KR101057768B1 - Apparatus and method for measuring environmental radiation in air - Google Patents

Abstract

The present invention relates to an apparatus for measuring environmental radioactivity in the air, and more particularly, the alpha radioactivity and beta radioactivity released from the debate and radon decay products in the air in the natural radiation state, the alpha radioactivity: beta radioactivity ratio is almost constant. The present invention relates to an apparatus for measuring environmental radioactivity in air, and a method thereof.

In addition, after collecting the airborne dust emitted from the reactor accident or nuclear test of the reactor facility, the alpha and beta radioactivity ratios are changed and recognized as external radioactivity, and compared with the total alpha and all beta count ratio and all alpha and all beta count ratios. The present invention relates to an apparatus for measuring environmental radioactivity in air for calculating and measuring environmental radioactivity.

Therefore, the present invention has the effect of shortening the radioactivity measurement time after collecting the air suspended particles by using the total alpha, the total beta count ratio, and the total alpha: pre beta count ratio.

Radioactivity, alpha, beta, counting rate, counting efficiency, radon, discussion

Description

Apparatus and method for measuring environmental radiation in air {Method and measuring appratus for environmental radition in the air}

The present invention relates to an apparatus for measuring environmental radioactivity in air, and more particularly, to measure environmental radioactivity from changes in radioactivity in air by inspecting airborne dust, which is a movement path of radioactive materials released into the atmosphere from nuclear facilities. The present invention relates to an apparatus for measuring environmental radiation in air and a method thereof.

Since air is a moving path of radioactive materials released into the atmosphere from nuclear facilities, it is possible to detect abnormalities of environmental radioactivity from changes in radioactivity in the air. For this reason, radioactive concentrations in the air are important investigation items in environmental radioactivity monitoring in various countries.

 In the Republic of Korea, the total beta radiation concentrations of airborne dust have been measured at 12 local radioactivity stations installed throughout the country until the day they began to monitor fallout from nuclear tests.

Radioactivity measuring equipment has been replaced by proportional counters that can also measure alpha lines in GM counters that can only measure beta rays. Nevertheless, there was a problem in that only the variation in beta radiation concentration was monitored, ignoring the alpha radiation concentration measured together.

Therefore, the present invention was created to solve the above problems, the object of the present invention is as follows.

First, the aim is to accurately calculate the radioactivity of radon and decay products in the filter paper and the radioactivity by total alpha and total beta counts to be counted by the measuring device.

Second, the purpose is to accurately calculate the radioactivity by comparing and calculating the ratio between the measured total alpha and total beta count.

Third, the purpose of this study is to accurately calculate the radioactivity by checking whether the total beta count is constant with respect to the total alpha count rate during the elapsed time after collecting the airborne dust.

Fourth, the purpose is to shorten the radioactivity measurement time after collecting the air floating dust, to reduce the radioactivity abnormality detection time.

Specific means for achieving the object of the present invention as described above, Alpha radiation detector; Beta radiation detector; A microcomputer for comparing and calculating the radiation levels detected by the alpha radiation detector and the beta radiation detector; And a display device for displaying the calculated value of the microcomputer.

The microcomputer is characterized by comparing and calculating the equations of the total alpha and the total beta count ratio and the total alpha: to beta count ratio.

Collecting air suspended solids in the filter paper; Measuring alpha and beta radiation concentrations in the filter paper, respectively; Comparing and calculating the measured alpha and beta radiation concentrations in a predetermined manner to detect radioactivity levels; And a display step of displaying the detected radioactivity value to the user.

Alpha, beta radioactivity uses Bateman equation from radon and debate radioactivity concentrations; Radioactivity measures 5 hours; The predetermined method is characterized by measuring the total alpha and the total beta radioactivity using the ratio of the total alpha count rate, the total beta count rate, and the total alpha count rate: total beta count rate.

The full alpha count rate is characterized by using the following equation using the full alpha measurement efficiency.

Here, N _x (t) is the number of atoms of the x nuclide in the filter paper at time t, and is the _alpha alpha detection efficiency (Counts / s / s).

