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Bromine-75 has a half-life of 97 minutes.[13] This isotope undergoes β+ decay rather than electron capture about 76% of the time,[6] so it was used for diagnosis and positron emission tomography (PET) in the 1980s.[4] However, its decay product, selenium-75, produces secondary radioactivity with a longer half-life of 120.4 days.[6][4]

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Bromine-76 has a half-life of 16.2 hours.[13] While its decay is more energetic than 75Br and has lower yield of positrons (about 57% of decays),[6] bromine-76 has been preferred in PET applications since the 1980s because of its longer half-life and easier synthesis, and because its decay product, 76Se, is not radioactive.[5]

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Like the radioactive isotopes of iodine, radioisotopes of bromine, collectively radiobromine, can be used to label biomolecules for nuclear medicine; for example, the positron emitters 75Br and 76Br can be used for positron emission tomography.[4][5] Radiobromine has the advantage that organobromides are more stable than analogous organoiodides, and that it is not uptaken by the thyroid like iodine.[6]

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Bromine-77 is the most stable radioisotope of bromine, with a half-life of 57 hours.[13] Although β+ decay is possible for this isotope, about 99.3% of decays are by electron capture.[9] Despite its complex emission spectrum, featuring strong gamma-ray emissions at 239, 297, 521, and 579 keV,[14] 77Br was used in SPECT imaging in the 1970s.[15] However, except for longer-term tracing,[6] this is no longer considered practical due to the difficult collimator requirements and the proximity of the 521 keV line to the 511 keV annihilation radiation related to the β+ decay.[15] The Auger electrons emitted during decay are nevertheless well-suited for radiotherapy, and 77Br can possibly be paired with the imaging-suited 76Br (produced as an impurity in common synthesis routes) for this application.[4][15]

Bromine (35Br) has two stable isotopes, 79Br and 81Br, and 35 known radioisotopes, the most stable of which is 77Br, with a half-life of 57.036 hours.