JPH07198856A - Method and apparatus for measuring concentration of particular radioactive substance in the air - Google Patents

Abstract

PURPOSE:To measure concentration of an object nuclide with high detecting performance by a relatively simple measurement when it is already known that a particle size of the nuclide to be the object is different from that of nuclide of natural radioactivity. CONSTITUTION:The air A containing particular radioactive substance is sucked, and the sucked air A is separated to first air A1 containing rough particle substance having a predetermined particle size or more and second air A2 containing fine particle substance having less than the predetermined particle size. The substance contained in the air A1 is collected on a first filter sheet 13c, and the substance contained in the air A2 is collected on a second filter sheet 23c. A radioactive ray emitted from the substance collected on the sheet 13c is detected by a first radioactive ray detector 14, a radioactive ray emitted from the substance collected on the sheet 13c is detected by a second radioactive ray detector 24, detected data of the detector 24 is measured mainly as natural radioactivity data, and detected data of the detector 14 is measured as radioactive data consisting of natural radioactivity and radioactivity except the natural radioactivity.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method and apparatus for measuring the concentration of particulate radioactive substances suspended in the air of radioactive substance handling facilities such as nuclear facilities.

[0002]

2. Description of the Related Art Conventionally, in this type of radioactive material handling facility, abnormalities in the concentration of particulate radioactive material in the air have been detected early on, and air pollution has been monitored in order to prevent radiation exposure to facility workers. ing. There are several methods for this monitoring, but as a real-time method, a dust monitor that collects particulate radioactive substances floating in the air on a filter paper and measures the radioactivity is generally used. There is. Among the conventional dust monitors, for example, in the case of a fixed filter paper type dust monitor, the particulate radioactive material in the air is drawn onto the filter paper held by the dust collector by sucking the air to be monitored by the suction pump into the dust collector. To collect.
Then, the radiation emitted from the collected particulate radioactive substances is detected by a radiation detector, and the count rate per unit time is measured and displayed from the detected value by a count rate meter and simultaneously recorded by a recorder. The count rate meter has an adjustable alarm output function and issues an alarm at a desired count rate.
Therefore, this monitor collects and measures almost all the amount of the particulate radioactive material suspended in the sucked air.

On the other hand, in the air, particles of radon daughter nuclide, which is a naturally occurring natural radioactivity, are always present. This natural radiation exposure to radiation is unavoidable and is not covered under normal radiation control.Radiation control at radiation handling facilities such as nuclear facilities should be carried out for the particulate radioactive materials being handled. Kimono. For this reason, the measurement of the concentration of particulate radioactive substances in the air should determine the concentration of nuclides, which is the original purpose of radiation control. The above-mentioned conventional dust monitor collects the particles of the radon daughter nuclide, which is a natural radioactivity, and measures the radiation emitted from the collected particles (for example, the actual development 5
8-151864, Kaikai 62-57195, Fair 5
-18711).

[0004]

Although the above-mentioned conventional dust monitor can achieve the purpose of measurement when the concentration of the nuclide requiring monitoring is sufficiently higher than the concentration of the radon daughter nuclide, the monitoring is not possible. When the required concentration of the nuclide is similar to or lower than the concentration of the radon daughter nuclide, there is a problem that the measurement purpose cannot be achieved as it is. Several methods have been known so far as means for solving the problem in the latter case and achieving the purpose of measurement. If the half-life of the target nuclide is relatively long, store the filter paper after air dust collection and perform radiation measurement after the radioactivity of the radon daughter nuclide decays over time, and then measure the concentration of the target nuclide. Has been adopted. However, this method has a drawback that the concentration of the target nuclide cannot be known in real time during air dust collection.

As a method for improving this point and knowing the concentration of a target nuclide in real time, for example, a method of discriminating by utilizing the difference in radiation energy between the target nuclide and the radon daughter nuclide, and a method of distinguishing the radon daughter nuclide Emitting α rays and β
There is known a method of quantifying an increase in radiation emitted by a target nuclide by calculation by utilizing the fact that the ratio of the number of lines is almost constant. However, the above and
In all cases, the measurement was complicated, data processing of the measured values was indispensable, and the detection ability of the target nuclide was sometimes insufficient.

