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Natural gallium (31Ga) consists of a mixture of two stable isotopes: gallium-69 and gallium-71. Twenty-nine radioisotopes are known, all synthetic, with atomic masses ranging from 60 to 89; along with three nuclear isomers, 64mGa, 72mGa and 74mGa. Most of the isotopes with atomic mass numbers below 69 decay to isotopes of zinc, while most of the isotopes with masses above 71 decay to isotopes of germanium. Among them, the most commercially important radioisotopes are gallium-67 and gallium-68.
Gallium-67 (half-life 3.3 days) is a gamma-emitting isotope (the gamma ray emitted immediately after electron capture) used in standard nuclear medical imaging, in procedures usually referred to as gallium scans. It is usually used as the free ion, Ga3+. It is the longest-lived radioisotope of gallium.
The shorter-lived gallium-68 (half-life 68 minutes) is a positron-emitting isotope generated in very small quantities from germanium-68 in gallium-68 generators or in much greater quantities by proton bombardment of 68Zn in low-energy medical cyclotrons,[4][5] for use in a small minority of diagnostic PET scans. For this use, it is usually attached as a tracer to a carrier molecule (for example the somatostatin analogue DOTATOC), which gives the resulting radiopharmaceutical a different tissue-uptake specificity from the ionic 67Ga radioisotope normally used in standard gallium scans.