Hazard indices and annual effective dose due to terrestrial radioactivity in Northern Kerala, India

Kerala is listed among the six highest background radiation areas of the world. The west coast of Kerala is very well studied. However, no data is available regarding the high ranges. This study reports measurement of terrestrial concentration of radionuclides in Wayanad district (altitude range 700-2100 m above mean sea level), a known tourist place of Kerala, India having a sizeable tribal population. Activities of K-40, Ra-226 and Th-232 in soil samples measured using gamma ray spectrometry were found to be 265 +/- 334, 21 +/- 15 and 39 +/- 38 Bq kg(-1) respectively. Similar studies were done for rock samples. The average indoor and outdoor hazard indices were found to be 0.24 and 0.20 for soil and 0.5 and 0.4 for rocks, respectively. The indoor radon and thoron concentrations were measured using solid state nuclear track detector. The annual average radon concentration was found to be 31 Bq m(-3) and the annual average thoron concentration was 96 Bq m(-3). Out of the samples, one house showed elevated thoron concentration with an annual average value of 621 Bq m(-3).