[en] The normal absorption and second derivative spectra of ten alcoholic complexes of HoCl₃ and SmCl₃ were recorded. From the observed bands, energies and intensity values were measured. To fit in these measured values with the theoretical values, a set of spectroscopic parameters namely, Judd-Ofelt (T₂, T₄, T₆), intensity (Ω₂, Ω₄, Ω₆) had been computed. A good fit of intensities was obtained between the experimental and theoretical data. The environmental influences on the intensities of the hypersensitive transitions of Sm(III) and Ho(III) ions were found to be noteworthy. (author). 7 tables, 20 refs

[en] Light pink single crystals of Nd(III):LiNH₄SO₄ have been grown under the slow evaporation method. The absorption spectrum of Nd(III) crystal has been recorded in the UV-VIS and NIR regions. The energies and intensities of thirteen levels have been measured. By applying a least-squares fit analysis and Judd-Ofelt parametric procedures, a good fit between the experimental and theoretical energies and intensities for the Nd(III) ion has been obtained. Based on the magnitude of the bonding parameter for the ion studied, the bonding in the crystal lattice is suggested to be covalent. The evaluated spectroscopic parameters relating to the ion are reported. (Auth.)

[en] The absorption spectrum of Pr³⁺:LiNH₄SO₄ single crystals have been recorded in the ultraviolet and near infrared region and the results are compared with the theoretical values. In addition to this the spectral intensities of the observed bands have been studied and results are verified with the computed data. (author)

[en] The Atomic Minerals Directorate for Exploration and Research (AMD) has conducted high-resolution airborne gamma ray spectrometer (AGRS), magnetometer and time domain electromagnetic (TDEM) surveys for uranium exploration, along the northern margins of Cuddapah Basin. The survey area includes well known uranium deposits such as Lambapur-Peddagattu, Chitrial and Koppunuru. The AGRS data collected for uranium exploration is utilised for estimating the average absorbed rates in air due to radio-elemental (potassium in %, uranium and thorium in ppm) distribution over these known deposit areas. Further, portable gamma ray spectrometer (PGRS) was used to acquire data over two nearby locations one from Lambapur deposit, and the other from known anomalous zone and subsequently average gamma dose rates were estimated. Representative in-situ rock samples were also collected from these two areas and subjected to radio-elemental concentration analysis by gamma ray spectrometer (GRS) in the laboratory and then dose rates were estimated. Analyses of these three sets of results complement one another, thereby providing a comprehensive picture of the radiation environment over these deposits. The average absorbed area wise dose rate level is estimated to be 130 ± 47 nGy h⁻¹ in Lambapur-Peddagattu, 186 ± 77 nGy h⁻¹ in Chitrial and 63 ± 22 nGy h⁻¹ in Koppunuru. The obtained average dose levels are found to be higher than the world average value of 54 nGy h⁻¹. The gamma absorbed dose rates in nGy h⁻¹ were converted to annual effective dose rates in mSv y⁻¹ as proposed by the United Nations Scientific Committee on the Effect of Atomic Radiation (UNSCEAR). The annual average effective dose rates for the entire surveyed area is 0.12 mSv y⁻¹, which is much lower than the recommended limit of 1 mSv y⁻¹ by International Commission on Radiation protection (ICRP). It may be ascertained here that the present study establishes a reference data set (baseline) in these areas to assess any changes in gamma radiation levels due to mining and milling activities in future. - Highlights: • Present work establishes a baseline data to assess any changes in radiation levels due to mining and milling activities. • Estimated average absorbed dose rates in the air due to terrestrial radio-elements over the known deposits using AGRS data. • Validated the dose rates estimated from the AGRS data utilizing the ground PGRS data. • Average annual dose rates for Lambapur-Peddagattu, Chitrial, Koppunuru deposits are 130 nGy/hr, 186 nGy/hr, 63 nGy/hr. • Annual effective dose rates computed for these deposits are much lower than the recommended limit.

