Copper (29Cu) has two stable isotopes, 63Cu and 65Cu, along with 28 known radioisotopes from 55Cu to 84Cu. The most stable radioisotope, 67Cu, has a half-life of only 61.83 hours, then follow 64Cu at 12.70 hours and 61Cu at 3.34 hours. The others have half-lives all under an hour and most under a minute. The isotopes with mass below 63 generally undergo positron emission and electron capture to nickel isotopes, while isotopes with mass above 65 generally undergo β− decay to zinc isotopes. The single example in between, 64Cu, decays both ways.