C. O. Ayieko

Department of Physics, University of Nairobi, P.O. Box 00100-30197, Nairobi, Kenya

R. J. Musembi

Department of Physics, University of Nairobi, P.O. Box 00100-30197, Nairobi, Kenya

A. A. Ogacho

Department of Physics, University of Nairobi, P.O. Box 00100-30197, Nairobi, Kenya

B. O. Aduda

Department of Physics, University of Nairobi, P.O. Box 00100-30197, Nairobi, Kenya

B. M. Muthoka

Department of Physics, University of Nairobi, P.O. Box 00100-30197, Nairobi, Kenya

P. K. Jain

Department of Physics, University of Botswana, Private Bag 0022, Gaborone, Botswana