A new system for the Rn-222 and Ra-226 assay of water and results in the BOREXINO project

We describe a very sensitive system for the Rn-222 and Ra-226 assay of water that we have constructed within the framework of the BOREXINO solar neutrino experiment. The technique that is applied for Rn-222 measurements is based on concentration of radon from water samples followed by gas purification and subsequent alpha counting in low-background miniaturized proportional counters. The same technique is applied to measure the Ra-226 concentration by determining the amount of Rn-222 in equilibrium with the Ra-226 in the water. Sensitivities of similar to1 mBq/m(3) for Ra-226 and similar to100 muBq/m(3) for Rn-222 have been achieved. We present results of measurements illustrating the performance of the system as well as investigations of samples from the BOREXINO water plant and the shielding water of the Counting Test Facility (CTF, a test facility for the BOREXINO detector). (C) 2002 Elsevier Science B.V. All rights reserved