“…In contrast to short-term measurements, many authors (e.g. Planinic and Faj, 1991;Sarenio and Guhr, 1991) have employed this concept in a so-called conventional differ ence method which estimates the total activity concentration of both alpha active radon daughters, 218 Po and 214 Po. Here the detector system usually consists of a diffusion sampler and a bare detector to determine A 0 and A 0 + Ai + A\, respectively, from the measured track densities.…”