The object of the present invention is that the particle size of the particulate matter in the air carrying the target nuclide (hereinafter, simply referred to as the “nuclide particle size”) is different from the particle size of the nuclide of natural radioactivity. It is an object of the present invention to provide a method and an apparatus for measuring the concentration of a particulate radioactive substance in the air, which, when known, measures the concentration of a target nuclide with a high detection ability by a relatively simple measurement.

[0007]

As shown in FIG. 3, the present inventor has found that the median diameter of aerodynamic activity of radon daughters having natural activity (AMAD, Activity Median Aerodynamic Diamet).
er) is about 0.4 to 0.6 μm and AMAD of the uranium nuclide at the uranium fuel processing facility is about 3 to 6 μm. The present invention has been achieved, focusing on the fact that radioactivity can be individually measured by classifying and collecting.

As shown in FIG. 1, the method for measuring the concentration of a particulate radioactive substance in the air of the present invention sucks air A containing the particulate radioactive substance, and sucks this sucked air A to a particle size of a predetermined value or more. The first air A ₁ containing the substance of coarse particles and the second air A ₂ containing the substance of fine particles having a particle size smaller than a predetermined particle size are separated into the first air A 1.
The particulate matter contained in the air A ₁ is collected on the first filter paper 13c, and the particulate matter contained in the second air A ₂ is collected in the second filter paper 2
Radiation emitted from the particulate radioactive material collected on the 3c and collected on the first filter paper 13c is detected by the first radiation detector 14, and is emitted from the particulate radioactive material collected on the second filter paper 23c. The radiation that is detected by the second radiation detector 24, the detection data of the second radiation detector 24 is mainly the natural activity data, and the detection data of the first radiation detector 14 is the natural activity and other activity. It is a method of measuring as radioactivity data consisting of.

Further, the concentration measuring apparatus for the particulate radioactive substances in the air of the present invention, the air intake port 10a and the first air discharge port 1
0b and the second air discharge port 10c, and the air intake port 10
The air A taken from a is separated into a first air A ₁ containing a substance of coarse particles having a predetermined particle size or more and a second air A ₂ containing a substance of fine particles having a particle size smaller than the predetermined particle size. ₁ to the first air outlet 10b and the second air A ₂ to the second air outlet 10b.
a classifier 10 configured to be capable of discharging to c respectively; a first dust collector 1 connected to the first air discharge port 10b and collecting the particulate matter contained in the first air A ₁ to the first filter paper 13c
3; a first suction pump 15 for sucking the first air A ₁ through the first dust collector 13 and the first air outlet 10b;
A first radiation detector 14 for detecting radiation emitted from the particulate radioactive material collected on the first filter paper 13c;
A first counting rate meter 19 for counting the number of radiation detected by the radiation detector 14 per unit time; a second air outlet 1
0c, and a second dust collector 23 that collects the particulate matter contained in the second air A ₂ on the second filter paper 23c; and the second dust collector 23 and the second air outlet 10c. 2 air A
_{A second} suction pump 25 for sucking 2; a second filter paper 23c
A second radiation detector 24 for detecting radiation emitted from the particulate radioactive material collected in the second radiation detector 2;
A second counting rate meter 29 for counting the number of radiations detected in 4 per unit time; and a numerical value of the first counting rate meter 19 and a numerical value of the second counting rate meter 29 are continuously and collectively recorded. A recorder 31 and a first counting rate meter 19 and / or a second counting rate meter 2
And an alarm device 32 for issuing an alarm when the instruction of 9 exceeds a predetermined standard.

The predetermined particle size of the particulate matter separated by the classifier 10 is preferably in the range of 1.0 to 2.5 μm, and particularly preferably 2 μm.

