1. Laboratory of Radiochemistry, Dep. of Chemistry, P.O. Box 55, FIN-00014 University of Helsinki, Finland
2. V. G. Khlopin Radium Institute, Second Murinsky Avenue 28, S t Petersburg 194021, Russia
3. Accelerator Laboratory Abo Akademi University, Porthansgatan 3, FIN-20500 Turku, Finland