JPH06258443A - Radiation measuring equipment - Google Patents

Abstract

PURPOSE:To measure radioactive elements in a gas efficiently by providing an adsorptive substance in an ionization chamber. CONSTITUTION:Air is sucked into a dust filter 10 where relatively large dusts are removed. An ionization chamber 30 comprises an adsorptive substance 32 arranged on the inner surface thereat, a meshed electrode 33 arranged farther inside, and a current collecting electrode 34, wherein a high voltage is applied between the electrodes from a DC power supply 22. A pump 16 produces a negative pressure in the ionization chamber 30 and the air passed through the ionization chamber 30 is discharged to the outside by means of the pump 16. When atoms of the gas are ionized by alpha-rays emitted from radon, electrons are captured by the current collecting electrode 34 which feeds a current to a vibrating capacitor electrometer head 24 where the signal is amplified and further amplified by a charged current amplifier 36 before it is recorded in a recorder 28.

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 gas flow type ionization chamber.

[0002]

2. Description of the Related Art Radon and thoron are daughter nuclei of uranium and radium, which can exist as gases and are released from the earth to the atmosphere, and also from structures to indoor air.

Radon and thoron existing as gases (hereinafter referred to as radon) emit α rays of about 5 MeV.

Radon concentration in the air is usually 1 Bq / m.
It is about ³ . However, the concentration of radon varies greatly depending on the weather and location, and in some cases, it may exceed the limit concentration. For example, in a room close to a closed state, radon released from the wall accumulates in the indoor space. Radon (also thoron) has a relatively short half-life, and after a certain period of time (for example, 3 days), a saturated state is formed in the indoor space.

As described above, radon is present in the air we breathe and causes internal exposure to the body. Therefore, continuous monitoring of its concentration is significant. Although the range of α-rays is smaller than that of other β-rays, the ionization density is high, so it is necessary to be careful when ingesting radon from excessive breath.

FIG. 3 shows the configuration of a conventional radon measuring device. The gas (air) containing radon is dusted by the dust filter 10 and then ionized by the ion precipitator 12 to be introduced into the ionization chamber 14. The pump 16 is sucking gas, and the air passing through the ionization chamber 14 is discharged into the atmosphere.

Here, the ionization chamber 14 is composed of a metal electrode container 18 forming one electrode and a collector electrode 20 arranged at the center of the electrode container. A high voltage is applied between the electrode container 18 and the collecting electrode 20 by a DC power source 22, and the radioactive element emits radiation to ionize part of the gas, and ions and electrons are carried to the electrodes by the electric field. , Is taken out as a signal. Specifically, after being amplified by the vibration capacitance electrometer head 24, a signal is measured by, for example, the vibration capacitance electrometer 26, and the radon concentration and the like are recorded in the recorder 28.

[0008]

However, the above-mentioned conventional radiation detecting apparatus cannot accurately measure radon and the like. In the prior art, since a gas containing a radioactive element was simply passed through the ionization chamber, efficient radiation detection could not be performed.

The present invention has been made in view of the above conventional problems, and an object thereof is to provide an improved radiation measuring apparatus capable of efficiently measuring radioactive elements (particularly, radon) existing in a gas. is there.

[0010]

In order to achieve the above object, the present invention provides an ionization chamber in which a gas containing a radioactive substance flows, which is provided with an adsorbent substance which comes into contact with and adsorbs the radioactive substance. Characterize.

[0011]

According to the above construction, when a gas containing a radioactive substance is circulated in the ionization chamber, the radioactive substance is incorporated into the adsorbent which is arranged in the ionization chamber or constitutes the ionization chamber container itself. As a result, the radioactive substance concentration in the ionization chamber is increased, and it becomes possible to measure radiation with high sensitivity.

In particular, when radon (including thoron) is measured, since the radon accumulates in the ionization chamber container and more α rays are emitted, it is possible to increase the signal output from the ionization chamber. it can. As described above, the half-life of radon is relatively short, so if the gas flow rate is constant, the radon concentration in the ionization chamber will saturate after a certain period of time. Is desirable, and continuous measurement can be performed after the saturation.

[0013]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT A preferred embodiment of the present invention will be described below with reference to the drawings.

FIG. 1 shows a preferred embodiment of the radiation measuring apparatus according to the present invention. The device shown in FIG. 1 measures the concentration of radon (and thoron) contained in air.

