JPH10186036A - Radon concentration measuring method and its device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To easily evaluate a radon concentration in the living environment by applying a voltage to a conductive thin film, detecting the α-rays from the daughter nuclide of radon collected on the thin film with a radiation detector, and measuring the radon concentration. SOLUTION: A conductive collecting electrode made of a thin film is arranged adjacently to a radiation detector, and a negative high voltage is applied to it. Since most of the daughter nuclide generated when radon in the air collapses has positive charges, it can be electrically collected. The collecting electrode, i.e., an extremely thin aluminum-deposited Mylar film, applied with a high voltage is arranged at a slight distance from the radiation detector to collect the daughter nuclide, and α-rays are emitted from the collected daughter nuclide. The radiation detector detecting the α-rays is arranged adjacently to the collecting electrode at the minimum distance that the high voltage gives no adverse effect to the radiation detector. The structure of this device is simple and more practical, and the cost can be reduced.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a radiation measuring device, and more particularly to a device for measuring the concentration of radon, which is radioactivity in the environment.

[0002]

BACKGROUND OF THE INVENTION The human body is constantly exposed to radiation (radiation) present in the natural environment. Natural radiation includes cosmic rays and γ-rays from the ground. Among them, Rn-222 (Radon) and α-rays emitted from its daughter nuclides give the greatest exposure to the human body. It is.

[0003] The United Nations Scientific Committee recognizes that UNSCEAR;
diation: Sources and Biological Effects, UNSCEAR Rep
According to a report by t. United Nations, New York (1982), more than half of radiation exposure from natural radiation was attributed to radon and its daughter nuclides, and it was speculated that internal exposure to these was one of the causes of lung cancer. I have.

[0004] On the other hand, it has been reported that the concentration of radon in groundwater changes before a major earthquake. Igarashi et al. “Ground
-water radon anomaly before the Kobe earthquake in
Japan ", Science, Vol. 269, No. 7, 60-, 1995, reported that the radon concentration, which had been continuously measured in Nishinomiya wells immediately before the Great Hanshin-Awaji Earthquake, increased significantly. As described above, the measurement of the radon concentration is important, but there is no simple method for measuring the radon concentration in real time with high sensitivity, so that only limited data on the radon concentration in the environment has been obtained.

As a method for measuring radon, a vented ionization chamber is most often used. However, this method cannot detect α-rays from radon and daughter nuclides as a pulse, so that energy discrimination cannot be performed, and there is a problem in accuracy due to the influence of γ-ray and β-ray background in the environment. Also, the sensitivity is low.
A scintillation cell method in which a scintillator is applied to the inner surface of a container and α-rays from radon and radon daughter nuclides are detected by a photomultiplier tube may be used. However, in this method, powdery ZnS (Ag) must be used for the scintillator, and energy discrimination cannot be performed. In addition, the device becomes quite large and lacks convenience. There are activated carbon method, liquid syn method and the like, but they are not simple. There are still methods such as the cup method, but there are problems that the sensitivity is low or that real-time measurement cannot be performed.

SUMMARY OF THE INVENTION An object of the present invention is to develop a simple apparatus for measuring the concentration of radon in the air with high sensitivity in real time so that the concentration of radon in the living environment can be easily evaluated. It is another object of the present invention to make it possible to know temporal and spatial changes in radon concentration, reduce internal exposure to radon and daughter nuclides, and provide information on earthquake prediction.

[0007]

A voltage is applied to a conductive thin film, and the radon concentration is detected by detecting an α-ray from a radon daughter nuclide collected in the thin film by an electric field collecting action with a radiation detector. The present invention relates to a method for measuring a radon concentration, which is characterized by measuring.

A conductive thin film; a high-voltage device for applying a voltage to the thin film; and a radiation detector for detecting α-rays from radon daughter nuclides collected in the thin film by an electric field collecting action. The present invention relates to a radon concentration measuring device comprising:

In addition, a conductive thin film is provided as an electric field collecting electrode in the container, and a high voltage device for applying a negative high voltage is provided on the thin film, and the thin film is collected by the electric field collecting action. 3. A radon concentration measuring apparatus according to claim 2, wherein a radiation detector for detecting α-rays from daughter nuclides of radon is arranged close to said thin film.

The radiation detector is disposed on both sides of the thin film.
The present invention relates to the radon concentration measuring device described in the paragraph.

The radon concentration measuring apparatus according to any one of claims 2 to 4, wherein a high voltage applied to said radiation detector itself is used for collecting radon daughter nuclides. is there.

[0012]

BEST MODE FOR CARRYING OUT THE INVENTION In the radon concentration measuring apparatus of the present invention, a conductive electrode having an electric field collecting action made of a thin film is disposed adjacent to a radiation detector capable of discriminating energy, and a negative high voltage is applied.

