Study on the deposition velocity of 222Rn/220Rn progeny at varying environmental conditions

Deposition of the Rn-222 (radon) and Rn-220 (thoron) progeny on surfaces is one of the important processes that reduces the progeny activity concentration and hence inhalation dose in the indoor as well as occupational environment. Deposition of Rn-222/Rn-220 progeny on surfaces is characterized by the term effective deposition velocity (V-e) which is highly influenced by parameters like air velocity, aerosol concentration (Z) and Relative Humidity (RH) etc. prevailing in any real indoor or occupational environment. In the present study, behavior of V-e of both Rn-222 and(220)Rn progeny for varying environmental conditions were studied by simulating these conditions in an 8 m(3) calibration chamber. It was observed that both Rn-222 and Rn-220 progeny behave in a similar manner with respect to the environmental parameters. With increase in air velocity, V-e of both Rn-222 and Rn-220 progeny was found to be increased, whereas, with increase in Z and RH, V-e was observed to be decreased. The experimentally obtained values of V-e were compared against the theoretical model calculation which showed good agreement. Measurement of V-e was also carried out in an occupational environment with varying humidity conditions and was found to agree well with the theoretical as well as the experimental values of V-e in controlled calibration chamber.