1. Division of Pharmaceutical Technology, Faculty of Pharmacy, University of Helsinki, FI-00014 Finland
2. Laboratory of Radiochemistry, Department of Chemistry, University of Helsinki, FI-00014 Finland
3. Laboratory of Industrial Physics, Department of Physics, University of Turku, FI-20014 Finland
4. Department of Physics, University of Kuopio, FI-70211 Kuopio, Finland