Affiliation: | aEnvironmental Radioactivity Laboratory, Physics Group, iThemba LABS, P.O. Box 722, Somerset West 7129, South Africa bDepartment of Physics, University of the Western Cape, P. Bag X17, Bellville 7537, South Africa cNECSA, P.O. Box 582, Pretoria 0001, South Africa dStichting EARTH, Weehorsterweg 2, 9321 XS Peize, The Netherlands |