KR101280235B1 - Simplified Method for Measurement of Radium in the Underground Water - Google Patents

Abstract

The present invention is a method of measuring the groundwater radium concentration using a time-integrated measuring instrument, and corresponds to a technique that allows non-analysts to analyze the concentration of radium present in the groundwater in a relatively small amount.

Description

Simplified Method for Measurement of Radium in the Underground Water}

The present invention is a technique for a simple measurement method for analyzing the concentration of radium (Radium) dissolved in a very small amount in the ground water using a time integration meter.

Recently, about 20% of groundwater used for drinking water in Korea was contaminated by Radon, a first-class carcinogen, exceeding the management standard, and the Japanese islands, including the East Sea, caused by the Fukushima nuclear accident. In particular, press releases related to large-scale environmental radioactive pollution have been published one after another, which has led to an explosion of public interest in environmental radioactive pollution. In particular, the published data on the contamination of domestic groundwater by natural radioactivity, including radon, is an interim result of the 'Survey on Natural Radioactive Substances in Groundwater', which is scheduled to be conducted in 2007 and to 2016. In summary, the results are shown in Table 1.

Investigation of the actual condition of natural radioactive substances in groundwater (Source: Ministry of Environment) division 2008 2009 2010 Remarks Survey Scrutiny Survey Scrutiny Survey Scrutiny sub Total Percentage Exceeding Percentage Radon Measurement Point 301 222 314 160 314 160 1,471
21% Overscore 68 56 61 45 56 26 312 uranium Measured Score 301 222 614 160 314 160 1,771
4% Overscore 13 16 14 4 16 6 69 Whole alpha Measurement Point 301 222 160 160 314 160 1,317
One% Overscore 0 13 0 6 0 0 19 Radium Measurement Point - 18 - 12 - 4 34
9% Overscore - 3 - 0 - 0 3

As can be seen in Table 1, the Ministry of Environment announced that the concentration of uranium, gross-α and radium, as well as the concentration of radon, a first-class carcinogen, was included. In Korea, there is no regulatory recommendation for natural radioactive materials, so the 'over-point score' in 'Table 1' exceeds the 'drinking water standard' set by the US Environmental Protection Agency in 'Table 2'. .

Regulatory Recommendations for Natural Radioactive Materials by Country (Source: Ministry of Environment) Item United States of America Canada Australia International Health Organization (WHO) Whole alpha 15pCi / L 2.7pCi / L 13.5pCi / L 13.5pCi / L radium Ra-226 5pCi / L
(Total) 16.2pCi / L 13.5pCi / L 27pCi / L Ra-228 13.5pCi / L 13.5pCi / L 2.7pCi / L uranium 30ug / L 20ug / L 20ug / L 15ug / L radon 4,000pCi / L - 2,700pCi / L 2,700pCi / L

From the results of the last three years, it can be seen that radon, uranium, total alpha, and radium are 21%, 4%, 1%, and 9%, respectively. In particular, it can be seen that the number of measurement points of radium is smaller than that of other items, and also shows a decreasing trend over the last three years.

 Radium, which has a half-life of about 1,600 years, is known to have calcium-like behavior in the human body and accumulate in bone causing bone sarcomas, which is considered to require special attention compared to other items. The reason why the measurement data is small is that it is fundamentally difficult to analyze the concentration of radium. Compared with 4,000 pCi / L of radon for groundwater, the standard for radium is significantly lower, 5 pCi / L, which is equivalent to about 5 pg / L. The chemical analysis method cannot analyze such low concentrations of substances, and even if the analysis by radiation / performance measurement is performed, the concentration is too low, so it is adsorbed to the sample bottle during the sampling process, or the pretreatment process such as concentration. Adsorption on the surface of analytical instruments, such as beakers, can cause serious errors. For reference, on the periodic table, calcium belonging to the same group of radium contains about 10 mg / L in the groundwater, which is equivalent to 1.51E + 20 / L in terms of the number of elements per unit volume, whereas the radium of 5pCi / L is only It corresponds to 1.35E + 10 / L, and calcium and radium are mostly dissolved in the form of bicarbonate or chloride in groundwater. As shown in Table 3, the solubility of radium is lower than that of calcium. The probability of adsorption on the inner surface of a sample bottle or beaker is very high.

