A CLOSER LOOK AT THE NATURAL RADIOACTIVITY IN SOILS by: H.Surbeck and G.Piller Lab.Fribourg of the Swiss Federal Commission for Radioactivity Surveillance

Enhanced indoor radon levels are frequently found in the western part of the Swiss Jura mountains, a karst region. The activity in the limestone bedrock is low ( 20 Bq/kg). In the thin soil overburden the =Ra activity concentration is 2 to 3 times higher than in soil samples from the Swiss Plateau but on the average still below 100 Bq/kg. It is supposed that the radon problem in this region is due to the high permeability of the karst bedrock. A sampling device for radon in soil gas measurement is described that permits a coarse in-situ soil permeability determination. Specific activity vs. grain size measurements for some Swiss soils and the high activities found in heavy minerals are presented and a possible aeolian origin of the soils in the Western Jura is discussed.