JP7154154B2 - Radioactive dust monitor and method for measuring radioactivity concentration - Google Patents

Description

This application relates to a radioactive dust monitor and a radioactivity concentration measuring method, in particular, a radioactive dust monitor and a radioactivity concentration measuring method for monitoring the radioactivity concentration in the air used in radioactive material handling facilities such as nuclear power plants. It is.

In a nuclear power plant or the like, a radiation monitor equipped with a plurality of radiation detectors or a plurality of radiation monitors are used in order to measure the radiation dose or the radioactivity amount of an object to be measured for each measured nuclide. As a radiation monitor equipped with multiple radiation detectors, there is a radioactive dust monitor that measures fission products and activation products.

Conventional radioactive dust monitors consist of an αβ detector that simultaneously detects α-rays and β-rays emitted from the measurement target, a γ-ray detector that detects γ-rays, a measurement unit corresponding to the detector, and the effects of environmental γ-rays. Equipped with a lead shield for reducing , a sampling unit equipped with a pump for sampling the sample air and filter paper for repairing the particulate radioactive material to be measured.

The air at the measurement point is sampled and passed through a filter paper, the dust suspended in the sample air is collected by the filter paper, the β rays emitted from the dust are detected by a radiation detector, and the amount of sample air that has passed through the filter paper and pulse signals output from the radiation detector to measure and monitor the concentration of particulate nuclides existing in the air at the measurement point.

When measuring β-rays from fission products and activation products, β-rays and γ-rays from daughter nuclides of radon and thoron, which are natural radionuclides, are mixed in the background, so the β-rays of the object to be measured are highly sensitive. When attempting to measure at , background effects become non-negligible and it becomes essential to compensate for daughter radon and thoron nuclides. In addition, since various γ-rays from the environment are mixed in as background, it is necessary to compensate for their effects.

2. Description of the Related Art Conventionally, various techniques have been used to accurately measure an object to be measured. As a method to reduce the effects of radon, thoron, or their daughter nuclides, after sampling the dust-repaired sampling filter paper, let the natural radionuclides decay for one to several days before measuring β-rays. was This type of dust monitor could not be used for real-time monitoring.

On the other hand, as a method for real-time measurement, conventionally, the α-ray and β-ray emitted from dust are counted, and the α-ray count rate is used to compensate the β-ray count rate. was taken. In facilities such as nuclear power plants, unlike nuclear fuel processing facilities, only the natural radionuclides radon, thoron and their daughter nuclides emit α-rays, so the α-ray count rate does not exceed the amount of radon. will represent. Radon emits β-rays in addition to α-rays, but the ratio of α-rays and β-rays can be obtained by experiments, etc. Therefore, by multiplying the α-ray count rate of the dust monitor by this ratio, the β-ray count rate can determine the contribution of radon, etc. to That is, this ratio is used as a conversion constant for determining the contribution of radon and the like to the β-ray count rate. By subtracting the contribution of radon and the like from the β-ray count rate, the β-ray count rate for only the artificial radionuclides can be obtained, and the concentration of the artificial radionuclides in the air can be obtained from this value.

In the case of this method, when the concentration of natural radionuclides such as radon increases, the error in the contribution to the β-ray count rate increases as the α-ray count rate increases. The β-ray count rate for artificial radionuclides alone, which is obtained by subtracting the contribution of , also contains an extremely large error.

Another approach has been taken to deal with such problems. The energy spectrum of the gamma rays emitted from the dust collected on the sampling filter paper is measured with a pulse height analyzer, a window corresponding to the energy of the gamma rays emitted by each artificial radionuclide is set, and the total count rate in this window is calculated. Ask for Furthermore, a window corresponding to the energy of gamma rays emitted by radon, thoron, and their daughter nuclides is set, the counting rate in this window is calculated, multiplied by a predetermined conversion constant, and corresponds to the energy of gamma rays emitted by each artificial radionuclide. The γ-ray count rate for artificial radionuclides only is obtained by subtracting from the total count rate in the window (for example, Patent Document 1).

