[1] Ist Nazl Fis Nucleare INFN, Lab Nazl Frascati, Via E Fermi 54, I-00044 Rome, Italy
[2] Museo Stor Fis, Ctr Ric Enr Fermi, Via Panisperna 89a, I-00184 Rome, Italy
[3] Ctr Studi & Ric Enr Fermi, Via Panisperna 89a, I-00184 Rome, Italy
[4] Austrian Acad Sci, Stefan Meyer Inst Subatom Phys, Kegelgasse 27, A-1030 Vienna, Austria
[5] Politecn Milan, Dipartimento Elettron Informaz & Bioingn, I-20133 Milan, Italy
[6] Politecn Milan, INFN Sez Milano, I-20133 Milan, Italy
[7] Ist Nazl Fis Nucleare INFN, Lab Nazl Gran Sasso, Via G Acitelli 22, I-67100 Laquila, Italy
[8] Institutul Natl Pentru Fiz & Ingn Nucleara Horia H, Str Atomistilor 407,POB MG-6, Magurele 077125, Romania