1. Atomic Physics Laboratory (040), Vinča Institute of Nuclear Sciences, University of Belgrade, P. O. Box 522, 11001 Belgrade, Serbia
2. Astronomical Observatory, Volgina 7, 11060 Belgrade, Serbia
3. Laboratory of Physics (010), Vinča Institute of Nuclear Sciences, University of Belgrade, P. O. Box 522, 11001 Belgrade, Serbia
4. Department of Physics, University of Oslo, Oslo, Norway
5. Department of Physics, Faculty of Science, University of Banja Luka, Mladena Stojanovića 2, 78000 Banja Luka, Bosnia and Herzegovina, Republic of Srpska