1. a Academy of Sciences of the GDR, Central Institute for Nuclear Research (CINR) Rossendorf , P.O.Box 19, DDR-8051, Dresden
2. b Department of Physics , Abo Akademi , Porthansgaten 3, SF-20500 Turku, Finland
3. c Turku University, Medical Cyclotron Project , Kiinanmyllynkatu 10, SF-20500 Turku 52, Finland