New Evaporation Set-Up for Uranium Compound Targets

Introduction In the past, thin uranium fluoride targets in the form of UF4 on carbon backings were applied for heavy-ion experiments repeatedly. With this compound targets we had several problems: UF4 had to be evaporated on thick carbon substrates of about 45 μg/cm2. The targets were mechanically very fragile and showed heavy sputtering in the beam. The durability of the targets upon irradiation was generally unsatisfying. For the heavy-element synthesis at GSI, targets of lead, bismuth and their compounds were applied successfully in cold-fusion reactions, where a low-Z projectile interacts with a target nucleus of lead or bismuth, respectively [1]. In recent experiments performed at Dubna [2] and at Berkeley [3] using recoil separators and at GSI using chemical separation [4], various types of U targets were irradiated with Ca beams with partly contradicting results. At the GSI SHIP it is planned to study the same reaction early in 2005 [5]. For this experiment a great number of targets of U in a good quality is needed. Because U is the only target that can be prepared according to safety regulations in the current radioactive target laboratory at GSI, it is planned to use this material in an extended experimental program in the future. For the preparation of the necessary high quality targets a new evaporation apparatus was set up. The target production has started in September 2004. A first test experiment with beams of C and V was completed in November 2004.