[en] Recent studies on airborne radiometric data followed by surface radiometric checking reported a wide radioactive zone near Ukinal (Lat.16045'45'N, Long.76039'59E), Gulbarga district, Karnataka which extends intermittently all along the major EW trending Gogi-Kurlagere fault over a stretch of 15 kms proximal to the southern margin of Bhima basin. In course of detailed ground checking all along this faulted margin, occurrence of significant uranium mineralisation hosted by both fractured granites and brecciated limestone at Gogi (Lat.16045'N, Long.76045'E) evoked considerable interest among the geoscientists due to its richer grade and shallow depth environment. Targeting this mineralized host in a complex structural set-up under soil cover turned out to be a challenging task and prime objective of the geophysical investigation at Gogi. (author)

[en] Remote sensing imageries and seismotectonic maps were studied in the light of recently published regional gravity data jointly by NGRI, OIL, GSI and SOl (2006) for accessing the structural fabric of the area to locate suitable site for nuclear power plant. Entire analysis of the data sets has been carried out in Geographical Information Systems (GIS) environment. The study area, Rawatbhata falls well within the Vindhyan Basin bounded by the towns Bundi in the North, Chittaurgarh in the West, Jhalwar in the Southeast and Kota in the Northeast. Interpretation of the arcuate shaped gravity low in the southeast reveals the probable extension of Hindoli Group of Rocks below the Vidhyans and Traps. The selected location is sitting on the gravity high. A gravity gradient of 5 mGal is observed within the 10km buffer zone which is marked in yellow on all the maps. Earlier workers interpreted the thickness of the Vindhyan sediments as 6-7km, based on the deep seismic and gravity surveys, conducted along the Kunjer-Nagaur transect. Study of the seismotectonic maps published by GSI doesn't indicate any seismic activity over the decades. NE-SW trending neotectonic faults and few thermal springs are noticed far away from the study area around 100 km NW of Great Boundary Fault (GBF). Numbers of NE-SW, NW-SE trending major and minor lineaments/faults are present in the region. However, analysis of the geophysical data sets doesn't reflect any such lineaments/faults within 25 km radius. Integrated study of the area helped in evaluating the existing nuclear power plant site. (author)

[en] Cuddapah basin is known for hosting unconformity proximal uranium deposits viz., Lambapur, Peddagattu, Chitirial and Koppunuru along the northern margin of the basin. It is well known that these deposits are mostly associated with basement granitoids in Srisailam Sub-basin, and with cover sediments in Palnad subbasin where basement topography and fault/fracture system influence the fluid flow causing basement alteration and ore deposition. Geological setup, surface manifestation of uranium anomalies and association of the hydro-uranium anomalies near Durgi area in southern part of the Palnad sub-basin, have prompted detail investigation by geophysical methods to probe greater depths. Controlled Source Audio Magneto Telluric (CSAMT) survey conducted over five decades of frequency (0.1-9600 Hz) delineated the various lithounits of Kurnool and Nallamalai Groups along with their thicknesses as there exist an appreciable resistivity contrast. Interpretation of CSAMT sounding data are constrained by resistivity logs and litholog data obtained from the boreholes drilled within the basin indicated three to four layered structure. Sub-surface 2-D and 3-D geo-electrical models are simulated by stitching 1-D layered inverted resistivity earth models. Stitched 1-D inverted resistivity sections revealed the unconformity between the Kurnool Group and Nallamalai Group along with basement undulations. The faults/fractures delineated from the CSAMT data corroborated well with the results of gravity data acquired over the same area. Simulated 3-D voxel resistivity model helped in visualising the faults/fractures, their depth extent, thickness of the Banganapalle quartzite and basement configuration. Integrated interpretation of CSAMT, gravity and borehole data facilitated in delineating the unconformity and the structural features favourable for uranium mineralisation in deeper parts of the Palnad sub-basin. (author)

