JP2003329775A - Method for measuring concentration of radioactive nuclide such as radon and apparatus used therefor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To continuously and highly accurately measure the concentration of a radioactive nuclide by making the radioactive nuclide absorbed into a plastic scintillator and emit light by leaving the plastic scintillator in a liquid or a gas. <P>SOLUTION: A fluorescent substance PPO is dispersed in a plastic scintillator 1, and the scintillator 1 is brought into contact with the liquid or the gas. the radioactive nuclide Rn in the liquid or the gas is made to be absorbed in the plastic scintillator 1 by the contact. The fluorescent substance PPO is caused to emit light by radiation 2 emitted by the radioactive nuclide Rn in the plastic scintillator 1. Light 3 emitted by the nuclide Rn and transmitted through a surface 4 of the plastic scintillator 1 by the light emission is detected by an optical sensor 5 arranged opposed to the surface 4 in the method for measuring the concentration of the radioactive nuclide in the liquid or the gas. <P>COPYRIGHT: (C)2004,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for measuring the concentration of radionuclides in a liquid or a gas, which is typified by the radon concentration measurement used for observing changes in the earth's core, and an apparatus used for this method.

[0002]

2. Description of the Related Art In Japanese Patent Application Laid-Open No. 2001-21652, the applicant has set a solid polymer substance such as a polystyrene block in a liquid or a gas for a certain period of time to absorb a radionuclide, and the polystyrene block having absorbed the radionuclide. Is dissolved in a solvent, and the concentration of the radionuclide in the liquid or gas is measured from the radiation count value of the solution.

[0003]

However, in the above-mentioned measuring method, the polystyrene block absorbing the radionuclide is immersed in a container containing a solvent to liquefy, and the liquid in which the radionuclide is dissolved is sealed in the container. Since the operation for applying the liquid scintillation detector is required and the so-called individual measurement is performed, continuous measurement is impossible, and in addition, measurement work of several steps is required.

[0004]

The present invention uses a plastic scintillator typified by a fluorescent substance-containing polystyrene scintillator, the plastic scintillator is kept in a liquid or gas, and the liquid or gas is contacted with the liquid or gas. The radionuclide therein is absorbed in the plastic scintillator, and the fluorescent substance is caused to emit light by the radiation emitted by the absorbed radionuclide in the plastic scintillator.

Then, the light transmitted through the surface of the plastic scintillator by the light emission is detected by an optical sensor arranged opposite to the surface to measure the concentration of the radionuclide in the liquid or gas.

Further, the apparatus used in the above measuring method comprises a plastic scintillator in which a fluorescent substance is dispersed in a container, and an inlet for introducing liquid or gas into the container and a liquid or gas from the container. And a liquid outlet in which the liquid or gas in the container is brought into contact with the plastic scintillator in the container so that the radionuclide in the liquid or gas is absorbed in the plastic scintillator, and the radionuclide is the plastic scintillator. The fluorescent substance is made to emit light by the radiation emitted therein.

On the other hand, an optical sensor facing the surface of the plastic scintillator is attached to the container, and light emitted from the plastic scintillator through the surface of the plastic scintillator is detected by the optical sensor.

The method and apparatus for measuring the concentration of a radionuclide in a liquid or a gas described above is such that a plastic scintillator capable of absorbing a radionuclide is left in a liquid or a gas, and the radionuclide is absorbed into the scintillator to emit light. The radionuclide concentration measurement can be continuously and accurately performed without any operation such as liquefaction of the fluorescent substance-containing plastic scintillator.

[0009]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described below with reference to FIGS.

As the radionuclide absorber, a plastic scintillator 1 in which a fluorescent substance PPO is dispersed, as shown in FIGS. 1 and 2, is used. The plastic scintillator 1 is transparent, that is, transparent.

As the plastic forming the above-mentioned radionuclide absorber, polystyrene, which is rich in the absorption of radionuclides and excellent in radiation energy transfer, is effective.
In addition, polyvinyl resins such as polymethylmethacrylate, polyethylene and polypropylene can be used.

The plastic scintillator is preferably a thin film. That is, the thin film is a radionuclide Rn represented by radon.
Absorbs rapidly and quickly forms an equilibrium state. In addition to the thin film, a plate, a block having an arbitrary shape, or the like can be used.

The above absorption means that the radionuclide Rn is taken into the tissue of the plastic scintillator 1,
Does not include adsorption that adheres to the material surface.

The plastic scintillator 1 is kept in a liquid or a gas, and the radionuclide in the liquid or the gas is absorbed into the plastic scintillator 1 by contact with the liquid or the gas, and the radionuclide is the plastic scintillator 1. The fluorescent substance PPO is caused to emit light by the radiation emitted therein.

Amorphous plastics are highly absorbent,
It is effective as the plastic scintillator 1 used in the above measuring method and apparatus.

The above-mentioned mechanism of light emission will be described in detail. As shown in FIG. 3, the radionuclide Rn typified by radon absorbed in the plastic scintillator 1 emits radiation (α-ray, β-ray) 2 and the radiation is emitted. 2 is a plastic scintillator 1, especially a benzene group constituting polystyrene, which propagates energy and reaches the fluorescent substance PPO.

As a result, the fluorescent substance PPO converts radiation energy into light energy having excellent multidirectionality and reachability, and emits light. In addition, the benzene ring has a π-electron cloud and has extremely high energy transfer properties, and the plastic scintillator 1
Efficiently induces light emission inside.

