Influence of air flow on the behavior of thoron and its progeny in a traditional Japanese house

Air flow influence on the spatial distribution of thoron (Rn-220) concentration in a typical Japanese traditional house was investigated at various indoor air flow levels, The effect of air flow on the behavior of both thoron and radon progeny were examined simultaneously, Measurements were carried out by using two types of passive monitors, the radon-thoron discriminative monitor and the Radtrak monitor, Thoron and radon progeny were measured by filter grab sampling with ZnS scintillation counting, Under static condition, a horizontal distribution with greatly varied thoron concentrations was found as reported by previous studies, Under turbulent conditions, thoron concentrations in the middle of the room increased and the concentration gradient of thoron gas became lower, An obvious vertical distribution of thoron was also observed, Prominent diurnal variation of radon progeny concentrations was observed whereas that of thoron progeny concentrations was not, Concentration of thoron progeny changed little at different air flow levels, although the thoron gas level at the middle of the room varied significantly, The influence of air flows on detection efficiencies of the two types of thoron monitors were also checked, The mechanism of behavioral change of thoron and its progeny in turbulent atmosphere is discussed.