JPH0520710B2 - - Google Patents

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to an improvement in a method for non-destructively and quantitatively measuring the radioactivity concentration of structures in water from a distance using a hollow straight pipe. be. In this measurement method, a hollow tube whose tip is sealed with a plate is placed close to the measurement point of the target structure, forming a gamma ray collimator using water as a shield, and the gamma rays emitted from the measurement point are passed through the straight tube. The radioactivity concentration of the structure is determined based on the spectrum analysis results.

[Prior Art] Conventionally, as shown in Fig. 1, the measurement method involves placing a hollow straight pipe 3 whose tip is sealed with a plate 2 in close proximity to a measurement point 1 of a target structure, and blocking water 4 with a shield. The gamma ray collimator 5 is configured as a gamma ray collimator 5, and the gamma rays 6 emitted from the measurement point are passed through a straight tube, guided to the gamma ray spectrum detector 7 placed on the opposite side, and measured, and the gamma rays obtained by analyzing this gamma ray spectrum. Radioactivity concentrations in structures have been determined based on the counting results.

[Problems to be Solved by the Invention] When measuring the radioactivity of underwater structures using a hollow straight pipe according to the conventional quantitative measurement method, as shown in FIG. If the length is long and the insertion angle 10 is large, the hollow straight pipe will bend due to buoyancy and it will be very difficult to ensure its straightness. There was a problem in that it was difficult to completely measure the gamma rays 12 at the other end using the gamma ray spectrum detector 13 placed at the other end, making quantitative measurements impossible.

[Means for Solving the Problems] One of the measurement methods of the present invention is to use a disc-shaped gamma ray source as a reference, even when the straightness of a hollow straight pipe cannot be obtained. This method is characterized by calibrating the gamma ray measurement results obtained using the method and determining the radioactivity concentration of the target structure.

Another measurement method of the present invention is to monitor a disc-shaped light source placed at the tip of a hollow straight tube in front of a gamma-ray spectrum detector, and then use the gamma-ray spectrum detector to detect the projected area of the light source. The system corrects the measured gamma ray counts and is characterized by the ability to quantify the radioactivity concentration in structures even when a hollow straight pipe is bent underwater.

[Example] The former measuring method of the present invention will be explained with reference to the drawings.

A principle diagram (embodiment) of the present invention is shown in FIG. A diameter 18 having the same diameter as the inner diameter of the straight pipe is attached to the distal end 17 of a hollow straight pipe 16 whose distal end is sealed with a plate 15 inserted into the water 14.
A standard radiation source 19 is mounted, which has a disc shape and emits gamma rays having a uniform distribution of radioactivity and having an energy different from that of the radioactivity to be measured. As the radioactive nuclide to be used, one or more types are selected from those other than the nuclide to be measured. This radiation source is fixed to a sealing plate as shown in FIG. In this case, the geometric conditions when the gamma rays emitted from the measurement point 20 of the structure where the hollow straight pipe is desired are incident on the gamma ray spectrum detector, and the gamma rays emitted from the disc-shaped source are the gamma ray spectrum detector. Geometric condition 2 when incident on 21
2 will be equivalent. Therefore, the straightness of the hollow pipe cannot be obtained, and even though some gamma rays are absorbed by the hollow pipe and the surrounding water, the hollow straight pipe is emitted from the desired measurement point of the structure. Both the gamma rays and the gamma rays emitted from the disc-shaped standard radiation source are reduced at the same rate by the time they reach the gamma ray spectrum detector.

For this reason, we used nuclides that emit gamma rays of various energies with known radioactive concentrations as the radioactive nuclides of the standard radiation source, and determined the detection efficiency of the gamma ray spectrum detector for gamma ray energies.
If the hollow straight pipe calibrates the gamma rays emitted from the desired measurement point of the structure based on this detection efficiency,
Even if the straightness of the hollow straight pipe cannot be completely achieved, it becomes possible to quantitatively measure the radioactivity concentration of the structure.

In addition, by using the quantitative measurement method of the present invention, even when using a hollow tube whose length can be changed, the detection efficiency is automatically determined using the disc-shaped standard radiation source, so quantification can be performed at any position. Can be measured.

The latter measuring method of the present invention will be explained with reference to the drawings.