Many of the daughter nuclides produced by the decay of radon in the air have positive charges, so that they can be collected electrically. Since the thin film is extremely thin, it is possible to detect α rays from not only the daughter nuclides collected on the back of the film but also various daughters collected on the front.

FIG. 1 shows an embodiment of the present invention. The device consists of a collecting electrode, a radiation detector, a high voltage, and an electronic circuit in a container. The container has an entrance window to allow air to enter the container through a filter. This is because in order to measure the radon concentration per unit volume, it is necessary to allow only radon, which is an inert gas, to enter the container.

Radon in the container decays into a radon daughter nuclide with a half life of 3.8 days. Since the daughter nuclide is positively charged, it can be electrically collected by applying an electric field. In the present invention, while keeping a little distance from the detector, a conductive electrode for collecting an electric field made of a thin film to which a high voltage is applied, that is, an extremely thin aluminum-deposited Mylar film is arranged, and this daughter nuclide is collected. I have. Α-rays are emitted from the daughter nuclides collected on this electrode, but because the aluminum-deposited Mylar film is extremely thin, not only from the daughter nuclides collected on the back of the film but also from those collected on the table α rays can be detected. As the radiation detector, for example, a silicon semiconductor detector or a plastic scintillation detector capable of energy discrimination is used. These radiation detectors are placed adjacent to the collection electrode, but the distance is such that the high voltage does not adversely affect the detector. The output of the radiation detector is subjected to energy discrimination by a single channel analyzer (SCA) to reduce the influence of background noise, and a counter is used to obtain an integrated count for a certain period of time, and the radon concentration is calculated from the obtained value. These calculations can be performed by sending the value of the counter to the microprocessor.

Further, in order to improve the sensitivity, a plurality of radiation detectors can be arranged so that the thin film can be seen from both sides. In this case, since the α-rays emitted to both sides are measured, the sensitivity can be doubled.

To increase the sensitivity, it is possible to increase the amount of air sent into the container by adding a fan. Further, if the filter is removed, the accuracy of the radon concentration is reduced, but it is needless to say that various charged components of the radon daughter in the air can be collected and the sensitivity can be further increased.

Further, the photomultiplier tube used for the scintillation detector can be used by applying a negative high voltage to its detection surface, so that a new embodiment becomes possible. This second embodiment is shown in FIG.

The detector of this embodiment has a structure in which a thin film scintillator is optically coupled to a photomultiplier tube. Here, when the photomultiplier is used at a negative high voltage, a negative high voltage is applied to the photoelectric surface on the back side of the glass surface to which the thin film scintillator is optically coupled. This negative high voltage works in the same manner as the high voltage applied to the conductive thin film, and allows the radon daughter nuclide to be collected on the thin film scintillator by forming an electric field. Α from collected radon daughter nuclides
The lines are converted to light by a thin film scintillator and converted to electrical signals by a photomultiplier tube.

According to this embodiment, it is possible to collect radon daughter nuclides without using a conductive thin film. Since the structure of the device is simplified, cost reduction and reliability improvement are achieved, and the device becomes more practical.

[0020]

According to the present invention, high-sensitivity radon measurement can be realized by collecting an electric field. Further, since the energy information of the α-ray from the collection electrode can be used, it is hardly affected by the background noise and the accuracy can be increased. Furthermore, since the configuration is simple, the cost is low, and miniaturization is possible, mass production can be performed as a portable device. These features make it possible to measure radon concentration at multiple points in real time,
It is possible to reduce internal exposure due to natural radioactivity and to provide information on earthquake prediction.

[Brief description of the drawings]

FIG. 1 is a schematic structural explanatory view of the present embodiment.

FIG. 2 is a schematic structural explanatory view of a second embodiment.

Claims (5)

[Claims] 1. A method for measuring a radon concentration by applying a voltage to a conductive thin film and detecting an α-ray from a daughter nuclide of radon collected by the thin film by an electric field collecting action with a radiation detector. Characteristic radon concentration measurement method. 2. A conductive thin film, a high-voltage device for applying a voltage to the thin film, and a radiation detector for detecting α-rays from radon daughter nuclides collected in the thin film by an electric field collecting action. Radon concentration measuring device. 3. A conductive thin film as an electric field collecting electrode is disposed in a container, and a high voltage device for applying a negative high voltage to the thin film is provided. The thin film is collected by an electric field collecting action. 3. The radon concentration measuring device according to claim 2, wherein a radiation detector for detecting α-rays from daughter nuclides of radon is arranged in close proximity to said thin film. 4. The radon concentration measuring device according to claim 2, wherein said radiation detector is arranged on both sides of said thin film. 5. The radon concentration measuring apparatus according to claim 2, wherein a high voltage applied to said radiation detector itself is used for collecting radon daughter nuclides.