superallowed transition

"Superallowed transitions" in physics refer to a specific class of beta decay processes where the rate of transition is significantly faster than most other beta decays. This rapid decay occurs when the nuclear matrix element, a quantum mechanical quantity representing the overlap between the initial and final nuclear states, is close to unity.1

These transitions are often observed between mirror nuclei, which have nearly identical numbers of protons and neutrons, differing by only one. Examples include the decay of tritium to helium-3 or the positron emission from carbon-11 to boron-11. The basic rate law for these superallowed transitions is well-defined, and they typically have short half-lives, with log ft values in the range of 3 to 3.5. In contrast, "allowed transitions" in atomic spectroscopy are those that occur with high probability, while "forbidden transitions" proceed much more slowly.12