65Cu

65Cu is a stable isotope of copper with mass number 65. It contains 29 protons and 36 neutrons. Together with 63Cu, which has 29 protons and 34 neutrons, it comprises the two stable copper isotopes. In natural copper, 65Cu accounts for about 30% of the isotopic mixture, with the remainder being 63Cu. 65Cu has a nuclear spin of 3/2 and a nonzero electric quadrupole moment, which makes it observable by nuclear magnetic resonance and related spectroscopic techniques. Because it is stable, 65Cu does not decay and has no half-life. It occurs naturally in copper minerals and metal, including chalcopyrite and native copper. In research, 65Cu is used as a stable isotope label and as a reference for isotopic tracing and calibration in analytical measurements; its known abundance facilitates trace analysis of copper-containing systems.