaneous linear equation from the n measured values C _i .

〔The invention's effect〕

As described above, according to the present invention, the depthwise distribution of γ-ray emitting nuclides in concrete can be easily and accurately obtained without relying on a large-scale calculation using a large-scale computer and without core boring. Can be measured.

[Brief description of drawings]

FIG. 1 is a diagram for explaining the principle of measuring the amount of γ-ray emitting nuclide in concrete according to the present invention, and FIG. 2 is a diagram showing an embodiment of a measuring device based on the measuring principle shown in FIG. Is. 1 ... Measuring instrument, 2 ... Shield, 3 ... Concrete surface, 4 ... Measurement target area, 5 ... Measuring instrument drive device, 6 ...
… Arithmetic device

Claims (3)

[Claims] 1. Radiation measurement is performed n times by focusing on a certain nuclide while changing the distance from the surface of the wall in which the γ-ray emitting nuclide is present, and n measurement values C _{1 at} that time, C ₂ ...... C
_{From n} , the abundances N ₁ , N ₂ ... N _n of the γ-ray emitting nuclides in the wall depth direction are However ε: Detection efficiency of the detector for γ-ray energy of a certain γ-ray emitting nuclide λ: Linear attenuation coefficient of wall for γ-ray energy of the γ-ray emitting nuclide t _n : Transmission distance in wall B _n : Transmission distance t build-up factor Karadasuru in the wall of the _n r _n: the γ-ray emitting nuclide existing inside the wall of the concrete or the like and obtaining from the multiple simultaneous linear equations of the distance from the wall to the detector depth To measure the distribution of. 2. A radiation measuring instrument and a radiation measuring instrument inside the gamma
A measuring instrument driving device that moves in the direction perpendicular to the surface of the wall body where the line-emitting nuclide is present, and a computing device that inputs each measurement value obtained at measurement positions where the distance to the wall surface is different. Comprising, the arithmetic unit, the γ-ray emitting nuclides distributed in the wall depth direction by solving a multi-dimensional simultaneous linear equation between each measured value and the abundance of γ-ray emitting nuclides distributed in the wall depth direction. A device for measuring the distribution in the depth direction of γ-ray emitting nuclides existing inside a wall body of concrete or the like, which is characterized by calculating the existing amount of. 3. The distribution of γ-ray emitting nuclides existing in the wall of concrete or the like in the depth direction according to claim 2, wherein the radiation measuring device is shielded by a shield. Measuring device.