1. Chromium Research Group, Department of Physics, University of Johannesburg, P.O. Box 524, Auckland Park, Johannesburg 2006, South Africa
2. Research and Technology Development Division, South African Nuclear Energy Corporation (Necsa) SOC Limited, P.O. Box 582, Pretoria 0001, South Africa
3. Australian Centre for Neutron Scattering, Australian Nuclear Science and Technology Organisation, Locked Bag 2001, Kirrawee DC, NSW 2232, Australia