[en] Airborne gamma ray spectrometer surveys have been used since many years for the exploration of natural radioactive bodies and lithological mapping. All rocks and soils are radioactive naturally containing different proportions of potassium, thorium, uranium and their daughters. The natural decay of these elements emits various types of radiation i.e. alpha, beta and gamma at specific energy levels. Only gamma rays has sufficient energy to be useful for geological mapping and mineral exploration. Airborne gamma-ray spectrometric surveys provides a method of measuring concentrations of potassium, uranium and thorium which is the basis for mapping rocks and soils by virtue of their radio-elemental signature. Variations in concentrations of K, U, Th among different rock types is used for mapping which has been applied to parts of Shillong Basin, Meghalaya, India. The acquired AGRS data over this basin has been subjected to spectral noise reduction (NASVD) and smoothed spectra was obtained. This is followed by window based correction techniques (background/radon removal), correction for spectral stripping and height normalization. Corrected counts have been converted into ground radio-elemental concentrations using sensitivities at flying height. K, U, Th, Total Counts (TC), Ternary (U-Th-K) followed by ratio images (U/Th, U/K and Th/K) facilitated in mapping of various geological units in the study area. Different geological domains viz., basement gneisses, Shillong Group of sediments-Khasi Greenstones, younger granitoids, Sung carbonatite complex, Tertiary cover sediments were clearly demarcated with distinct radiometric signatures. Further, variation within these domains helped in identifying individual lithological units within the geological formations. Many of these units were ground validated with the help of hand held portable gamma-ray spectrometric data, as well as ground observations. A detailed geological map was generated after thorough ground validation. This exercise successfully demonstrated the utility of high resolution gamma-ray spectrometric data in mapping geology. (author)

[en] The Proterozoic Shillong Basin of Meghalaya in north-eastern India is one of the promising thrust areas for unconformity type uranium deposits. The unconformity contact between the Lower Tyrsad Formation and Upper Barapani Formation of Shillong Group of rocks is a favorable loci for unconformity type uranium mineralization. The Shillong Group of rocks are traversed by the shear/fault/fractures forming dilatant structures such as Tyrsad-Barapani Shear (TBS) and Jongkaksha Shears (JS) are favourable for uranium mineralisation. High resolution heliborne magnetic data acquired over the Shillong Basin helped in demarcating various magnetic domains and structures which inturn facilitated in mapping the subsurface geology. Processed magnetic images highlighted the NE-SW trending curvilinear sheared basement-basin contact near Mariang. Along the TBS, prominent NE-SW trending linear magnetic anomalies are observed over the Barapani and Tyrsad Formation. These anomalies are terminated due to the younger granitic intrusive (South Khasi Batholith) in the south-west of the surveyed area. The strong magnetic signature over the TBS is inferred to be due to metavolcanics of Khasi greenstone and Tyrsad metasediments. High amplitude curvilinear magnetic anomalies on the reduced to the pole map clearly demarcated the sheared contact of basement with Tyrsad Formation to the south-east of Mairang. A magnetic profile extending from Mariang to Mangwap that runs across the basement-sediment contact and TBS zone was modeled considering the available surface geological information. A maximum sediment thickness of 1200 m is inferred from modeling of magnetic data. High magnetic anomalies are inferred to be caused by two mafic bodies occurring at a depth of around 300 m. Modeling and interpretation of magnetic data along the TBS provided valuable subsurface geological and structural information that aided uranium exploration in Shillong Basin. (author)

[en] Uranium mineralisation is reported in the basement fracture if Sambalpur granitoids in Dulapali area of Raigarh district, M.P. VLF-EM surveys are conducted using Scintrex IGS-2/ VLF-4 equipment to demarcate the spatial locations of these fractures filled with ferruginous breccia of magnetite, hematite, ilmetite, pyrite and chalcopyrite vis-a-vis, the EM conductors. Three parameters - vertical in-phase (DZR), vertical out-of-phase (DZI) normalised by horizontal magnetic field (Hy) and VLF-EM resistivity (r_a) are recorded and analysed. (author)