| Popis: |
The beam intensities of short-lived carbon isotopes at Isotope Separation On-Line (ISOL) facilities have been limited in the past for technical reasons. The production of radioactive ion beams of carbon isotopes is currently of high interest for fundamental nuclear physics research. To produce radioactive ions a target station consisting of a target in a container connected to an ion source via a transfer line is commonly used. The target is heated to vaporize the product for transport. Carbon in elementary form is a very reactive element and react strongly with hot metal surfaces. Due to the strong chemisorption interaction, in the target and ion source unit, the atoms undergo significant retention on their way from the target to the ion source. Due to this the short lived isotopes decays and are lost leading to low ion yields. A first approach to tackle these limitations consists of incorporating the carbon atoms into less reactive molecules and to use materials for the target housing and the transfer line that only weakly interact with these molecules. Therefore, the adsorption properties of carbon monoxide (CO) and carbon dioxide (CO2) on a range of materials of interest were investigated in thermochromatography experiments at PSI (Switzerland) by using the carbon isotope 11C. The adsorption enthalpy was retrieved for several materials. A second approach consists of the optimization of target materials and structure, both f or the effusion and diffusion of the nuclides of interest. Corresponding on-line experiments were performed at GANIL (France). For the production, diffusion and ionization efficiencies out of different target materials on-line and off-line experiments with carbon and nitrogen isotopes were performed at ISOLDE (CERN). The work performed within this thesis shows that the use of a coated transfer line, fibre felt targets and an electron cyclotron resonance (ECR) ion source would strongly decrease the losses, and provide the experiments with up to 1000 times higher beam currents than today. |
