Review of ISOL target–ion-source systems

Abstract

Any review of target–ion-source systems (TISS) is necessarily a variation of the ISOL-theme “efficient, fast, selective”. In the first part, more than 30 years of TISS development are examined in view of these key characteristics. By looking at the lines of development that were successful, at the lines that were abandoned (partly for good, partly for less good reasons), the lines with the most promising perspectives emerge. The second part deals with on-line chemistry in the TISS and its possibly double benefits: enhanced selectivity or increased separation speed, or both in favourable cases, as the relatively new sulfide chemistry. For the group-IVa-elements germanium and tin, the separation as sulfide-ions does not only suppress strongly the contamination by the neighbouring elements. It also reduces the effusion part of the release by orders of magnitude to the level of the intrinsic delay caused by molecular flow. The homologue chemistry is likely to work for silicon, but not for lead. While selectivity requires that both the formed molecules and molecular ions are thermally stable, a gain in speed requires only sufficient stability of the molecule: e.g. antimony, which hardly forms sulfide ions, also migrates orders of magnitude faster in the presence of sulphur vapour.