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  • Author or Editor: D. Das x
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Summary  

Nuclear quadrupole interaction study using Time Differential Perturbed Angular Correlation technique has been carried out to identify the sites where hafnium can reside in hydroxyapatite in order to mimic the behavior of plutonium adsorption on hydroxyapatite. Hf(IV) has been found to occupy three sites with the quadrupole interaction frequency(ωQ) and its asymmetry(η): (i) ωQ = 136.7(5) Mrad/s, η = 0.54(1); (ii) ωQ = 300.1(9) Mrad/s, η = 0.35(2); (iii) ωQ = 124.6(5), η = 0.0(1). Narrow frequency distributions indicate the sites are well-defined. This study has been extended to barium orthophosphate to confirm our inference for the apatite structure.

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Abstract  

Procedures for the determination of bromine by the reactions81Br(n, γ)82Br (T=35.4 h) and79Br(n, γ)80mBr (T=4.4 h). In the case of82Br a flat coaxial Ge(Li) crystal is used to measure the 619 keV photopeak. For80mBr a planar Ge(Li) detector is applied to measure the 39 keV γ-ray. The agreement between the data obtained with both techniques for some Standard Reference Materials is satisfactory.

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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.

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Abstract  

Thermodynamic stability of CdMoO4 was determined by measuring the vapor pressures of Cd and MoO3 bearing gaseous species. Th vaporization reaction could be described as CdMoO4(s)+MoO2(s) =Cd(g)+2/n(MoO3)n (n=3, 4 and 5). The vapor pressures of the cadmium (p Cd) and trimer (p (MoO3)3) measured in the temperature range 987≤T/K≤1111 could be expressed, respectively, as ln (p Cd/Pa) = –32643.9/T+29.460.08 and ln(p (MoO3)3/Pa) = –32289.6/T+29.280.08. The standard molar Gibbs free energy of formation of CdMoO4(s), derived from the vaporization results could be expressed by the equations: f G CdMoO4 (s) 0= –1002.0+0.267T14.5 kJ mol–1 (987≤T/K≤1033) and f G CdMoO4 (s) 0 = –1101.9+0.363T14.4 kJ mol–1 (1044≤T/K≤1111). The standard enthalpy of formation of CdMoO4(s) was found to be –1015.414.5 kJ mol–1 .

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Abstract  

Sr2CeO4 has been prepared by sol-combustion and co-precipitate routes and the resulting products have been characterized by XRD analysis. The molar enthalpies of solution of Sr2CeO4, Sr(NO3)2(s) and Ce(NO3)36H2O(s) in 0.150 dm3 of (4.41 mol dm3 H2O2+4.23 mol dm-3 of HNO3) solvent as well as the molar enthalpies of solution of Sr2CeO4(s), SrCl2(s) and CeCl3(s) in 0.150 dm3of (1.47 mol dm-3 H2O2+3.05 mol dm-3 of HClO4) solvent have been measured using an isoperibol type calorimeter. From these results and other auxiliary data, the standard molar enthalpy of formation of Sr2CeO4 has been derived to be -2277.33.1 kJ mol-1 at 298.15 K. This is the first reported thermodynamic data on this compound.

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Abstract  

Selected numbers of representative banded iron formations collected from various mines of iron ore supergroups were investigated using ore microscopy and Mössbauer spectroscopy. The ore microscopy results have been corroborated and compared with Mössbauer spectroscopy outcome. Different iron-bearing minerals present in these banded iron-formations have been quantified by 57Fe Mössbauer spectroscopy. The obtained results have been discussed on the basis of degree of martization and goethite-hematite abundance.

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Abstract  

A new method for the possible incorporation of nuclear wastes has been attempted here by using ceramic matrix of TiO2 as a host precursor for confinement. Hafnium is used as a simulant for actinide high-level waste. After incorporating 181Hf tracer into TiO2 matrix, the leaching property of the resulting matrix was studied in water, sodium chloride and humic acid solutions. The leaching was measured in each of the case by following the radioactivity of 181Hf. TiO2 matrix has also been exposed to γ-radiation in order to simulate the radiation field for nuclear waste. It has been investigated with a nuclear technique called time differential perturbed Angular Correlation (TDPAC) that the lattice structure of titania remains undisturbed even under a strong radiation field. The leaching of 181Hf has also been studied after irradiating the TiO2 matrix with γ-radiation and the leaching behavior was observed not to change from that before irradiation.

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Bipolaris sorokiniana (Sacc.) Shoemaker (Teleomorph: Cochliobolus sativus (Ito and Kuribayashi) Drechs. Ex. Dastur) is a serious necrotrophic pathogen of wheat and barley in several countries. In this paper we report on mechanism of resistance and histopathological changes that occur on pathogen attack in resistant and susceptible genotypes. Callose deposition was observed in the epidermal cell wall of resistant genotype, Pusa T3336 at 2DAI. Lignin deposition around mesophyll tissues was also strongly observed by Phloroglucinol-HCl test in Pusa T3336. Four days after inoculation (4DAI), the pathogen colonized the leaf tissues showing inter and intracellular hyphae in susceptible genotype, Agralocal. In resistant genotype, no colonization was observed. The host tissue in susceptible genotype showed degeneration away from the site of colonization and also showed loss of structural integrity thereby indicating the role of toxin in pathogenesis. Separation of plasmalemma from the cell wall was observed due to loss of electrolytes and degradation of chloroplast at 5 DAI in the susceptible genotypes was prominently seen through light microscopy.

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