Geochemical characterization of monazite sands based on rare earth elements, thorium and uranium from a natural high background radiation area in Tamil Nadu, India

The Kanyakumari coastal area in the southernmost part of Tamil Nadu, India is a well-known natural high background radiation area due to the abundance of monazite in beach placer deposits. In the present study, the concentrations of major oxides, rare earth elements (REEs), Th and U were measured to understand geochemical characteristics of these monazite sands. Based on the ambient dose rate, 23 locations covering an area of about 60 km along the coast were selected for sample collection. The concentrations of U and Th ranged from 1.1 to 737.8 μg g^-1 and 25.2-12250.6 μg g^-1, respectively. The Th/U ratio ranged from 2.2 to 61.6, which clearly indicated that Th was the dominant contributing radionuclide to the enhanced natural radioactivity in this coastal region. The chondrite-normalized REEs pattern of the placer deposits showed enrichment in light REEs and depletion in heavy REEs with a negative Eu anomaly that indicated the monazite sands were derived from granite, charnockite, and granitoid rocks from the Nagercoil and the Trivandrum Blocks of the Southern Granulite Terrain.

NATURAL RADIOACTIVITY MEASUREMENT AND DOSE ASSESSMENT OF BEACH PLACER SANDS IN THE COASTAL REGION OF TAMIL NADU (INDIA)

A preliminary study was carried out to determine the radioactivity concentration of 232Th, 226Ra and 40K in beach placer sands from 13 locations along the coast line of Tamil Nadu state, India. The ambient dose rates varied from 9 to 467 nGy h-1. The activity concentrations of radionuclide 232Th, 226Ra and 40K ranged from 5.2 to 683 Bq kg-1, 13 to 198 Bq kg-1 and 107 to 421 Bq kg-1, respectively. The annual effective dose rate ranges from 27 to 620 μSv y-1 and was higher at seven beaches in comparison to the UNSCEAR annual worldwide average value.

IMPACT ON ABSORBED DOSE RATE IN AIR IN KANTO REGION BY FUKUSHIMA DAIICHI NUCLEAR POWER PLANT ACCIDENT

Absorbed dose rates in air were measured for the whole area of the Kanto region in 2015, 2016 and 2017 (n = 31 147). The mean absorbed dose rates in air for each prefecture measured by car-borne surveys were from 44 to 67 nGy h-1 (13-289 nGy h-1). The absorbed dose rate in air from artificial radionuclides (134Cs + 137Cs) measured by fixed-point observation (n = 507) was from 1 to 14 nGy h-1 (0-105 nGy h-1), and meaning that the contribution ratios of 134Cs and 137Cs were 3-22%. The deposited location of artificial radionuclides was less than 1000 m from ground level and depended on the topography, wind direction and precipitation field.

Measurement of uranium distribution coefficient and 235U/238U ratio in soils affected by Fukushima dai-ichi nuclear power plant accident

Fukushima Daiichi Nuclear Power Plant (FDNPP) accident resulted radioactive contamination in soil due to deposition of mainly radiocesium as well as many long-lived radionuclides surrounding a large area around FDNPP. Depending upon environmental conditions, radionuclides in soil can be mobilized in aquatic systems. Therefore, the fate and transfer of these radionuclides in the soil water system is very important for radiation protection and dose assessment. In the present study, soil and water samples were collected from contaminated areas around FDNPP. Inductively coupled plasma mass spectrometry (ICP-MS) is used for total uranium concentration. Emphasis has been given on isotope ratio measurement of ²³⁵U/²³⁸U ratio using thermal ionization mass spectrometry (TIMS) that gives us the idea about its contamination during accident. For the migration behavior, its distribution coefficient (K_d) has been determined using laboratory batch method. Chemical characterization of soil with respect to different parameters has been carried out. The effect of these soil parameters on distribution coefficient of uranium has been studied in order to explain the radionuclide mobility in this particular area. The distribution coefficient values for uranium are found to vary from 30 to 36000 L/kg. A large variation in the distribution coefficient values shows the retention or mobility of uranium is highly dependent on soil characteristics in the particular area. This variation is explained with respect to soil pH, Fe, Mn, CaCO₃ and organic content. There is a very good correlation of uranium K_d obtained with Fe content. There is no enrichment of ²³⁵U has been noticed in the studied area.