Core polarization for l-forbidden M1 transitions in light nuclei

The experimental systematics of $\text{2}\text{s}{}_{\mathrm{<mtext>1</mtext><mtext>2</mtext>}}\text{?}\text{ld}{}_{\mathrm{<mtext>3</mtext><mtext>2</mtext>}}\text{1-}\text{forbidden}$ M1 transition rates in light nuclei with N, Z ? 20 are studied. Some surprising deviations from the expected behavior are qualitatively discussed in terms of an interplay between first- and second-order core polarization contributions. The B(M1) values in mirror pairs turn out to be close to each other within the experimental errors, the proton transition strengths being slightly larger. Isovector dominance is shown to account for this phenomenon.