[0011]

The air A to be measured is separated by the classifier 10 into air A ₁ containing a substance of coarse particles having a predetermined particle size or more and air A ₂ containing a substance of fine particles having a particle size smaller than the predetermined particle size. And 23c. The detectors 14 and 24 individually detect the radiation of the substance collected on the filter paper, each radiation is measured by the counting rate meters 19 and 29, and the counting rate is displayed. In FIG. 1, as an example, the counting rate meter 19 displays “13.
5 cpm "and" 125 cpm "are displayed on the counting rate meter 29. The recorder 31 records the measurement data of the two count rate meters 19 and 29 continuously and collectively. If the aerodynamic particle size of the specific nuclide is known and this is different from the aerodynamic particle size of the radon daughter nuclide, the measurement data of the counting rate meter 29 is used as the counting rate of the natural radioactivity radon daughter nuclide, that is, the background. Treated as radioactivity counting rate, counting rate meter 19
The concentration of the specific nuclide can be measured by treating the measurement data of as a radioactivity counting rate composed of the background radioactivity and the radioactivity of the specific nuclide.

[0012]

Embodiments of the present invention will now be described in detail with reference to the drawings. As shown in FIG. 1, the measuring apparatus of this embodiment comprises a single classifier 10 and a fixed filter paper type dust monitor 2 of two systems.
It is a mobile measuring device in which 0 and 30 are combined. Classifier 1
In this example, 0 is a cyclone classifier using centrifugal force, and includes an air intake port 10a, a first air exhaust port 10b, and a second air exhaust port 10b.
It has an air outlet 10c. The air intake port 10a is provided at the upper end of the classifier so as to take in the air A in the horizontal direction and generate a swirling flow inside the classifier, and the first air discharge port 10b is provided at the lower center part of the classifier. The second air outlet 10c is provided concentrically with the outlet 10b at the upper center of the classifier. This classifier 10 includes a first air A ₁ containing a substance of coarse particles having a predetermined particle size or more and a fine substance having a particle size of less than a predetermined particle size by centrifugal force to the air A taken from the air intake port 10a. It is configured such that it is separated into two airs A ₂ and the first air A ₁ can be discharged to the first air discharge port 10b and the second air A ₂ can be discharged to the second air discharge port 10c. In this example, the classifier 10
Is designed such that the diameter of the inlet 10a, the outlets 10b and 10c, the air inflow speed, the inner diameter of the main body of the classifier and the like are appropriately set so that the predetermined particle diameter is 2 μm. The relationship between the predetermined particle size and the set value is described, for example, in "Powder Engineering Handbook", 6th edition (Asakura Shoten, 1972), page 369. The air inlet 13a of the first dust collector 13 is connected to the first air outlet 10b via the conduit 11, and the air of the second dust collector 23 is connected to the second air outlet 10c via the conduit 21. The intake port 23a is connected. Filter paper holders 13b and 23b are provided inside the dust collectors 13 and 23.
The first filter paper 13c and the second filter paper 23c are respectively held by the filter paper holders 13b and 23b. The dust collectors 13 and 23 have filter papers 13c and 23c.
The first radiation detector 14 and the second radiation detector 24 are fixed so as to face each other. In this example detectors 14 and 2
4 is a ZnS scintillation detector, which is a filter paper 13
The α rays emitted from the particulate radioactive substances collected in c and 23c are respectively detected.

A first suction pump 15 and a second suction pump 25 are connected to the air outlets 13d and 23d of the dust collectors 13 and 23 via conduits 12 and 22, respectively. A flow meter 16, a pressure gauge 17, and a flow rate adjusting valve 18 are installed in the conduit 12, and a flow meter 26, a pressure gauge 27, and a flow rate adjusting valve 28 are installed in the conduit 22. The respective detection outputs of the detectors 14 and 24 are connected to the first counting rate meter 19 and the second counting rate meter 29. Counting rate meters 19 and 29 are detectors 14 and 24.
The number of detected radiations per unit time is measured and displayed as a count rate. Counting rate meter 1
The measured outputs of 9 and 29 are connected to a single recorder 31. As shown in FIG. 2, the recorder 31 is a counting rate meter 19
The data input from moments 29 and 29 are recorded continuously and individually. An alarm 32 is connected to another output of the first counting rate meter 19 and another output of the second counting rate meter 29, which issues an alarm when the instruction of the counting rate meter 19 or 29 exceeds a predetermined standard. When the instruction of the counting rate meter 19 exceeds the predetermined standard, it means that the target nuclide other than the radon daughter nuclide of natural radioactivity is contained in the air at a certain level or more, and the instruction of the counting rate meter 29 is The time when the predetermined standard is exceeded may be the case where the concentration of the radon daughter nuclide of natural radioactivity is abnormally increased or the suction pump 15 is stopped due to a failure or the like. When the concentration of the radon daughter nuclide of the former rises abnormally, the background radioactivity count rate becomes too high and the ability to detect the target nuclide decreases, and the suction pump 15 of the latter also abnormally stopped during measurement. In this case, the total amount of the air A is collected by the filter paper 23c and the count rate abnormally rises. Therefore, it is possible to take an action such as stopping the measurement by an alarm.