When measuring a nuclide that emits α-rays, such as plutonium, the three regions of plutonium, radon daughter nuclides, and thoron daughter nuclides are shown in the spectrum obtained by the pulse height analyzer. is measured, and the measured values of the radon daughter nuclide area and the thoron daughter nuclide area are multiplied by their respective coefficients to calculate the background amount due to radon and thoron, that is, the estimated count value, and from the measured value of plutonium A method of obtaining the count value of plutonium by subtracting the estimated count value is adopted to reduce the influence of the background (for example, Patent Document 2).

JP-A-8-285944 JP-A-9-015336

However, in the case of gamma-ray measurement, the conventional radioactive dust monitor multiplies the contributions of radon, thoron and their daughter nuclides by a predetermined conversion constant. When the environmental conditions change and the contribution of radon, thoron and their daughter nuclides fluctuates, the accuracy of the measurements is affected.

Also, in the case of the above α-ray measurement, the contribution of radon and thoron is multiplied by a predetermined conversion constant, so if the environmental conditions at the measurement point fluctuate, the accuracy of the measured value will be affected. put away. Furthermore, in order for the estimated count values of the contributions of radon and thoron to agree with each other with good accuracy, a large amount of daughter nuclides of radon and thoron must be collected inside the filter paper to reach a steady state. There was a problem that a long preparatory collection time was required because it was several days after the collection.

The purpose of this application is to compensate for the measurement results in real time even when the environmental conditions at the measuring point change and the contribution of radon, thoron and their daughter nuclides changes or even in the transient state before reaching the steady state. and to provide a radioactive dust monitor capable of measuring the radioactivity concentration of an object to be measured with high accuracy, and to provide a method of measuring the radioactivity concentration with high accuracy.

A radioactive dust monitor according to this application includes a target collection unit that collects air containing particulate radioactive material at a measurement point as a detection target, a radiation detector that detects the radiation dose emitted from the detection target, and the a natural radiation dose calculation unit that obtains radiation doses of a plurality of naturally radioactive substances contained in a detection target; a compensation amount database storage unit that holds, as a database, compensation amounts corresponding to radiation dose ratios of the plurality of naturally radioactive substances; a compensation amount determination unit that determines, from data held in the compensation amount database storage unit, a compensation amount corresponding to a radiation dose ratio in the plurality of natural radioactive substances based on a calculation result of the natural radiation dose calculation unit; Radioactivity for determining the radioactivity concentration of the detection target based on the radiation dose detected by the detector, the compensation amount determined by the compensation amount determination unit, and the amount of air collected by the target collection unit It is characterized by having a density calculator.

Further, in the method for measuring radioactivity concentration according to this application, air containing particulate radioactive material at a measurement point is collected as a detection target by a target collection unit, and the radiation dose emitted from the detection target is measured by a radiation detector. In addition to detecting, the radiation dose of a plurality of natural radioactive substances contained in the detection target is obtained by a natural radiation dose calculation unit, and the radiation dose ratio of the plurality of natural radioactive substances contained in the detection target is calculated according to the radiation dose ratio. A compensation amount is stored as a database, and a compensation amount determination unit determines a compensation amount according to the radiation dose ratio of the plurality of natural radioactive materials from the data stored as the database based on the calculation result of the natural radiation dose calculation unit. radioactivity concentration of the detection target based on the radiation dose detected by the radiation detector, the compensation amount determined by the compensation amount determination unit, and the amount of air collected by the target collection unit is characterized by asking for

According to the radiation dust monitor disclosed in this application, it is possible to obtain a highly accurate radioactive dust monitor by accurately compensating for the effects of natural radioactive substances. According to the measurement method, it is possible to accurately measure the radioactivity concentration by accurately compensating for the effects of natural radioactive substances.

