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Germanium has five naturally occurring isotopes, Ge, Ge, Ge, Ge, and Ge. Of these, Ge is very slightly radioactive, decaying by double beta decay with a half-life of 1.78 × 10 years.
Stable Ge is the most common isotope, having a natural abundance of approximately 36%. Ge is the least common with a natural abundance of approximately 7%. When bombarded with alpha particles, the isotopes Ge and Ge will generate stable As and Se, releasing high energy electrons in the process.
At least 27 radioisotopes have also been synthesized ranging in atomic mass from 58 to 89. The most stable of these is Ge, decaying by electron capture with a half-life of 270.95 d. It decays to the medically useful positron-emitting isotope Ga.. The least stable known germanium isotope is Ge with a half-life of 30 ms.
While most of germanium's radioisotopes decay by beta decay, Ge and Ge decay by β delayed proton emission. Ge through Ge also have minor β delayed neutron emission decay paths.