Comparison of Solubility in Calcium and Radium Salts in Water (Unit: mg / 100mL) division 2 CL ^-1 2 NO ₃ ^-1 SO ₄ ^-2 2 HCO ₃ ^-1 Ra ⁺² 19.6 12 0.00021 - Ca ⁺² 74.5 121.2 0.255 16.6

A brief introduction of the known groundwater radium analysis method is generally applicable to the analysis of the concentration of radium-226, and it waits until the radial equilibrium with the radium and radon, and then blows inert gas to inject radon into the Lucas cell. Bubble collection method, which is a method of inducing radium concentration from radon concentration measurement after collection, is known to be the longest used method and is known to have high accuracy, but the method currently used is released when radium-226 decays. The alpha ray of 4.785 MeV is measured by the liquid scintillation counting method and converted into the radium concentration. In addition, the method converts to the radium concentration by measuring the gamma ray of 186keV after concentrating with ion exchange resin. Bubble trapping using lucascell is not suitable for large scale measurements, and liquid scintillation counting is suitable for large scale measurements, but there are countless alpha rays emitted from uranium and thorium, together with radon in groundwater, and their prokaryotes. Noise makes it difficult to select and measure the 4.785 MeV alpha rays emitted from radium, and 0.186 MeV gamma rays emitted from uranium 235 present in groundwater in the method of measuring 0.186 MeV gamma rays and converting them into radium concentrations. The error due to can be expected. For this reason, the Ministry of Environment recommended that the total alpha only be analyzed when the total alpha exceeds 5 pCi / L. However, the total alpha measurement method also inevitably causes errors due to the self-absorption of alpha rays in the evaporation step and in the dry state after evaporation. The reality is that it must happen.

The present invention corresponds to a technique for analyzing the concentration of radium present in the groundwater in a very small amount by increasing the measurement time using a time-integrated measuring instrument, the problem to be solved by the present invention during a long measurement time Quantify the effect of the change in the distribution ratio of radon in the groundwater layer and air layer inside the container according to the ambient temperature change, and then consider whether the error due to the temperature change is within the allowable range assuming that the measurement is made on site. If the analysis is carried out by taking the groundwater containing the very small amount of radium dissolved into a separate sample bottle and transferring it to a separate measuring container, the groundwater environment and the sample bottle should be collected when it is located in several tens or hundreds of meters underground. Afterwards, the groundwater environment will make a big difference in temperature and pressure. The mechanical change is that some of the radium contained in the groundwater sample may be adsorbed on the inner surface of the sample bottle or may be precipitated with other ions, so that the error does not occur, and a time integration meter is installed. Introducing the equation required to convert the radon concentration measured in the air layer of the sampling bottle to the radium concentration of groundwater.

