1. University of Yaounde I Faculty of Science Department of Physics Yaounde Cameroon
2. University of Yaounde I National Advanced School of Engineering Department of Mathematic and Physical Science Yaounde Cameroon
3. Elettra-Sincrotrone Trieste s.s. 14 - km 163,5 in AREA Science Park 34149 Basovizza Trieste Italy
4. Université de Lorraine, CNRS, CRM2 54000 Nancy France