Atomic Beam Merging and Suppression of Alkali Contaminants in Multi Body High Power Targets: Design and Test of Target and Ion Source Prototypes at ISOLDE

The next generation of high power ISOL-facilities will deliver intense and pure radioactive ion beams. Two key issues of developments mandatory for the forthcoming generation of ISOL target-ion source units are assessed and demonstrated in this thesis. The design and production of target and ion-source prototypes is described and dedicated measurements at ISOLDE-CERN of their radioisotope yields are analyzed. The purity of short lived or rare radioisotopes suffer from isobaric contaminants, notably alkalis which are highly volatile and easily ionized elements. Therefore, relying on their chemical nature, temperature controlled transfer lines were equipped with a tube of quartz that aimed at trapping these unwanted elements before they reached the ion source. The successful application yields high alkali-suppression factors for several elements (ie: 80, 82mRb, 126, 142Cs, 8Li, 46K, 25Na, 114In, 77Ga, 95, 96Sr) for quartz temperatures between 300ºC and 1100ºC. The enthalpies of adsorption on quartz were measured for Rubidium and Caesium. The enthalpies ΔHad (Rb) = -242 ± 20 kJ/mol and ΔHad (Cs) = -145 ± 20 kJ/mol are in good agreement with those obtained by isothermal chromatography. For proton beam power of the order of 100 kW such as foreseen in the EURISOL-DS project for direct ISOL targets, multi-body target units connected to a single ion-source are proposed. The so-called “Bi-Valve” target prototype aims to benchm ark the engineering tools required to simulate effusion related decay losses and to validate the multi body target concept. Four isotopes were investigated online: 34,35Ar and 18,19Ne. The efficiency of the double line merging was found to be in the range of 75 to 95%. The diffusion (analytical) and effusion (Monte Carlo) code RIBO provided the profile of the effusion distribution of the isotopes within the Bi-Valve unit for the different operation modes. A mathematical expression for the probability, p(t) that an isotope diffuses and effuses through the system is proposed. The simulated release efficiencies were in agreement with the experimental ones for 34, 35Ar at 95% thus opening the way to the engineering of multi body target units for future facilities.