Isotopes of germanium

Germanium (₃₂Ge) has five naturally occurring isotopes, ⁷⁰Ge, ⁷²Ge, ⁷³Ge, ⁷⁴Ge, and ⁷⁶Ge. Of these, ⁷⁶Ge is very slightly radioactive, decaying by double beta decay with a half-life of 1.78 × 10²¹ years (130 billion times the age of the universe).

Stable ⁷⁴Ge is the most common isotope, having a natural abundance of approximately 36%. ⁷⁶Ge is the least common with a natural abundance of approximately 7%.

At least 27 radioisotopes have also been synthesized ranging in atomic mass from 58 to 89. The most stable of these is ⁶⁸Ge, decaying by electron capture with a half-life of 270.95 d. It decays to the medically useful positron-emitting isotope ⁶⁸Ga. (See gallium-68 generator for notes on the source of this isotope, and its medical use.) The least stable known germanium isotope is ⁵⁹Ge with a half-life of 13.3 ms.

While most of germanium's radioisotopes decay by beta decay, ⁶¹Ge and ⁶⁵Ge can also decay by β⁺-delayed proton emission. ⁸⁴Ge through ⁸⁷Ge also have minor β⁻-delayed neutron emission decay paths.

⁷⁶Ge is used in experiments on the nature of neutrinos, by searching for neutrinoless double beta decay.