Branching Fraction

In particle physics and nuclear physics, the branching fraction for a decay is the fraction of particles which decay by an individual decay mode with respect to the total number of particles which decay. It is equal to the ratio of the partial decay constant to the overall decay constant. Sometimes a partial half-life is given, but this term is misleading; due to competing modes it is not true that half of the particles will decay through a particular decay mode after its partial half-life. The partial half-life is merely an alternate way to specify the partial decay constant λ, the two being related through:

For example, for spontaneous decays of 132Cs, 98.1% are ε or β+ decays, and 1.9% are β− decays. The partial decay constants can be calculated from the branching fraction and the half-life of 132Cs (6.479 d), they are: 0.10 d−1 (ε + β+) and .0020 d−1 (β−). The partial half-lives are 6.60 d (ε + β+) and 341 d (β−). Here the problem with the term partial half-life is evident: after 346 days almost all the nuclei will have decayed.

Isotopes with significant branching of decay modes include copper-64, arsenic-74, rhodium-102, indium-112, iodine-126 and holmium-164.

Famous quotes containing the words fraction and/or branching:

    The mother as a social servant instead of a home servant will not lack in true mother duty.... From her work, loved and honored though it is, she will return to her home life, the child life, with an eager, ceaseless pleasure, cleansed of all the fret and fraction and weariness that so mar it now.
    Charlotte Perkins Gilman (1860–1935)

    The moose will, perhaps, one day become extinct; but how naturally then, when it exists only as a fossil relic, and unseen as that, may the poet or sculptor invent a fabulous animal with similar branching and leafy horns ... to be the inhabitant of such a forest as this!
    Henry David Thoreau (1817–1862)