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  • Author or Editor: A. Joshi x
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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.

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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.

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Abstract  

Double nitrates of Na and K having the composition 2MINO3·LnIII(NO3)3·2H2O(LnIII=Pr, Nd, Sm, Eu, Gd, Tb and Dy) and of Ni and Cu with the composition 3MII(NO3)2·2LnIII(NO3)3·24H2O (LnIII=La, Ce, Pr, Nd, Sm, Eu, Gd, Tb and Dy) have been prepared and their -radiolytic decomposition studied up to 500 kGy. G(NO 2 ) values of K double nitrates at 230 kGy follow the order Dy3+>Pr3+=Nd3+=Sm3+>Tb3+>Eu3+> Gd3+·G(NO 2 3+ ) for NI double nitrates are higher than those of Cu double nitrates. Variation of G(NO 2 ) with cationic radii and the number of f electrons in lanthanide ion show a minimum at Eu. Thermal decomposition studies of double nitrates were also carried out.

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Abstract  

A controlled potential coulometric method developed earlier for the determination of uranium in the presence of iron or plutonium using platinum working electrode was extended for individual determination of uranium and iron or plutonium in single aliquot. After uranium determination, Fe(III) or Pu(IV) in the aliquot is reduced electrolytically to Fe(II) or Pu(III) and subsequently determined by electrolytic oxidation to Fe(III) or Pu(IV), respectively. Analysis of synthetic solutions indicated that the values for uranium, iron and plutonium obtained by this method are reproducible within±0.2% and are in good agreement with values obtained using conventional redox methods 1, 2.

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Abstract  

A controlled potential coulometric method for the determination of uranium in the presence of iron or plutonium using a platinum working electrode has been developed. The method consists of reduction of uranium in 8M H2SO4 by Ti(III) followed by destruction of excess Ti(III) and selective oxidation of Fe(II) or Pu(III) to Fe(III) or Pu(IV), respectively, by sodium nitrite. The U(IV) is subsequently determined by electrolytic oxidation at Pt electrode using Fe(III) as an intermediate. The method was employed for the determination of uranium in synthetic mixtures of U+Fe and U+Pu containing varying ratios of U/Fe or U/Pu. The precision obtained for uranium results was ±0.25%.

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Abstract  

Gamma-radiolytic decomposition of zirconium nitrate and its binary mixtures with potassium halides viz. KCl, KBr and KI has been studied at different compositions up to an absorbed dose of 550 kGy. Radiolytic decomposition has been found to decrease with the absorbed dose. It also varies with the concentration of zirconium nitrate in the binary mixtures. G(NO 2 ) values are enhanced by the addition of halides but only at 75% composition. It is not affected so significantly by KI. A plot of G(NO 2 ) vs. composition of the binary mixtures of the nitrates shows a somewhat parabolic curve with a minimum at 75% Zr(NO3)4+25% KX composition. A part of the energy absorbed by the system is being taken up by the halides depending upon their nature and concentration. Thermal decomposition shows slow decomposition, finally yielding an oxynitrate of indefinite composition.

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Summary

Enantiomeric resolution of two commonly used β-blockers, namely, (±)-propranolol and (±)-atenolol, has been achieved on silica gel layers which were bulkimpregnated with β-cyclodextrin. Solvent systems DMF-ethyl acetate-butanol (3:2:5, υ/υ) and butanol-acetic acid-ethyl acetate-ammonia (5:2:2:0.5, υ/υ) successfully resolved the enantiomers of (±)-propranolol and (±)-atenolol, respectively. The spots were located with iodine vapor. The effects of concentration of the chiral selector and mobile phase variation were also studied.

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Abstract  

Precipitation and solvent extraction methods have been investigated for the purification of plutonium from silver from the solution generated during oxidative dissolution of plutonium oxide using Ag(II) ions. Initial experiments have been carried out using thorium as representative of plutonium. Selecting the optimum conditions, the experiments were repeated with plutonium. The results revealed that Pu can be purified from silver ions either by precipitating silver as silver chloride or silver metal followed by Pu(IV) oxalate precipitation or by selective extraction of Pu(IV) into 20% Aliquat-336 or 30% TBP.

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Abstract  

The purpose of the present study is the association of natural uranium in seawater with colloidal and suspended-particulate matter was determined. The separation of suspended particulate material (>0.45 µm) and colloidal fraction (as dissolved fractions) in seawater were done by suction and ultra filtration techniques. Seawater samples were collected at 1 km away from the shore and subjected to sequential fractionation in nine stages ranging from 2.7 µm to 1.1 nm. Suspended particulate matter were separated in three different size groups namely >2.7 µm, <2.7–>0.45 µm and <0.45–>0.22 µm by suction filtration using cellulose acetate and nitrate membranes filters. To concentrate the solution with colloidal particles <0.22 µm–1.1 nm (0.5 k Nominal Molecular Weight cut-off Limit {NMWL}), the solution obtained from filtration through <0.22 µm was passed through stirred ultra-filtration cell. The pH and conductivity at different stages of fractionation (dissolved) showed minor variations. The concentration of uranium was measured in suspended and dissolved fractions by using a pulsed nitrogen laser at 337.1 nm. In order to evaluate the role of mineral colloids in various stages of filtration, concentration of calcium, magnesium, potassium were measured by using ion chromatography and atomic absorption spectrometry. The clay mineral at seawater pH (approximately 8) behave as negative ions and provides binding site for the positively charge species of uranium. Among the dissolved fraction, the maximum concentrations of colloidal uranium was observed about 4 times higher than that compared to average concentration of 6.93±3.10 ppb in other fractions. In the case of suspended particulate matter, the concentration of uranium was below detection limits (<1 ppb). The maximum concentration of Ca, Mg and K in the dissolved fraction were in the <1.1 nm fraction, while for suspended particulate matter, the concentration of Ca, Mg and K decreased with the decrease in size and it is highest in the fraction of 0.22 –0.45 µm.

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Abstract  

Fluoride and sulphate complexing of Np(VI) has been studied by controlled-potential coulometry at a constant ionic strength. The values of 1 * and 2 * for fluoride complexes were found to be 9.4 and 8.9, respectively, at an ionic strength =0.5. At an ionic strength =1.0, 1 * and 2 * obtained were 6.6 and 10.5, respectively. Sulphate complexing of Np(VI) was studied only at an ionic strength =0.5. The value of 1 * obtained was 5.6.

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