Measurement of the indoor and outdoor 220Rn (thoron) equilibrium factor: application to lung dose

Abstract

A miniature four-chamber alpha track detector was developed that measures both (222)Rn (radon) and (220)Rn (thoron), in duplicate. Using this detector and the previous long-term measurements of the (220)Rn decay products (212)Pb, and (212)Bi, an equilibrium factor, F(eq), is derived for both outdoor and indoor (220)Rn environments (0.004±0.001 outdoors and 0.04±0.01 indoors). The lung airway dose can then be calculated from a dose factor from UNSCEAR that requires the equilibrium equivalent thoron concentration (EEC), i.e. the product of F(eq) and the (220)Rn gas concentration. The lung dose from thoron in domestic or occupational surveys is often overlooked. The values of F(eq) for thoron in several published studies are in general agreement with the values reported here. Thus, a long-term alpha track measurement of thoron multiplied by an appropriate indoor or outdoor equilibrium factor yields the EEC, which can be used to assess bronchial lung dose.

Outdoor thoron and progeny in a thorium rich area with old decommissioned mines and waste rock

“…Instead, we observed a weaker correlation and much smaller ratios between filter-sampled 212 Pb and in situ-measured thoron, as compared to the stronger correlation and larger ratios between the integrative TnP and thoron measurements. Such low activity concentrations and equilibrium factors were also reported in another study using filter samples to assess TnP (Harley et al, 2010). One potential explanation could be a reduced filter sampling efficiency for the attached progeny of certain aerosol sizes.…”

Radon and thoron levels in the dwellings of Buddonithanda: a village in the environs of proposed uranium mining site, Nalgonda district, Telangana state, India

“…With the given constant values for D and ; the concentration of thoron at 1 m from the source should decrease to less than one percent of the initial concentration 23 . However, studies showed that the decrement is not that rapid and thoron concentration observed to drop to 10–40% at 1 m distance from the source 24 – 26 . The air circulation in the room promotes the thoron gas to diffuse more distance.…”

Comparative analysis of radon, thoron and thoron progeny concentration measurements

“…In the past, Rn studies were more common than those of Tn, but recent studies in Serbian [1–3], Chinese [4, 5], Indian [6] Canadian [7–9], Japanese [10], Korean [11, 12], Hungarian [13], Slovenian [14], Irish [15, 16] and USA [17] dwellings have show that Tn can be a significant contributor to the radiation exposure. The contributions of Rn and Tn and its progeny (TnP) to radiation exposure are quite different.…”