1. a Philipps-University, Kernchemie , FB 14, D-3550 Marburg, F. R., Germany
2. b Joint Institute for Nuclear Research , Laboratory of High Energy, SU-141 980, Dubna, USSR
3. c Philipps-University, Fachbereich Physik , D-3550 Marburg, F. R., Germany
4. d Technische Hochschule Leipzig , SNW 2, Kernchemie, DDR-7030, Leipzig