1. Département de Physique, Faculté des Sciences, Université de Bangui, Bangui, Central African Republic
2. PG and Research Department of Physics, N. M. S. S. V. N College, Madurai, Tamil Nadu, India
3. Department of Physics, Faculty of Science, University of Maroua, Maroua, Cameroon
4. Departement of Physics, Faculty of Science, The University of Ngaoundere, Ngaoundere, Cameroon
5. Higher Teacher’s Training College, The University of Maroua, Maroua, Cameroon