Natural Radioactivity in the Sub-slab Filling Gravel of Finnish Houses

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