JPH0553388B2 - - Google Patents

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention is an underground radon concentration measuring device, and in particular, a device for accurately measuring the radioactivity concentration of radon, which generates multiple daughter nuclides, by removing background influences. Related to underground radon concentration measuring device.

[Prior Art] In recent years, the concentration of radon in underground air has been frequently measured in order to obtain geophysical, geochemical, and geological data and to predict earthquakes.

FIG. 4 shows a conventional ventilation type underground radon concentration measuring device. Subterranean air is supplied to the detector 14 from a gas intake port 12 provided in the gas hole 10, and this supply is performed by controlling a pump 16. The detector 14 detects alpha rays emitted from the radon present in a predetermined amount of the supplied underground air, and this alpha ray dose is counted by the scaler 18 to finally determine the radon concentration. be measured.

In this way, the radon concentration present in the underground air is measured, and various measurements, especially earthquake prediction, can be performed based on this radon concentration.

[Problems to be Solved by the Invention] However, there is a problem in that radon decays into a plurality of daughter nuclides, and the radiation emitted from these daughter nuclides prevents accurate measurement of the radon concentration itself.

In other words, radon in the air is an inert gas and a radioactive substance that constantly decays with a half-life of 3,825 days. The decay sequence is shown below.

²²² Rnα ray――――――→ (3.825 days) ²¹⁸ Po (RaA) α ray――――――→ (3.05 minutes) ²¹⁴ Pb (RaB) B ray α ray――――――→ ( 26.8 minutes) ²¹⁴ Bi (RaC) B line α line――――――→ (19.7 minutes) ²¹⁴ Po (RaC′) α line――――――――――→ (0.00016 seconds) ²¹⁰ Pb (RaD) →…
… In this way, radon will eventually become a stable nuclide of lead.
It becomes 206Pb and becomes stable. Therefore, as is clear from this decay series, radon daughter nuclides are generated as radon decays, and various radiations are emitted from these radon daughter nuclides.

By the way, underground radon concentration measurement is generally performed using ZnS.
(Ag) This is performed using an α-ray detector coated with a scintillator, and as mentioned above, underground air is sampled and α-rays are measured from radon and its daughter nuclides contained in this underground air.

However, the radon α-ray intensity measured by the detector 14 has a characteristic that it reaches its maximum value after about 3 hours due to the growth of radon daughter nuclides. Also,
Radon daughter nuclides are 218Po, 214Pb, 214Bi, respectively.
It is a metal element such as 214Po, and after being distributed in the detector 14 in the form of an aerosol, it is deposited on the wall surface of the flow tube in the detector 14.

Therefore, in a device that continuously measures changes in radon concentration by ventilating underground air into the detector 14 at a constant flow rate, as described above, the radon decay sequence peculiar to the radon decay sequence deposited on the wall surface of the detector flow pipe is used. The background value increased due to the daughter nuclide with a long half-life, making it impossible to measure changes in radon concentration quickly and accurately.

In addition, thoron (Tn), an α-ray radioactive material, is present in underground rocks, and it is said that this thoron mixes into the collected underground air and affects the background value of radon concentration measurements. There was a problem.

Purpose of the Invention The present invention was made in view of the above-mentioned conventional problems, and its purpose is to eliminate the background that changes due to the influence of radon daughter nuclides or underground α-ray radioactive materials in the measurement of underground radon concentration. Therefore, it is an object of the present invention to provide an underground radon concentration measuring device that accurately measures underground radon concentration.

[Means for Solving the Problems] In order to achieve the above object, the present invention uses a detector to detect α in underground air supplied from an underground gas hole.
It has a measurement unit that detects the radiation and measures the radon concentration, and an air circulation mechanism that has a valve and a pump that introduces underground air (air) or fresh air (air) into the detector and exhausts it. Then, cleaning inside the detector flow pipe by circulating fresh air → background measurement → constant depressurization inside the detector flow pipe →
It is characterized in that the detector and the air circulation mechanism are controlled so that these operations are automatically performed for a predetermined time in the order of suction of a certain amount of underground air and measurement of radon concentration.

