Band 90, Heft 1 -

The radioisotope 90 Nb decays with a positron branching of 53% and a relatively low β + -energy of E mean = 0.66 MeV and E max = 1.5 MeV. Its half-life of 14.6 h makes it especially promising for quantitative investigation of biological processes with slow distribution kinetics using positron emission tomography. To optimise its production, the excitation functions of 90 Zr( p, xn )-processes were studied over the proton energy range of 7.5 to 19 MeV via the stacked-foil technique using both nat Zr and 99.22% enriched 90 ZrO 2 as targets. Thick target yields of 90 Nb were calculated from the measured excitation functions and were verified experimentally. The optimum energy range for the production of 90 Nb via the 90 Zr( p, n )-process was found to be E p = 17 → 7 MeV, with a yield of 600 MBq 90 Nb/µA h. The yield and radionuclidic purity of 90 Nb over the energy range of E p = 17.6 → 8.1 MeV were determined experimentally using nat Zr. At 4 h after EOB the yield of 90 Nb was found to be 290 MBq/µA h and its radionuclidic purity ≥ 95%.

The characterisation of alpha-emitting nuclides in low and medium level radioactive waste from Spanish nuclear power reactors leads to several difficulties because they cannot be assayed by non-destructive methods due to their low concentration. Thus, long and complex radiochemical procedures are required. In this paper an alternative method for establishing a sufficiently accurate and reliable inventory of long-lived alpha emitting nuclides, is described. The method is based on the application of the factors obtained by correlating the gross alpha activity and the concentration of 238 Pu, 239/40 Pu, 241 Am, 242 Cm and 244 Cm in a set of samples of concentrates and resins from Spanish NPP's. Several statistical tests are performed to evaluate the validity of the assumed relationship and the quality of the correlation. Also, uncertainties are calculated for the parameters of the linear equation relating the concentrations. This work has been performed in the framework of the CIEMAT-ENRESA Association Agreement.

Synergistic extraction of hexavalent uranium was studied using acidic extractants HTTA/HPMBP with two different bifunctional neutral donors, DHDECMP and CMPO, from HNO 3 medium at various fixed temperatures. The equilibrium constants for the organic phase addition reaction (log K s ) were correlated with the basicity ( K h ) of the neutral donors. The data reported earlier for monofuctional neutral donors (DPSO, TBP, TOPO) were used for the comparison. A linear correlation between log K s and log K h was observed for U(VI)/HTTA/S (S = neutral donor) system. However, in U(VI)/HPMBP/S system, the observed log K s values for bifunctional neutral donors were much lower than those expected from linear correlation. This was attributed to the different mechanisms operative in the synergistic extraction i.e . substitution in the former vs . addition in the latter. These conclusions are also supported by the thermodynamic data obtained in the present studies. Nevertheless, it is seen that bifunctional neutral donors act only as monofunctional with both HTTA and HPMBP.

The present paper describes the preparation of a novel barium silico-phosphate filter paper supported membrane. It is based on precipitation reaction of barium silico-phosphate on the outer surface and in the interstices of a filter paper by means of electrodialysis. The main physical and electrical properties of the membrane are given and its electrodialysis behaviour is assessed for Th(IV) and U(VI). The transport of Th(IV) in presence of U(VI) was studied. The cationic fluxes of Th(IV) and U(VI) were found to be 1.2 × 10 −8 and 6.5 × 10 −9 g eq cm −2 s −1 , respectively. Transport of Th(IV) and U(VI) in presence of EDTA was investigated. The cationic flux of U(VI) is found to be 9.8 × 10 −9 g eq cm −2 s −1 at a current density of 25 mA/cm 2 . A comparative study on the electro osmotic effect was carried out using the developed membrane and commercially available Nafion membranes. In this context, different parameters like current density, electrolyte concentration, etc. were investigated. The electro-osmotic permeability coefficient, D e , of Th(IV) through barium silico-phosphate and Nafion membranes were 6.9 × 10 −2 and 1.0 × 10 −2 cm 3 /A s, respectively. It can be concluded that inorganic membranes have very marked electro-osmotic properties unlike their organic counterparts.

