[1] Natl Inst Laser Plasma & Radiat Phys, Bucharest, Romania
[2] Australian Nucl Sci & Technol Org, Menai, NSW 2234, Australia
[3] Commiss European Communities, Joint Res Ctr, Inst Hlth & Consumer Protect, I-21020 Ispra, VA, Italy
[4] Univ Birmingham, Sch Engn, Dept Met & Mat, Birmingham B15 2TT, W Midlands, England