1. The Unit of Chemistry Teacher Education, Department of Chemistry, Faculty of Science, University of Helsinki, A.I. Virtasen aukio 1, P.O. Box 55, Helsinki, FI-00014, Finland
2. Radiochemistry Unit, Department of Chemistry, Faculty of Science, University of Helsinki, A.I. Virtasen aukio 1, P.O. Box 55, Helsinki, FI-00014, Finland
3. Institute of Biomedicine, University of Eastern Finland, P.O. Box 1627, Kuopio, FI-70211, Finland