JP3534456B2 - Radiation measurement device - Google Patents

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 radon thoron.

[0002]

2. Description of the Related Art Radon ( ²²² R) which is a radioisotope
n: atomic number 86) and thoron ( ²²⁰ Tn: atomic number 8)
6) exists as a gas in the air. Therefore, it is necessary to pay attention to the internal radiation exposure.

In recent years, radon and thoron as environmental radiation emitted from concrete walls have been regarded as a problem, and it is necessary to measure radon and thoron not only in radiation handling facilities but also in general building rooms and basements. It is rising.

FIG. 5 shows the radon decay series (A) and the thoron decay series (B). Only the leftmost radon and thoron are gases, and their daughters are solids. As will be described later, those daughter nuclides other than radon and thoron emit α rays or β rays, and the nuclides that emit α rays are positively charged.

FIG. 4 shows an example of a conventional Radon-Tron measuring device. In the figure, the sample gas (gas to be measured) is first sent to the dust filter 10 to remove large foreign matters such as dust. Next, in the ion precipitator 12, the ions contained in the sample gas are removed using the electric field. This is the next ionization chamber 1
4 is provided to prevent the ionization current due to unnecessary ions from being measured. This resulted in the removal of radon daughters and thoron daughters.

In the ionization chamber 14, the gas in the ionization chamber 14 is ionized by α rays emitted when radon or thoron is collapsed, and the ionization charge generated at this time is collected by the central electrode 14a. To be collected. The resulting output signal from the ionization chamber 14 is sent to the oscillating capacitance electrometer 18 via the oscillating capacitance electrometer head 16 to display the Radon-Tron concentration. A flow meter 20 and a pump 22 are connected to the ionization chamber 14.

[0007]

However, in the above-mentioned conventional apparatus, radon and thoron cannot be separately measured. Moreover, in the above-mentioned conventional apparatus, since the radon daughter nuclide and the thoron daughter nuclide are removed by the ion precipitator 12, it is not possible to measure these nuclides. It is desired to improve the measurement sensitivity of Radon-Tron.

The present invention has been made in view of the above conventional problems, and an object of the present invention is to separately measure radon and thoron.

Another object of the present invention is to realize the measurement of radon daughters and thoron daughters.

A further object of the present invention is to improve measurement sensitivity.

[0011]

In order to achieve the above object, the invention according to claim 1 provides a gas introducing chamber into which a gas to be measured is introduced, and a first α on one side of the gas introducing chamber. A first ionization chamber which is arranged so as to desire a ray incidence window, a second ionization chamber which is arranged so as to desire a second α-ray incidence window on the other side of the gas introduction chamber, and the gas introduction chamber At a first electrode arranged close to the first α-ray entrance window, and in the gas introducing chamber facing the first electrode and close to the second α-ray entrance window. A disposed second electrode, and a voltage applying means for applying a voltage between the first electrode and the second electrode with a polarity that collects the radon daughter nuclide and the thoron daughter nuclide on the first electrode. And detecting radon and its daughter nuclide and thoron and its daughter nuclide in the first ionization chamber. , And performs the detection of radon and thoron in the second ionization chamber.

[0012]

According to a second aspect of the present invention, the output from the first ionization chamber and the output from the second ionization chamber are used,
It is characterized by having a signal processing unit for obtaining the Radon count value and the Tron count value.

[0014]

According to the structure described in claim 1, when the gas to be measured is introduced into the gas introducing chamber, the charged nuclide is attracted to and collected by the first electrode by the action of the electric field. Since the first electrode is arranged close to the first radiation entrance window,
Radiation from the nuclide captured by the first electrode efficiently enters the radiation entrance window and is detected by the first radiation detector. That is, the detection efficiency of the charged nuclide can be increased by the pair of electrodes. The non-charged nuclides are uniformly dispersed in the gas introduction chamber, and thus are detected by both the first radiation detector and the second radiation detector.

That is, when the gas to be measured is introduced into the gas introducing chamber, the radon daughter nuclide and the thoron daughter nuclide, which are charged nuclides, are attracted to and collected by the first electrode and detected by the first ionization chamber. To be done. Radon and thoron will be detected in both the first and second ionization chambers without being affected by the electric field. That is, in the first ionization chamber, radon and its daughter nuclides and thoron and its daughter nuclides are all detected, while in the second ionization chamber, only radon and thoron are detected.

[0016] Thus, the signal processing unit according to claim 2, determining the radon count and thoron count from the output of the two ionization chamber.

