The effect of the delta resonance on the magnetic dipole properties of the $1p$-shell nuclei with $A\ge 11$ 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 ${\frac{3}{2}}^{-}$ and ${\frac{1}{2}}^{-}$ states. The effect on $M1\mathrm{}$ 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 $A=11\mathrm{}$ 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 $M1\mathrm{}$ transition rates predicted when the effect of the delta is included does not resolve some of the discrepancies between calculation and experiment.

• Received 30 January 1984

DOI:https://doi.org/10.1103/PhysRevC.29.2303