Speaker
Description
The Isotope Separation On-Line (ISOL) method is a powerful technique to produce radioactive ion beams (RIB), and thus, is an essential tool when studying the properties of atomic nuclei far away from the valley of stability. The ISOL method gives, in principle, access to a large number of the known (radio-)isotopes of the chart of nuclides, with relatively large intensity and purity. Key component of an on-line isotope separator is the target-ion source unit, which, depending on the RIB of interest, requires thoughtful optimization in view of target microstructural properties, radiochemistry and high temperature chemistry. In that regard, the choice of the target material and its processing routes is of utmost importance, since the release from the target matrix is often considered as one of the major bottlenecks in RIB production. Generally, small target grain sizes, high open porosity and high temperatures are favorable for increased release efficiencies. However, due to the high temperatures during target operation, issues such as grain growth and densification (pore shrinkage) need to be considered, and more importantly, avoided when developing new target materials. Therefore, a new research line was launched at KU Leuven (Belgium), focusing on new target developments and isotope purification systems based on laser ionization, which are to be implemented at ISOLDE, MEDICIS, and in the future at ISOL@MYRRHA. This contribution aims to present the target developments that are currently carried out in collaboration of the Institute of Nuclear and Radiation Physics (IKS) and the Department of Materials Engineering at KU Leuven. In detail, this comprises powder metallurgical routes for TaC and TiC target materials towards the production of $^{149,152,155}$Tb and $^{44,47}$Sc, respectively. Different processing routes are discussed, regarding their capability of yielding porous targets that present a stable microstructure during operation, i.e. limited or no densification. Furthermore, in 2018 a new test bench to measure release fractions was developed at MEDICIS, allowing to study, off-line, release characteristics of new targets. This is very useful, as from such measurements on-line release efficiencies can be estimated and target properties, such as diffusion coefficients, may be studied. In that regard, the fractional release of $^{11}$C was measured from a porous boron nitride (BN) target, developed at IKS for the production of intense $^{11}$C beams. The authors would like to acknowledge the strong support from the teams at ISOLDE, MEDICIS and SCK•CEN concerning the characterization and testing of those materials.