Outdoor and indoor natural background gamma radiation across Kerala, India

Abstract

The major share of the total radiation exposure in human beings is from natural sources and hence its measurement is vital to the fundamental understanding of radiation exposure. Natural background gamma radiation of 72 outdoor sites and 32 indoor sites covering all 14 districts of Kerala, a southern state of India, was monitored over a period of two years. Thermo Luminescent Dosimeters (TLDs) and a radiation survey meter were used for the detection. Kollam district (2.32 mGy per year) showed the maximum and Malappuram district (0.64 mGy per year) showed the minimum outdoor values. In the case of indoor radiation, a house in Palode, Thiruvanathapuram district and a house in Thumpamon in Pathanamthitta district showed maximum radiation dose levels (1.69 mGy per year and 1.64 mGy per year, respectively). Indoor environments showed higher radiation dose than the outdoor environment which may be attributed to the contribution from construction materials. The highest Annual Effective Dose (AED) was observed in Chavara area as it is located in a High Background Radiation Area (HBRA). The highest radiation values were observed in concrete houses. Since most of the studied houses were concrete except three or four, no significant difference was observed in the radiation level. In the present study, the maximum indoor to outdoor ratio (I/O) was obtained from a house in Pathanamthitta district. In certain sites it was found that the indoor dosage levels were 1.5 times higher than the outdoor levels, as almost all the sites had outdoor gamma dosage above the world average. These results have a high importance as the values are not common and very specific to this region.