RADON AND THORON EXHALATION RATES FROM EARTHEN BUILDING MATERIALS USED IN HIGH BACKGROUND RADIATION AREAS OF HOMA AND RURI, KENYA.

222Rn and 220Rn surface exhalation rates from earthen building materials used in high background radiation areas of Homa and Ruri, Kenya have been measured using an accumulation chamber coupled with RAD7 detector. Activity concentrations of 226Ra and 232Th in the building materials were determined by γ-ray spectroscopy. In Homa the average 222Rn surface exhalation was 1 ± 0.1 mBqm-2 s-1, while that of 220Rn was 18 ± 2 Bqm-2 s-1; in Ruri 222Rn was 0.9 ± 0.1 mBqm-2 s-1 and 220Rn was 25 ± 3 Bqm-2 s-1. 222Rn was 26 times lower than world average and 220Rn was higher by a factor of 21. Average 232Th in Ruri was 1094 ± 55 Bq/kg, three times that in Homa; 226Ra was 129 ± 10 and 111 ± 6 Bq/kg in Homa and Ruri, respectively. There was a strong correlation between exhalation rate of 222Rn and concentration of 226Ra, as well as between 232Th and 220Rn. Thus, 220Rn was the major contributor to the inhaled dose in earthen dwellings of the two regions.