Types of time-integrated measuring instruments for measuring radon concentrations include those using solid non-target detectors such as LR-115 and CR-39, such as alpha tracks, and solids such as E-Perm. There may be a measuring device using an ionizing box and a measuring device using activated carbon, and all of them may be applied to the present invention except for a measuring device using activated carbon, but it is necessary to analyze the trace amount of radium present in the groundwater. Since it will take a long time, solid ratios such as LR-115 and CR-39 can ignore the effects of environmental radiation rather than solid ionization equations that require correction of gamma and environmental radiation emitted from natural radiation dissolved in groundwater. A meter that uses a detector can be said to be advantageous. In the structure of the main body, a filter-type measuring instrument using a filter having a pore size of about 1 μm for the purpose of eliminating the effects of radon progeny and debate, as well as about 10 μm air gap or hole in the main body. The measuring instrument may also be used, but since the measuring device located inside the measuring container may be wet depending on the flow of groundwater after sampling, in the case of the filter type measuring device, the function of permeating air may be maintained, but the wetness may be prevented. Filters must be watertight or water repellent, and measures that use air gaps or holes will require measures to ensure that the air gaps or holes are not blocked by water. In general, the time-integrated measuring instrument generates an error according to the change of temperature and humidity. In the present invention, the radon, which is an Excel program reflecting the influence of temperature and humidity when analyzing the groundwater radium concentration using an alpha track (α-track), is used. Sheet-A "was used to calculate the deviation according to the change in the temperature of the field on the basis of the results calculated at 20 ℃, the results are shown in 'FIG. In addition, in using a standardized measuring container, if the volume ratio (Va / Vw) of the air layer to the groundwater layer is large, the radon concentration in the air layer will be relatively low after sampling, so that the measurement error will be increased when analyzing the trace amount. Since it will be advantageous to reduce the volume ratio (Va / Vw) of the air layer to the groundwater layer, it will be necessary to optimize the size of the measuring vessel in consideration of the size of the measuring instrument. In addition, to minimize the volume ratio (Va / Vw), it is possible to use a narrow container at the top and a large container at the bottom. However, there is an additional cost for making the container compared to using a commercially available container. something to do.

Using the present invention, the general public will be able to directly measure the radium concentration of the groundwater they use, and if the relevant recommendations are modified to precisely measure only the point where the concentration is measured after the analysis of the radium concentration by the simple measurement method. It will be possible to economically obtain a lot of data on the radium concentration of groundwater and eventually contribute to the public health.

FIG. 1 shows a superimposed radiation decay curve showing that radon remaining in groundwater collapses and disappears over time at the beginning of measurement and a radiation generation curve indicating that radon is generated from radium dissolved in groundwater. As a figure, it is the result of assuming that the sum of the radioactivity of radon and that of radium is 1.
Figure 2 is a graph showing the variation according to the ambient temperature change when measuring the radium concentration of groundwater using alpha track (α-track), the room temperature is 35 at 5 ℃ 35 based on the calculated value at 20 ℃ The maximum error is about ± 20%, and the error of measured value is less than ± 15% if the variation of room temperature is assumed to be 10 ℃ to 30 ℃.
3 is a diagram for explaining the structure of the measuring vessel marked with the sampling line, the groundwater radium concentration if the shelf in the form of a net is prepared, not only the ring-integrated time-integrated measuring instrument but also the ring-integrated time-integrating measuring instrument. It shows that it can utilize for a measurement.
Fig. 4 is a photograph of a sealed container containing ground water and a time integration measuring instrument with radon removed. The side of the main body has a sample outlet for discharging excess ground water to collect a predetermined amount of ground water. It can be seen that the upper part is attached to the hook that can be mounted in the form of hanging alpha track (α-track).

The measuring container used to explain the present invention is a closed container with a lid, and a ring for attaching and detaching a time integration meter is attached to the upper side, and a sampling line is indicated on the side, and the position of the sampling line is In order to ensure consistent data, the level of water surface corresponding to the predetermined amount of groundwater is indicated. As a means of removing and mounting the time integration measuring instrument inside the measuring vessel, attaching the ring to the upper portion of the measuring vessel may use a time integral measuring instrument with a ring such as an alpha track. Inserting a mesh into the top of the can be used even with a measuring instrument without a ring attached. In the material of the measuring vessel, organic polymers such as rigid polyvinyl chloride, polypropylene, polyethylene, nylon, Teflon, polystyrene, polycarbonate, iron or iron alloy including stainless steel, and glass may be used. A transparent material would be advantageous to check whether the volume of the groundwater layer is maintained at the stage, and glass or stainless steel would be advantageous to minimize the absorption of radon on the surface of the vessel. Hereinafter, the present invention will be described in more detail with reference to the following examples. However, the present invention is not limited thereto.

