text: A very small minority of free neutron decays (about four per million) are so-called "two-body decays", in which the proton, electron and antineutrino are produced, but the electron fails to gain the 13.6 eV energy necessary to escape the proton, and therefore simply remains bound to it, as a neutral hydrogen atom. In this type of beta decay, in essence all of the neutron decay energy is carried off by the antineutrino.
  For fully ionized atoms (bare nuclei), it is possible in likewise manner for electrons to fail to escape the atom, and to be emitted from the nucleus into low-lying atomic bound states (orbitals). This cannot occur for neutral atoms with low-lying bound states which are already filled by electrons.
  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  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 -  - is stable only in the fully ionized state and will decay via electron capture into  in the neutral state. The half life for neutral  is 4750 years.
  Another possibility is that a fully ionized atom undergoes greatly accelerated β decay, as observed for Re by Bosch et al., also at Darmstadt. Neutral Re does undergo β decay with a half-life of  years, but for fully ionized Re this is shortened to only 32.9 years. For comparison the variation of decay rates of other nuclear processes due to chemical environment is less than 1%. Due to the difference in the price of rhenium and osmium and the high share of  in rhenium samples found on earth, this could some day be of commercial interest in the synthesis of precious metals.