In FIG. 1, the sucked air is introduced into a dust filter 10 to remove relatively large dust or the like. The ion precipitator shown in FIG. 3 and the like may be provided in the subsequent stage.

The ionization chamber 30 is composed of a container 40, an adsorbing substance 32 disposed on the inner surface thereof, a mesh electrode 33 disposed further inside thereof, and a collecting electrode 34, and a DC power source is provided between the electrodes. Applies a high voltage.

The pump 16 is for making the inside of the ionization chamber a negative pressure, and the air which has passed through the ionization chamber 30 is pump 1
It is discharged from 6 to the outside world.

In the ionization chamber 30, α emitted from the radon
When the gas atom is ionized by the line, the electron is captured by the collecting electrode 34 and becomes an electric current, which is sent to the oscillating capacitance electrometer head 24. Then, the signal is the vibration capacitance electrometer head 24.
After being amplified by, the current is further amplified by a current amplifier 36 which is a charge type amplifier, and the result is recorded in a recorder 28. Note that other methods can be applied to the signal processing.

FIG. 2 shows a specific structure of the ionization chamber 30. In this embodiment, a grounded metal container 4
The entire surface of the inner surface of the adsorbent 32 with the thickness of 1 mm
Are arranged. As the adsorbent, for example, activated carbon is used. Inside the adsorbing substance 32, a cage-shaped electrode 33 made of metal in this embodiment is arranged. When the adsorbing substance 32 is electrically conductive, the adsorbing substance 32 can also have a function as an electrode.

The reason why the container 40 is grounded is to absorb external noise, and the reason why the electrode 33 is provided inside the adsorbing substance 32 in the form of a mesh is that the container 40 is used as an electrode. This is because the trapping of ions can be prevented by the adsorbing substance inside, and according to the present embodiment,
The α-rays from inside the adsorbing substance 32 can be emitted into the ionization chamber without being largely prevented by the mesh electrode 33.

In FIG. 2, 50 is a lead for applying a DC voltage, and 52 and 54 are insulators.

FIG. 4 shows a modified example. In this modified example, a guard ring 70 is provided on the support portion of the collector electrode 34. Specifically, the ring-shaped insulating member 72,
74 is disposed between the container and the collecting electrode 34. Then, the guard ring 70 is grounded.

As a result, the collector electrode 34 and the guard ring 7 are
Since 0 has the same potential, a potential gradient is generated between the guard ring 70 and the container, while there is no potential gradient between the guard ring 70 and the collecting electrode 34, and as a result, leakage between them occurs. It is possible to prevent current and the like and improve the measurement accuracy. Therefore, the current type measurement can be performed in addition to the pulse type measurement.

Further, the ionization chamber 30 is provided with a gas inflow port 42 and a gas outflow port 44 to constitute a gas flow type ionization chamber for continuously measuring the radon contained in the room air.

Therefore, when air is circulated in the ionization chamber 30, a part of the radon contained in the air is taken into the adsorbent 32. For this reason, radon accumulates in the ionization chamber 30, and the detection sensitivity is increased by the integration effect.

The radon taken in by the adsorbent 32 is
After reaching a half-life in about 3.8 days and passing a certain amount of air per hour, and after a certain period (for example, 3 days), the decay rate including the daughter nuclide is almost saturated. Therefore, even if a constant concentration of radon is continuously incorporated into the adsorbent,
The amount of radiation does not continue to rise, but remains constant.
If the concentration changes in this state, the saturated state showing a constant value changes. Radon concentration is detected from this change.

[0027]

As described above, according to the present invention,
There is an effect that radioactive substances can be accumulated in the adsorbed substance to measure radiation with high sensitivity.

[Brief description of drawings]

FIG. 1 is an explanatory diagram showing an overall configuration of a radiation measuring apparatus according to the present invention.

FIG. 2 is a cross-sectional view showing a specific configuration of an ionization chamber.

FIG. 3 is an explanatory diagram showing a configuration of a conventional radiation measuring apparatus.

FIG. 4 is an explanatory diagram showing a guard ring 70.

[Explanation of symbols]

 30 Ionization chamber 32 Adsorbed substance 33 Electrode 34 Collection electrode

Claims (1)

[Claims] 1. A radiation measuring apparatus, which is an ionization chamber in which a gas containing a radioactive substance flows, and which includes an adsorbent that adsorbs the radioactive substance in contact with the gas.