[0017]

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 the overall construction of a radiation measuring apparatus according to the present invention. The radiation measuring apparatus in this embodiment is a Radon-Tron measuring apparatus.

This radiation measuring apparatus comprises a detector 24 and a signal processor 26. The detection unit 24 is roughly divided into
Measuring container 28 formed of an insulating member and forming a gas introduction chamber
And an ionization chamber 30 formed on one side surface of the measurement container 28.
And an ionization chamber 32 formed on the other side surface of the measurement container 28.
It consists of and.

In the metal shell 34 of the ionization chamber 30, 2
Linear collector electrode 4 supported by two insulating members 36 and 38
0 is arranged parallel to the α-ray incident window 42. The α-ray incident window 42 is made of an extremely thin member such as mica, and its inner surface is coated with a conductive coating. This conductive coating and shell 34
The outer electrode is constituted by and the outer electrode and the collecting electrode 4
Between 0 and the high voltage (for example,
500 V) is applied.

The ionization chamber 32 has the same structure as that of the ionization chamber 30, and the same members as the components of the ionization chamber 30 are numbered with 100 added, and the description thereof is omitted.

As is apparent from the above description, the α-ray incident windows 42 and 142 are provided inside the measurement container 28 so as to face each other so as to partially configure the measurement container 28. Then, in the measurement container 28, the α-ray incident window 42
A planar electrode 44 is arranged in the vicinity of the
On the other hand, in the vicinity of the α-ray incident window 142, a planar electrode 46 is arranged in parallel with it. Distance between both electrodes (strictly speaking, distance between the electrode 44 and the α-ray incident window 142)
Is 5 cm, considering that the range of α rays is about 5 cm
That is all. As described later, as long as the α-rays from the charged nuclide captured by the electrode 44 are not incident on the α-ray entrance window 142, the α-rays from the uncharged nuclide dispersed in the measurement container 28 are separated into the ionization chambers 30, 32. Therefore, in order to detect as efficiently as possible, the above distance should not be too large.

A high voltage (for example, 1000 to 2000 V) is applied between the electrodes 44 and 46 by the power source 48 so that the electrode 44 is the negative electrode and the electrode 46 is the positive electrode, and an electric field is formed between the both electrodes. ing.

As shown in FIG. 2, it is preferable that a dust filter 48 is provided in the front stage of the detection unit 24 and a pump that forms a gas flow as close to natural convection as possible is disposed in the rear stage. In the present embodiment, even if unwanted ions enter the measurement container, they will not be detected unless they emit α rays, so that the conventional ion precipitator is not necessary.

Next, the operation of the detector 24 and the signal processor 26 will be described.

When the gas to be measured is introduced into the measuring container 28, the positively charged radon daughter nuclide and thoron daughter nuclide are attracted to the electrode 44 and collected. On the other hand, the parent nuclides, radon and thoron, are uniformly dispersed in the measurement container 28.

In the ionization chamber 30, the α rays from the radon daughter nuclide and the thoron daughter nuclide captured by the electrode 44 are detected.
In addition, α rays from radon and thoron floating in the measurement container 28 are detected. Considering the range of α rays, it is difficult to detect α rays from radon and thoron existing near the electrode 46 side in the ionization chamber 30, but α rays from those nuclides are detected in the ionization chamber 32. it can.

Here, the operation of the ionization chamber 30 will be described as a representative. The α-rays that have passed through the α-ray incident window 42 are ionized chambers 3.
0 atmosphere of 1 atmosphere of atmospheric air or an inert gas such as argon is ionized, and the charge generated at that time is collected by the collecting electrode 40. As a result, the detection pulse is output to the outside.

As described above, in the ionization chamber 30, radon and its daughter nuclide and thoron and its daughter nuclide are detected,
On the other hand, in the ionization chamber 32, only radon and thoron will be detected. Radon and thoron daughter nuclides are collected at the electrodes, so that their detection sensitivity is enhanced. Radon and thoron are detected from both one side and the other side, so that their detection sensitivity is enhanced.

The detection pulse output from the ionization chamber 30 is
After being amplified by the preamplifier 52 and the amplifier 54 of the signal processing unit 26, it is input to the counting circuit 56 through a waveform shaping circuit and a wave height discrimination circuit (not shown). Counting circuit 56
Counts the detection pulses and outputs the count value. This count value shows the counting results of radon and its daughter nuclide and thoron and its daughter nuclide, but the detection efficiency of radon and thoron is lower than the detection efficiency of the daughter nuclide detected by electrode collection, As will be described later, in the next adding circuit 66, the counted values of radon and thoron detected on the opposite side are added.

