Change in valence of Ce ions induced by hydrogen absorption : CeRu2 G.X. Tessema, J. Peyrard, A. Nemoz, J.P. Senateur, A. Rouault et R. Fruchart J. Physique Lett., 40 5 (1979) 105-107 DOI: 10.1051/jphyslet:01979004005010500