A comparison of RIST and ISOLDE tantalum targets and geometries used on-line at ISOLDE

A comparison is made of the performance of RIST and ISOLDE tantalum targets used on-line at the CERN-ISOLDE isotope separator. The data is taken from a combination of recent measurements st the CERN-PSB and from the former ISOLDE facility at the CERN-SC. Developments in the target geometry have been necessary for the RIST project which aims to design a target capable of dissipating the power developed by an 800 MeV, 100 mu A proton beam. These designs are being tested at the ISOLDE-PSB facility and the initial results are reported in comparison with data obtained from typical ISOLDE tantalum-foil targets. The study shows that improvements in the release properties of a number of elements can be made by a judicious choice of target matrix geometry. The target represents a complex system where, in general, modelling alone involves too many parameters to generate a reliable model of the target. From this study, it is clear that further practical work, following simple ideas such as those based on modifications of the target geometry, is necessary in order to obtain progress in the optimisation of the target design.