Isospin and spin-orbital structures ofJπ=1+states excited in28Si

Gamow-Teller (GT) states with $J^{\pi }$ = 1${}^{+}$ excited by a $\mathrm{}(p,n)\mathrm{}$-type charge-exchange reaction on $N=Z$ nuclei with ground-state isospin $T=0\mathrm{}$ have isospin $T=1\mathrm{}$, while $M1\mathrm{}$ states excited by inelastic scattering of electrons or protons can have either $T=0\mathrm{}$ or $T=1\mathrm{}$. The latter are the isobaric analog states of the GT states. By comparing the GT states observed in the good-resolution ${(}^3\mathrm{He},t)$ reaction at 150 MeV/nucleon with the $M1\mathrm{}$ states observed in inelastic electron and proton reactions, the isospin structure of the $1^{+}$ states in ${}^{28}\mathrm{Si}$ has been determined. From an analysis of the strengths of corresponding $1^{+}$ states observed in the ${(}^3\mathrm{He},t)$ and ${(e,e}^{\prime })$ reactions, the spin and orbital contributions to the $M1\mathrm{}$ excitations have been deduced.