Passive Measurements of Thoron and its Progeny in some Dwellings in Ireland

In this paper, an account is given of the development, calibration and field use of a passive alpha track detector sensitive to thoron as well as to radon. No database of thoron and thoron progeny concentrations in dwellings in Ireland exists and, as a result, the level of exposure of the Irish population to thoron and its progeny is unknown. As an initial or pilot stage in establishing such a data base measurements of thoron and thoron progeny concentrations (the latter expressed in Equilibrium Equivalent Thoron Concentration (EETC)) were made in 40 randomly chosen Irish dwellings. The EETC measurements were made using a passive thoron progeny deposition rate monitor designed and supplied by NIRS (Japan). In addition standard unmodified SSI passive radon detectors were used to measure radon in these dwellings. The measured thoron concentrations ranged from below the level of detection to 154 Bq/m3 while the radon gas ranged from 15 to 179 Bq/m3. The thoron progeny EETC values for these dwellings ranged from 0.03 to 7.7 Bq/m3. An account is also given of the dosimetric implications of these measurements