Among the many challenging problems concerning the structure of the $L-S$ closed shell ${}_{}{}^{16}{}_{}{}^{}\mathrm{O}$, the question of the origin of the $M1\mathrm{}$ strength still predominates. We address this problem specifically, investigating within the context of the shell model the influence of $\Delta$ excitations, core polarization, and meson exchange on $M1\mathrm{}$ transition rates. Although these mechanisms are usually responsible for quenching $M1\mathrm{}$ transitions, we present quantitative results indicating for the first time the possibility that $M1\mathrm{}$ transitions could be enhanced due to the above mechanisms.

• Received 11 October 1983

DOI:https://doi.org/10.1103/PhysRevC.29.1912