JPH07122575B2 - Radiation thickness measurement method - Google Patents

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for measuring thickness by radiation, and more particularly to a method for measuring thickness of a pipe buried in soil by radiation.

PRIOR ART When γ rays emitted from a radiation source pass through an object,
Some of the gamma rays collide with the atoms of the object and scatter back. At this time, the probability of scattering increases as the thickness of the object increases. Therefore, it is possible to measure the thickness of the object by measuring the energy of the backscattered γ-rays and the number thereof.

According to such a measuring method, the wall thickness of the pipe buried in the soil can be measured inside the pipe. In this case, a characteristic curve of a measuring device such as a scintillator is created in advance using a test piece of known thickness, and the measured value obtained by the measuring device is used as the characteristic curve when measuring the actual wall thickness. You can apply it.

By the way, when measuring the thickness of a measuring object using radiation, the signal according to the thickness of the measuring object and the background signal at the time of measurement are superimposed on the measurement data. Of these, the background signal may change over time. This is because the characteristics of the sodium iodide (NaI) crystal used in the scintillator as a measuring device change depending on the ambient temperature.

As a countermeasure against this, if the difference between the background value when creating the characteristic curve and the background value when measuring the thickness is calculated and the measured value is corrected, the effect due to aging is eliminated and accurate thickness measurement is possible. It will be possible.

The problem to be solved by the invention is that when the object to be measured is a pipe buried in the soil, the influence of backscattering from the pipe wall is required when determining the background value during thickness measurement. In order to avoid being affected by this, there is a problem in that the measuring device must be taken out of the tube, which requires time and effort.

Therefore, an object of the present invention is to solve such a problem and to make it possible to measure the background value under the condition that the measuring device is present inside the measuring object such as in the pipe.

Means for Solving the Problems In order to solve the above problems, the present invention provides a background value when a characteristic curve is created by radiation measurement of a known thickness of a test piece and a thickness of a minimum measurement object. Obtaining the difference from the background value when measuring radiation, after correcting the measurement value of the thickness of the measurement object by this difference value, when determining the thickness corresponding to this correction value from the characteristic curve, The background value at the time of creating the characteristic curve is obtained by covering the test piece with a shield member capable of preventing scattered radiation from the test piece from entering the measuring device, and the object to be measured is covered with the shield member. The background value at the time of measuring the thickness of the measurement object is obtained at the position of the measurement object.

Action In this way, the backscattered rays from the measurement object may enter the measuring device because the shielding member covers the measurement object to obtain the background value when measuring the thickness of the measurement object. Without, it is possible to measure the background value inside the measurement object. Further, since the shield member is used not only when measuring the thickness of the measurement object but also when creating the characteristic curve, both background values include the influence of backscattered rays from the shield member. Therefore, the influence of the shielding member can be eliminated by obtaining the difference between the two background values when correcting the measured value.

Example FIG. 3 is a diagram for explaining the operation of creating the characteristic curve.
Here, 1 is a scintillator as a measuring device, and 2 is its detection part. On the side of the scintillator 1 is a container 3 made of lead.
The radiation source 4 such as cesium 137 is contained in the container 3. 5 is a test piece,
The pipe is formed of the same material as the pipe as the measurement object, for example, ductile cast iron, and has the same curve as the pipe.

A plurality of test pieces 5 having different thicknesses are prepared, each test piece 5 is brought close to the scintillator 1 as shown in FIG.
Measure the line. Then, since the peak value of the scattering spectrum or the total number of counts in a certain range is proportional to the plate thickness of the test piece 5, a characteristic curve as shown in FIG. 4 is obtained.

Further, the background value A is obtained when the characteristic curve is created. This is obtained by obtaining the measured value of the number of counts when the surface of the test piece 5 is covered with the shielding member 6, as shown in FIG. The shield member 6 is
The scintillator 1 is formed of an iron plate or a lead plate having a thickness that does not measure scattered radiation from the test piece 5, and has a curvature so that it can be overlapped with the inner surface of the test piece 5. Further, at the time of measuring the background value A, the distance L is set from the shield member 6 to the scintillator 1.

When measuring the wall thickness of a pipe as a measurement object buried in the soil, the scintillator 1 is inserted into the pipe 7 and the same position as that when the test piece 5 shown in FIG. 3 is measured. The measurement value B of the count number corresponding to the wall thickness of the tube 7 is obtained.

Moreover, as shown in FIG. 2, the background value A'at that time is obtained. This is because the same shielding member 6 as shown in FIG. 1 is used to cover the inner surface of the tube 7 and the distance L from the shielding member 6 to the scintillator 1 is set equal to that in FIG. It is obtained by obtaining a measured value of 1.

Then, the correction value C is calculated by the following equation.

C = B- (A-A ') If the correction value C is obtained in this way, the measured value of the wall thickness of the pipe 7 is set as the count number, as indicated by the broken line in the characteristic curve of FIG. obtain.

In this way, the shielding member 6 prevents the backscattered rays from the tube 7 as the measurement object from entering the scintillator 1 as the measuring device, and obtains the background value A ′ at the time of measurement inside the tube 7. be able to. Further, since the shielding member 6 is also used when obtaining the background value A when creating the characteristic curve, both background values A and A'include the influence of backscattered rays from the shielding member 6. It will be. Therefore, the influence of the shielding member 6 can be removed by obtaining the difference between the background values A and A'when the measured value B is corrected. When the soil 8 existing on the outer periphery of the pipe 7 affects the measurement result of the scintillator 1, the test piece 5
Soil may be placed on the test piece 5 at the time of measurement.

EFFECTS OF THE INVENTION As described above, according to the present invention, since the background value at the time of measuring the thickness of the measuring object is obtained by covering the measuring object with the shielding member, the measuring device is a measuring object such as a pipe. The background value can be obtained inside the device without being output. Further, since the test piece is covered with the shielding member even when the characteristic curve is created, the influence of the shielding member included in the background value can be removed when the measurement value is corrected.

[Brief description of drawings]

The drawings show one embodiment of the present invention, and FIG. 1 shows a method of measuring a background value when a characteristic curve is created.
FIG. 4 is a diagram showing a background value measuring method during thickness measurement, FIG. 3 is a diagram showing a test piece measuring method, and FIG. 4 is a diagram showing an example of a characteristic curve. 1 ... Scintillator (measuring device), 5 ... test piece, 6 ... shielding member, 7 ... tube (measurement object).

Claims (1)

[Claims] 1. A difference between a background value when a characteristic curve is created by measuring a known thickness of a test piece and a background value when a thickness of an object to be measured is measured. Then, after correcting the measurement value of the thickness of the measurement object by this difference value, when obtaining the thickness corresponding to this correction value from the characteristic curve, scattered rays from the test piece are incident on the measuring device. To obtain a background value at the time of creating the characteristic curve by covering the test piece with a shielding member capable of preventing the measurement target object with the shielding member, and at the position of the measurement target object, the measurement target object. A method for measuring thickness by radiation, which comprises obtaining a background value when measuring the thickness of.