Natural radioactivity in and radon exhalation from Finnish building materials.

A total of 369 samples of Finnish building materials were tested for their 226Ra, 232Th and 40K concentrations. The rate of radon exhalation was measured from 19 samples of material and 34 dwellings were tested for their room air ventilation rate and radon concentration. The mean values of 226Ra, 232Th and 40K concentrations in ballast materials for concrete production were 34.2 Bq X kg-1, 39.0 Bq X kg-1 and 964 Bq X kg-1, with standard deviations of 18.7 Bq X kg-1, 19.5 Bq X kg-1 and 265 Bq X kg-1, respectively. The activity concentrations were higher in clay bricks than in concrete, the mean values being 79.8 Bq X kg-1, 61.6 Bq X kg-1 and 986 Bq X kg-1 for 226Ra, 232Th and 40K, respectively. The normalized radon exhalation rates from 15-cm-thick concrete, slag-aggregate concrete and by-product gypsum were 0.38 (Bq X m-2 X h-1)/(Bq X kg-1), 0.15 (Bq X m-2 X h-1)/(Bq X kg-1), and 0.06 (Bq X m-2 X h-1)/(Bq X kg-1), respectively. The ventilation rates in dwellings varied between 0.27 and 1.99 air changes per h, the mean value being 0.60 h-1, and the corresponding steady state radon concentrations in room air varied from 17.0 to 149 Bq X m-3 in blocks of flats made of concrete and from 11.2 to 61.9 Bq X m-3 in blocks of flats made of brick.