Online measurement of unattached and total radon and thoron decay products

Radon and thoron decay products appear in two size modes: unattached and attached to aerosol particles. They deposit at different regions of the human respiratory tract causing different inhalation doses. A separate measurement of the concentration of both modes is realized by a new device based on a working level monitor and screen sampling. In addition, a new operation and evaluation procedure of the working level monitor is described to identify the thoron decay products 212Pb and 212Bi separately. First measurements reveal consistent results. The developments in measurement technique will enhance radon and thoron dose assessment.