A method of using the thus-configured measuring device will be described. (a) First, after installing this measuring device in a general environment in an office, operate the suction pumps 15 and 25, and
6 and 26 and pressure gauges 17 and 27 while adjusting flow rate adjusting valves 18 and 28 to connect the conduits 12 and 22 to 1 minute per minute.
Maintain 0 liters of air and 90 liters of air per minute, respectively. As a result, the air A becomes the classifier 10
The air is taken in through the air intake port 10a and separated by the classifier 10 into air A ₁ containing a substance of coarse particles having a particle diameter of 2 μm or more and air A ₂ containing a substance of fine particles having a particle diameter of less than 2 μm. The air A ₁ contains a substance in a proportion substantially equal to the flow rate ratio of the air A _{1 to} the air A, that is, about 10% of the whole fine particles having a particle diameter of less than 2 μm. Air A ₁ is the first dust collector 1
3 and is collected by the filter paper 13c. Further, the air A ₂ enters the second dust collector 23 and is collected by the filter paper 23c.

The radiation detectors 14 and 24 detect the radiation collected on the filter papers 13c and 23c, respectively, and the detection data are input to the counting rate meters 19 and 29. Count rate meters 19 and 29 display the count rate. The numerical values of these counting rate meters 19 and 29 are input to the recorder 31 and recorded in the time chart shown in FIG. Figure 2
In (a), the code c ₁ is measured by the counting rate meter 29,
The count rate of fine particle substances having a particle size of less than 2 μm is plotted with the passage of time, and the reference numeral d ₁ is measured by a counting rate meter 19 and plotted with the passage of time, mainly the particle size is 2 μm or more. 3 shows the count rate of coarse-grained substances. Since the concentration of radioactive particulate matter in the air in the office was measured here, the particles collected on the filter paper 13c, which is the basis of the counting rate of the code d ₁ , are the fine particles that should be collected on the filter paper 23c. Dust collector 1 at such a ratio
Most of them were mixed in 3, and there were few coarse particles of 2 μm or more, and only the particles of the radon daughter nuclide, which is a natural radioactivity, were measured. That is, regarding the counting rate, it was found that the ratio of the numerical value of the code c _{1 to} the numerical value of the code d ₁ remained constant at about 10: 1.

(B) Next, this measuring device was installed in a uranium fuel processing facility in a work space where uranium was handled in an unsealed state. In the same manner as in (a) above, the conduits 12 and 22 have a flow rate of 10
Air of 1 liter and air of 90 liters per minute are maintained so as to flow respectively, and the air A ₁ containing the substance of coarse particles having a particle diameter of 2 μm or more enters the first dust collector 13 and is collected by the filter paper 13c. . Further, the air A ₂ containing a substance of fine particles having a particle diameter of less than 2 μm enters the second dust collector 23 and is collected by the filter paper 23c. Detectors 14 and 24 for radiation emitted from the substances collected on the filter papers 13c and 23c as in (a) above.
The count rate meters 19 and 29 display the count rate according to the detection data of 1, and these numerical values are input to the recorder 31 and recorded in the time chart shown in FIG. 2B. In FIG. 2 (b), reference numeral c ₂ indicates the counting rate of the substance of fine particles having a particle diameter of less than 2 μm, which is measured by the counting rate meter 29, and reference numeral d ₂ is measured by the counting rate meter 19, mainly. The count rate of coarse particles having a particle diameter of 2 μm or more is shown. Here, since the concentration of radioactive particulate matter in the air of the workplace where uranium is handled in an unsealed state was measured, the counting rate of code c ₂ indicating the particles of the radon daughter nuclide that is a natural radioactivity is about After 2 hours, it remained almost constant, but the count rate of code d ₂ consisting of natural radioactivity and radioactivity of other nuclides fluctuated with time.

