1. Radiation Protection Measurements Laboratory, National Centre for Nuclear Research (NCBJ), 7 A. Sołtana Str., 05-400 Otwock/Świerk, Poland, Tel.: +48 22 273 1150, Fax: +48 22 273 1200
2. Faculty of Chemistry, University of Warsaw, 1 Pasteura Str., 02-093 Warsaw, Poland and Department of Electrochemistry, Industrial Chemistry Research Institute, 8 Rydygiera Str., 01-793 Warsaw, Poland