In the 16th edition of the chart of nuclides, it lists Cu-64 as decaying to Zn-64 by beta minus decay. OK, no problem here. Then it lists Zn-64 decaying back to Cu-64 by positron decay with a half life of 1.1 x 10^19 years. Assuming this isn't some typo, I have 2 questions. 1) How in blazes did they manage to figure this half life out?! The specific activity for Zn-64 is (very) roughly 19 Becquerels per 1000 kg of Zn-64, meaning how did they get a large enough sample to analyze it so that it could be distinguished from background? and 2) How in blazes is it possible for nuclide #1 to decay to #2 then #2 decay back to #1?!?!?! Is this some quantum mechanical tunneling effect?