The light 3 which is transmitted by the surface of the plastic scintillator 1 by the above-mentioned light emission and the surface 4 of the scintillator 1
A method of measuring the concentration of the radionuclide Rn in the liquid or gas by detecting it with an optical sensor 5 arranged opposite to The photosensor 5 is a known photomultiplier tube or the like.

FIG. 4 shows an apparatus used in the method for measuring the concentration of radionuclide in the liquid or gas.

As shown in the figure, one or more plastic scintillators 1 such as polystyrene scintillator or the like in which the fluorescent substance PPO is dispersed are arranged in a container 6 having an airtight and light-shielding structure. . The plastic scintillator 1 is vertically installed in a container 6 so that its surface 4 is vertical.

For example, a plurality of plastic scintillators 1 are vertically installed in a container 6 such that their surfaces 4 are parallel to each other and perpendicular to each other.

Liquid or gas 10 is added to the container 6 into the container.
In addition to providing an inlet 7 for introducing the liquid, a lead-out port 8 for leading out the liquid or gas 10 from the container 6 is provided so that the container 6 is always filled with new liquid or gas 10.

The liquid or gas 10 in the container 6 is brought into contact with the plastic scintillator 1 in the container 6 so that the radionuclide Rn in the liquid or gas 10 is absorbed in the plastic scintillator 1, and the radionuclide Rn is The fluorescent substance PPO is caused to emit light by the radiation 2 emitted in the plastic scintillator 1.

The radon concentration in the plastic scintillator 1 is proportional to the concentration of 10 in liquid or gas. For example, if the concentration in water doubles, the concentration in the plastic scintillator 1 also doubles. Therefore, the concentration in the liquid can be known by measuring the light emission of the plastic scintillator 1 in the equilibrium state.

An optical sensor 5 facing the surface 4 of the plastic scintillator 1 is attached to the container 6, and the light 3 transmitted through the surface 4 of the plastic scintillator 1 by the light emission is received by a light transmitting window 9 of the optical sensor 5. And detect. The transparent window 9 is always in contact with the liquid or gas.

The fluorescent substance PPO emits pulsed light in proportion to the number of molecules of the radionuclide Rn, and the number of times this light 3 is generated (the number of pulses) is detected by the optical sensor 5 to measure the concentration.

The liquid or gas inlet port 7 is provided near the bottom of the container 6, for example, the bottom plate, and the outlet port 8 is provided near the upper part of the container 6, for example, the top plate, and the liquid or gas is transferred from the bottom to the top of the container 6. To flow upward along the surface 4 of the plastic scintillator 1, while the optical sensor 5 is attached to the side plate of the container 6 so that its light receiving axis is orthogonal to the surface 4 of the plastic scintillator 1. Deploy.

Radon in water is distributed in the plastic scintillator 1 at a constant ratio according to the kinetic energy it holds. Since this distribution coefficient is a variable that depends only on temperature, radon that is directly proportional to the concentration in water will be distributed in the plastic scintillator 1 under constant temperature conditions, and there is a linear relationship between the measured value and the concentration of radon water. Is recognized.

[0029]

According to the present invention, any operation such as the liquefaction operation as in the above-mentioned conventional example is carried out by absorbing the radionuclide into the scintillator while allowing the plastic scintillator to remain in the liquid or gas to emit light. Without this, the radionuclide concentration can be measured continuously and with high accuracy. In addition, the measurement operation or device is simple, and the measurement can be performed at low cost.

The present invention is effective for the radon measurement used for the observation of earth movement (earthquake prediction).

[Brief description of drawings]

FIG. 1 is a plan view of a thin film fluorescent substance-containing plastic scintillator that constitutes a radionuclide absorber.

FIG. 2 is an enlarged sectional view of the same portion.

FIG. 3 is an enlarged cross-sectional view of a scintillator having a benzene ring for explaining a light emitting mechanism in the plastic scintillator.

FIG. 4 is a vertical sectional view of the radionuclide concentration measuring device.

[Explanation of symbols]

1 ... plastic scintillator, 2 ... radiation, 3 ... light,
4 ... Surface of plastic scintillator, 5 ... Optical sensor,
6 ... Container of airtight light shielding structure, 7 ... Inlet for introducing liquid or gas,
8 ... Liquid or gas outlet, 9 ... Transparent window, 10 ... Liquid or gas, PPO ... Fluorescent substance, Rn ... Radionuclide represented by radon

Claims (3)

[Claims] 1. A plastic scintillator in which a fluorescent substance is dispersed is brought into contact with a liquid or gas, and the radionuclide in the liquid or gas is absorbed in the plastic scintillator by the contact, and the radionuclide is emitted in the plastic scintillator. A method for measuring the concentration of a radionuclide such as radon, which is characterized in that the fluorescent substance is caused to emit light by radiation, and the light transmitted through the surface of the plastic scintillator by the emitted light is detected by an optical sensor arranged opposite to the surface. 2. The method for measuring the concentration of radionuclide such as radon according to claim 1, wherein the plastic scintillator in which the fluorescent substance is dispersed is polystyrene. 3. A plastic scintillator in which a fluorescent substance is dispersed is arranged in a container, and an inlet for introducing liquid or gas into the container and an outlet for discharging liquid or gas from the container are provided in the container. Provided, the liquid or gas in the container is brought into contact with the plastic scintillator in the container, and the radionuclide in the liquid or gas is absorbed in the plastic scintillator by the contact, and the radioactive nuclide emits in the plastic scintillator. The fluorescent substance is caused to emit light by the other, while an optical sensor facing the surface of the plastic scintillator is attached to the container,
A device for measuring the concentration of a radionuclide such as radon, characterized in that the light sensor detects light transmitted through the surface of the plastic scintillator by the light emission.