The total beta count rate is characterized by using the following equation using the total beta measurement efficiency.

Here, N _x (t) is the number of atoms of the x nuclide in the filter paper at time t, and ε _α beta ray detection efficiency (Counts / s / ㏃).

The ratio of total alpha count rate to total beta count rate is characterized by using the following equation.

Where ε _PB and ε _BB are the measurement efficiency of beta rays emitted from ²¹² Pb and ²¹² Bi, respectively, and ε _BA is the alpha ray measurement efficiency emitted from ²¹² Bi and its daughter nuclides.

By using the ratio of the total alpha count rate and the total beta count rate, it is characterized in that the radiation value can be measured only by the count rate of either the total alpha or the total beta count rate.

Full alpha measurement efficiency is 0.30cpm / ㏃; And before beta measurement efficiency is characterized by 0.29cpm / ㏃.

According to the present invention, the effects of the apparatus for measuring environmental radioactivity in the air and the method are as follows.

First, the alpha radioactivity present in the air flotation is confirmed by the decay products of radon and debate, so that accurate radioactivity can be measured.

Second, by confirming that almost all of the beta radioactivity in the air flounder is caused by the decay products of radon and debate, it is possible to measure the exact radioactivity level.

Third, by removing the contributions of radon and decay decay products from measured beta counts to airborne dust, it has the effect of lowering the detection limit of artificial nuclides.

Fourth, it is possible to shorten the radioactivity measurement time after collecting the air suspended particles, there is an effect of reducing the radioactivity abnormality detection time.

Hereinafter, with reference to the accompanying drawings will be described in detail a preferred embodiment of the present invention.

<Technical configuration according to the present invention>

1 is a schematic diagram showing an apparatus for measuring environmental radioactivity in air according to the present invention.

As shown in FIG. 1, the apparatus 1 for measuring environmental radioactivity in air according to the present invention collects suspended solids in air and detects alpha and beta radioactivity by an alpha radiation concentration detector 11 and a beta radiation concentration detector ( 12).

The display device 14 which forms the microcomputer 13 which compares and calculates the radiation value with the radioactivity concentration measured by this alpha and beta radiation concentration detectors 11 and 12, and displays the numerical value computed by the microcomputer 13 to a user. )

In this case, the alpha and beta radiation detectors 11 and 12 use a known detector, and the microcomputer is configured to compare and calculate by the equation according to the present invention, and the display device is configured to be easily seen by the user.

The microcomputer 13 uses the formulas of the total alpha and all beta count ratios and the total alpha: all beta count ratios in order to compare and calculate radioactivity values. (The equations for pre-alpha and pre-beta counts and pre-alpha: pre-beta count ratios are omitted again, as mentioned below.)

<Measurement Method According to the Present Invention>

2 is a flowchart illustrating a method for measuring environmental radioactivity in air according to the present invention.

As shown in Figure 2, the method of measuring the environmental radioactivity in the air according to the present invention comprises a large step of four steps to collect the air floating dust (S100), the step of measuring the alpha and beta radioactivity (S200), comparison Comprising the step of calculating the radioactivity value (S300), the step of displaying the radioactivity value (S400).

In the air float collection step (S100), the air float is collected on a filter paper for detecting radioactivity.

Alpha and beta radioactivity measurement step (S200), it detects the alpha and beta radiation concentration in the filter paper. At this time, the concentration of alpha and beta radiation can be measured at the same time or alpha and beta radioactivity in one or two filter paper, respectively.

Comparing and calculating the radioactivity level (S300), the total alpha and the total beta count ratio and the total alpha: to beta count ratio are compared by a mathematical formula that calculates the ratio, and calculated to detect the alpha and beta radiation levels do. The full alpha and pre beta counts are calculated using the full alpha and pre beta counting efficiencies (the equations for the pre-alpha and pre-beta counts and the pre-alpha: pre-beta count ratios will be omitted below).

In the display step (S400) of the radioactivity value, the detected radioactivity value is configured to be easily seen by the user through an external display device and is visible to the user.

