1. Department of Physics and Astronomy, University College London, Gower Street, London WC1E 6BT, U.K.
2. European Commission, Joint Research Centre, Institute for Transuranium Elements, Postfach 2340, Karlsruhe, D-76125 Germany
3. European Synchrotron Radiation Facility, BP 200, F-38403 Grenoble Cedex, France
4. Department of Metallurgy and Materials, University of Birmingham, Edgbaston, Birmingham, B15 2TT, U.K.