Radon progeny as sources of gross-alpha radioactivity anomalies in ground water

Gross-alpha radiation data from ground water samples are subject to variability introduced as a result of analytical procedure. For example, ground water in the surficial aquifer of central Florida commonly has gross-alpha radioactivity in excess of 555 Bq m-3 (15 pCi L-1). This activity, commonly unsupported by Ra, often results from the 222Rn progeny. The relatively short-lived daughters of 222Rn can give rise to variations in gross-alpha measurements of up to 2 orders of magnitude in replicate samples. Polonium-210, a longer-lived Rn daughter, is also found in concentrations greater than predicted by the Ra content. As a consequence, it is suggested that gross-alpha measurements include Po analyses with Ra and U when standards are exceeded. It should be recognized that, depending on the activity of 210Pb, 210Po activity may vary significantly with holding time. Variations of measured Po activity in replicate samples collected and prepared by present methods indicate that Po analyses may be inconsistent and frequently underestimate total Po activity. Sample preparation methods and measurement techniques are discussed which greatly improve the overall accuracy and consistency of gross-alpha and Po analyses.