[1] Univ Namur, Dept Phys, B-5000 Namur, Belgium
[2] Higher Educ Pedag Inst, Bukavu, DEM REP CONGO
[3] Belarusian State Univ, Inst Nucl Problems, Minsk 220030, BELARUS
[4] Tomsk State Univ, Fac Radiophys, Radioelect Dept, Tomsk 634050, Russia
[5] Narrando Srl, I-84084 Fisciano, Italy
[6] Univ Salerno, Dept Ind Engn, I-84084 Fisciano, Italy
[7] Univ Eastern Finland, Inst Photon, FI-80100 Joensuu, Finland