Development of an energy discriminate CR-39 ® nuclear track etch dosimeter for Radon-220 gas measurements

An energy discriminate CR-39 ® nuclear track etch dosimeter for use in a 220Rn and 222Rn gas monitor has been developed and experimentally assessed. It utilises a thin film of Mylar ® C to attenuate the alpha particle energies to allow only the damage tracks created by the 8.785 MeV alpha particles emitted from 212Po of the 232Th decay chain to be registered in the CR-39 ® plaque, allowing for the direct measurement of 220Rn gas concentrations. The dosimeter was developed through a combination of experimental investigations and theoretical simulations using the Monte Carlo ion transport modelling program Stopping and Range of Ions in Materials (SRIM 2008). A film thickness of 54 μm has been shown to attenuate all alpha energies less then 7.7 MeV.