The expected value d ₃ of the count value of the Radon daughter nuclide, which is the background, is subtracted from the count rate indicated by the reference numeral d _{2, and} the hatched area indicated by the reference numeral e is increased by an amount corresponding to the above case (a). Especially at times t ₁ , t ₂ and t ₃ , the count rate increased, and it was found that the air was contaminated with nuclides other than the Radon daughter nuclide. The concentration of the target nuclide, that is, uranium can be measured by calculating the temporal change rate of the count rate corresponding to the code e. The alarm 32 is activated when the rate of change over time exceeds a predetermined value, and notifies the operator of radioactive contamination of the air.

In the above example, the case where the measurement data is directly input to the recorder 31 from the two counting rate meters 19 and 29 has been described, but each output of the counting rate meters 19 and 29 is connected to the data processing device 33. Then, the data processing device 33 may be configured to estimate the background radioactivity counting rate from the output of the counting rate meter 29 and calculate the radiation of the specific nuclide from the output of the counting rate meter 19. Further, in the above example, the fixed filter paper type dust monitor for holding the filter paper of the device of the present invention in the filter paper holder has been described, but the device of the present invention is not limited to this, and can be applied to a moving filter paper type. Furthermore, in the above example, the radiation detector was described as an α-ray detector, but a β-ray detector or other detector may be used as the radiation detector depending on the purpose.

[0019]

As described above, according to the present invention, when it is known that the particle size of the target nuclide is different from the particle size of the natural radionuclide as shown in FIG. It is sucked into a classifier, separated by particle size, passed through two dust monitors, individually collected on filter paper, these radiations are individually detected, the counting rate is measured, and the results are combined. By making a judgment, the concentration of the target nuclide can be measured with a high detection ability by a relatively simple measurement.

[Brief description of drawings]

FIG. 1 is a block diagram of a measuring apparatus of the present invention.

FIG. 2 is a time chart recorded by the recorder of the present invention.

FIG. 3 is a distribution map of particles of a radon daughter nuclide and particles of a specific nuclide that are natural radioactivity.

[Explanation of symbols]

 10 Classifier 10a Air intake port 10b First air discharge port 10c Second air discharge port 13,23 Dust collector 13c, 23c Filter paper 14,24 Radiation detector 15,25 Suction pump 19,29 Count rate meter 31 Recorder 32 alarm device 33 data processing device

─────────────────────────────────────────────────── ───

[Procedure amendment]

[Submission date] August 18, 1994

[Procedure Amendment 1]

[Document name to be amended] Statement

[Name of item to be corrected] 0003

[Correction method] Change

[Correction content]

On the other hand, in the air, particles of radon daughter nuclide, which is a naturally occurring natural radioactivity, are always present. Since this exposure to radiation of natural radioactivity is that the inevitable, not subject is on top of the normal radiation management, radiation control of radiation handling facilities of nuclear facilities and the like that are dealt
And the like should be performed for radioactive materials. For this reason, the measurement of the concentration of particulate radioactive substances in the air should determine the concentration of nuclides, which is the original purpose of radiation control. The above-mentioned conventional dust monitor collects the particles of the radon daughter nuclide, which is a natural radioactivity, and measures the radiation emitted from the collected particles (for example, SAIKAI Sho 58-
151864, 62-57195, Shohei 5-1
8711).

[Procedure Amendment 2]

[Document name to be amended] Statement

[Correction target item name] 0010

[Correction method] Change

[Correction content]

[0010] Note that the predetermined particle size of the particulate material classifier 10 is separated, it is good <br/> preferable in the range of 1.0 to 2.5 [mu] m.

