- Abstract The vanishing of C 60 + EPR centers during the intercalation of polycrystalline C 60 with rubidium is described as a two-stage process with inter- and intragrain penetration of rubidium into the C 60 sample. This process leads to quenching of C 60 + hole states through a recombination process. Two aspects of the results are discussed: 1. EPR assignment of the spectrum usually observed in pristine polycrystalline C 60 samples. 2. Similarity of the kinetics of alkali inter- and intragrain penetration into powdered C 60 to the kinetics of oxygen penetration through C 60 film, accompanied by the generation of C 60 + centers.