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).

Isotopes of germanium (32Ge)
Main isotopes Decay
abun­dance half-life (t1/2) mode pro­duct
68Ge synth 270.8 d ε 68Ga
70Ge 20.5% stable
71Ge synth 11.3 d ε 71Ga
72Ge 27.4% stable
73Ge 7.76% stable
74Ge 36.5% stable
76Ge 7.75% 1.78×1021 y β−β− 76Se
Standard atomic weight Ar°(Ge)
  • 72.630±0.008
  • 72.630±0.008 (abridged)

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.

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