1. Department of Nuclear Physics and Biophysics; Faculty of Mathematics, Physics and Informatics; Comenius University; 84248 Bratislava Slovakia
2. Laboratori Nazionali del Gran'Sasso-INFN; 67100 Assergi (AQ) Italy
3. Department of Geosciences; University of Arizona; Tucson Arizona 85721 USA
4. NSF Arizona AMS Laboratory; University of Arizona; Tucson Arizona 85721 USA
5. Institute for Nuclear Research; Hungarian Academy of Sciences; 4026 Debrecen Hungary
6. Natural History Museum; Burgring 7 A-1010 Vienna Austria
7. Department of Lithospheric Research; University of Vienna; A-1090 Vienna Austria