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- Author or Editor: D. Kumar x
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Abstract
57Fe Mössbauer spectroscopy has been employed to characterize the chemical composition of iron aerosols collected from three distinct groups of sites representing remote, urban and industrially active areas. The Mössbauer spectra clearly show this environmental difference. The fact that the spectra of the samples collected from the remote areas are quite similar to those of clay minerals corroborates the view that iron aerosols are soil derived. Similarly the predominant presence of 
-Fe2O3 and Fe3O4 in the close vicinity of industrial activities suggests that the Mössbauer spectroscopy can help identify the anthropogenic processes against the natural ones.
Abstract
Cobalt(II) complexes of tetradentate Schiff bases of the type CoL [H2L=C20H16N2O2 (H2dsp), C21H18N2O2 (H2dst), C20H15N3O4 (H2ndsp) and C16H16N2O2 (H2salen)] have been synthesized and characterized by UV-visible, IR, and magnetic studies. Various thermodynamic parameters have been calculated for the decomposition step using TG/DTA. C20H14N2O2Co complex has the minimum and C16H14N2O2Co complex has the maximum activation energy.
Abstract
Desorption studies of137Cs from marine sediments by artificial sea water and artificial sea water devoid of individual major cations such as Na, K, Ca, Mg and Sr indicated that only Na and K were effective in the desorption of137Cs. Studies with various ionic strengths ranginf from 0.01 to 1.6M KCl and NaCl solutions showed that KCl desorbs constantly about 45%137Cs at and above an ionic strength of 0.1. In case of NaCl, the percent desorption increases linearly with ionic strength. The difference in desorption by K and Na is attributed to the contraction of the clay mineral layers by K ion and expansion of the layers by Na ion.
Abstract
Bioassay technique is used for the estimation of actinides present in the body based on their excretion rate through body fluids. For occupational radiation workers urine assay is the preferred method for monitoring of chronic internal exposure. Determination of low concentrations of actinides such as plutonium, americium and uranium at low level of mBq in urine by alpha spectrometry requires pre-concentration of large volumes of urine. This article deals with standardization of analytical method for the determination of 241Am isotope in urine samples using Extraction Chromatography (EC) and 243Am tracer for radiochemical recovery. The method involves oxidation of urine followed by co-precipitation of americium along with calcium phosphate. This precipitate after treatment is further subjected to calcium oxalate co-precipitation. Separation of Am was carried out by EC column prepared by PC88-A (2-ethyl hexyl phosphonic acid 2-ethyl hexyl monoester) adsorbed on microporous resin XAD-7 (PC88A-XAD7). Am-fraction was electro-deposited and activity estimated using tracer recovery by alpha spectrometer. Ten routine urine samples of radiation workers were analyzed and consistent radiochemical recovery was obtained in the range 44–60% with a mean and standard deviation of 51 and 4.7% respectively.
Abstract
Miniature annular centrifugal contactors are nearly perfect for shielded hot-cell applications during flowsheet evaluation but these contactors require complex maintenance of electrical drive-motors during radioactive experiments. To reduce the number of electrical drives in the shielded cell, an indigenous design of miniature Taylor Couette (TC) mixing based countercurrent differential extraction column has been developed. In this paper, results of mass transfer experiments for an indigenously developed TC column with 30% TBP/aqueous nitric acid solutions are reported. The developed device worked perfectly in counter–current differential mode and demonstrated equivalence to multiple-extraction stages while working with a single electrical drive. The developed TC unit demonstrated operation with a reduced efficiency without flooding even in absence of rotor rotation. This observation is a vital step towards designing of robust contactors, which do not flood during temporary power failure or failure of drive mechanism.
Abstract
Bioassay technique is used for the estimation of actinides present in the body based on their excretion rate through body fluids. For occupational radiation workers urine assay is the preferred method for monitoring of chronic internal exposure. Determination of low concentrations of actinides such as plutonium, americium and uranium at low level of mBq in urine by alpha spectrometry requires pre-concentration of large volumes of urine. This paper deals with standardization of analytical method for the determination of Pu-isotopes in urine samples using anion exchange resin and 236Pu tracer for radiochemical recovery. The method involves oxidation of urine followed by co-precipitation of plutonium along with calcium phosphate. Separation of Pu was carried out by Amberlite, IRA-400, anion exchange resin. Pu-fraction was electrodeposited and activity estimated using tracer recovery by alpha spectrometer. Twenty routine urine samples of radiation workers were analyzed and consistent radiochemical tracer recovery was obtained in the range 74–96% with a mean and standard deviation of 85 and 6% respectively.
