Volume 93, Issue 2 -

Transmutation experiments have been carried out using the NUCLOTRON, a new accelerator for relativistic particles. The experiments were carried out in the Veksler and Baldin Laboratory of High Energies of the Joint Institute for Nuclear Research in Dubna, Russian Federation. Earlier experiments using an 8 cm Ø Pb-target of 20 cm length and surrounded by 6 cm paraffin (GAMMA-2 target) have been continued to study the transmutation of 139 La and the highly radiotoxic radwaste nuclides 129 I and 237 Np using spallation neutrons produced by relativistic protons with energies 0.5 GeV ≤ E p ≤ 4.15 GeV. Results of previous experiments were complemented with additional results, thus yielding data systematics with small uncertainties over the probably commercially relevant energy range of 0.5 GeV ≤ E p ≤ 1.0 GeV and also in the scientifically interesting range above 1 GeV. Moreover, neutron density distributions in irradiations with 0.65 GeV, 1 GeV and 3.7 GeV protons were determined on the surface of the paraffin moderator for two energy regimes of slow and intermediate/fast neutrons. A large set of high quality experimental data with small uncertainties has been generated that can serve as benchmark data for modelling purposes.

Electrochemical reactions of UO 2 ( β -diketonato) 2 -dmso, UO 2 (trop) 2 dmso, UO 2 (sap)(dmso) 2 , and UO 2 (salen)dmso (dmso = dimethyl sulfoxide, β -diketonate = benzoylacetonate (ba), benzoyltrifluoroacetonate (btfa), and thenoyltrifluoroacetonate (ttfa), trop = tropolonate, sap = 2-salicylidenaminophenolate, and salen = N , N ´-disalicylidenethylenediaminate) complexes in dmso solutions containing tetrabutylammonium perchlorate as a supporting electrolyte have been studied with cyclic voltammetry. These uranyl(VI) complexes were found to be reduced quasi -reversibly to U(V) species. The formal redox potentials ( E °, vs . ferrocen/ferrocenium) for U(VI)/U(V) couples were determined to be -1.416 V for UO 2 (ba) 2 dmso, -1.073 V for UO 2 (btfa) 2 dmso, -1.082 V for UO 2 (ttfa) 2 dmso, -1.379 V for UO 2 (trop) 2 dmso, -1.500 V for UO 2 (sap)(dmso) 2 , and -1.602 V for UO 2 (salen)dmso. Furthermore, the resulting U(V) complexes, [UO 2 (btfa) 2 dmso] - , [UO 2 (ttfa) 2 dmso] - , and [UO 2 (salen)dmso] - , were found to be able to exist stably in dmso solutions.

The solubility of X-ray amorphous Th(IV) hydroxide or hydrous oxide was determined in carbonate solution at I =0.5 M (NaHCO 3 -Na 2 CO 3 -NaOH-NaCl) and 22 °C. Two series of open system experiments were performed under CO 2 partial pressures of 1.0 and 0.1 bar at -log [H + ]=4.5– 7.5. In three series of closed system experiments at constant total carbonate concentrations of C tot =[HCO 3 - ]+[CO 3 2- ]=0.1, 0.04 and 0.015 M, the H + concentration was varied in the range -log [H + ] = 8.5–13.5. Some additional solubility data were determined in 0.25–2 M Na 2 CO 3 containing 0.1 M NaOH. There was no indication for the formation of a thorium carbonate solid. The simultaneous evaluation of the different sets of experimental data at I =0.5 M shows that Th(OH)(CO 3 ) 4 5- and Th(OH) 2 (CO 3 ) 2 2- are the most important ternary complexes. Further contributions to the Th(IV) solubility are coming from Th(OH) 2 (CO 3 )(aq), Th(OH) 3 (CO 3 ) - and Th(OH) 4 (CO 3 ) 2- . Their formation constants, extrapolated to I =0 with the SIT and combined with the solubility product of log K ° sp =-47.8±0.3, are calculated to be log β ° 114 =35.8±0.3, log β ° 122 =37.0±0.4, log β ° 121 =30.7±0.4, log β ° 131 =38.5±0.6 and log β ° 141 =40.6±0.5. Pure carbonate complexes and other ternary complexes have no significant contributions to the solubility in the present studies at I =0.5 M. Upper limits are derived for their formation constants. Using the SIT for ionic strength corrections, the evaluated set of equilibrium constants is also consistent with the solubility in Na 2 CO 3 -NaOH mixtures of higher ionic strength.

