Abstract
South coast of India is known as the high-level background radiation area (HBRA) mainly due to the emission from sea sands that contain natural radionuclides as components of the monazite. The rich deposit of monazite unevenly distributes in longer than 100km along the coastal belt of Tamil Nadu and Kerala. We measured radioactivity of sea sands collected from the coastal spot in Tamil Nadu where the anomalously high level of external radiation was detected. In the beach of Chinna Vilai in town of Manavalakurichi of Kanyakumari district, approximately 30km far from the south tip of the Indian peninsula, we found HBRA spot that lays in 2m (width) x 7m (long) along the sea. By the in situ radiation measurements using a field meter, the highest dose in this spot was 162.7mSv/y (18.8μSv/h) that was considerably higher than the previous report in 2007 by Singh et al. which showed 11.4μGy/h in somewhere in Manavalakurichi. The direct measurement by GM survey meter of approximately 100g of the sea sands samples, that were collected from four different places in the HBRA spot and were packed in an independent plastic bag, demonstrated the count rate higher than 1000cpm for all the samples. From these samples, 6 nuclides of Thorium series (Ac-228, Th-228, Ra-224, Pb-212, Bi-212, Tl-208), 4 nuclides of Uranium series (Pa-234m, Ra-226, Pb-214, Bi-214), and Th-231 belonging to Actinium series were found over the detection limit of the HPGe semi-conductor detector. The radioactivity of each nuclide was estimated within the range between 1.08Bq/g (Bi-214) and 43.7Bq-g (Th-228), which appears as the comparable level to the results obtained in Kerala (Shetty at al. 2006).
