Search Results

You are looking at 1 - 10 of 17 items for

  • Author or Editor: L. Joshi x
  • Refine by Access: All Content x
Clear All Modify Search

Abstract  

A rapid radiochemical method has been developed for the separation of radium in the presence of excess calcium from environmental samples such as spring waters and marine sediments. Radium is preconcentrated by co-precipitation as carbonates along with other alkaline earths. Subsequently, most of the alkaline earths are complexed with EDTA at pH 7.5 and the solution is passed through a column of Zeokarb-225 (NH 4 + ). Radium, along with traces of calcium, is sorbed on the exchanger. Radium is desorbed with 2N HNO3 and finally coprecipitated with 400 μg of barium as isulfate. The alphas of226Ra are counted in a silicon surface barrier detector and228Ra betas are counted in an end-window GM Counter.

Restricted access

Abstract  

Coastal sediment samples are collected from the top surface layers of the sediments from Bombay to Kottilppad along the West coast of India in order to understand the geochemical behaviour of231Pa and the activity ratios of231Pa/235U in this region of the Indian sub-continent. These coastal regions offer a unique advantage for studying the geochemistry and transport of natural radioactivity due to the placer deposits of monazite in the southern part of India. The top layers of the surface sediments are leached with 1.0M oxalic acid for the extraction of protactinium activities without attacking the mineral core of the particles.233Pa tracer is added to the samples. The chemical recovery obtained by counting233Pa is found to vary from 40 to 90%. Total uranium leached from the sediment surface is determined by fluorimetric method and the concentrations of235U in the leachates are calculated. Using these data, the activity ratios of231Pa/235U have been calculated. These ratios lie in the range of 11.0 to 21.0 for sediments from Bombay to Kottilppad. The data of231Pa activity indicates that there is a deficiency of231Pa in coastal waters of the ocean and that231Pa is removed by precipitation as soon as it is formed by radioactive decay of235U.231Pa is observed to be bound mostly to organic humous material on the surface of the sediment.

Restricted access

Abstract  

Measurements of thorium and uranium isotopic activity ratios have been carried out with top layers of the sediments of the West coast of India in order to understand the behaviour and distribution of these isotopes in the coastal region. The southern part of the West coast contains a large amount of placer deposits while the northern region is free from such deposits.

Restricted access

Abstract  

Samples of coastal marine sediments of the East Coast of India were leached with a saturated solution of ammonium carbonate for the extraction of uranium from the sediment particle surface without attacking the mineral core of the particles. All the sediment samples were found to exhibit a234U/238U activity ratio in the range of 1.07 to 1.14. On removal of surface organic matter, the234U/238U activity ratio is close to 1.00, indicating that the anomaly between238U and234U exists only on the labile surface layer. However, no such variations are observed in235U/238U activity ratios. These ratios are close to 0.045 which is the same as that of natural uranium.

Restricted access

Abstract  

The carbonate cements of conglomeritic deposits of late Pleistocene age have been leached with 0.2N hydrochloric acid and analyzed radiochemically. The leachate and the residue fractions were separately measured for238U,234U and230Th, using isotope-dilution and alpha-spectrometric techniques. The data are used to estimate the isotopic activities of uranium and thorium in the carbonate phase. These activities give age information for the carbonate cementation. Ages in the range of 185–320·103 years were obtained for the samples studied.

Restricted access

Abstract  

Measurements of210Pb at various dephts in a sediment core from the Santa Cruz Basin off the coast of California have been made. The radiochemical separation of210Pb was carried out after ashing the sediment at 400 °C. The activities of the purified210Pb was assayed in a low background beta counter by counting the 1.17 MeV betas of its daughter product210Bi. The method for the chemical separation of210Pb and the results are discussed in the paper.

Restricted access

Abstract  

Nearshore surface sediments from various locations of the West Coast of India were leached by saturated ammonium carbonate solution for the extraction of uranium isotopes. The reagent chosen was found to have high efficiency for leaching uranium isotopes without attacking the mineral core of the sediment particle. The activity ratios of234U/238U are in the range of 1.11 to 1.14 and the activity ratios of235U/235U are in the range of 0.045 to 0.047. The respective activity ratios in leachates, and residues after removal of surface organic matter from the sediment particles by treatment with hydrogen peroxide and 0.05M HCl, revealed disequilibrium between238U and234U only in the surface organic matter. The activity ratios of234U/238U and235U/238U have also been determined in some seawater samples from the Arabian Sea.

Restricted access

Abstract  

Measurements carried out recently with surface labile layers of the estuarine sediments have indicated remarkable dis-equilibrium between234U and238U activaties. The234U/238U activity ratios on the surface of the sediments collected from Mindola estuary of Gujarat State in India have been found to vary in the range of 1.12 to 1.43 while235U/238U activity ratios lie in the range of 0.045. On removing the labile layers and leaching uranium from the core of the sediment particles gave, an equilibrium ratio of 1.00 for234U/238U. There is however no change in the activity ratios of235U/238U.

Restricted access

Abstract  

The measurements of natural radioactivity due to thorium isotopes have been carried out in estuarine sediments of Mandovi river (Goa). The geochemical behaviour of these sediments has been studied by leaching the samples with 5 % ethylenediaminetetraacetic acid at pH 3.0 in order to investigate the processes occurring on the surface of the sediment particles and the distribution of natural thorium in estuarine sediments. The228Th/232Th activity ratios have been found to be in the range of 2.00 to 2.12. This anomaly between232Th and228Th has been attributed to the preferential leaching of228Ra by water flowing over these sediments. The activities of228Ra on the surface labile layers of the sediments have also been determined. The230Th/232Th activity ratios have been found to be in the range of 0.94 to 1.04. These ratios are mainly dependent on the precipitation action of230Th on adjacent sediments.

Restricted access

Abstract  

The surface leaching of the labile component of uranium has been carried out in estuarine sediments of Zuari river in Goa. The measurements of alpha activities of238U,235U and234U in the leachates indicated a remarkable anomaly between the activities of238U and234U. The activity ratios of234U/238U in these leachates have been found to be in the range of 1.10 to 1.14. However, the activity ratios of235U/238U have been found to be 0.045 which is close to that in natural uranium. It has also been observed that the anomaly between238U and234U exists only on the surface organic layers of the backwater sediments of the Zuari river.

Restricted access