Methods of determining radon concentration in natural water by liquid scintillation counting

Direct extraction is a useful and easy method for the measurement of radon concentrations in water. A small amount of a toluene-based liquid scintillation (LS) cocktail is added to a I-liter environmental water sample (in a polyethylene bottle) and Rn is extracted by shaking the solution. The LS layer is transferred to a vial and Rn is determined by liquid scintillation counting (LSC) using the integrated counting technique. The concentration of Rn is calculated after establishing radioactive equilibrium among Rn and its daughters, which takes ca. 3.5 h. The detection limit, if no other alpha or beta contaminants are present, is ca. 0.02 Bq liter(-1) for a l-liter water sample (Horiuchi and Murakami 1977, 1978). This is a very simple, reliable and suitable method for field work. The PICO-RAD water system is also an integrated counting technique, designed for analysis of tapwater in houses in the United States. This is a direct LS counting method in which the water sample (10 mi) is placed in a 20-ml scintillation measuring vial with 10 mi of a commercially available LS cocktail, shaken and counted. The detection limit is ca. 4 Bq liter(-1) for a 10-ml water sample (Kessler 1988; Packard 1988). This method will adapt well to measuring Rn concentrations in natural water samples.