Rn-mitigation in a traditional austrian farmhouse

An Austrian farmhouse has been mitigated; it was built around the turn of the century in theconventional farmhouse style of that time. Two main reasons for the high Rn concentrations found inthe building could be identified: the construction style, that allowed enhanced Rn transport from theunderlying soil into the building, and the furnace slag used as bulk material for the construction of theceiling and as filling material underneath the ground floor.Prior to mitigation the Rn activity concentrations determined in the building varied between700 Bq/m3(groundfloor) and 250 Bq/m3 (upper floor) as a yearly average, with appr. twice as highvalues in the heating season from October to April. Rn Mitigation was accomplished as a side issue ofa general renovation of the building which was done over a longer period that offered the uniquepossibility to observe the influence and the effectiveness of the single renovation steps on Rnreduction. From the main 3 different steps, (1) removing the bulk material of the ceilings, (2)excavating the ground floor and replacing it by gravel and overlying concrete and (3), covering theconcrete with 5mm bituminous sealant the latter turned out to be most efficent, while step (1) and (2)caused only minor reductions.