In addition, another invention includes a measuring unit that measures radon concentration by detecting alpha rays in underground air supplied from an underground gas hole by a detector, and introducing underground air or fresh air into the detector. an air circulation mechanism having a valve and a pump for evacuating the underground air, and a tank for containing the amount of underground air necessary for one measurement before supplying the underground air to the detector, Cleaning inside the detector flow pipe by fresh air circulation → Background measurement → Constant depressurization inside the detector flow pipe → Suction of a certain amount of underground air contained in the tank → Radon concentration measurement Each of these operations is performed for a predetermined period of time. The present invention is characterized in that the detector and the air circulation mechanism are controlled so as to be performed automatically.

[Operation] According to the above configuration, when the fresh air intake valve and the pump side valve are opened and the pump is operated, the fresh air is circulated in the detector flow pipe, and the radon daughter nuclides are absorbed by this fresh air. Cleaning is performed.

Then, by closing all valves and stopping the pump, background measurements are performed, and then by opening only the pump-side valve and operating the pump, a constant pressure reduction inside the detector flow pipe is performed. be exposed.

Next, when the underground air intake valve is opened, a certain amount of underground air is sucked in and sent to the detector. Then, all the valves are closed and the pump is also stopped, and the radon concentration is measured by the measurement unit detector.

In this case, the operations of the valves and pumps are automatically controlled, and the influence of changing background can be successfully removed by automatic cleaning of the detector flow pipe and measurement of the background. becomes.

In addition, in the case of other inventions, underground air is not directly fed into the detector, but is temporarily stored in a tank, and when the pressure inside the measuring instrument flow pipe is reduced to a constant pressure and the feed valve is opened. The underground air in the tank is fed into the detector, and new underground air is stored in the tank from the underground gas hole.

Therefore, while the thoron is stored in the tank, the thoron present in the underground air is attenuated and no longer affects the background.

[Example] Hereinafter, a preferred first example of the present invention will be described based on the drawings.

FIG. 1 shows a schematic configuration of the underground radon concentration measuring device according to the present invention, in which a measurement section 100 consisting of a detector 14 and a scaler 18, a pump 16, and an underground gas hole 10 are connected to an underground radon concentration measuring device. The arrangement of the flow pipes through which the water flows is the same as in the conventional device.

The characteristic feature of the present invention is that instead of continuously supplying underground air to one detector as in the past, fresh air is supplied into the detector and deposited on the wall of the detector flow pipe. The purpose is to clean the radon daughter nuclides, measure the background and radon concentration in this state, and automatically control the supply of underground air or fresh air.

Therefore, a control circuit 20 for automatically controlling the air circulation mechanism is provided, and the air circulation mechanism has a flexible air intake 22 and a circulation pipe from the flexible air intake 22 to the detector 14, and The configuration includes a valve A in a distribution pipe for supplying underground air, a valve B in a distribution pipe for supplying fresh air, and a valve C provided between the detector 14 and the pump 16. Note that a vacuum gauge 24 is provided between the detector 14 and the pump 16 to measure the reduced pressure inside the flow pipe.

In addition, a characteristic feature of other inventions is that the influence of α-ray radioactive substances present in underground rocks, in this case thoron, on the background value has been removed, and this means that the radioactivity of thoron is attenuated. This is done by waiting until the sample is detected and then supplying the sample into the detector 14.

Therefore, in the present invention, the tank 26 that accommodates the amount of underground air necessary for one measurement is connected to the underground air intake port 1.
2 and the valve A.

The present invention and other inventions consist of the above-mentioned configuration, and the operation thereof will be explained based on FIG. 3.

The underground radon concentration measuring device repeatedly feeds underground air into the detector 14 and continuously measures the radon concentration. As shown, one cycle is performed by a measurement operation consisting of five steps.

That is, cleaning the inside of the detector flow pipe by circulating fresh air (1 step) → Background measurement (2 steps) → Constant depressurization inside the detector flow pipe (3 steps) → Suction of a certain amount of underground air (4 steps) → Radon The above operations are performed in the order of concentration measurement (5 steps), and each step takes 40 minutes;
2 steps are 20 minutes, 3 steps and 4 steps are 5 minutes each, 5 steps are 20 minutes, one cycle
It is designed to be completed in 1.5 hours.

Therefore, in each step, valves A, B, and C are
In one step, valve A is closed, valves B and C are opened, and the pump 16 is operated to flow fresh air into the detector flow pipe. A cycle takes place. This fresh air is fresh air that does not contain radioactive substances such as radon daughter nuclides and thoron, and the radon daughter nuclides in the detector flow pipe are removed by this fresh air.

