JPH0513472B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to a radioactive contamination detection device, and particularly to a device for detecting weak radioactivity on the surface of a sample.

In the nuclear industry or in fields that handle radioactive materials, great care is taken to prevent radioactive contamination. For example, when equipment or items used for processing, molding, or handling radioactive materials are to be taken outside or disposed of, the surfaces of these equipment or items should be It is necessary to confirm that the radioactive concentration of the substance is below the management standards established based on the ``Act on Prevention of Radiation Hazards Due to Radioactive Isotopes, etc.''

[Prior Art] FIG. 1 shows a schematic configuration of a conventional radioactive contamination detection device, in which an α-ray survey meter detector 12 is arranged facing a sample 10, and the radioactive concentration on the sample surface, the first In the apparatus shown in the figure, the α-ray concentration is detected by the α-ray survey meter detector 12.

The α-ray survey meter detector 12 includes a second
As shown in the figure, a light shielding film 14 for shielding external light is provided on the radiation incident surface, and this light shielding film 14
A scintillator plate 16 is disposed near the. A photomultiplier tube 18 is provided at the rear of the scintillator plate 16, and the radiation intensity is converted into an electrical signal by the photomultiplier tube 18, and further the desired signal processing is performed by the bleeder circuit 20. , the radioactivity concentration is displayed in a radiation measuring section (not shown).

However, this type of device has a drawback in that it cannot detect the weak radiation from the sample 10 with high precision.

That is, when the sample 10 has an uneven shape as shown in the figure, there is a problem that radiation emitted from the recesses cannot be reliably detected.

That is, the range of α-rays is 3 to 4 cm, and therefore it is extremely difficult to set the distance from the concave surface of the sample 10 to the scintillator surface of the α-ray survey meter detector 12 within the range of the radiation. Therefore, although it is possible to detect radiation from the convex surface of the sample 10, it is difficult to detect radiation from the concave surface of the sample 10. Therefore, it is difficult to accurately measure the amount of radiation emitted from the entire surface of the sample 10. The disadvantage was that it could not be detected.

Purpose of the Invention The present invention has been made in view of the above-mentioned conventional problems, and its purpose is to detect radioactive contamination that can detect radiation emitted from the surface of a sample with high accuracy even in an uneven sample. The goal is to provide equipment.

[Structure of the Invention] In order to achieve the above object, the present invention provides a vacuum container in which a sample mounting stage is provided, a photomultiplier tube fixedly arranged on the wall of the vacuum container, and a photomultiplier tube. It is characterized in that it includes a scintillator plate placed between samples and fixed to a vacuum container, and radioactive contamination on the sample surface is detected in a vacuum atmosphere.

[Example] FIG. 3 shows the configuration of a radioactive contamination detection device according to the present invention, and the same members as those in the conventional device are denoted by the same reference numerals, and the explanation thereof will be omitted. A feature of the present invention is that the radiation intensity from the sample surface is detected in a vacuum atmosphere.

That is, the present invention focuses on the fact that the range of radiation from the sample surface increases as the degree of vacuum increases, as shown in FIG. The system is configured to detect the amount of radioactive contamination at the site.

For example, in FIG. 4, the range of 5 Me V alpha rays is about 3.5 cm in the atmosphere, but by setting the degree of vacuum to about 26 mmHg, the range is increased to 100 cm. Therefore, by increasing the degree of vacuum in this manner, the range of the radiation can be increased, and it becomes possible to reliably capture the radiation emitted from the sample surface.

In this embodiment, a plurality of photomultiplier tubes 18 are arranged on the wall surface of the vacuum container 21 in a dotted manner. A sample mounting table 22 is provided inside the vacuum container 21, and the sample 10 is placed on this sample mounting table 22. Then, sample 10 and photomultiplier tube 1
A scintillator plate 16 is disposed between 8 and 8. On the other hand, the vacuum container 21 is provided with an exhaust pipe 23, and by driving the vacuum pump 24, it is possible to create a vacuum atmosphere inside the vacuum container.

In this example, by creating a vacuum atmosphere inside the vacuum container 21, it is possible to increase the range of the radiation from the sample 10, and therefore, the radiation emitted from the recessed portion of the sample 10 can be reduced. It becomes possible to detect with high precision.

In addition, in this embodiment, the very weak radiation of the sample 10 is detected with the inside of the vacuum container 21 in a vacuum atmosphere, so the amount of radon in the vacuum container can be reduced, so there is no back-up during measurement. This has the advantage that the ground can be reduced and, as a result, detection sensitivity can be improved.

Furthermore, in this embodiment, as described above, as a result of disposing a plurality of photomultiplier tubes 18 over almost the entire circumference of the wall surface of the vacuum container 21, it is possible to direct the uneven surface of the sample 10 in either direction. Even sample 10
It is possible to detect weak radiation with high precision. Also, so-called 4π measurement of the sample becomes possible.

The radiation intensity of this sample 10 is
By processing the electrical signals from 8, it becomes possible to display them on a display section (not shown). In this embodiment, as shown in the figure, blocks are divided into groups (A to D) of photomultiplier tubes arranged on each wall of the vacuum vessel 21, and the electric signals from the photomultiplier tubes 18 of each block are divided into blocks. As shown in FIG. 5, the signal is guided to a signal processing circuit 26, and a desired signal operation is performed by this signal processing circuit 26. For example, it is possible to extract a detection signal for each block from the signal processing circuit 26, and it is also possible to extract the signal sum of one block and the other block. In some cases, it is also possible to extract signals from each photomultiplier tube constituting each block. Therefore, by such signal calculation, the radiation intensity from the sample surface can be detected with high precision.

[Effects of the Invention] As described above, according to the present invention, it is possible to detect the radiation intensity emitted from the surface of the sample with high accuracy even when the sample has an uneven shape.

[Brief explanation of the drawing]

Fig. 1 is a schematic configuration diagram showing a conventional radioactive contamination detection device, Fig. 2 is a cross-sectional view of the α-ray survey meter detector of the device shown in Fig. 1, and Fig. 3 shows a radioactive contamination detection device according to the present invention. FIG. 4 is a characteristic diagram showing the range of radiation for each degree of vacuum, and FIG. 5 is a block diagram showing signal processing of the apparatus of the present invention. 10...Sample, 16...Scintillator plate, 18
...Photomultiplier tube, 21...Vacuum container, 22...
Sample mounting table.

Claims (1)

[Claims] 1. A vacuum container having a sample mounting stage provided therein;
It includes a photomultiplier tube fixedly placed on the wall of the vacuum container and a scintillator plate placed between the photomultiplier tube and the sample and fixed to the vacuum container, and radioactive contamination on the sample surface is detected in a vacuum atmosphere. A radioactive contamination detection device characterized by: 2. The radioactive contamination detection device according to claim 1, wherein a plurality of photomultiplier tubes are scattered over substantially the entire circumferential wall of the vacuum container.