1. Department of Physics, University of Oslo, N-0316 Oslo, Norway
2. Institut für Kernphysik, Technische Universität Darmstadt, D-64289 Darmstadt, Germany
3. Department of Physics, Western Michigan University, Kalamazoo, Michigan 49008, USA
4. National Superconducting Cyclotron Laboratory, Michigan State University, East Lansing, Michigan 48824, USA
5. GANIL, CEA/DRF-CNRS/IN2P3, F-14076 Caen, France
6. Institut d'Astronomie et d'Astrophysique, Université Libre de Bruxelles, CP 226, B-1050 Brussels, Belgium