1 is a block diagram showing the overall configuration of a radioactive dust monitor according to Embodiment 1; FIG. 2 is a curve diagram showing an example of a γ-ray energy spectrum obtained by measurement in Embodiment 1. FIG. FIG. 5 is a schematic diagram showing the configuration of a detector of a radioactive dust monitor according to Embodiment 2; FIG. 11 is a schematic diagram showing the configuration of a detector of a radioactive dust monitor according to Embodiment 3; FIG. 11 is a block diagram showing the overall configuration of a radioactive dust monitor according to Embodiment 4;

Embodiment 1.
A radioactive dust monitor according to Embodiment 1 will be described with reference to FIGS. 1 and 2. FIG. FIG. 1 is a block diagram showing the overall configuration of a radioactive dust monitor according to Embodiment 1. FIG. FIG. 2 is a curve diagram showing an example of a γ-ray energy spectrum obtained by measurement.
A flow path 1 through which air flows is formed inside a shielding container 3 that constitutes the sampling part SP of the radioactive dust monitor, and a pump 6 is connected to one side of this flow path 1 . By operating the pump 6 , external air is introduced into the flow path 1 through an inlet 1 a provided in the flow path 1 . The amount of introduced air is measured by the flow meter 5 . The introduced air passes through the sampling filter paper 4, passes through the pump 6, and is exhausted from the exhaust port 1b. The sampling filter paper 4 collects dust contained in the inhaled air. In the configuration shown in FIG. 1, the filter paper 4 is a fixed filter paper, but it may be a continuous or intermittent configuration using reel-shaped sampling filter paper.

A radiation detector 2 for detecting γ rays emitted from the dust collected by the sampling filter paper 4 is installed at a position facing the sampling filter paper 4 . A scintillation detector is used as the radiation detector 2 . The sampling filter paper 4 and the radiation detector 2 are made of a material having a high radiation shielding capability, such as lead, in order to reduce background gamma rays that enter the radiation detector 2 from sources other than the dust collected by the sampling filter paper 4. Alternatively, it is installed in a shielding container 3 made of iron or the like. A shield made of copper or the like may be provided inside the shielding container 3 .

When the gamma rays emitted from the dust collected by the sampling filter paper 4 are incident on the radiation detector, the scintillator emits scintillation light. This scintillation light is converted into an electric pulse signal by a photomultiplier tube. After being amplified and waveform-shaped by the signal processing unit 7, the pulse signal is subjected to pulse height analysis by the pulse height analyzer provided in the same unit, and the coefficient is obtained for each channel of the pulse height analyzer. Find the energy spectrum.

An example of the obtained energy spectrum is shown in FIG. The natural radiation dose calculation unit 8 corresponds to Bi-214 as the isotope of bismuth Bi and Tl-208 as the isotope of thallium Tl, which are major daughter nuclides of radon and thoron, which are natural radionuclides. A window is set on the peak portion where the peak is observed, and the ratio Bi-214/Tl-208 is calculated based on the counts in each window.

For example, when measuring Co-60 as a measurement target, the coefficient due to the contribution of Bi-214 or Tl-208 is mixed in the window range corresponding to the peak of the Co-60 portion. By subtracting this contamination from the Co-60 window counts, an accurate Co-60 factor can be obtained.

The mixing ratio of Co-60 in the window at each ratio of Bi-214/Tl-208 is obtained in advance by simulation or experiment, and is stored in a database as shown in Table 1 below. Store in 10. A database may be created for each count of Bi-214 and Tl-208 separately, but by creating a database as a ratio, the database can be simplified and the capacity can be reduced.

In the compensation amount determination unit 9, the mixing ratio of Co-60 in the ratio of Bi-214/Tl-208 calculated in the natural radiation dose calculation unit 8 is extracted from the compensation amount database storage unit 10, determined, and the radioactivity concentration Send to the calculation unit 11 .

In the radioactivity concentration calculation unit 11, from the count of the window corresponding to the Co-60 to be measured from the energy spectrum obtained by the signal processing unit 7, the mixing ratio determined by the compensation amount determination unit 9 and the actually measured Bi-214 or Tl By subtracting the mixed amount multiplied by -208, the count of only Co-60 was obtained, and the flow rate measured by flow meter 5, the measurement time, the branching ratio of γ-rays emitted by Co-60, and the radiation detector Based on the detection efficiency, the radioactivity concentration is calculated according to the formulas (1) and (2) shown in Equation 1 below. The calculated radioactivity concentration is displayed on the display unit 12 .

As described above, in Embodiment 1, the mixing rate of each ratio of Bi-214/Tl-208 to the measurement target is stored as a database in the compensation amount database storage unit, and the count of each window of the measured energy spectrum is calculated. By calculating the amount of compensation on a real-time basis and subtracting it from the count of the object to be measured, the radioactivity concentration of the object to be measured can be measured in real time with high accuracy.