Abstract
L III edge X-ray Absorption Fine Structure (XAFS) spectroscopic study of Eu(III) sorbed on γ-alumina from aqueous solutions of different pH (values ranging from 6 to 8) has been carried out at XAFS beam line of Elettra Synchrotron facility, Italy, in transmission mode. Extended X-ray Absorption Fine Structure spectra of reference compounds, namely, Eu2O3, Eu(OH)3 and Eu-aquo complex in solution, were also measured. The data were analyzed using the IFEFFIT suite of code. XAFS spectra of the sorption samples is dominated by the Eu–O near neighbor co-ordination at distance 2.4 ± 0.1 Å. 8–9 oxygen atoms, coming from both coordinating water molecule and oxygen atoms from alumina surface, surround the Eu(III) in the surface complex. Next near neighbor atoms in all the sorption samples consist of Al at distance ~3.6 and 3.8 Å, which on comparison with literature data indicates towards Eu(III) bidentate binding to apical oxygen of two different alumina octahedra on γ-alumina surface.
Abstract
Sorption behavior of 241Am (~10−9 M) on naturally occurring mineral pyrite (particle size: ≤70 μm) has been studied under varying conditions of pH (2–11), and ionic strength (0.01–1.0 M (NaClO4)). The effects of humic acid (2 mg/L), other complexing anions (1 × 10−4 M CO3 2−, SO4 2−, C2O4 2− and PO4 3−), di- and trivalent metal ions (1 × 10−3 M Mg2+, Ca2+ and Nd3+) on sorption behavior of Am3+ at a fixed ionic strength (I = 0.10 M (NaClO4)) have been studied. The sorption of 241Am on pyrite increased with pH from 2.8 (84%) to 8.1 (97%). The sorption of 241Am decreased with ionic strength at low pH values (2 ≤ pH ≤ 4), but was insensitive in the pH range of 4–10, suggesting the formation of outer-sphere complexes on pyrite surface at lower pH, and inner-sphere complexes at higher pH values. The sorption of 241Am increased in the presence of (i) humic acid (5 < pH < 7.5), and (ii) C2O4 2− (2 < pH < 3). By contrast, other complexing anions such as (carbonate, phosphate, and sulphate) showed negligible influence on 241Am sorption. The presence of Mg2+, Ca2+ ions showed marginal effect on the sorption profile of 241Am; while the presence of Nd3+ ion suppressed its sorption significantly under the conditions of present study. The sorption of 241Am on pyrite decreased with increased temperature indicating an exothermic process.
Abstract
Bioassay technique is used for the estimation of actinides present in the body based on the excretion rate of body fluids. For occupational radiation workers urine assay is the preferred method for monitoring of chronic internal exposure. Determination of low concentrations of actinides such as plutonium, americium and uranium at low level of mBq in urine by alpha-spectrometry requires pre-concentration of large volumes of urine. This paper deals with standardization of analytical method for the determination of U-isotopes in urine samples using anion-exchange resin and 232U tracer for radiochemical recovery. The method involves oxidation of urine followed by co-precipitation of uranium along with calcium phosphate. Separation of U was carried out by Amberlite, IRA-400, anion-exchange resin. U-fraction was electrodeposited and activity estimated using tracer recovery by alpha-spectrometer. Eight routine urine samples of radiation workers were analyzed and consistent radiochemical tracer recovery was obtained in the range of 51% to 67% with a mean and standard deviation of 60% and 5.4%, respectively.
Influence of temperature on thermodynamic properties of acid–base liquid mixtures
An ultrasonic, volumetric, and viscometric study
Abstract
Ultrasonic velocity, u density, ρ and viscosity, η of mixtures of N,N-dimethyl acetamide with equimolar mixture of ethanol + isopropyl alcohol/isobutyl alcohol/isoamyl alcohol, including those of pure liquids over the entire composition have been measured at T = 308.15, 313.15, and 318.15 K. Using this data, various thermo-acoustic parameters such as deviations in ultrasonic velocity, Δu, isentropic compressibility, Δk
s
, viscosity, Δη, excess molar volume, 
and excess Gibb's free energy of activation for viscous flow, ΔG
∗E have been calculated at different temperatures. The calculated deviation and excess functions have been fitted to the Redlich–Kister type polynomial equation. The influence of temperature on the observed negative and positive values of deviation and excess thermodynamic properties has been explained in terms of molecular interactions present in the investigated acid–base liquid mixtures. The experimental data of ultrasonic velocity have been used to check the applicability of velocity models of Nomoto, Van Dael and Vangeel and Junjie and viscosity data have also been availed to test the applicability of standard viscosity models of Grunberg-Nissan, Hind-Mc Laughlin, and Katti-Chaudhary for all the systems investigated at various temperatures.
