Copper (₂₉Cu) has two stable isotopes, ⁶³Cu and ⁶⁵Cu, along with 28 radioisotopes. The most stable radioisotope is ⁶⁷Cu with a half-life of 61.83 hours. Most of the others have half-lives under a minute. Unstable copper isotopes with atomic masses below 63 tend to undergo β⁺ decay, while isotopes with atomic masses above 65 tend to undergo β⁻ decay. ⁶⁴Cu decays by both β⁺ and β⁻.^[1]

There are at least 10 metastable isomers of copper, including two each for ⁷⁰Cu and ⁷⁵Cu. The most stable of these is ^68mCu with a half-life of 3.75 minutes. The least stable is ^75m2Cu with a half-life of 149 ns.^[1]

Both stable isotopes of copper (⁶³Cu and ⁶⁵Cu) have nuclear spin of 3/2−, and thus produce nuclear magnetic resonance spectra, although the spectral lines are broad due to quadrupolar broadening. ⁶³Cu is the more sensitive nucleus while ⁶⁵Cu yields very slightly narrower signals. Usually though ⁶³Cu NMR is preferred.^[6]

Copper offers a relatively large number of radioisotopes that are potentially useful for nuclear medicine.

There is growing interest in the use of ⁶⁴Cu, ⁶²Cu, ⁶¹Cu, and ⁶⁰Cu for diagnostic purposes and ⁶⁷Cu and ⁶⁴Cu for targeted radiotherapy. For example, ⁶⁴Cu has a longer half-life than most positron-emitters (12.7 hours) and is thus ideal for diagnostic PET imaging of biological molecules.^[7]