Problems of the Invention

The air contains radon and decay products from the earth's crust. The radioactive concentrations of these nuclides vary with weather conditions.

In particular, radon decay products have high radioactivity concentrations and varying concentrations that interfere with the detection of artificial radioactivity. This disturbance can be eliminated by measuring radioactivity after a certain time after airborne collection, so that the radioactivity of radon decay products is reduced substantially.

²¹⁴ Pb, ²¹⁴ Bi, ²⁰⁸ Tl of radon decay products have a half-life of less than 30 minutes and their radioactivity levels are reduced to 1/2 ¹⁰ after 5 hours of airborne collection. On the other hand, the decay product of the discussion, ²¹² Pb, has a half-life of 10.6 hours, so the radioactive decay is not significant.

Therefore, fluctuations in the radioactivity of the decay products in the air cause fluctuations in the beta radioactivity in the air even when there is no outflow of artificial radioactive material.

Of the decay products of the debate, ²¹² Pb is 100% beta decay, but its daughter, ²¹² Bi, is 64% beta decay and 36% alpha decay.

The half-life of ²¹² Bi is 60.5 minutes. After 5 hours of collecting the airborne dust, ²¹² Bi collected from the air almost collapses, and only ²¹² Bi generated from the mother nucleus ²¹² Pb is present in the filter paper. Done.

As a result, in the absence of artificial radionuclides emitting beta rays in the air, the radioactivity ratio of ²¹² Bi to the radioactivity of ²¹² Pb of the filter paper will be constant, and the ratio of the coefficients will be constant, regardless of the radioactive concentration of the decay decay product. .

This ratio can be used to remove the contribution by the decay decay product from the beta radioactivity concentration in the air.

Based on this fact, the present invention calculates the radioactivity of radon and decay decay products present in the filter paper and the pre-alpha and pre-beta counts which will be counted by them at all times, from the collection of air suspended particles to the measurement of radioactivity. It is to measure environmental radioactivity in air.

As a result, the measured total alpha and total beta counts were compared, and after 5 hours of collection of airborne dust, all beta counts for all alpha counts were determined to be constant.

Theoretical Background of the Invention

In Korea, environmental radiation monitoring collects airborne dust on filter paper with an air pump for 24 hours, and measures the total beta radioactivity after 5 hours. Radon's daughter ²¹⁸ Po has a half-life compared to airborne dust collection time. (3.05 min) is short and does not accumulate in the filter paper.

Instead, the collected ²¹⁸ Po collapses and accumulates in the filter paper at ²¹⁴ Pb. ²¹⁴ Pb with a half-life of 26.8 min and ²¹⁴ Bi with 19.9 min accumulate in the filter paper, and the decay series for calculating their radioactivity is as follows.

²²² Rn series: ²¹⁸ Po → ²¹⁴ Pb → ²¹⁴ Bi

In the case of discussion, the half-lives of ²¹² Po and ²⁰⁸ Tl are 0.3㎲ and 3.1min, respectively, which are very short compared to the air suspended collection time. Therefore, the cumulative amount of filter paper of these nuclides is also very small. Nevertheless, these nuclides are generated from the decay of the parent nuclide ²¹² Bi and thus contribute to the measured radioactivity concentrations.

Since the half-lives of these nuclides are very short compared to the half-life of the parent nuclide, the radionuclide is in equilibrium with the parent nuclide so that the radioactivity concentrations can be calculated from the radionuclide concentrations of the parent nuclide ²¹² Bi. Thus, the decay sequence to calculate the radioactivity of the decay products of the discussion collected on the filter paper is simply as follows.

²²⁰ Rn Series: ²¹⁶ Po → ²¹² Pb → ²¹² Bi

In general, the decay of nuclides that form a decay series is described by the Bateman equation.

In Equation 1, N _i (t) is the atomic number of the i th nuclide in the decay sequence at time t, and λ _i is the decay constant (s ⁻¹ ) of the i th nuclide. Equation 1 is suitable for describing the radioactivity of radon and decay decay products collected on filter paper.

