Branching fraction
In
For example, for decays of 132Cs, 98.1% are ε (electron capture) or β+ (positron) decays, and 1.9% are β− (electron) 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 0.0020 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 (341+6.60) days almost all the nuclei will have decayed, not only half as one may initially think.
Isotopes with significant branching of decay modes include
Branching fractions of atomic states
In the field of atomic, molecular, and optical physics, a branching fraction refers to the probability of decay to a specific lower-lying energy states from some excited state. Suppose we drive a transition in an atomic system to an excited state |e⟩, which can decay into either the ground state |g⟩ or a long-lived state |d⟩. If the probability to decay (the branching fraction) into the |g⟩ state is , then the probability to decay into the other state |d⟩ would be .[2] Further possible decays would split appropriately, with their probabilities summing to 1.
In some instances, instead of a branching fraction, a branching ratio is used. In this case, the branching ratio is just the ratio of the branching fractions between two states. To use our example from before, if the branching fraction to state |g⟩ is , then the branching ratio comparing the transition rates to |g⟩ and |d⟩ would be .
Branching fractions can be measured in a variety of ways, including time-resolved recording of the atom's fluorescence during a series of population transfers in the relevant states.[3][2]
References
External links
- LBNL Isotopes Project
- Particle Data Group (listings for particle physics)
- Nuclear Structure and Decay Data - IAEA for nuclear decays