Effect of delta admixture on 1p-shell M1 matrix elements

The effect of the delta resonance on the magnetic dipole properties of the 1p-shell nuclei with A> or =11 has been investigated. When the quark model phasing between the central and tensor transition potentials is used, the delta has little effect on the magnetic moments of the yrast (3/2)- and (1/2)- states. The effect on M1 transition matrix elements is to reduce them by about 6% with some tendency towards a smaller reduction for the lighter nuclei. For seven transitions this quenching improves the agreement between theory and experiment. However, three transitions in the A = 11 and 12 nuclei already have shell model values which are too small so that the suppression worsens the agreement between theory and experiment. Thus the almost state independent reduction in M1 transition rates predicted when the effect of the delta is included does not resolve some of the discrepancies between calculation and experiment