A principle diagram (embodiment) of the present invention is shown in FIG. Hollow straight pipe 23, sealing plate 24, disc-shaped light source 2
5, a reflection plate 26, a projection plate 27, and a gamma ray spectrum detector 28. The disc-shaped light source is
The light source has the same diameter as the inner diameter of the hollow tube. This light source is fixed inside the tip of a hollow straight tube as shown in FIG. In this case, if the hollow straight pipe is long enough, the hollow straight pipe can be used at the desired measurement point 29 of the structure.
The geometric conditions when the gamma rays emitted from the circular light source enter the gamma ray spectrum detector are the same as the geometric conditions when the light emitted from the circular light source is reflected by the reflector and projected onto the projection plate. Therefore, even if the hollow straight pipe bends due to buoyancy or other factors and becomes unable to travel straight, and some gamma rays are absorbed by the hollow straight pipe, the hollow straight pipe will still emit it from the desired measurement location of the structure. Both gamma rays emitted from the circular light source and the light source emitted from the circular light source decrease at the same rate before reaching the gamma ray spectrum detector and projection plate at the other end, so the gamma ray counting results should be corrected based on this ratio. For example, even if the straightness of a hollow straight pipe cannot be achieved completely, the radioactivity of the structure can be measured with high accuracy. Furthermore, as long as a thin reflector is used and the material and thickness are known, gamma ray absorption correction can be performed, so there is no need to remove it during measurement.

[Effect of the invention] The present invention makes it possible to quantitatively measure the radioactivity concentration of underwater structures even if the straightness of straight pipes is impaired. It has now become possible to determine the radioactivity concentration of structures placed at deep locations. Moreover, since detection efficiency is also measured simultaneously for each measurement, measurement accuracy can be improved.

[Brief explanation of drawings]

FIG. 1 is a diagram showing the principle of a conventional quantitative radioactivity measurement method. Figure 2 is an example of measuring the radioactivity concentration of a structure located deep underwater using the conventional quantitative radioactivity measurement method. FIG. 3 is a diagram (embodiment) of the principle of the present invention. FIG. 4 is a principle diagram (embodiment) of the present invention. 14...Water, 15...Sealing plate, 16...Hollow straight pipe, 17...Tip part, 18...Same diameter as the straight pipe inner diameter,
19...Standard radiation source that is disc-shaped and has a uniform radioactivity distribution and emits gamma rays with energy different from the radioactivity to be measured, 20...Measurement location of a structure where a hollow straight pipe is desired, 21...Gamma ray spectrum detection vessel, 2
2...Geometric conditions when gamma rays emitted from the disc-shaped source enter the gamma-ray detector, 23...Hollow straight tube, 24...Sealing plate, 25...Disc-shaped light source, 26...Reflector plate , 27... Projection plate, 28... Gamma ray spectrum detector, 29... Measurement location of the structure where a hollow straight pipe is desired.

Claims (1)

[Claims] 1. A gamma ray collimator is configured by placing a hollow straight pipe whose tip is sealed with a plate close to the surface of a structure in water, using water as a shield, and directly directing gamma rays emitted from the structure. In the method of quantitatively measuring the radioactivity concentration of the structure by passing through the inside of the tube and measuring with a gamma ray spectrum detector placed at the other end, a straight tube is placed at the tip of a hollow straight tube whose tip is sealed with a plate. A standard radiation source that is disc-shaped with the same diameter as the inner diameter and has a uniform radioactivity distribution and emits gamma rays with energy different from the radioactivity to be measured is attached, and the gamma rays emitted from the standard radiation source and the hollow straight tube are attached. The gamma rays emitted from the desired measurement point of the structure are simultaneously measured by a gamma ray spectrum detector placed at the other end of the hollow straight tube, and from the measurement results of the gamma rays emitted from the disc-shaped standard radiation source. Quantitative measurement of radioactivity in underwater structures to determine the radioactivity concentration at the measurement point by calibrating the measurement results of gamma rays emitted from the measurement point of the structure using a hollow straight pipe based on the obtained detection efficiency curve. Law. 2. A gamma ray collimator is constructed by placing a hollow straight pipe whose tip is sealed with a plate close to the surface of an underwater structure, using water as a shield, and allowing the gamma rays emitted from the structure to pass through the inside of the straight pipe. In the method of quantitatively measuring the radioactivity concentration of the structure by measuring with a gamma ray spectrum detector placed at the end, a tube with the same diameter as the inner diameter of the straight pipe is placed inside the tip of a hollow straight pipe whose tip is sealed with a plate. A disc-shaped light source is placed, and the shape of this disc-shaped light source is projected using a reflection plate and a projection plate placed just in front of the gamma ray spectrum detector at the other end, and the time when all the light sources are visible is used as a reference. , find the percentage of the projected area that decreases due to bending of the hollow straight pipe, and based on this percentage, calculate the amount of light emitted from the desired measurement point of the structure by the hollow straight pipe measured by the gamma ray spectrum detector. A method for quantifying radioactivity in underwater structures that corrects the gamma ray counting results and makes it possible to quantify the radioactivity concentration in structures even when the gamma rays emitted from the structure cannot be measured completely due to hollow straight pipes bending underwater.