Study of behaviour of Radon and Thoron progeny at varying humidity and turbulent conditions

SSNTD based Radon (²²²Rn) / Thoron (²²⁰Rn) progeny sensors DRPS/DTPS is being presently used widely for measurement of ²²²Rn/²²⁰Rn progeny concentration and hence the inhalation dose assessment, in indoor and occupational environments. But the conditions in indoors are quite different from occupational environment of uranium mines and thorium plants, wherein high humidity and turbulent conditions are encountered. In these conditions, the behaviour of radon progeny and thoron progeny aerosols will be different. ²²²Rn/²²⁰Rn progeny aerosols in any environment exist in two states, unattached and aerosol-attached state. These two states of progeny aerosols tend to deposit on any available surfaces, not only in indoors or occupational environments, but also in human respiratory tract upon inhalation. The deposition on any surface can be quantified by deposition velocity (V_d) of the progeny atoms, which is an environment dependent parameter. Hence V_d will vary with aerosol concentration, humidity, air velocity etc. In the present work, V_d measurements were carried out in controlled conditions varying the air circulation conditions and humidity. V_d was measured as a ratio of deposited atom flux to room atom concentrations at different environmental conditions. Studies were carried out in controlled conditions in an 8m³ calibration chamber using ²²⁰Rn/ ²²²Rn Pylon source with an activity of 100 kBq each. Air velocity was measured using Hot-wire anemometer