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. [GoldBookRef|title=branching fraction|url=http://goldbook.iupac.org/B00725.html] 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:

:$t\_\{1/2\}\; =\; frac\{ln\; 2\}\{lambda\}.$

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.

References

External links

* [http://www.nucleonica.net NUCLEONICA Nuclear Science Portal]
* [http://www.nucleonica.net:81/wiki/index.php/Help:Decay_Engine NUCLEONICA wiki: Decay Engine]
* [http://ie.lbl.gov/toi LBNL Isotopes Project]
* [http://pdg.lbl.gov Particle Data Group] (listings for particle physics)