RN-222 ABSORPTION IN PLASTIC HOLDERS FOR ALPHA-TRACE DETECTORS - A SOURCE OF ERROR

Experiments show that the plastic holder used for the Swedish Radiatio n Protection Institute's (SSI) alpha track detector absorbs Rn-222 (ra don) and subsequently outgasses it slowly when stored in a lower radon concentration environment. This phenomenon is not unique to the plast ic holder used at SSI. A discrepancy in the results found at an intern ational intercomparison of radon detectors highlighted the problem. Th e observation implies that the practice of enclosing the detectors in plastic bags after exposure should be limited as it can lead to furthe r etching of the detector. and an overestimation of the intended measu rement. This article describes a procedure for estimating the error th at exposure caused by outgassing of radon from the detector housing wo uld give under different exposure conditions. The calculated overexpos ure agrees with the observed one in the intercomparison. One conclusio n is that film and plastic holders should be separated, especially aft er short-term exposures.