Matrix Elements in Superallowed Transitions

The nuclear matrix element for superallowed transitions between two states of an isobaric spin multiplet can be expressed in terms of a diagonal matrix element of the spin operator difference ${\mathrm{S}}_n-{\mathrm{S}}_p$. Known theoretical results on the nuclear matrix element in image transitions are summarized and the methods which have proved useful in the study of image transitions are extended to superallowed transitions within the lowest $T=1\mathrm{}$ isobaric spin multiplet in the $4n$ series.