[1] Silesian Tech Univ, Inst Phys, Ctr Sci & Educ, Div Geochronol & Environm Isotopes, Konarskiego 22B, PL-44100 Gliwice, Poland
[2] Gas meth Energy Ltd, KBC Bldg,KN5 Rd, Kigali, Rwanda
[3] Univ Rwanda, Coll Sci & Technol, KN 67, Kigali 3900, Rwanda
[4] Duke Univ, Durham, NC 27708 USA
[5] Chinese Acad Sci, Inst Geog Sci & Nat Resources Res, Key Lab Ecosyst Network Observat & Modeling, Beijing 100101, Peoples R China
[6] Univ Chinese Acad Sci, Beijing 100049, Peoples R China