Band 102, Heft 3

Production cross-sections of the isotope 256 Lr in the 249,250,251 Cf + 11 B, 243 Am + 18 O, and 248 Cm + 14 N reactions were measured using a He/KCl gas-jet transport system and a rotating wheel α -particle detection apparatus. The α -particle energy of 256 Lr was distributed from 8.3 to 8.7 MeV and its half-life, T 1/2 , was measured to be 28 ± 1 s. The maximum cross sections in the 249 Cf( 11 B, 4 n ) 256 Lr and 243 Am( 18 O, 5 n ) 256 Lr reactions were determined to be 122 ± 36 nb at the beam energy of 63 MeV and 26 ± 7 nb at 96 MeV, respectively. In the 248 Cm( 14 N, 6 n ) 256 Lr reaction, the cross section was measured to be 27 ± 10 nb at 91 MeV.

The 96 Zr( γ ,  n ) 95 Zr reaction cross-section was experimentally determined at end point bremsstrahlung energies of 10 and 12.5 MeV using off-line γ -ray spectrometric technique. The cross-section increases sharply from the end point energy of 10 to 12.5 MeV, which indicates the role of excitation energy. The reaction cross-section as a function of photon energy was also calculated theoretically using the TALYS 1.2 computer code. The flux weighted average value of the 96 Zr( γ ,  n ) 95 Zr reaction cross-section for the end-point bremsstrahlung energies of 10 and 12.5 MeV was also calculated using the experimental and theoretical data of mono-energetic photons to compare with the present data. The cross-section given in the present work at end- point bremsstrahlung energy of 10 MeV is closer to the flux-weighted value of TALYS but higher than the literature data. On the other hand, at 12.5 MeV, it is higher than the flux weighted value of TALYS and the literature data.

The existence of Pu(VIII) was shown in alkaline solutions and in nonpolar solvents (CCl 4 and CHCl 3 ) on the ground of such experimental facts like extraction of plutonium species, obtained by means of ozonization of Pu(VI) alkaline solutions into CCl 4 and CHCl 3 ; volatility of Pu compounds out of aqueous alkaline solutions, and the mentioned solvents. The product of interaction between PuO 3  · 0.8H 2 O and XeF 2 in CCl 4 and CHCl 3 was of the same chemical form for both cases and identical with the form of the product of volatility of Pu out of these organic solutions. The electronic absorbance spectra of these products in CCl 4 and CHCl 3 were fairly similar to the ones for OsO 4 and RuO 4 . The band of absorption in these spectra with the maximum at 332 nm corresponds to the charge transfer of metal-ligand type [ π (O)→Pu], as the value of molar extinction coefficient ε was found to be higher than 2 · 10 3  L/mole cm. A satisfactory agreement between the energies for the transitions of PuO 4 molecule designed by X α -SW method and experimental data was observed. A similar accordance was observed for the designed vibration frequency (DFT-method) with the one found as result of analysis of the vibration structure of the experimental spectra.

Groundwaters (borewell and handpump) were sampled from two districts (Bathinda and Mansa) of Punjab state and analyzed for their major ionic concentrations and uranium isotope compositions in order to assess the possible origins of the waters and water–rock interactions that occurred in the deep aquifer system. The major ionic concentrations of waters were plotted on a Piper diagram and grouped into four dominant hydrochemical facies as (Na+K)-SO 4 +Cl type (69% – 73%), (Ca+Mg)-SO 4 +Cl type (6% – 21%), (Ca+Mg)–HCO 3 type (4% – 6%) and (Na+K)-HCO 3 type (2% – 19%). It was observed that mobility of uranium in groundwater was very much influenced by TDS (total dissolved solids). To investigate the various mechanisms for deriving the elevated uranium concentrations in groundwater, 234 U/ 238 U activity ratios (ARs) were calculated using the determined activity levels of 234 U and 238 U. The mean ARs was found to be near unity ( i.e. secular equilibrium) in the study regions confirmed that uranium in groundwaters was mainly resulted from its host/parent rocks through weathering processes. The concentration of HCO 3 − in ground water showed one order of magnitude higher than the total dissolved SiO 2 indicates that carbonate weathering was the dominant process due to major water–rock interaction. The uranium speciation in groundwaters was investigated by an equilibrium model calculation using MEDUSA (make equilibrium diagrams using sophisticated algorithms) under the influence of redox conditions and complexant concentration. At the observed range of pH values, the predominant redox speciation of uranium was observed as hydroxo-carbonato complexes of (UO 2 ) 2 (CO 3 )(OH) 3 − and hydroxyl complexes of UO 2 (OH) 3 − which might be caused for increasing the solubility of uranium. Due to very low concentration of phosphate in groundwater, its effects on U(VI)-aqueous speciation was negligible.

Present work reports on synthesis, characterization and application of titania powder (anatase) for sorption of 137 Cs (monovalent), 133 Ba (divalent) and 154 Eu (trivalent) radionuclides in the presence and absence of humic acid (Aldrich). In order to obtain a detailed sorption behavior of all the three aforementioned radionuclides, a series of experiments were conducted with respect to effect of pH, humic acid (HA), and concentration of radionuclides. Sorption studies of 137 Cs, 133 Ba and 154 Eu onto synthesized titania have been carried out over a wide range of pH scale varying from 3 to 11 in the presence and absence of Aldrich Humic acid (2 mg/L). Sorption of all the three radionuclides rises sharply with the pH of the suspension with saturation value of ∼ 70%, 80% and 85% respectively for monovalent, bivalent and trivalent radionuclides. Humic acid could not make any influence for sorption of 137 Cs, but significantly altered with respect to 133 Ba and 154 Eu sorption. The sorption data at various concentrations were fitted with Freundlich isotherm model.

A novel separation method for Cu radionuclides from proton bombardment of nat Zn is presented. A solid phase extraction procedure using a modified dithizone (diphenylthiocarbazone) XAD-8 chelating resin was used for the purification of the Cu radionuclides from up to 5 g of nat Zn and other radionuclides. More than 95% of the Cu radionuclides was recovered.

The thermal decomposition of untreated and γ -irradiated samples of anhydrous cadmium nitrate was performed under non-isothermal conditions at different heating rates (5, 10, 15 and 20 ℃ min – 1 ). The results showed that the decomposition proceeds in one major step with the formation of cadmium oxide as solid residue. The data were analysed by using both isoconversional and non-isoconversional methods. The activation energy was calculated by various model-free isoconversional methods: Flynn-Wall-Ozawa (FWO), Kissinger-Akahira-Sunose (KAS) and Friedman (FR) methods. Irradiation enhances the decomposition and the effect increases with the irradiation dose. The activation energy decreases on irradiation. The appropriate conversion model for the thermal decomposition process selected by means of the master-plot method agrees with phase boundary reaction with spherical symmetry (R3 mechanism) for both untreated and irradiated salts at all heating rates.