As shown in FIGS. 1 and 2, the following configuration is applied to the radioactive dust monitor in the first embodiment.
A target collection unit consisting of a sampling unit SP that collects air containing particulate radioactive material at a measurement point as a detection target, a radiation detector 2 that detects the radiation dose emitted from the detection target, and the detection target. A natural radiation dose calculation unit 8 that obtains radiation doses for a plurality of natural radioactive substances contained, a compensation amount database storage unit 10 that holds compensation amounts according to the radiation dose ratios of the plurality of natural radioactive substances as a database, and natural radiation a compensation amount determination unit 9 that determines, from data held in the compensation amount database storage unit 10, a compensation amount corresponding to the radiation dose ratio in the plurality of naturally radioactive materials according to the calculation result of the amount calculation unit 8, Radiation of the detection target based on the radiation dose detected by the detector 2, the compensation amount determined by the compensation amount determination unit 9, and the amount of air collected by the target collection unit consisting of the sampling unit SP It is characterized by having a radioactivity concentration calculator 11 for obtaining the activity concentration.
Then, the natural radiation dose calculation unit 8 obtains the radiation dose for Bi-214 and Tl-208 as the plurality of natural radioactive substances, and the compensation amount database storage unit 10 stores the Bi- It is characterized in that the amount of compensation according to the radiation dose ratio Bi-214/Tl-208 between 214 and Tl-208 is stored as a database.

That is, the sampling unit SP sucks the air at the measurement point with a pump or the like and samples it, collects the particulate radioactive substances contained in the sample air on a filter paper, and detects the gamma rays emitted from the sampling unit SP to generate a pulse signal. A radiation detector 2 that emits, a signal processing unit 7 that amplifies and shapes the sampling signal, measures the wave height, measures the wave height spectrum based on the wave height data, and natural radionuclides radon, thoron and their A natural radiation dose calculation unit 8 that sets a window corresponding to the energy of gamma rays emitted by Bi-214 and Tl-208, which are the main daughter nuclides, and obtains the radiation dose of natural radionuclides from the counts within that window; 214/Tl-208 ratio, the results obtained by the compensation amount database storage unit 10, which holds the mixture ratio in the window corresponding to the energy of the nuclide to be measured as a database, and the natural radiation dose calculation unit 8. A compensation amount determination unit 9 that determines the optimum compensation amount from the data held in the compensation amount database storage unit, and the window count corresponding to the energy of γ rays emitted from the measurement object obtained by the signal processing unit 7. A radioactivity concentration calculation unit that obtains the radioactivity concentration of the object to be measured based on the compensation amount determined by the compensation amount determination unit 9 and the amount of air sucked by the sampling unit SP, and a display unit 12 that displays the obtained radioactivity concentration. characterized by having

With this configuration, it is possible to obtain a highly accurate radioactive dust monitor by accurately compensating for the effects of natural radioactive substances.
In other words, instead of fixing the conversion constant for compensation as in the past, the window corresponding to the gamma rays emitted by the natural radionuclides radon and thoron and their major daughter nuclides, Bi-214 and Tl-208, is By storing the amount of compensation for each ratio of counts as a database, even if the environmental conditions change or the collected natural radionuclides are in a transient state, the optimum amount of compensation can be applied in real time. , it is possible to obtain a radioactive dust monitor that enables highly accurate measurement of radioactive concentration.

As shown in FIGS. 1 and 2, the following contents are applied to the radioactive concentration measuring method according to the first embodiment.
The air containing particulate radioactive material at the measurement point is collected as a detection target by the target collection unit consisting of the sampling unit SP, the radiation dose emitted from the detection target is detected by the radiation detector 2, and the detection target is detected. A compensation amount corresponding to a radiation dose ratio of the plurality of natural radioactive substances contained in the detection target is calculated by a natural radiation dose calculation unit 8 in a compensation amount database It is stored as a database in the storage unit 10, and the compensation amount corresponding to the radiation dose ratio of the plurality of natural radioactive materials is calculated by the compensation amount determination unit 9 in the compensation amount database storage unit 10 according to the calculation result of the natural radiation dose calculation unit 8. The amount of radiation detected by the radiation detector 2, the compensation amount determined by the compensation amount determination unit 9, and the target collection unit consisting of the sampling unit SP The radioactivity concentration of the detection target is obtained based on the amount of air.

