An elevation of thoron (and radon) equilibrium factor close to walls based on long-term measurements in dwellings

Long-term surveys of time-integrated measurement of thoron (220Rn) progeny concentrations are scarce, owing to the unavailability of established standard techniques. Consequently, sufficient field data on thoron equilibrium factor is also unavailable, and it is well known that it is strongly dependent on the distance from the source (walls in case of indoor environments) as exhibited by thoron. Therefore a survey for long-term equilibrium factor estimation of thoron as well as radon was conducted in 43 dwellings in Sokobanja municipality, Serbia. Considering the inhomogeneous distribution of thoron, all measurements were performed in a 5-month period in a specified and controlled position, i.e. very close to the wall. Thus, a thoron equilibrium factor"close to the wall"(FTnW) was determined. Long-term thoron and radon progeny concentrations were measured by direct thoron (radon) progeny sensors (DTPS/DRPS)(aluminized mylar mounted LR115 nuclear track detectors for selective registration of alpha particle energies); thoron concentration was measured with "radon-thoron discriminative monitor with nuclear track detector"(RADUET); radon (222Rn) concentration was measured both with RADUET and a different closed-type device housing a CR-39 as detector. The equilibrium factor FTnW ranged from 0.0014 to 0.077 with GM(GSD) of 0.0060 (2.2), whereas the equilibrium factor of radon (FRn) ranged from 0.06 to 0.95 with GM(GSD) of 0.23 (2.0). The results are further elaborated and discussed in the paper.7th International Conference on Protection Against Radon at Home and at Wor