Preparation of Nuclear Accelerator Targets by Focused Ion Beam Sputter Deposition

A duoplasmatron ion source with einzellens extraction was used to prepare focused beams of 10-30 kV of Ar ions with intensities of 1 mA. An em/m-analysis was performed to study the general behaviour of the source. The composition of the beam was investigated to trace and reduce contaminations from extraneous source materials. The Ar-ion beam was applied to sputter milligram-amounts of chemical elements and enriched isotopes of elements having high melting points, such as Zr, Mo, Ru, Ta, W, Ir, etc. The sputtered substances were collected in thicknesses varying from 0.01-2.0 mg/cm2 onto thin target backings of C, Ti, Cu, or Pb. Self-supported targets were obtained by dissolving backings chemically. Among others, targets of 182W and 184W with thicknesses from 0.19-0.65 mg/cm2 were thus prepared. Sputtering yields were measured for a series of different target materials. The results are discussed in detail. The targets have been fabricated for various experiments involving high intensity heavy ion bombardments with energies of up to 15 MeV/u of 58Ni, 208Pb, and 238U ions at the GSI UNILAC accelerator.