As a result, it is possible to obtain a radioactivity concentration measuring method capable of accurately measuring radioactivity concentration by accurately compensating for the influence of natural radioactive substances.
In other words, instead of fixing the conversion constant for compensation as in the past, the window corresponding to the gamma rays emitted by the natural radionuclides radon and thoron and their major daughter nuclides, Bi-214 and Tl-208, is By storing the amount of compensation for each ratio of counts as a database, even if the environmental conditions change or the collected natural radionuclides are in a transient state, the optimum amount of compensation can be applied in real time. , it is possible to measure radioactivity concentration with high accuracy.

Embodiment 2.
Embodiment 2 will be described with reference to FIG. FIG. 3 is a schematic diagram showing the configuration of the detector of the radioactive dust monitor according to Embodiment 2, and FIG. , and FIG. 3(b) is a plan view schematically showing the light receiving surface of the multi-anode photomultiplier tube 21. As shown in FIG.
The radiation detector 2a in the radioactive dust monitor of Embodiment 2 employs a combination of a multi-anode photomultiplier tube 21 and a thin columnar scintillator 22 matching the size of the light receiving surface of each anode. A reflective material or the like is coated between the scintillators 22 in order to prevent crosstalk, and the coating with the reflective material or the like contributes to an improvement in light collection efficiency. The signal processing unit 7 is structured to process the pulse signal of each channel of the radiation detector 2a. The rest of the configuration is the same as that of the first embodiment.

Normally, the detection efficiency of a radiation detector is applied to a value determined using a plane radiation source in which radionuclides are evenly attached to the filter paper portion. In actual measurement, the sucked dust does not necessarily adhere uniformly to the filter paper 4 . When the radioactivity concentration is calculated using the value of the detection efficiency obtained by using the surface radiation source to which the radionuclide is uniformly attached in a state where the dust is not evenly attached to the filter paper 4, the measurement accuracy will be affected.

When the radiation detector 2a of Embodiment 2 is used, a large number of radiation counts will be observed in channels near which a large amount of dust adheres to the filter paper 4 . That is, the dust distribution on the filter paper 4 can be measured.

The detection efficiency of each channel when dust is attached to each position on the filter paper 4 is obtained in advance, and according to the measured dust distribution on the filter paper 4, formula (3) and formula Using (4), subtract the influence of natural radionuclides from the counts from each position on the filter paper 4 for the measurement results in the same manner as in Embodiment 1, add them up, and then determine the radioactivity concentration.

The radioactive dust monitor according to the second embodiment has the following configuration applied to the configuration according to the first embodiment, as shown in FIG.
The radiation detector 2a includes a multi-anode photomultiplier tube 21 and a plurality of columnar scintillators 22 corresponding to the light-receiving surfaces of the anodes in the multi-anode photomultiplier tube 21. Crosstalk between the scintillators 22 is It is characterized in that a prevention member is provided and a signal processing section for processing a pulse signal is provided for each channel of the multi-anode in the multi-anode photomultiplier tube 21 .
That is, the radiation detector 2a employs a combination of a multi-anode photomultiplier tube 21 and thin columnar scintillators 22 corresponding to the light-receiving surface size of each anode. is coated with a reflective material or the like, and the signal processing section is configured to process pulse signals for each channel of the multi-anode of the radiation detector 2a.
With this configuration, the radiation dose can be accurately detected by the radiation detector, and a highly accurate radioactive dust monitor can be obtained by accurately compensating for the influence of natural radioactivity.

