Alkali-based barium borosilicate glasses having similar composition to the Trombay nuclear research reactor waste base glass containing iron were prepared and irradiated by gamma rays. The radiation-induced defect centers were investigated using electron paramagnetic resonance (EPR) technique. The results showed the formation of silicon hole centers and electron trap centers apart from boron-based oxy hole centers in the glass due to the irradiation. The EPR Hamiltonian parameters for these radicals were evaluated by simulation technique using Bruker SIMFONIA computer program. Glasses with varying iron content were irradiated with the same dose to evaluate the effect of iron content on the defect center concentration. A spin counting technique was employed to evaluate the number of defect centers produced in each glass. It was observed that the defect center concentration reduced as a function of increasing iron content. This was attributed to the charge trapping process of ferric ions in the amorphous system. *manojm@barc.gov.in

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The fission fragment anisotropies for 12 C 1 198 Pt populating 210 Po are found to be systematically higher than that for 12 C 1 194 Pt, the difference decreasing over the energy range 1.0 # E͞V B # 1.4. The parameters required for a statistical model analysis of the data were constrained by fission cross section data and by measuring evaporation residue cross sections. While the measured anisotropies for 12 C 1 194 Pt are in agreement with the saddle point model calculations, those for 12 C 1 198 Pt are considerably larger. The data are suggestive of a significant shell effect in the anisotropies of fission fragments emitted from 210 Po with neutron magic number, N 126. [S0031-9007(98)08289-1] PACS numbers: 25.70.JjShell effects play a central role in determining the stability of nuclei and the nuclear structure. It is generally believed that shell effects are washed out at high excitation energies and angular momenta produced in medium energy heavy ion reactions. It is of interest to investigate an energy region where shell effects are still visible and observe the gradual decrease of the effect with increasing excitation energy. This information is important in the context of production and stability of super heavy elements.In recent years, the unexpected deviation of some fission fragment angular anisotropies from the transition state model has been taken to imply noncompound reaction mechanisms [1]. Anomalous anisotropies have also been interpreted in terms of target deformation [2] and target spin [3]. It is interesting to consider fission fragment anisotropies as a probe for shell effects. We have made anisotropy measurements for 12 C 1 194,198 Pt. This allows a comparison of the fragment anisotropies for 210 Po (with N 126) to be made with that for 206 Po (with N 122). In the limited number of such measurements in the literature for this mass region, no significant isotopic dependence was observed for 12 C 1 182,183,184,186 W [4] and 6 Li 1 194,198 Pt [5].Statistical model calculations which take into account differences in angular momenta, fusion cross sections, fissility values, prefission neutrons and shell corrections to the level densities between the two systems have been made. The statistical model parameters have been constrained by making measurements of partial evaporation residue (ER) cross sections in addition to fission cross sections and also comparing the calculations with the earlier measurements [6-9] for 210,206 Po compound nuclei. Since shell corrections in the level densities are included in the calculation, comparison with the measured anisotropies for 206,210 Po could reveal the effects of the underlying shell structure on other nuclear properties such as the deformation at the fission saddle point.The measurements were carried out using 12 C beams from the BARC-TIFR 14UD Pelletron accelerator at Bombay in the energy range from 59 to 85 MeV. The targets were self supporting rolled foils of 194 Pt (97.4% enriched, 1 mg͞cm 2 thick) and 198 Pt (95.7% enriched, 1.3 mg͞cm 2 thick). The e...

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Electrochemical methodology to investigate the redox speciation of uranyl–citrate complexes.