The fluorescence of humic acid (HA) is quenched due to its complexation with UO 2 2+ ions, leading to the evolutionary quenched intensity profile (quenching profile) as a function of UO 2 2+ concentration. This quenching behavior was investigated using 3-dimensional (3D) and synchronous (SyF) fluorescence spectroscopy. The quenching profile obtained by means of SyF spectroscopy was deconvoluted by SIMPLISMA, which is an interactive self-modeling mixture analysis method. Two sites, which contribute to the fluorescence of HA and whose fluorescence is quenched due to its complexation with UO 2 2+ , have been extracted, and the quenching profile was resolved to the fluorescence intensity profiles of these sites and the corresponding spectra. Based on these intensity profiles, the apparent stability constant (log K app ) and the concentration of site ( C L ) were evaluated for each site, using nonlinear least-squares regression to the Multisite Ryan-Weber Model.

The sorption studies Tb(III) was investigated on HTTA loaded PUR foam. The adsorption conditions were optimized with respect to pH, shaking time, loading capacity and adsorbent weight. The adsorption data followed the classical Freundlich and Langmuir type isotherms successfully. The Freundlich constant (1/ n ) is estimated to be 0.47 ± 0.01, reflects a surface heterogeneity of the PUR foam. Langmuir isotherm gives a saturated capacity of 0.042 ± 0.001 mmole g −1 which suggests a monolayer coverage of the surface. The Dubinin-Radushkevich (D–R) isotherm is applied and the sorption mean free energy ( E ) is calculated and found to be 11.32 ± 0.14 kJ mol −1 suggesting that chemisorption involving chemical bonding is responsible for the adsorption process. The isosteric heat of adsorption of Tb(III) is high which decipher the surface heterogeneity, new bond formation and endothermic type chemisorption. The thermodynamics parameters such as enthalpy (Δ H ), entropy (Δ S ) and Gibbs free energy (Δ G ) were calculated and interpreted. The positive values of Δ H indicate that the adsorption of metal ions on HTTA-loaded PUR foam is an endothermic process. A possible explanation of this endothermicity and sorption mechanism have been discussed. The selectivity and sensitivity of the adsorbent was also studied. The sorption of Tb(III) is greatly affected in the presence of oxalate and fluoride. The sorptive affinity of different cations towards HTTA loaded PUR foam was also discussed.

Competitive Cs + ion transport by polymer inclusion membranes (PIMs) with bis(dodecyloxy)calix[4]arene-crown-6 or calix[4]arene-biscrown-6 was investigated under various conditions. The PIM matrix consisted of cellulose triacetate and ortho-nitrophenyloctyl ether. Special attention was paid to PIM performance employing complex source-phase mixtures, including simulant solutions of acidic nuclear wastes present at Idaho National Engineering and Environmental Laboratory. PIMs exhibited highly efficient and selective Cs + transport under competitive conditions. Membranes containing calix-monocrown carrier exhibited slightly less efficient but more selective Cs + transport than those with calix-biscrown carrier. PIMs with bis(dodecyloxy)calix[4]arene-crown-6 exhibited excellent stability in terms of carrier loss to the aqueous phase. The variation of cesium transport with composition of aqueous phase was adequately described by a diffusion-limited transport model.

Adsorption of Zn(II) ions on barium titanate has been studied as a function of concentration of Zn(II) (1.0 × −5 –5.0 × 10 −7 M), temperature (281–313 K) and pH (4–8) of the adsorptive solution using 65 Zn tracer and γ-ray spectroscopy. The adsorption process was found to obey the first order rate law and the Freundlich adsorption isotherm for the range of concentration studied. The uptake increases from 32 to 70% with the increase in dilution (from 1.0 × 10 −5 to 5.0 × 10 −7 M). The extent of adsorption also increases with increasing temperature and pH of solution. The activation energy for the process was determined to be 12.3 kJ mol −1 . The removal of Zn(II) ions by barium titanate appears to be endothermic and irreversible.

Magnesium isotope enrichment was investigated by chemical ion exchange with a synthesized 2′-aminomethyl-15-crown-5(AM15C5) bonded Merrifield peptide resin using elution chromatography. The capacity of the novel crown ion exchanger was found to be 2.3 meq/g dry resin. The heavier isotopes of magnesium were enriched in the solution phase, while the lighter isotopes were enriched in the resin phase. The separation factor was determined according to the method of Glueckauf from the elution curve and isotopic assays. The separation factors of 24 Mg 2+ – 25 Mg 2+ , 24 Mg 2+ – 26 Mg 2+ , and 25 Mg 2+ – 26 Mg 2+ isotope pair fractionations were 1.013, 1.024, and 1.012, respectively.