RELAXED EXCITED-STATES AND ANOMALOUS HYPERFINE-STRUCTURE OF MUONIUM CENTERS IN KBR

We report on the luminescence induced by positive muons implanted (wit h 4 MeV) into KBr crystal, which evidences a long-lived (lifetime = 13 .3 mus) excited state produced by muon radiolysis. The temperature dep endence of the luminescence yield has a strong correlation with the am plitude of an ''anomalous'' muonium center: both are observed only bel ow approximately 50 K. This correlation strongly suggests that the muo nium center is perturbed by the muon-induced excitons to cause the ano malous hyperfine structure. Moreover, the luminescence energy and deca y time indicate that the observed luminescence is not associated with the intrinsic or impurity-related self-trapped excitons, but with a re laxed excited state specific to the muon(ium)-KBr system.