Measurement of the radon-222 content of soil gas by liquid scintillation counting

A method is described for measuring the ²²²Rn content of soil gas using a conventional liquid scintillation counter. Gas samples, collected in wetted ground-glass syringes, are equilibrated with a scintillation cocktail which is then expelled into a scintillation vial and counted. The method is straightforward and relatively fast (5–6 min. of operator's time per sample), and yields results having 95% confidence limits of ∼ ± 10% for samples containing ≥ 2·10⁴ Bq m⁻³ of ²²²Rn. The method is applied to a watershed near Bickford Reservoir in Massachusetts, U.S.A., where soil-gas ²²Rn content is found to be reasonably constant horizontally, but strongly and systematically increasing with depth, to > 5·10⁴ Bq m⁻³ at soil depths of ∼ 1 m.