Embodiment 3.
Next, a radioactive dust monitor according to Embodiment 3 will be described with reference to FIG. FIG. 4 is a schematic diagram showing the configuration of a detector of a radioactive dust monitor according to Embodiment 3. FIG.
In FIG. 4, the radiation detector 2b consists of a photomultiplier tube 31 and a scintillator 32. As shown in FIG. In the third embodiment, the scintillator 32 has a U-shaped configuration surrounding the filter paper 4 . The γ-rays emitted from the dust collected by the filter paper 4 are emitted in the 4π direction. Therefore, if the detector structure is such that only one side of the filter paper 4 has an effective surface capable of measuring radiation, more than half of the radiation is not used for measurement.

When the scintillator 32 is arranged to surround the filter paper 4 in a U-shape as in the third embodiment, the number of radiations to be measured increases compared to a detector having a scintillator on only one side. That is, since the detection efficiency is increased, the measurement time can be shortened. Therefore, by subtracting the influence of natural radionuclides from this configuration in the same manner as in the first embodiment, it is possible to provide a radioactive dust monitor capable of performing highly accurate radioactivity concentration measurement in a short time.

The radioactive dust monitor according to Embodiment 3 has the following configuration applied to the configuration according to Embodiment 1 or Embodiment 2, as shown in FIG.
The target collection unit consisting of the sampling unit SP has a filter paper 4 for collecting the air containing the particulate radioactive material as a detection target, and the radiation detector 2b includes a photomultiplier tube 31 and a scintillator 32. , and the scintillator 32 is characterized in that it has a shape surrounding the filter paper 4 from at least three sides.
That is, the radiation detector 2b employs a combination of a photomultiplier tube 31 and a thin columnar scintillator 32 corresponding to the size of the light receiving surface of each anode. It is characterized by having a shape.
With this configuration, the radiation dose can be reliably detected by the radiation detector, and a highly accurate radioactive dust monitor can be obtained by accurately compensating for the influence of natural radioactivity.

Embodiment 4.
Next, a radioactive dust monitor according to Embodiment 4 will be described with reference to FIG. FIG. 5 is a block diagram showing the configuration of a radioactive dust monitor according to Embodiment 4. As shown in FIG.
In FIG. 5, a semiconductor detector is applied to the radiation detector 2c. A semiconductor detector is composed of an n-type semiconductor and a p-type semiconductor, and generates a depletion layer by applying a reverse voltage. When gamma rays are incident on this depletion layer, ionization occurs and holes and electrons are generated. Radiation can be detected by collecting this charge and amplifying it into a pulse signal.

Semiconductor detectors generally have higher energy resolution than scintillator detectors. Therefore, each peak of the natural radionuclides and the peak of the radionuclides to be measured in the energy spectrum become sharp. Therefore, the width of the window for detecting each peak can be narrowed. If the window width can be narrowed, the contribution itself of the natural radionuclides contained in the peaks of the radionuclides to be measured becomes smaller, and the measurement accuracy of the peaks of the natural radionuclides themselves also increases. Therefore, the measurement accuracy of the ratio of Bi-214/Tl-208 is also improved, so that the contamination rate of the nuclide to be measured can be determined more accurately.

According to the fourth embodiment, it is possible to provide a radioactive dust monitor with improved accuracy in measuring the contribution of natural radionuclides and the radioactivity concentration of radionuclides to be measured.

As described above, according to the radioactive dust monitor according to this application, instead of fixing the conversion constant for compensation as in the past, natural radionuclides such as radon and thoron and major Bi- By storing the amount of compensation for each ratio of the counts in the window corresponding to the gamma rays emitted by 214 and Tl-208 as a database, when the environmental conditions change or when the collected natural radionuclides are in a transient state Also, by applying the optimum amount of compensation in real time, it is possible to measure radioactivity concentration with high accuracy.

In addition, because gamma rays are measured, there is no need to consider attenuation due to the collection depth of the filter paper, etc., as in the case of alpha ray measurements, and the analysis of the measurement results is facilitated.
In addition, since it is not necessary to wait several days for the contribution of natural radionuclides to decay, and it is not necessary to spend several days for preliminary collection, the availability of the radioactive dust monitor can be increased.
Moreover, since only one radiation detector and one signal processing unit are required, the configuration of the apparatus is simplified.
In addition, since a heat-insulating container is used to protect the detector, like a dust monitor that draws in high-temperature gas, the effects of natural radionuclides are reduced in gamma-ray measurements even when α-ray and β-ray measurements are difficult. It is possible to measure the radioactivity concentration of the object to be measured with high accuracy.

