Development and calibration of a portable radon sampling system for groundwater 222Rn activity concentration measurements

The assembling of a system for field sampling and activity concentration measurement of radon dissolved in groundwater is described. Special attention is given in presenting the calibration procedure to obtain the radon activity concentration in groundwater from the raw counting rate registered in a portable scintillation detector and in establishing the precision of the activity concentration measurements. A field procedure was established and the system tested during one year of monthly observations of 222Rn activity concentration in groundwater drawn from two wells drilled on metamorphic rocks exposed at Eastern São Paulo State, Brazil. The observed mean 222Rn activity concentrations are 374 Bq/dm3 in one well and about 1275 Bq/dm3 in the other one. In both wells the 222Rn activity concentrations showed a seasonal variation similar to variations previously reported in the literature for the same region.