 Two other nuclides in which double beta decay has been observed, and , can also theoretically single beta decay, but this decay is extremely suppressed and has never been observed.Fourteen isotopes have been experimentally observed undergoing two-neutrino double beta decay (β–β–) or double electron capture (εε).The table below contains nuclides with the latest experimentally measured half-lives, as of December 2016, except for 124Xe (for which double electron capture was first observed in 2019).