An Etymological Dictionary of Astronomy and Astrophysics
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A quantity used to describe a → radionuclide that has more than one → decay mode. For a particular decay mode, the ratio of the number of atoms decaying by that decay mode to the number decaying in total: BR_i = k_i/(k₁ + k₂ + ...) = k_i/k, where k is → decay constant.

→ branching; → ratio.