[1] Univ Athens, Dept Phys, Athens 15784, Greece
[2] Tech Univ Szczecin, Inst Phys, PL-70310 Szczecin, Poland
[3] Tech Univ Szczecin, Inst Chem & Environm Protect, PL-70310 Szczecin, Poland
[4] Joint Inst Nucl Res, Frank Lab Neutron Phys, Dubna 141980, Russia
[5] Natl Tech Univ Athens, Dept Appl Phys, Athens, Greece