1. Joint Institute for Nuclear Research, 141980 Dubna, Moscow Region, Russia, Kyiv Taras Shevchenko National University, Volodymyrska Street 64, 01033 Kyiv, Ukraine, Lomonosov Moscow State University, Vorobjovy Gory, 119899 Moscow, Russia, Institute for Therapy of Ukrainian AMS, Postyshev Avenue 2-a, 61039 Kharkov, Ukraine, Research Institute for Solid State Physics and Optics, P.O. Box 49, H-1525 Budapest, Hungary, and GKSS Research Centre, 21502 Geesthacht, Germany