Research and development for the SPES target

The target is one of the key issues of isotope separation on line (ISOL) facilities. SPES, now under development at LNL-INFN, is an innovative ISOL facility possessing a target chatacterized by seven separate uranium dicarbide thin disks. The research on the materials development and target prototyping is discussed in the following.     

Complexation of thorium(IV) with acetate at variable temperatures

The complexation between Th(IV) and acetate in 1.05 mol kg(-1) NaClO4 was studied at variable temperatures (10, 25, 40, 55 and 70 degrees C). The formation constants of five successive complexes, Th(Ac)j(4-j)+ where Ac = CH3COO- and j = 1-5, and the molar enthalpies of complexation were determined by potentiometry and calorimetry. Extended X-ray absorption fine structure spectroscopy (EXAFS) provided additional information on the complexes in solution. The effect of temperature on the stability of the complexes is discussed in terms of the electrostatic model.     

Neutron-rich isotope production using the uranium carbide multi-foil SPES target prototype

In the framework of the R&D program for the SPES (Selective Production of Exotic Species) project of the Istituto Nazionale di Fisica Nucleare (INFN), production yields of neutron-rich isotopes have been measured at the Holifield Radioactive Ion Beam Facility (HRIBF, Oak Ridge National Laboratory, USA). This experiment makes use of the multi-foil SPES target prototype composed of 7 uranium carbide discs, with excess of graphite (ratio C/U = 4 . 77 isotopes of medium mass (between 72 and 141amu), produced via proton-induced fission of uranium using a 40MeV proton beam, have been collected and analyzed for the target heated at 2000 ^° C target temperature.     

Hydrolysis of uranium(VI) at variable temperatures (10-85 degrees C)

The hydrolysis of uranium(VI) in tetraethylammonium perchlorate (0.10 mol dm(-3) at 25 degrees C) was studied at variable temperatures (10-85 degrees C). The hydrolysis constants (*beta(n,m)) and enthalpy of hydrolysis (Delta H(n,m)) for the reaction mUO(2)(2+) + nH(2)O = (UO(2))(m)(OH)(n)((2m-n))+) + nH(+) were determined by titration potentiometry and calorimetry. The hydrolysis constants, *beta(1,1), *beta(2,2), and *beta(5,3), increased by 2-5 orders of magnitude as the temperature was increased from 10 to 85 degrees C. The enthalpies of hydrolysis, Delta H(2,2) and Delta H(5,3), also varied: Delta H(2,2) became more endothermic while Delta H(5,3) became less endothermic as the temperature was increased. The heat capacities of hydrolysis, Delta C(p(2,2)) and Delta C(p(5,3)), were calculated to be (152 +/- 43) J K(-1) mol(-1) and -(229 +/- 34) J K(-1) mol(-1), respectively. UV/Vis absorption spectra supported the trend that hydrolysis of U(VI) was enhanced at elevated temperatures. Time-resolved laser-induced fluorescence spectroscopy provided additional information on the hydrolyzed species at different temperatures. Approximation approaches to predict the effect of temperature were tested with the data from this study.     

Release time calculations for the SPES direct UCx target

A Direct Target for a mid-term RIB ISOL-type facility is being developed at LNL, in the framework of the R&D for the SPES project [1]. Using a 40 MeV proton beam impinging on a UCx thick target of 2.5 g/cm³ density, a production rate of 10¹³ in target fissions per second is expected [2]. The crucial point, when short-lived isotopes are produced in the target, is to build systems (target + ion source) with good release properties and high efficiency. Monte Carlo simulations were performed using the GEANT4 toolkit [3] and the RIBO code [4] in order to optimize our target geometry and to estimate the average release time.     

Temperature dependence of yields from multi-foil SPES target

The temperature dependence of neutron-rich isotope yields was studied within the framework of the HRIBF-SPES Radioactive Ion Beams (RIB) project. On-line release measurements of fission fragments from a uranium carbide target at $\ensuremath 1600 {}^{\circ}\mathrm{C}$\ensuremath 1600 {}^{\circ}\mathrm{C} , 1800 ^°C\ensuremath 1800 {}^{\circ}\mathrm{C} and 2000 ^°C\ensuremath 2000 {}^{\circ}\mathrm{C} were performed at ORNL (USA). The fission reactions were induced by a 40MeV proton beam accelerated into a uranium carbide target coupled to a plasma ion source. The experiments allowed for tests of performance of the SPES multi-foil target prototype loaded with seven UC₂/graphite discs (ratio C/U = 4 with density about 4g/cm³.     

Spectrophotometric and Calorimetric Studies of Np(V) Complexation with Acetate at Various Temperatures from <Emphasis Type="Italic">T</Emphasis>=283 to 343 K

Spectrophotometric titrations were performed to identify the Np(V)/acetate complex and determine the equilibrium constants at various temperatures (T=283 to 343 K) and at the ionic strength 1.05 mol⋅kg⁻¹. The enthalpies of complexation at the corresponding temperatures were determined by microcalorimetric titrations. Results show that the complexation of Np(V) with acetate is weak but strengthens as the temperature increases. The complexation reaction is endothermic and entropy driven. The enhancement of complexation at higher temperatures is primarily due to the increasingly larger entropy gain when the solvent molecules are released from the highly-ordered solvation spheres of NpO₂⁺\mathrm{NpO}_{2}^{+} and acetate to the bulk solvent where the degree of disorder is higher at higher temperatures.     

Complex formation of N-donor ligands with group 11 monovalent ions

Thermodynamic data on complex formation between nitrogen donor ligands (amines, pyridines) and group 11 monovalent ions in water and non-aqueous media are reviewed here. Particular emphasis is paid to Ag(I) complex formation in water and dimethylsulfoxide (DMSO), due to the amount and quality of data available. The influence of different basicities and steric properties of ligands, together with the solvation of the species involved, on the stability and nature of the resulting complexes is discussed. It emerges generally that the coordination properties of amines towards 1+ ions are all modulated through the number and basicity of nitrogen atoms present in the ligand, chelate ring sizes, degree of N-functionalisation, and the nature of the solvent. When possible, the thermodynamic properties of the complexes are related to the structural features of the ligands.