1. Physics Department, Nuclear Research Centre—Negev, PO Box 9001, 84190 Beer-Sheva, Israel
2. Department of Physics Chemistry and Biology, Linköping University, SE-581 83 Linköping, Sweden
3. Israel Atomic Energy Commission, PO Box 7061, 61070 Tel-Aviv, Israel
4. Department of Materials Science and Engineering, Drexel University, Philadelphia 19104, Pennsylvania, USA