Superallowed beta decay

An especially strong allowed beta decay, conventionally including pure Fermi transitions between $0^{+}$ isobaric analog states. Those states have closely related spatial and spin structure, so the isospin ladder operator has a large overlap. A $0^{+}\to 0^{+}$ assignment alone fixes the allowed Fermi character, but does not establish analog-state overlap or a large rate; a small comparative half-life supplies additional evidence.