In step 2, all valves A, B, and C are closed, the pump 16 is stopped, and the measuring section 100 is closed.
By detecting alpha rays with the detector 14 and counting for 20 minutes with the scaler 18,
Background measurements are taken. In this measurement, the radon daughter nuclides are removed, so stable measurement values can be obtained without the background changes that occur when measuring underground radon concentration. .

In the third step, valves A and B are closed, valve C is opened, and the pump 16 is operated to reduce the pressure in the detector flow pipe to a predetermined pressure. At this time,
The vacuum gauge 24 is in operation, and when the value of the vacuum gauge 24 reaches a predetermined pressure, the valve C is automatically closed and the pump 16 is stopped.

In step 4, valve A is opened, valves B and C are closed, and a certain amount of underground air is collected as a sample.

In this case, the apparatus of the embodiment is equipped with a tank 26 according to another invention, and underground air is stored in the tank 26 from the underground gas hole 10 during suction in the 4 steps. This tank 26
The capacity is a predetermined amount that is fed into the detector 14 in one measurement, and becomes the sample that is fed into the detector 14 in the next measurement. In this way, tank 26
By temporarily storing radon in the underground air, it is possible to remove the effects of radioactive substances other than radon, especially thoron, which enter the underground air.

In other words, the half-life of tron (Tn) is 54.5 seconds, which is a short life, and the time required for the next measurement is 1 hour.
After 10 minutes, the radiation dose becomes significantly attenuated. Therefore, the influence of thoron, which is an α-ray radioactive substance present in rocks, on the background value can be almost completely eliminated.

In the last five steps, all valves A, B, and C are closed and the measurement unit 100 consisting of the detector 14 and scaler 18 is operated to measure the radon concentration in the sample fed to the detector 14. Measure.

In the example, this measurement is carried out for 20 minutes, and the measured value is displayed on a display device provided in the scaler 18.

Next, a second embodiment of the present invention will be described based on FIG.

As mentioned above, the present invention is a so-called intermittent automatic measuring device that measures the original radon concentration after cleaning the inside of the detector flow pipe and measuring the background value in order to prevent the influence of radon daughter nuclides. , the configuration is such that the preparation stage for measuring radon concentration requires a relatively long time.

For this reason, in the second embodiment, a plurality of detectors and an air circulation mechanism are used to continuously measure the radon concentration so as to fill the time during the preparation stage. At the same time, if an abnormality occurs in one detector, it can be backed up by another detector.In the second embodiment, the radon concentration can be measured using two types of measurement cycles using four detectors. Take measurements.

That is, in FIG. 2, the detectors 14-1 to
14-4, and two pumps 16-1, 1
6-2 is used to separately perform depressurization and fresh air circulation within the detector flow pipe.

Therefore, in addition to valves _A1 to _A4 , _B1 to _B4 , and _C1 to _C4 , valves _D1 to _D4 and valve E are provided, and two pumps 16-1 and 16-2 are provided. Control circuits 28-1 and 28-2 are provided separately from the control circuit 20.

The measurement of alpha rays is carried out using a 4-channel scaler 3.
0, which is controlled by a control circuit 32,
As shown in the figure, a measuring section 100, a gas suction section 101 including a vacuum gauge 24, and a gas exhaust section 102 are provided.

Furthermore, four tanks 26- constituting another invention
1 to 26-4 are provided for the detectors 14-1 to 14-4, respectively, and are configured to temporarily store underground air from the underground gas hole 10. And, although the underground gas hole 10 may be in one place,
In the second embodiment, there are four underground gas holes 10-1 to 1.
0-4 is provided.

In the second embodiment device having such a configuration,
The measurement operation is performed in two types of cycles, and as shown in FIG. 3b, the detector 14-1
and 14-2 are the time cycles of A and the detector 14-
3 and 14-4, each step operation is performed in the time cycle B. Therefore, each step operation is controlled according to these two types of time charts, and when cleaning the inside of the detector flow pipe by circulating fresh air, valves A and C are closed,
With valves B and D open, the gas exhaust section 102
The pump 16-2 is operated.

