Population exposure at the natural high background radiation areas in India

Natural High Background Radiation Areas (NHBRA) exist in many parts of the country. Notable among them are Chavara-Neendakara, Midalam- Manavalakurichi, Kudiraimozhi, Bhimilipatnam and Chatrapur. A population of nearly half a million who are subjected to radiation exposures generally ranging from 3 to 20 mSv per capita per year, reside in these areas. Based on the exposure the population can be divided into sub-groups such as (a) low (b) medium and (c) high exposure categories. The highest exposed category is in the Midalam-Muttom stretch at the tip of the southern peninsula, where isolated villages show exposure up to 45 mSv per capita per year. The internal exposures here account for less than 10% of the total dose. The rate of mobilization of radionuclide from monazite mineral is very low which explains the low transfer factor to the food chain. The ratio of outdoor to indoor exposure work out to 1.7 in recent years which is higher than the earlier reported value of 1.1 to 1.3. This is attributed to better housing facilities at the NHBRA in recent years. The study has identified groups of people who are subjected to higher exposures due to their occupation in NHBRA. (author)