[Procedure 3]

[Document name to be amended] Statement

[Correction target item name] 0011

[Correction method] Change

[Correction content]

[0011]

The air A to be measured is separated by the classifier 10 into air A ₁ containing a substance of coarse particles having a predetermined particle size or more and air A ₂ containing a substance of fine particles having a particle size smaller than the predetermined particle size. And 23c. The detectors 14 and 24 individually detect the radiation of the substance collected on the filter paper, each radiation is measured by the counting rate meters 19 and 29, and the counting rate is displayed. In FIG. 1, as an example, the counting rate meter 19 displays “13.
5 cpm "and" 125 cpm "are displayed on the counting rate meter 29. The recorder 31 records the measurement data of the two count rate meters 19 and 29 continuously and collectively. If the aerodynamic particle size of the specific nuclide is known and this is different from the aerodynamic particle size of the radon daughter nuclide, the measurement data of the counting rate meter 29 is used as the counting rate of the natural radioactivity radon daughter nuclide, that is, the background. Treated as radioactivity counting rate, counting rate meter 19
By dealing with the measurement data as a count rate that Do from radioactivity background radioactivity and specific nuclide, it is possible to measure the concentration of a specific nuclide.

[Procedure amendment 4]

[Document name to be amended] Statement

[Name of item to be corrected] 0015

[Correction method] Change

[Correction content]

The radiation detectors 14 and 24 detect the radiation collected on the filter papers 13c and 23c, respectively, and the detection data are input to the counting rate meters 19 and 29. Count rate meters 19 and 29 display the count rate. The numerical values of these counting rate meters 19 and 29 are input to the recorder 31 and recorded in the time chart shown in FIG. Figure 2
In (a), the code c ₁ is measured by the counting rate meter 29,
The count rate of fine particle substances having a particle size of less than 2 μm is plotted with the passage of time, and the reference numeral d ₁ is measured by a counting rate meter 19 and plotted with the passage of time, mainly the particle size is 2 μm or more. 3 shows the count rate of coarse-grained substances. Here is the particulate radiation in the office air
Because it was the concentration measurement of sexual substances, particles are trapped in the filter paper 13c underlying the counting rate of the code d _1, originally filter paper 23c
Most of the fine particles to be collected in the dust collector 13 were mixed in the dust collector 13 as described above, and the number of coarse particles of 2 μm or more was small, and only the particles of the radon daughter nuclide that is a natural radioactivity were measured. . That is, regarding the counting rate, it was found that the ratio of the numerical value of the code c _{1 to} the numerical value of the code d ₁ remained constant at about 10: 1.

[Procedure Amendment 5]

[Document name to be amended] Statement

[Correction target item name] 0016

[Correction method] Change

[Correction content]

(B) Next, this measuring device was installed in a uranium fuel processing facility in a work space where uranium was handled in an unsealed state. In the same manner as in (a) above, the conduits 12 and 22 have a flow rate of 10
Air of 1 liter and air of 90 liters per minute are maintained so as to flow respectively, and the air A ₁ containing the substance of coarse particles having a particle diameter of 2 μm or more enters the first dust collector 13 and is collected by the filter paper 13c. . Further, the air A ₂ containing a substance of fine particles having a particle diameter of less than 2 μm enters the second dust collector 23 and is collected by the filter paper 23c. Detectors 14 and 24 for radiation emitted from the substances collected on the filter papers 13c and 23c as in (a) above.
The count rate meters 19 and 29 display the count rate according to the detection data of 1, and these numerical values are input to the recorder 31 and recorded in the time chart shown in FIG. 2B. In FIG. 2 (b), reference numeral c ₂ indicates the counting rate of the substance of fine particles having a particle diameter of less than 2 μm, which is measured by the counting rate meter 29, and reference numeral d ₂ is measured by the counting rate meter 19, mainly. The count rate of coarse particles having a particle diameter of 2 μm or more is shown. Here, since at a concentration measurement of the particulate radioactive materials in the air of the workplace handling uranium unsealed state,
The counting rate of code c ₂ showing particles of radon daughter nuclide which is natural radioactivity remained almost constant after about 2 hours from the start of sampling, but from natural radioactivity and radioactivity of other nuclides The count rate of the symbol d ₂ fluctuated with the passage of time.

