1. Department of Radiation Safety and Security, Paul Scherrer Institute, Forschungsstrasse 111, 5232 Villigen, Switzerland
2. Laboratory for Multiscale Materials Experiments, Paul Scherrer Institute, Forschungsstrasse 111, 5232 Villigen, Switzerland
3. National Institute of Advanced Industrial Science and Technology (AIST), Ikeda, Osaka 563-8577, Japan
4. Radiology Division, Agfa NV, 2640 Mortsel, Belgium
5. Graduate School of Human and Environmental Studies, Kyoto University, Kyoto 606-8501, Japan