[1] Johannes Gutenberg Univ Mainz, D-55099 Mainz, Germany
[2] Petersburg Nucl Phys Inst, Gatchina 188300, Russia
[3] St Petersburg Electrotech Univ LETI, Prof Popov St 5, St Petersburg 197376, Russia
[4] Univ New South Wales, Sch Phys, Sydney, NSW 2052, Australia