JPS6010244B2 - How to measure the gap behind the sheathing - Google Patents

Description

Detailed Description of the Invention This invention uses a sealed neutron source, a thermal neutron counter, and a sealed gamma ray source and gamma ray counter to non-destructively detect the distance between the covering and an object behind it from the surface of the covering. The present invention relates to a method of measuring gap distance.

In recent years, accidents due to excessive uneven settling of oil tanks or oil leakage from oil tanks have occurred, which has become a major social problem.

If the foundation ground of the oil tank has uneven settlement, the gap distance between the bottom plate of the tank and the foundation ground should be adjusted, or if the tank with excessive uneven settlement has been corrected, the area under the bottom plate should be adjusted. It is necessary to know the gap distance.

In such cases, conventionally, a method of cutting the bottom plate and directly measuring the gap distance has often been adopted.

However, when it comes to large-capacity oil tanks, the diameter of the tank ranges into tens of diameters, so the method of drilling a hole in the bottom plate provides accurate measurements, but it is difficult to grasp the overall trend. The bottom plate must be cut at many locations, which poses technical and economical problems.

Therefore, a new measurement method that can non-destructively measure the gap distance from the bottom plate surface has been desired. This invention was newly developed to solve the above problems.
A neutron source and a thermal neutron counter, and a gamma ray source and a gamma ray counter are used together, and are appropriately placed on the top surface of the bottom plate of an oil tank to non-destructively measure the gap distance under the bottom plate.

That is, it takes advantage of the property that radiation passes through a covering such as a steel plate, and the property that the radiation dose changes when it is scattered by an object behind the covering, such as soil or concrete, and returns.

As the radiation, neutron beams and gamma rays are used together. Neutron beams are particularly effective when the hydrogen content of the object behind the coating is known, while gamma rays are effective when the density and composition of the material behind the object is known but the hydrogen content is unknown. By using both neutron beams and gamma rays, it is possible to reliably and accurately measure the gap between the covering and the object behind it. By the way, this invention is applicable not only to the gap between the bottom plate of an oil tank and the ground below it, but also to the gap between the lining surface of a tunnel and the ground behind it, or the gap between the wall of a building and the core body behind it. This is useful when measuring.

The covering of the present invention is made of a material such as a metal plate through which neutron beams and gamma rays can pass.

Further, the background object is made of ±, concrete, backfilling material, or the like. The present invention will be explained below with reference to the embodiments shown in the drawings. FIG. 1 shows a measuring device which is installed, for example, on the bottom plate of an oil tank, and measures the distance between the bottom plate 1 and the surface of the ground 2 below. This figure shows how the gap D is measured.

3 is a neutron beam source, from which neutron beams are emitted.

The neutron beam passes through the bottom plate 1, repeatedly collides with the atomic nuclei that make up the ground 2, and is decelerated and scattered.
They gradually lose energy and return to the device as thermal neutrons. The thermal neutron quantity is detected by a thermal neutron counter 4 and displayed on an output display section 6 via an electronic circuit 5. On the other hand, 7 is a gamma ray source, and the gamma rays emitted from it pass through the bottom plate 1.
Collisions with ground 2.

The amount of part of the scattered light that returns to the apparatus side is detected by a gamma ray counter 8 and displayed on an output display section 6 via an electronic circuit 5. 9 is a shielding body for blocking gamma rays from directly entering the gamma ray counter tube 8.

In this way, if the neutron dose is detected, the neutron beam collides with the hydrogen nuclei that make up the moisture in the ground, loses energy, and returns to the device as thermal neutrons, which is equal to the hydrogen content of the ground. If is constant, the gap D can be measured because there is a relationship that the larger the gap ○ between the bottom plate and the ground, the smaller the gap.

Furthermore, by detecting the gamma ray dose, the returned gamma ray dose is correlated with the gap D, so the gap D can be measured. When the inventors investigated the correlation between the neutron dose, gamma ray dose, and gap D using the above-mentioned apparatus in an actual oil tank, the results shown in Figures 2 and 3 were obtained, respectively. .

That is, while the neutron amount decreased almost exponentially with respect to the gap D, the gamma ray dose showed an almost quadratic curve-like change with a peak near the skin of the gap D=3. here,
When using gamma rays, two gap values can be obtained from the correlation shown in the drawing for a given gamma ray dose, but it is not possible to estimate the exact gap value by comparing with the results obtained with neutron beams. can. As described above, the present invention can accurately and quickly measure the gap between a covering and an object behind it at various sites where measurements are performed using a combination of neutron beams and gamma rays.

[Brief explanation of the drawing]

Figure 1 is a schematic diagram showing the measurement method, Figure 2 is a correlation diagram between the neutron ray count rate and the gap when using neutron beams, and Figure 3 is the correlation diagram between the gamma ray count rate and the gap when using gamma rays. It is a correlation diagram. 1...bottom plate, 2...ground,
3...Neutron beam source, 4...Thermal neutron counter, 5...Electronic circuit, 6...Output display section, 7... - Gamma ray source, 8... Gamma ray counter, 9... Shielding body. Figure 1 Figure 2 Figure 3

Claims (1)

[Claims] 1 A neutron ray source and a gamma ray source are arranged in front of the sheathing, and these sources emit neutron rays and gamma rays, respectively, and the amount of thermal neutrons and gamma rays that return from the object behind the sheathing to the front side of the sheathing are A method for measuring a gap behind a covering, the method comprising detecting the gap between the covering and an object behind the covering by detecting the amount of the gap.