Natural environmental radiation mapping in parts of Meghalaya, India

Abstract

This paper presents new data on natural environmental radiation mapping in Meghalaya for the first time in India. Two alternate methods have been used to map (1) a regional low-density environmental radiation mapping by using radiation meters, (2) high-resolution radiation mapping of Shillong Basin using the data generated by an integrated litho- and pedo-geochemical sampling program using gamma ray spectrometric measurements on both rock and soils samples. The variation in radio-elemental concentrations and radiation levels are related to bedrock geology and structures. The high levels of radiation levels are observed in the areas occupied by Mylliem Granite (3.935 mSv/a, 51 μR/h, 178.066 nGy/s) followed by South Khasi Batholith with pink feldspar (2.42 to 3.652 mSv/a, 31 μR/h, 109.502–165.249 nGy/s), graphitic schists (avg. 52.10 pGy/s, 1.06 mSv/a), Chlorite Schist (avg. 51.16 pGy/s, 1.13 mSv/a), Phyllites (avg. 47.98 pGy/s, 1.06 mSv/a), volcanics (avg. 46.9 pGy/s, 1.04 mSv/a), The Chlorite schist of Tyrsad formation (21 μR/h, 1.643 mSv/a, 74.321 nGy/s) and Barapani arenite (16 μR/h 1.21 mSv/a, 54.773 nGy/s), Tertiary sandstone (21 μR/h, 1.633 mSv/a, 73.885 nGy/s), Shella subgroup (12 μR/h, 0.914 mSv/a, 41.376 nGy/s), Langpars (13 μR/h, 1.006 mSv/a, 45.502 nGy/s), Upper Mahadek (26 μR/h, 2.062 mSv/a, 93.298 nGy/s), Lower Mahadek (38 μR/h, 2.935 mSv/a, 132.785 nGy/s), and the lowest environmental radiation levels are observed over Sylhet traps (9 μR/h, 0.725 mSv/a, 32.786 nGy/s). The soils generally show higher radiation levels as compared to their bed rocks. Comparisons are made with high radiation areas of the world results, showing that they are lower than high background radiation areas. These radiation images are the first series of environmental images for Meghalaya and will serve as the baseline data for the upcoming uranium mining projects in Meghalaya. Baseline environmental radiation images are necessary information to policy makers and provide a sound basis for addressing the public concerns for radiation levels.