Distribution patterns of gamma radiation dose rate in the high background radiation area of Odisha, India

Distribution of naturally occurring radionuclides and gamma dose rate assessment in the soils of high background natural radiation area Odisha, India

A study on the activity concentration of primordial radionuclides 226Ra, 232Th and 40K was carried out on the surface soil samples collected from the coastal villages between Chhatrapur and Gopalpur regions of high background natural radiation area Odisha, India, using high purity germanium gamma spectroscopy. The mean activity concentrations of 226Ra, 232Th and 40K were found to be 231, 1692 and 250 Bq/kg, respectively. The total mean absorbed dose owing to the presence of 226Ra, 232Th and 40K was 1139 nGy/h. The mean annual effective dose was found to be 1397 μSv/y and higher than the UNSCEAR average value 70 μSv/y.

234U/238U disequilibrium and 235U/238U ratios measured using MC-ICP-MS in natural high background radiation area soils to understand the fate of uranium

The Chhatrapur-Gopalpur coastal area in Odisha, India is a well-known natural high background radiation (HBRA) area due to the abundance of monazite (a thorium bearing radioactive mineral) in beach sands and soils. Recent studies on Chhatrapur-Gopalpur HBRA groundwater have reported high concentrations of uranium and its decay products. Therefore, the soils of the Chhatrapur-Gopalpur HBRA are reasonably suspected as the sources of these high uranium concentrations in groundwater. In this report, first the uranium concentrations in soil samples were measured using inductively coupled plasma mass spectrometry (ICP-MS) and they were found to range from 0.61 ± 0.01 to 38.59 ± 0.16 mg kg^-１. Next, the ²³⁴U/²³⁸U and ²³⁵U/²³⁸U isotope ratios were measured to establish a baseline for the first time in Chhatrapur-Gopalpur HBRA soil. Multi-collector inductively coupled plasma mass spectrometry (MC-ICP-MS) was used for measurement of these isotope ratios. The ²³⁵U/²³⁸U ratio was observed to be the normal terrestrial value. The ²³⁴U/²³⁸U activity ratio, was calculated to understand the secular equilibrium between ²³⁴U and ²³⁸U in soil and it varied from 0.959 to 1.070. To understand the dynamics of uranium in HBRA soil, physico-chemical characteristics of soil were correlated with uranium isotope ratios and this correlation of ²³⁴U/²³⁸U activity ratio indicated the leaching of ²³⁴U from Odisha HBRA soil.

ICP-MS Measurement of Trace and Rare Earth Elements in Beach Placer-Deposit Soils of Odisha, East Coast of India, to Estimate Natural Enhancement of Elements in the Environment

Inductively coupled plasma mass spectrometry (ICP-MS) has been used to measure the concentration of trace and rare earth elements (REEs) in soils. Geochemical certified reference materials such as JLk-1, JB-1, and JB-3 were used for the validation of the analytical method. The measured values were in good agreement with the certified values for all the elements and were within 10% analytical error. Beach placer deposits of soils mainly from Odisha, on the east coast of India, have been selected to study selected trace and rare earth elements (REEs), to estimate enrichment factor (EF) and geoaccumulation index (I_geo) in the natural environment. Enrichment factor (EF) and geoaccumulation index (I_geo) results showed that Cr, Mn, Fe, Co, Zn, Y, Zr, Cd and U were significantly enriched, and Th was extremely enriched. The total content of REEs (ƩREEs) ranged from 101.3 to 12,911.3 µg g⁻¹, with an average 2431.1 µg g⁻¹ which was higher than the average crustal value of ΣREEs. A high concentration of Th and light REEs were strongly correlated, which confirmed soil enrichment with monazite minerals. High ratios of light REEs (LREEs)/heavy REEs (HREEs) with a strong negative Eu anomaly revealed a felsic origin. The comparison of the chondrite normalized REE patterns of soil with hinterland rocks such as granite, charnockite, khondalite and migmatite suggested that enhancement of trace and REEs are of natural origin.

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.