It takes 1 trillion times the age of the universe for a xenon-124 sample to shrink by half For the first time, researchers have directly observed an exotic type of radioactive decay called two-neutrino double electron capture.The decay, seen in xenon-124 atoms, happens so sparingly that it would take 18 sextillion years (18 followed by 21 zeros) for a sample of xenon-124 to shrink by half, making the decay extremely difficult to detect. The long-anticipated observation of two-neutrino double electron capture, reported in the April 25 Nature, lays the groundwork for researchers to glimpse a yet unseen, even rarer version...