To describe the radioactivity change in the filter paper during the collection of air flotation, the amount of nuclides collected in Equation 1 must be added. The flow rate of air passing through the filter paper is V (m 3 / min), If the average number of atoms in the air of the i-th nuclide during the collection time is n _i (atoms / ㎥), the Bateman equation is modified as in Equation 2 below.

Solutions to this equation have been proposed by several researchers.

Alternatively, the solution can be found by numerical calculation by the Euler method. Either way, the result is the same. In Equation 2, the initial condition is n _i (0) = 0, and the solution n _i (t _F ) at the time of collecting the air suspended collection time t _F is the initial condition of Equation 1.

Figure 3 is a graph showing the relative amount of radioactive decay products in the filter paper after termination according to the present invention, Figure 4 is a graph showing the relative amount of radioactive decay product in the filter paper after termination according to the present invention.

3 shows the same radioactivity concentrations of ²¹⁸ Po, ²¹⁴ Pb, and ²¹⁴ Bi in air, and calculates the relative radioactivity of the filter paper by Equation 1 and Equation 2. 4 shows the same radioactivity concentrations of ²¹² Pb and ²¹² Bi, and calculates the relative radioactivity on the filter paper.

As shown in FIG. 3, the radioactivity concentration of the collapse product of ²²² Rn in the filter paper is greatly reduced after 5 hours of air-flooded collection. However, as shown in Figure 4, the radioactivity concentration of the ²²⁰ Rn decay product is not significantly reduced even after 5 hours after air suspended collection.

Equation 3 and Equation 4 show that the filter paper collected by the air suspended solids is measured by the measuring device, and the count rate of radiation emitted from these nuclides during the measurement time, and the average total alpha count rate measured from time T ₀ to t Equation 3 and the total beta count rate is calculated as in Equation 4.

Where _x is the N (t) is the number of atoms of the nuclide x in the filter paper at the time t (atoms), ε and _α ε _β is the detection efficiency (counts / s / ㏃) of alpha and beta rays, respectively

<Measurement results and analysis according to the experimental example of the present invention>

F & J (USA) Portable Digital Low Volume Air Sampler was used to collect airborne dust, and the air flow rate was 2.35 ± 0.06ℓ / min, which is used for environmental radiation monitoring in Korea.

The filter paper for collecting air suspended solids is a 2 "Φ Glass microfiber filter (Whatman GF / C), which is installed in the air inlet of the collector. Was measured.

This counter distinguishes alpha and beta lines at the same time by using the difference in signal size by alpha and beta lines.

The beta background was 3.4 ± 0.6 cpm, measured for 60 minutes, with clean filter paper in the sample dish. KCI1.5g was completely dissolved in 20.0cc of distilled water, and then 1.0, 1.5, and 2.0g of aqueous solution was widely applied on the filter paper in the sample dish, and the measurement efficiency of the counter measured using the dried sample was 0.482 ± 0.015 cpm / ㏃.

Figure 3 is measured at the Cheongju local radioactivity station for 120 hours at intervals of 1 hour after collecting the airborne dust. The attenuation trends of all alpha pre-beta radiation are similar, as shown in FIG. 7, which is due to the release of radon and decay decay products to alpha and beta rays.

Comparing this decay pattern with FIG. 3 and FIG. 4, abrupt radiation decay up to about 5 hours is mainly due to the decay of child decay products, and radiation decay up to 80 hours after that is mainly due to decay of debate products. have. The beta count of 4.0 ± 0.4 cpm before 80 hours is believed to be due to the radon decay product ²¹⁰ Pb in addition to the intrinsic beta background of the measurement system.

Thus, the radioactivity contained in the collected air flotation is largely due to radon and decay decay products.

In order to calculate the radioactivity contribution of the radon decay product in the radioactivity of the filter paper, the radiometric time should be about half the life of 3.05 min of 218 Po. On the other hand, more than 80 hours of radiometric data are needed to calculate the contribution of the debate.

The total alpha or total beta radiation coefficient data can be used to calculate the contribution of radon or decay decay products. The use of alpha ray coefficient data is less background than that of beta ray coefficient data, so there is less error due to background evaluation.

