Gold cluster ions in the mass range of 4 x 104-2 x lo6 u were produced by bombarding a thin f i l m of gold with =*Cf fission fragments. The gold film which covered a carbon-aluminium substrate formed islets having a mean diameter of 44 di. It turned out that nearly each second fission fragment penetrating an islet desorbed this islet as a whole. Most of these desorbed gold grains were negatively charged. They were investigated by means of a tandem time-of-flight (TOF) instrument. In the first TOF section, the cluster ions gained a kinetic energy of z x 40 keV (where z is the charge state) and hit a converter, from where secondary ions and electrons were ejected. The most efficient converter material found so far is cesium iodide which particularly emits Cs+, I-and cluster ions. Less efficient were the contaminated or clean metals Au, Ag, Cu and Pb and the alloy AgMgO. At an energy of z x 40 keV, the mean secondary electron yield from CsI was 0.011 per cluster ion. The detection efficiency for a cluster ion by ion-to-ion conversion was found to decrease from 99.7% to 96.5% in the available mass range.
After correction for detection efficiency the complete mass-to-charge distribution between 4 x lo4 and 2 x lo6 ufz was determined and compared with a corresponding mass distribution of the gold-islets covering the substrate. The mean charge state of the negatively charged clusters was estimated to be 1-2 and the mean mass z x 295 OOO u.