The sorption behavior of Eu(III), Sm(III), Np(V), Pu(V), and Pu(IV) in the presence of calcite and as a function of pH and carbonate alkalinity was measured by batch sorption experiments. Eu(III) and Sm(III) sorption is similar, consistent with their observed aqueous speciation and precipitation behavior. For both rare earth elements, sorption decreases at the highest and lowest measured pHs. This is likely the result of speciation changes both of the calcite surface and the sorber. An increase in the equilibrium CO 2 (g) fugacity results in a shift in the sorption behavior to lower pH, consistent with a predicted aqueous speciation shift. Np(V) and Pu(V) sorption exhibited a strong pH dependence. For Np(V), K d s range from 0 to 217 mL/g suggesting that carbonate aqueous speciation as well as changes in the calcite surface speciation greatly affect Np(V) sorption to the calcite surface. Similar behavior was found for Pu(V). Pu(IV) sorption is also strongly pH dependent. Sorption decreases significantly at high pH as a result of Pu-carbonate complexation in solution. A surface complexation model of Sm(III), Eu(III), Np(V), Pu(V), and Pu(IV) sorption to the calcite surface was developed based on the calcite surface speciation model of Pokrovsky and Schott [1]. Sorption data were fit using one or two surface species for each sorber and could account for the effect of pH and CO 2 (g) fugacity on sorption. A relatively poor model fit to Pu(IV) sorption data at high pH may result from our poor understanding of Pu(IV)-carbonate aqueous speciation. While our surface complexation model may not represent a unique solution to the sorption data, it illustrates that a surface complexation modeling approach may adequately describe the sorption behavior of a number of radionuclides at the calcite surface over a range of solution conditions.

The molar enthalpies of dissolution of a number of well-characterized hexagonal hydroxycarbonates Ln(OH)CO 3 (hex) (Ln = La, Nd, Sm, Eu) in 6.00 mol dm -3 HCl were measured at 298.15 K. A new sealed solution micro-calorimeter was developed for this purpose. It was made of an 18-carat gold alloy in order to improve the performances of a calorimeter previously built in our laboratory. The following standard molar enthalpies of formation, Δ f H ° m [Ln(OH)CO 3 , hex], in kJ mol -1 , were calculated: -(1627.8±1.6), -(1614.8±1.9), -(1613.4±1.6), and -(1523.0±3.0), for the La, Nd, Sm, and Eu compounds, respectively. These results allowed an extrapolation to Δ f H ° m [Eu(OH)CO 3 ·0.5H 2 O, orth]=-(1653.4±3.6)kJ mol -1 and to Δ f H ° m [Am(OH)CO 3 , hex]=-(1552.5±3.3)kJ mol -1 . Using auxiliary data and estimated entropies, the solubility products of the hexagonal hydroxycarbonates were calculated. They are compared here with values deduced from solubility and calorimetric measurements for the corresponding orthorhombic hydroxycarbonates. Our approach generally leads to values similar to those deduced from solubility studies. The orthorhombic form is found to be metastable with respect to the hexagonal form.

Yttrium-90 ( 90 Y) has attracted much research attention in targeted radionuclide therapy because its many favorable properties and availability from a long shelf-life generator system. Although numerous generator systems have been developed for the production of 90 Y, a common disadvantage is that the 90 Y is not eluted in an ionic form suitable for direct labeling of chelating agents bound to useful targeting molecules. In this study, we have adapted previously published procedures and developed a 740 MBq (20 mCi) of generator system in which the parent activity 90 Sr was retained on a cation exchange resin, while the daughter 90 Y activity was eluted with acetate buffer solution and used directly to label useful radioconjugates without further manipulations. A safety column, not loaded with 90 Sr, was connected in series with the generator resulting in an eluate free of any 90 Sr breakthrough for at least eight months. The features of this new generator make it suitable for clinical applications.

This study investigates the corrosion of OL–37, OL–60 and 316L type steel samples immersed in acidic media (HCl, HClO 4 , H 2 SO 4 and HNO 3 ), based on a new radioactive tracer method. This procedure, used for the determination of the global rate constant of metal corrosion reaction, is based on the screening of β - -rays emitted by 204 Tl + radionuclides, present in the aggressive medium of the iron ions which are formed during the process. The global rate constants of corrosion reaction decrease, for a certain metallic sample, in the series HCl > HClO 4 > H 2 SO 4 > HNO 3 , and increase with the concentration of the used acid. For a given aggressive solution, the corrosion process decreased with the decreasing of the carbon amount in each steel sample.

Two methods for measuring the selectivities of ion exchange reactions in zeolites were compared. Three zeolites (NaA, mordenite and ZSM-5) of differing ion exchange capacity were studied for uni-univalent (Rb + /Na + ) and for uni-divalent (Sr 2+ /2Na + ) exchanges. The first method involved rigorous chemical analysis of exchanged ions (Na + and Rb + or Na + and Sr 2+ ) in the solid and solution phases at equilibrium. The second method was based on the use of 86 Rb and 85 Sr tracers, which were measured in the solution phase after equilibrium, and the remaining concentrations were calculated by difference. The corrected selectivity coefficient ( K G A/B ) was calculated from the equilibrium data. Both methods gave reasonable accuracy (10–15%) when the metal loading in the zeolite was low to medium. The radioactive tracer method, however, resulted errors larger than 100% at high metal ion loading (>80%).