In the second step, as in the first embodiment, all the valves and pumps are stopped and only the measuring section 100 is operated, thereby detecting the two corresponding detectors 1.
Measure the background at 4.

In step 3, valves A, B, and D are closed,
The valve C is opened to operate the pump 16-1 of the gas suction section 101, and the valve E is opened to evacuate the inside of the detector flow pipe. Then, when the vacuum gauge 24 reaches a predetermined set value, the valve E
is closed, the pump 16-1 is stopped, and the pressure inside the detector flow pipe is reduced to a constant pressure.

In step 4, only valve A is opened to collect a certain amount of underground air as a sample. In this case, as in the first embodiment, the tank 2
At step 6, a certain amount of underground air is stored in advance, and the sample is fed into the detector 14 with the radioactivity of tron attenuated. Then, in step 5, all the valves are closed, the two pumps 16 are stopped, and the radon concentration in the measurement sample is measured using the detector 14 and the 4-channel scaler 30.

Each of these steps is performed in its own time chart, but in the embodiment, the detector 14-
Since the measurement cycle is set so that the operation of detectors 14-3 and 14-4 is a 5-step radon concentration measurement while the operation of detectors 1 and 14-2 is a 2-step background measurement, the radon concentration can be measured continuously. measurements can be made.

Further, by combining measurement cycles such that the five steps of the detectors 14-1 to 14-4 are set at separate times, it is possible to carry out more continuous measurements.

Furthermore, in the second embodiment, since the radon concentration is measured in the same time period by two detectors 14,
If any abnormality occurs in one of the detectors, a measured value can be obtained from the other detector, and the reliability of the measured data obtained at a predetermined measurement time is significantly improved.

[Effects of the Invention] As explained above, according to the present invention, before measuring the radon concentration, cleaning the inside of the detector flow pipe with fresh air and measuring the background,
In addition, since the detector and air circulation mechanism for measuring radon concentration are automatically operated, errors caused by changes in the background due to radon daughter nuclides can be automatically removed. It becomes possible to accurately measure radon concentration.

As a result, various types of geological data, especially data for earthquake prediction, can be obtained satisfactorily.

Further, according to another invention, it is possible to remove bulk ground caused by thoron present in underground rocks, etc., and it is possible to significantly improve the reliability of radon concentration measurement data.

[Brief explanation of drawings]

FIG. 1 is a block diagram showing the first embodiment of the underground radon concentration measuring device according to the present invention, FIG. 2 is a block diagram showing the second embodiment of the present invention, and FIG. FIG. 4 is a time chart showing the step operation and a configuration diagram showing a conventional underground radon concentration measuring device. 10...Underground gas hole, 12...Underground air intake, 14...Detector, 16...Pump, 18,3
0... Scaler, 20, 28, 32... Control circuit, 22... Flexible air intake, 26... Tank, 100... Measurement section.

Claims (1)

[Claims] 1. A measurement unit that measures radon concentration by detecting alpha rays in underground air supplied from underground gas holes using a detector, and introducing underground air or fresh air into the detector. and an air circulation mechanism with a valve and a pump for exhausting the air. An underground radon concentration measuring device characterized in that the detector and the air circulation mechanism are controlled so that these operations are automatically performed for a predetermined time in the order of suction and then radon concentration measurement. 2. The underground radon concentration measuring device according to claim 1, wherein a plurality of the detectors are provided, and underground air is sequentially supplied to these detectors to continuously measure the radon concentration. 3. A measuring unit for measuring the radon concentration by detecting alpha rays in the underground air supplied from the underground gas hole with a detector, and a measuring unit for introducing underground air or fresh air into the detector and exhausting it. A detector using fresh air circulation, which has an air circulation mechanism with a valve and a pump, and a tank that accommodates the amount of underground air necessary for one measurement before supplying the underground air to the detector. Each of these operations is automatically performed for a predetermined time in the order of cleaning inside the flow pipe → background measurement → constant depressurization inside the detector flow pipe → suction of a certain amount of underground air stored in the tank → measurement of radon concentration. An underground radon concentration measuring device characterized in that the detector and the air circulation mechanism are controlled in accordance with the invention. 4. The underground radon concentration measuring device according to claim 3, wherein a plurality of the detectors are provided, and underground air is sequentially supplied to these detectors to continuously measure the radon concentration.