The radioactivity of each of these decay products present in the filter paper from the radon concentration in the air and the debate can be calculated using equations (1) and (2).

The alpha count rate is calculated by substituting the calculated radioactivity and alpha counting efficiency of ²¹⁸ Po, ²¹⁴ Bi, and ²¹² Bi into equation (3). do. From the radioactivity of the calculated radon and decay decay products, Equation 4 can also be used to calculate the beta count rate, which should match the measured beta count rate.

Figure 5 is a graph showing the count of pre alpha and pre beta measured after termination in accordance with the present invention.

The total alpha and total beta counts measured continuously for 10 hours at intervals of 2 minutes after collecting the airborne dust are shown in FIG. 5, and the calculated counts are also shown in FIG. 5.

Here, the total beta count is derived from the radioactivity of radon and decay decay products calculated from the total alpha count. In the present invention, since the alpha measurement efficiency was not measured, the beta counting rate calculated from the alpha counting rate was matched with the measured beta counting rate, and the alpha measuring efficiency thus calculated was 0.30 cpm / m.

In addition, when the measurement efficiency for 0.574MeV beta-ray emitted from ²¹² Pb was 0.29cpm / kV, which is lower than 0.482cpm / kV applied to other beta emitters, the calculated beta count rate was consistent with the measured count rate.

This is probably because the energy of beta rays emitted from ²¹² P _b is lower than the energy of beta rays emitted from other beta emitters. As shown in FIG. 5, the measured beta count rate and the calculated beta count rate agree well.

FIG. 6 is a graph showing the amount of total alpha and total beta radioactivity measured after termination according to the present invention, and FIG. 7 is a graph of radon decay products P _b and B _i , calculated using the total alpha data shown in FIG. 6. Graph showing the amount of radioactivity of the decay products P _b and B _i .

6 shows the radioactivity of the resulting radon and decay decay products. After 5 hours of air suspended collection, as shown in Figure 7, the filter paper almost attenuates radon decay products and leaves only ²¹² Pb and ²¹² Bi, which are decay decay products.

8 is a graph showing the count ratio of total beta to total alpha in filter paper after termination.

FIG. 8 shows the ratio of the total beta count to the total alpha count of FIG. 6. In FIG. 8, the ratio of the beta count rate to the alpha count rate due to the radioactivity of ²¹² Pb and ²¹² Bi is also displayed. After 5 hours of collecting air suspended particles, the ratio of the total beta count rate to the total alpha count rate is completely matched.

This reason is explained theoretically as follows. If the number of atoms of ²¹² Pb and ²¹² Bi collected in the filter paper is N _PF and N _BF , respectively, when the time t after collection is solved, the number of atoms of ²¹² Pb and ²¹² Bi N _P , N _{B of} radioactivity is solved, respectively. Equations 5 and 6 are obtained.

Λ _P and λ _B are the decay constants of ²¹² Pb and ²¹² Bi, respectively. Five hours after the airborne collection, exp (-λ _B ) << exp (-λ _P ), so the first term in Equation 6 can be ignored. Therefore, the ratio of the total beta count to the total alpha count is expressed by Equation 7.

Where ε _PB and ε _BB are the measurement efficiency of beta rays emitted from ²¹² Pb and ²¹² Bi, respectively, and ε _BA is the alpha ray measurement efficiency emitted from ²¹² Bi and its daughter nuclides.

Thus, the ratio of total beta radioactivity to total alpha radioactivity is dependent on the detector's measurement efficiency, but is constant regardless of the ratio of debate concentration in the air. This is true only when no radionuclides other than radon and decay decay products are present.

As described above, those skilled in the art will understand that the present invention can be implemented in other specific forms without changing the technical spirit or essential features. Therefore, the above-described embodiments are to be understood in all respects as illustrative and not restrictive. The scope of the present invention is defined by the appended claims rather than the detailed description and all changes or modifications derived from the meaning and scope of the claims and their equivalents should be construed as being included within the scope of the present invention.