[Procedure correction 6]

[Document name to be amended] Statement

[Correction target item name] 0017

[Correction method] Change

[Correction content]

[0017] In this case, the counting rate of the code d ₂ is obtained by subtracting the expected value d ₃ of the count values of radon daughters is the background from the count rate of the code d _2, only the hatched region amount indicated by symbol e in (a ). In particular, in the time zones t ₁ , t ₂ and t ₃ , the count rate of the code d ₂ increased compared to the code c ₂ and it was found that the air was contaminated with nuclides other than the Radon daughter nuclide. The concentration of the target nuclide, that is, uranium can be measured by calculating the temporal change rate of the count rate corresponding to the code e.

Claims (5)

[Claims] 1. An air (A) containing a particulate radioactive substance is sucked, and the sucked air (A) is mixed with a first air (A ₁ ) containing a substance of coarse particles having a predetermined particle size or more and the predetermined air. The particulate matter contained in the first air (A ₁ ) is separated into the second air (A ₂ ) containing fine particles having a particle size smaller than the particle diameter, and the first filter paper (13
c) The particulate matter contained in the second air (A ₂ ) collected on the second filter paper (23
c) The radiation emitted from the particulate radioactive material collected on the first filter paper (13c) is detected by the first radiation detector (14) and collected on the second filter paper (23c). Radiation emitted from the collected particulate radioactive material is detected by a second radiation detector (24), and the detection data of the second radiation detector (24) is mainly used as natural radioactivity data, and the first radiation detector is used. A method for measuring the concentration of particulate radioactive substances in the air, wherein the detection data of (14) is measured as radioactivity data consisting of natural radioactivity and other radioactivity. 2. A first count rate, which is the number of radiation detected by the detection data of the first radiation detector (14) per unit time, and radiation detected by the detection data of the second radiation detector (24). And the second count rate, which is the number per unit time, are calculated, the background radioactivity count rate is estimated from the second count rate, and the estimated background radioactivity count rate is subtracted from the first count rate. The method according to claim 1, wherein the radioactivity counting rate of the specific nuclide is calculated by 3. The method according to claim 1, wherein the predetermined particle size of the particulate matter to be separated is in the range of 1.0 to 2.5 μm. 4. An air intake port (10a) and a first air exhaust port (10b)
And a first air (A ₁ ) which has a second air outlet (10c) and which contains the substance of coarse particles having a predetermined particle size or more from the air (A) taken from the inlet (10a) The air is separated into second air (A ₂ ) containing fine particles having a particle size smaller than the predetermined particle size, and the first air (A ₁ ) is supplied to the first air discharge port (10b) and the second air (A _2). ) Is connected to the first air exhaust port (10b), and the first air exhaust port (10b) is connected to the first air exhaust port (10b).
A _first dust collector (13) for collecting the particulate matter contained in (A ₁ ) on the first filter paper (13c), and the first dust collector (13) and the first air outlet (10b). A _first suction pump (15) for sucking the first air (A ₁ ) through the first radiation detector, and a first radiation detector for detecting radiation emitted from the particulate radioactive material collected in the first filter paper (13c). (14), a first counting rate meter (19) for counting the number of radiation detected by the first radiation detector (14) per unit time, and a second air outlet (10c) , The second air
A _second dust collector (23) for collecting the particulate matter contained in (A ₂ ) on the second filter paper (23c); and the second dust collector (23) and the second air outlet (10c). A _second suction pump (25) for sucking the second air (A ₂ ) through the second suction detector, and a second radiation detector for detecting the radiation emitted from the particulate radioactive material collected in the second filter paper (23c). (24), a second count rate meter (29) for counting the number of radiation detected by the second radiation detector (24) per unit time, and a numerical value of the first count rate meter (19) A recorder (31) for continuously and collectively recording the numerical value of the second count rate meter (29), and the first count rate meter (19) and / or the second count rate meter (29)
The alarm device (3
2) A device for measuring the concentration of particulate radioactive substances in the air, which comprises and. 5. The device according to claim 4, wherein the predetermined particle size of the particulate matter separated by the classifier (10) is in the range of 1.0 to 2.5 μm.