Description

       Radon-222 (²²²Rn) concentration in surface water is a good indicator for identifying where groundwater appears at the surface. However, it is necessary to concentrate ²²²Rn in order to measure it. This operation is painstaking and requires special equipment. In this study, we developed a simple method in which ²²²Rn is extracted from the sample water by passing air through the sample and then through toluene cooled with dry ice submerged in ethanol.
Since the origin of ²²²Rn is radium-226 (²²⁶Ra) underground, ²²²Rn concentration in groundwater is much higher than that in surface water. When groundwater appears on the surface, the ²²²Rn concentration in surface water increases markedly. We propose an apparatus for concentrating ²²²Rn in toluene cooled in ethanol/dry ice based on the characteristic of ²²²Rn that it dissolves very readily in cooled toluene (Fig. 1). The air is circulated for 60 min. After concentrating, the toluene is poured into a 20-mL glass vial and the radioactive rays from ²²²Rn and its progeny are counted using a liquid scintillation counter.
The relationship between ²²²Rn concentration and counting rate of the liquid scintillation counter was approximately linear, with the line passing through the origin of the coordinate axes, confirming the practicability of the method (Fig. 2).
Application of the method to a study site around Khon Kaen revealed that groundwater leaks into rivers and lakes in areas with elevations below 180 m, a result that agrees with the results from a simulation of groundwater flow (Fig. 3, Table 1).

Figure, table

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   Fig. 1. Apparatus for concentrating ²²²Rn in water samples.

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   Fig. 2. Relationship between ²²²Rn concentration and count rate.

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   Fig. 3. Location of sampling water.

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