1. University of Yaoundé I,Faculty of Science,Department of Physics,Yaoundé,Cameroon
2. University of Salerno,INFN - Napoli, Salerno group and Department of Physics,Fisciano,Salerno,Italy
3. University of Sannio,INFN - Napoli, Salerno group and Department of Engineering,Benevento,Italy
4. University of Douala,Department of Physics, Faculty of Science,Douala,Cameroon
5. University of Sannio,INFN - Napoli, Salerno group and Department of Science and Technology,Benevento,Italy