Measurement of 222Rn and 226Ra in water by absorption of radon in polycarbonates and etching alpha-tracks

This work describes a new method for measurement of the activity concentrations of 222Rn and 226Ra in water by exposure of a polycarbonate detector in the water and etching it for alpha-tracks. A theoretical model that gives the in-depth distribution of tracks inside polycarbonate detectors exposed in water is developed and used to optimize the method. The presented experimental results demonstrate the feasibility of the method for measurement of activity concentrations of both 222Rn and 226Ra in water. The lower detection limit is estimated at 0.06 kBq m-3 for 30 days exposure time and is achieved without preconcentration of the water or radiochemical separation of 226Ra. The method allows radon measurements directly in the water source, which could be carried simultaneously in a large number of points.