The following drawings, which are attached in this specification, illustrate the preferred embodiments of the present invention, and together with the detailed description thereof, serve to further understand the technical spirit of the present invention, and therefore, the present invention is limited only to the matters described in the drawings. It should not be interpreted.

1 is a schematic diagram showing an apparatus for measuring environmental radioactivity in the air according to the present invention.

Figure 2 is a flow chart illustrating a method for measuring environmental radioactivity in the air according to the present invention.

3 is a graph depicting the relative amounts of radioactivity of radon decay products in filter paper after termination in accordance with the present invention.

4 is a graph showing the relative amount of radioactivity of the decay decay product in a filter paper after termination according to the present invention.

Figure 5 is a graph showing the count of pre alpha and pre beta measured after termination in accordance with the present invention.

Figure 6 is a graph showing the total alpha and total beta radioactivity measured after termination in accordance with the present invention.

FIG. 7 is a graph depicting the radioactivity of radon decay products P _b and B _i , debate decay products P _b and B _i calculated using all alpha data shown in FIG. 6.

8 is a graph depicting the count ratio of pre-beta to pre-alpha in filter paper after termination.

<Explanation of symbols for the main parts of the drawings>

1: Environmental radioactivity measuring device in air

11: Alpha radiation concentration meter

12: beta radiation concentration meter

13: Micom

14: display device

Claims (12)

Alpha radiation detector 11; Beta radiation detector 12; A microcomputer 13 for comparing and calculating the radioactivity values detected by the alpha radiation detector 11 and the beta radioactivity detector 12; And It includes a display device 14 for displaying the calculated value of the microcomputer 13, The microcomputer 13 is an environmental radioactivity measuring apparatus in the air, characterized in that for comparing and calculating the equation of the total alpha and all beta count ratio and the total alpha: to beta count ratio. delete Collecting air suspended particles in the filter paper (S100); Measuring alpha and beta radiation concentrations in the filter paper, respectively (S200); The measured alpha radioactivity and beta radioactivity concentrations are compared and calculated by measuring total alpha and total beta radioactivity using a ratio of total alpha count rate, total beta count rate, and total alpha count rate: to beta count rate to detect radioactivity levels. Step (S300); And Method of measuring environmental radioactivity in the air, characterized in that consisting of a display step (S400) showing the detected radioactivity value to the user. The method of claim 3, The alpha, beta radioactivity is a method of measuring environmental radioactivity in the air, characterized in that using the Bateman equation from the radioactive concentration of radon and debate. The method of claim 3, The radioactivity figure is the environmental radioactivity measuring method in the air, characterized in that for measuring 5 hours. delete The method of claim 3, The total alpha count rate is a method for measuring environmental radioactivity in air, characterized in that using the following equation using the total alpha measurement efficiency.

Here, N _x (t) is the number of atoms of the x nuclide in the filter paper at time t, and is the _alpha alpha detection efficiency (Counts / s / s). The method of claim 3, The total beta count rate is a method for measuring environmental radioactivity in air, characterized in that using the following equation using the total beta measurement efficiency.

Here, N _x (t) is the number of atoms of the x nuclide in the filter paper at time t, and ε _α beta ray detection efficiency (Counts / s / ㏃). The method of claim 3, The ratio of the total alpha count rate to the total beta count rate is a method of measuring the environmental radioactivity in the air, characterized in that the following equation.

Where ε _PB and ε _BB are the measurement efficiency of beta rays emitted from ²¹² Pb and ²¹² Bi, respectively, and ε _BA is the alpha ray measurement efficiency emitted from ²¹² Bi and its daughter nuclides. The method of claim 9, Using the ratio of the total alpha count rate: all beta count rate, the radioactivity value can be measured by only one count rate of all alpha or all beta count rate. The method of claim 7, wherein The total alpha measurement efficiency is 0.30cpm / 환경 air radioactivity measuring method, characterized in that. The method of claim 8, The total beta measurement efficiency is 0.29cpm / 환 environmental radioactivity measurement method in the air, characterized in that.

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