1. Department of Physics, Faculty of Science, The University of Maroua, P.O. Box 814, Maroua, Cameroon
2. Higher Teachers’ Training College of Maroua, The University of Maroua, P.O. Box 46, Maroua, Cameroon
3. Department of Physics, Faculty of Science, The University of Ngaoundéré, P.O. Box 454, Ngaoundéré, Cameroon