Natural radiation levels in Tamil Nadu and Kerala, India

摘要

Natural radiation measurements were preliminarily carried out in high background areas, in India, so as to understand the biological effects on human beings due to natural radiation exposures. The following parameters were taken into account for dose assessment: (1) ~(222)Rn (radon) concentration, (2) ~(220)Rn (thoron) concentration, (3) equilibrium equivalent thoron concentration (EETC), and (4) indoor/outdoor gamma dose rates. These measurements were made at 15 sites in Tamil Nadu and 5 sites in Kerala, India. The sites include houses and schools. The radon concentration, thoron concentration and EETCs ranged between 2-70, 6-690 and 0.1-1.6 Bqm~(-3), respectively. The indoor and outdoor gamma dose rates ranged from 0.3 to 3.9 and from 0.4 to 6.2 μGyh~(-1) for radon and thoron, respectively. After classifying the dose by exposure, the annual effective dose at each site for radon and thoron was calculated with several assumptions. From the sampled data, the annual effective dose ranged from 4 to 22 mSv with an arithmetic mean of 9.3 mSv and the dose contribution was significantly due to external exposure.