Orbital Recoupling Dominance in theA=20Isovector GiantM1Transition

The photon spectrum from ${}_{}{}^{20}{}_{}{}^{}\mathrm{Ne}$(${\pi }^{-}$,$\gamma$)${}_{}{}^{20}{}_{}{}^{}\mathrm{F}$ has been measured. The branching ratio to ${}_{}{}^{20}{}_{}{}^{}\mathrm{F}$($1^{+}$, 1.06 MeV) is compared to the analogous $M1\mathrm{}$ decay width ${}_{}{}^{20}{}_{}{}^{}\mathrm{Ne}$($1^{+}$, 11.24 MeV) →${}_{}{}^{20}{}_{}{}^{}\mathrm{Ne}$(g.s.). This determines the relative importance of spin and orbital magnetization in the transition amplitude. The $M1\mathrm{}$ amplitude is found to contain only (47 ± 16)% spin flip, in agreement with shell-model calculations. Excitation of $2^{-}$ states by ${}_{}{}^{20}{}_{}{}^{}\mathrm{Ne}$(${\pi }^{-}$,$\gamma$) is also observed.