Characterization of CR 39 nuclear track detector for use as a radon/thoron dosemeter

For the estimation of radon, thoron and their short-lived daughter products in air radon diffusion chambers with passive α-track etch detectors have been used. The report describes the properties of CR 39 track etch detectors in particular with respect to the spectrometric detection of α-particles in the energy range up to 8.77 MeV using chemical and a combination of chemical-electrochemical etching technique. In order to optimize the etching conditions for an α-energy discrimination in the energy range up to 8.77 MeV, the ECE track size diameter and the track density have been investigated as a function of the chemical pre-etching time using three electrical field strengths. In a mixed α-spectrum the contributions of various α-particles with energies between 4.6 to 8.77 MeV have been determined experimentally in CR 39 and compared with the spectral measurement using a surface barrier detector and the same irradiation geometry. Beside CR 39 detectors etched chemically and electrochemically, in addition surface barrier detectors and a Monte Carlo calculation have been used to evaluate the α-energy spectrum for thoron and its daughter products emitted by α-decays in the air volume and the plate-out of daughters at the inner surface on the diffusion chamber. (orig./HP)