Natural radioactivity in the sub-slab filling gravel of Finnish houses

The study aims at measuring the gamma activity concentration (226Ra, 232Th and 40K) of sub-slabfilling gravel of Finnish houses. This study forms a part of a wider study aiming at exploring factorsaffecting high indoor radon concentrations in Finnish dwellings. The gamma activity and radonemanation were measured from gravel samples sent from 229 Finnish municipalities, the gammaactivity was reported. Gamma activity was determined by HPGe gamma spectrometry. The averageradium and thorium concentrations of the filling gravel were 23 and 27 Bq/kg, respectively. Theaverage potassium (40K) concentration was 780 Bq/kg. The highest gamma activity concentrationswere found in the southern part of Finland and the lowest concentrations in the northern part ofFinland. High radium concentrations were found in the same areas where thorium and potassiumconcentrations were elevated. The results in this study indicated that indoor radon concentrationcorrelates fairly well with the radium concentration of the filling sand under houses.