<Examples>

Mark the sampling line 9.5cm high from the bottom on the side of a commercially available container with a volume of 1.3L that is easily available, and then attach an 'O' type nut to attach an alpha track to the inside of the lid. Build a container. The groundwater is collected so that the surface of the sampling vessel of the measuring vessel coincides with the sampling vessel of Sammuri Park in Dunsan-dong, Daejeon, where groundwater is used as drinking water. After bringing the measuring container to the lab or home, inject air for about 1 hour with the lid open using a bubble generator of about 1.2L / min to allow the radon dissolved in the groundwater to be discharged into the air. Seal after installing the alpha track (α-track). In the step of removing radon contained in groundwater through the generation of air bubbles, if the groundwater is very high in radon concentration or if the material of the container can adsorb radon well, air is injected for 1 hour. Although radon may be adsorbed on the inner surface of the measuring vessel even if it is generated, it may be necessary to leave about 1 day in the state of air injection to remove the extra radon adsorbed on the inner surface of the container. About 3 months after the sealing date, the container is opened and the alpha track (α-track) is taken out to measure the radon concentration in the air layer, and the resultant is substituted into Equation 4 to calculate the radium concentration of groundwater. As a result, a measured value of 1.58 pCi / L was obtained. In order to perform sampling and measurement in the same container, there is no problem in deriving the measurement result by collecting ground water in a separate sample bottle and later transferring it to a measuring container without using a dedicated measuring container for radium analysis. It may not be considered, but if it is assumed that a very small amount of radium is adsorbed to the sample bottle or precipitates with other mineral components in this process, the radium adsorbed or precipitated in the sample bottle during transfer to the measuring vessel is assumed. It should not be overlooked that problems may occur in the reliability of the measured values since they may not be moved to the measuring container. To summarize the present invention by dividing step by step, the step of directly collecting a predetermined amount of groundwater in the measuring container, removing the radon dissolved in groundwater using air bubbles, sealing after mounting the time integration meter Then, after one month to one year from the time of sealing can be divided into the step of measuring the radon concentration in the air layer of the measuring vessel, the step of converting the measured value of radon concentration in the air layer to the radium concentration of the groundwater layer into the equation. In the equation for converting the measured value of radon concentration in the air layer of the measuring vessel into the radium concentration of the groundwater layer, the air layer is completed by completing Equation 4 based on Equation 1 representing the generation of radon in radium. From the radon concentration measured at, it was possible to calculate the radium concentration of the groundwater layer.

In the above formula, 'A, Ra' is the radioactivity of the radium, 'A, Rn' is the radioactivity of the radon generated in the radium over time, 'λ' is the decay constant of radon, 't' is the elapsed time. 'Ra, w' is the concentration of radium in the groundwater layer inside the sampling bottle, 'Rn, w' is the radon concentration in the groundwater layer inside the sampling bottle, and 'D' is the time-integrated meter on top of the measuring vessel containing the groundwater from which radon has been removed. Represents the measurement time from the time of sealing to taking out the measuring instrument. 'Rn, a' is the average value of radon concentration during the measuring time measured in the inner air layer of the sampling bottle, and 'Va' is the inner air layer of the measuring container. Vw is the volume of the groundwater layer inside the measuring vessel, and k is the Ostwald distribution coefficient at 20 ° C, corresponding to 0.2593 (Washington JW and Arther WR, Geophysical Research Letters, 1990). In the Ostwald distribution coefficient, the present invention assumes that the temperature at the point where the measuring vessel is located during the measurement time has a temperature distribution of 10 ° C. to 30 ° C. and assumes that 20 ° C. corresponding to the median is a typical room temperature. 0.2593 'is applied, but this value is equivalent to the average value obtained through repeated experiments, and if the temperature is selected other than 20 ℃, the value will change, so instead of' 0.2593 'generally Other values within acceptable tolerances may be used.

