Preparation of radioactive targets for tandem accelerator experiments by high vacuum evaporation–condensation

Radioactive thin film targets have been prepared by high vacuum evaporation–condensation in the hot-lab facility of the University of Munich. Targets made by this technique are of high density and excellent smoothness, being well suited for experiments aimed at the production and spectroscopy of fission fragments. Cold crucible electron beam heating is the preferred method for evaporation of actinide isotopic material of sufficient abundance, for instance 230Th, 232Th, 233U, 235U, 238U and 239Pu. Exotic isotopes, which are available only in submilligram quantities, are processed in a micro-evaporator module consisting of a chimney-type crucible heated by low-tension electron bombardment. This set-up is characterised by a high collection efficiency and was used for the production of 244Pu and 10Be targets.