The detection pulse output from the ionization chamber 32 is
After being amplified by the preamplifier 60 and the amplifier 62 of the signal processing unit 26, it is input to the counting circuit 64 through a waveform shaping circuit and a wave height discrimination circuit (not shown). Counting circuit 64
Counts the detection pulses and outputs the count value. This count value indicates the count value of radon and thoron only.

In the adder circuit 66, the outputs of the counting circuit 64 and the counting circuit 56 are added while performing predetermined weighting, respectively, so that the count values of the radon and its daughter nuclide and the thoron and its daughter nuclide, that is, the total sum. Numerical values can be obtained accurately. Input of the counting circuit 64
The force and the input of the counting circuit 56 are combined and input to a known delayed coincidence counting circuit 58. This delayed coincidence counting circuit 58
Is a circuit for obtaining the count value of only TRON. The half-life of ²¹⁶ Po generated from the thoron is extremely short at 0.15 seconds, so that the ²¹⁶ Po detection pulse is immediately followed by the tron detection pulse. Therefore,
Using that phenomenon, 2 within a certain period (for example, 1 second)
It detects the case where two pulses are continuous (detection of continuous pulse), and estimates the detection of the thoron when it is detected. Of course, stochastically, two pulses other than Tron- ²¹⁶ Po can be consecutively detected, but in a monitor of environmental radiation, the concentration of radon or the like is low, so the probability is low, and the influence on measurement accuracy is small. Therefore, the output of the delayed coincidence counting circuit 58 shows the count value of only TRON.

In the difference calculation circuit 68, by subtracting the output of the counting circuit 64 from the output of the counting circuit 56, the count value of only the daughter nuclide (Radon daughter nuclide + Tron daughter nuclide) can be obtained.
Further, in the difference calculation circuit 70, by subtracting the output of the counting circuit 58 from the output of the counting circuit 64, the count value of only Radon can be obtained.

Therefore, according to the signal processing unit 26, the total count value and the details thereof can be obtained in detail. Note that each count value is calculated while being corrected in consideration of detection efficiency and the like.

FIG. 3 shows a concrete example of the electrodes 44 and 46. The electrodes 44 and 46 may be formed in an extremely thin conductive film shape as shown in (A), or may have a parallel thin wire structure as shown in (B). Alternatively, the lattice thin line structure shown in (C) may be used. The electrode 44 is replaceable because the radionuclide attached to the electrode 44 accumulates and increases with time.

[0036]

As described above, according to the present invention,
Radon and thoron can be measured separately. Also,
It is possible to realize the measurement of radon daughters and thoron daughters. Furthermore, the measurement sensitivity can be improved, and the measurement can be performed in real time simply and economically.

[Brief description of drawings]

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

FIG. 2 is a diagram showing a structure for introducing and discharging a gas to be measured.

FIG. 3 is a diagram showing an example of a structure of an electrode.

FIG. 4 is a diagram showing a configuration of a conventional Radon-Tron monitor.

FIG. 5 is a diagram showing a Radon sequence and a Tron sequence.

[Explanation of symbols]

24 Detector 26 Signal processing unit 28 Measuring container 30, 32 ionization chamber 44,46 electrodes

Front Page Continuation (72) Inventor Takao Iida 1-63-32 Kitasenshi, Chikushi-ku, Nagoya, Aichi Prefecture 2-402 (56) References: 54-77898 (JP, U) (58) Survey Fields (Int.Cl. ⁷ , DB name) G01T 1/00-7/12

Claims (2)

(57) [Claims] 1. A gas introducing chamber into which a gas to be measured is introduced, a first ionization chamber arranged on one side of the gas introducing chamber so as to have a first α-ray incident window, and the gas. A second ionization chamber, which is arranged on the other side of the introduction chamber so as to have a second α-ray incidence window, and a first ionization chamber, which is arranged in the gas introduction chamber in proximity to the first α-ray incidence window. Electrode, a second electrode facing the first electrode in the gas introduction chamber, and arranged in proximity to the second α-ray entrance window; and a radon daughter nuclide in the first electrode. A voltage applying means for applying a voltage between the first electrode and the second electrode with a polarity for collecting the thoron daughter nuclide, and radon and its daughter nuclide and thoron in the first ionization chamber. And its daughter nuclide are detected, and radon and thoron are detected in the second ionization chamber. A characteristic radiation measuring device for radon and thoron measurement . 2. A device according to claim 1, using an output from the output and the second ionization chamber from the first ionization chamber, a signal processing unit for determining the radon count and thoron count Radon Tron characterized by
Radiation measuring device for measurement.