Bound-state β decays were predicted by Daudel, Jean, and Lecoin in 1947, and the phenomenon in fully ionized atoms was first observed for Dy in 1992 by Jung et al. of the Darmstadt Heavy-Ion Research Center. Although neutral Dy is a stable isotope, the fully ionized Dy undergoes β decay into the K and L shells with a half-life of 47 days. The resulting nucleus - Ho - is stable only in the fully ionized state and will decay via electron capture into Dy in the neutral state. The half life for neutral Ho is 4750 years.