1. Marien Ngouabi University, Faculty of Science et Technology , BP 69 Brazzaville , Congo
2. Laboratory of Nuclear Physics and Applications (LPNA), National Institute for Research in Exact et Natural Sciences (IRSEN) , P.O. Box 2400 Brazzaville , Congo
3. General Directorate of Radiation Protection and Nuclear Safety, Ministry of Energy and Hydraulic Resources , BP 1172 Libreville , Gabon
4. Laboratory of Nuclear Physics , Faculty of Science, University of Yaounde I, P.O. Box 812 Yaounde , Cameroon
5. Department of Radiation Physics, Institute of Radiation Emergency Medicine, Hirosaki University , 66-1, Hon-cho, Hirosaki-shi, Aomori, 036-8564 , Japan
6. Department of Radiation Science, Graduate School of Health Sciences, Hirosaki University , 66-1, Hon-cho, Hirosaki-shi, Aomori, 036-8564 , Japan
7. Research Centre for Nuclear Science and Technology, Institute of Geological and Mining Research , P.O. Box 4110 Yaounde , Cameroon
8. Laboratory of Nuclear Physics, Faculty of Science, University of Yaounde I , P.O. Box 812 Yaounde , Cameroon