In the radioactive dust monitor according to the fourth embodiment, the following configuration is applied to any of the configurations according to the first to third embodiments, as shown in FIG.
The radiation detector 2c is characterized in that it is constituted by a semiconductor detector whose circuit elements are semiconductor elements composed of an n-type semiconductor and a p-type semiconductor.
With this configuration, the radiation dose can be detected more reliably by the radiation detector, and a highly accurate radioactive dust monitor can be obtained by accurately compensating for the effects of natural radioactive substances.

It should be noted that, within the technical scope of the disclosed matter as the technical concept of this application, the embodiments can be freely combined, and each embodiment can be appropriately modified or omitted.

1 flow path, 1a suction port, 1b exhaust port, 2, 2a, 2b, 2c radiation detector, 3 shielding container, 4 filter paper, 5 flow meter, 6 pump, 7 signal processing unit, 8 natural radiation dose calculation unit, 9 Compensation amount determination unit 10 Compensation amount database storage unit 11 Radioactivity concentration calculation unit 12 Display unit 21 Multi-anode photomultiplier tube 22 Columnar scintillator 31 Photomultiplier tube 32 Scintillator.

Claims (6)

A target collection unit that collects air containing particulate radioactive material at a measurement point as a detection target, a radiation detector that detects the amount of radiation emitted from the detection target, and a plurality of natural radioactivity contained in the detection target. A natural radiation dose calculation unit that obtains the radiation dose of a substance, a compensation amount database storage unit that holds a compensation amount corresponding to the radiation dose ratio of a plurality of natural radioactive substances as a database, and a calculation result by the natural radiation dose calculation unit a compensation amount determination unit that determines a compensation amount corresponding to the radiation dose ratio of the plurality of naturally radioactive substances from data held in the compensation amount database storage unit, and the radiation dose detected by the radiation detector and the and a radioactivity concentration calculation unit that obtains the radioactivity concentration of the detection target based on the amount of compensation determined by the compensation amount determination unit and the amount of air collected by the target collection unit. radioactive dust monitor. The natural radiation dose calculation unit obtains radiation doses for Bi-214 and Tl-208 as the plurality of natural radioactive substances, and the compensation amount database storage unit Bi-214 and Tl-214 in the plurality of natural radioactive substances 2. The radioactive dust monitor according to claim 1, wherein the amount of compensation according to the radiation dose ratio with Tl-208 is stored as a database. The radiation detector comprises a multi-anode photomultiplier tube and a plurality of columnar scintillators corresponding to the light-receiving surfaces of the anodes in the multi-anode photomultiplier tube, and crosstalk prevention members are arranged between the scintillators. 3. The radioactive dust according to claim 1, wherein the multi-anode photomultiplier tube is provided with a signal processing unit for processing a pulse signal for each channel of the multi-anode photomultiplier tube. monitor. The target collection unit has filter paper for collecting air containing the particulate radioactive material as a detection target, and the radiation detector includes a photomultiplier tube and a scintillator, and the scintillator is the 3. The radioactive dust monitor according to claim 1, wherein the filter paper is surrounded from at least three sides. 3. A radioactive dust monitor according to claim 1, wherein said radiation detector is composed of a semiconductor detector whose circuit elements are semiconductor elements. The air containing particulate radioactive material at the measurement point is collected as a detection target by a target collection unit, the radiation dose emitted from the detection target is detected by a radiation detector, and a plurality of natural substances contained in the detection target are detected. A radiation dose of a radioactive substance is obtained by a natural radiation dose calculation unit, and a compensation amount corresponding to a radiation dose ratio of the plurality of natural radioactive substances contained in the detection target is stored as a database, and the natural radiation dose calculation is performed. The amount of compensation according to the radiation dose ratio of the plurality of natural radioactive substances is determined by the compensation amount determination unit from the data held as the database according to the calculation result by the unit, and the radiation dose detected by the radiation detector is determined. A radioactivity concentration measuring method, wherein the radioactivity concentration of the detection target is determined based on the amount of compensation determined by the compensation amount determination unit and the amount of air collected by the target collection unit.

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