In the means of releasing the dissolved radon in the groundwater, if air is generated by the bubble generator, the radon existing in the air will remain in the groundwater even if the bubble is generated by supplying air for a long time. This will act as an error in the method of measuring the radon concentration in the air layer and converting it into radium concentration, but as shown in Table 4, the error becomes longer as the measurement time increases or the concentration of radium to be analyzed. It can be seen that the higher the decreases.

Initial radon concentration remaining in groundwater and error over time Start concentration (pCi / L) division Measurement time radon radium 10 days 50 days 100 days 150 days 200 days 250 days One One Early radon 42 10 5 3 3 2 Radon 58 90 95 97 97 98 error (%) +72 +11 +5 +3 +3 +2 5 Early radon 13 2 One One One One Radon 87 98 99 99 99 99 error (%) +15 +2 +1 +1 +1 +1 5 One Early radon 78 34 21 15 11 9 Radon 22 66 79 85 89 91 error (%) +354 +52 +27 +18 +12 +10 5 Early radon 42 10 5 3 3 2 Radon 58 90 95 97 97 98 error (%) +72 +11 +5 +3 +3 +2

In Table 4, 'starting concentration' is based on the assumption of the concentration of radon dissolved in groundwater and the analyte in the groundwater immediately before the measurement is started after the air is injected to generate bubbles to remove radon. 'Initial radon' is the percentage of total radon concentration inside the measuring vessel that the radon corresponding to the starting concentration decreases over time. 'Radon generated' is the ratio of radon generated from radium present in groundwater. The increase in concentration over time corresponds to a percentage of the total radon concentration inside the measuring vessel. Assuming that radon dissolved in groundwater was released using a bubble generator and assuming that the concentration of radon remaining in groundwater at the start of measurement was 5pCi / L, if the measurement time is 50 days, the actual value of groundwater radium concentration is 1pCi / L. The measured value will be about 1.56pCi / L, and if the actual value is 5pCi / L, the control value of radium, the measured value will be about 5.55pCi / L. Considering that the average radon concentration in the room is 1.4 pCi / L and considering that the Ostwald distribution coefficient near 0.25 ° C is 0.2593, a bubble generator is used to supply sufficient air and the lid of the measuring container is opened. If left at about 1 day, the amount of radon remaining in the sample will be less than 1 pCi / L. If the measurement time is about 1 month, the initial contribution of radon to the groundwater contaminated with 1 pCi / L of radium will be It will be about 11%, and if the control level is close to 5pCi / L, the error will be about 2%, which is an acceptable error. If the measurement time is extended, it will be possible to analyze even lower concentrations of radium. In the end, the present invention can be said to be sufficient as a simple measurement method for measuring the groundwater radium concentration. Even if it is compared with the measurement method using the equipment, it can be said that it is an analysis method which is never behind. Of course, if the start of the measurement after removing the radon dissolved in groundwater over a sufficient time through the generation of bubbles using pure gas instead of air, the error due to the radon remaining in the groundwater at the measurement start step may be further reduced, in the present invention The bubble generator includes not only an air pump for supplying air but also all devices and equipment capable of supplying gas to groundwater, such as a pressurized container for supplying helium, argon and nitrogen.

Claims (2)

In the groundwater radium concentration measurement method,
Taking ground water samples directly to the measuring vessel, removing radon dissolved in groundwater using air bubbles, sealing after mounting the time-integrated measuring instrument, and after one month to one year from the time of sealing, Measuring the radon concentration in the air layer, the radon concentration measured in the air layer was measured in the following equation (Ra, w: radium concentration of the groundwater layer inside the sampling bottle, Rn, a: during the measurement time measured in the inner air layer of the sampling bottle Average value of radon concentration in λ: decay constant of radon, D: measurement time from the time of sealing to taking out the instrument after the time integration meter is mounted on top of the measuring vessel containing the radon-free ground water, Va: measurement Characterized in that it is converted into the radium concentration of the groundwater layer by substituting the volume of the air layer in the vessel, Vw: volume of the groundwater layer in the measuring vessel, k: the Ostwald distribution coefficient). Sewage Radium Concentration Measurement Method

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