Oxide targets for Gammasphere

We here report on recent experiments at GAMMASPHERE employing highly inverse, near-barrier reactions with silicon dioxide targets and use the Fragment Mass Analyzer (FMA) to collect the recoils. The 16O(58Ni,2n)72Kr reaction was studied with beams of 220 MeV 58Ni in excess of 15 pnA. Relatively few stable beam and target combinations are available to populate excited states in 72Kr, and the small cross sections of these reactions necessitate the use of targets that can withstand high intensity beam currents. A variety of oxygen containing targets were produced, with those made of silicon dioxide performing best. Over a period of 24 h of irradiation the oxygen content in these targets monotonically declined to about 1/3 of the original value. The silicon content did not appear to change. By inserting new sets of targets each 18-h-cycle an impressive data set was collected.