Radiation exposure at the high background area at Manavalakurichi ― the changing trends

Abstract Large-scale surface mining and refilling of the mined areas with monazite-free tailings have reduced the external radiation fields by an order of magnitude, at some locations at the natural high background areas situated in the coastal regions of peninsular India. Significant reduction by a factor of 3 has been observed in the airborne activity due to lower emanation of thoron (220Rn) at the refilled areas. The thathched huts in the area are giving way to brick and concrete structures, thus radically altering the indoor exposures. The exposure due to gamma radiation from the external surroundings was reduced by a factor of 4 due to the shielding by the construction materials. 220 Rn levels as high as 420 Bq m −3 have been observed in some of the mud houses. Significant levels of 232 Th and 228 Ra were found in the urine samples collected from the adult residing in a village, situated in the high background area.