Evidence for Target-Excitation Effects in a Single-Particle-Transfer Reaction

Abstract

The transitions to the ${\frac{7}{2}}^{+}$ and ${\frac{9}{2}}^{+}$ states in ${\mathrm{Mg}}^{25}$ have been measured with both the ${\mathrm{Mg}}^{26}({\mathrm{He}}^3,\alpha ){\mathrm{Mg}}^{25}$ and ${\mathrm{Mg}}^{26}\mathrm{}(d,t)\mathrm{}{\mathrm{Mg}}^{25}$ reactions. The only angular distribution that is fitted reasonably well by distorted-wave Born-approximation calculations is the ${\mathrm{Mg}}^{26}({\mathrm{He}}^3,\alpha ){\mathrm{Mg}}^{25}$ transition to the ${\frac{7}{2}}^{+}$ state. The larger cross section for the ${\frac{7}{2}}^{+}$ transition in the (${\mathrm{He}}^3,\alpha$) reaction, and the differences between the shapes of the angular distributions of the transitions to the ${\frac{7}{2}}^{+}$ and ${\frac{9}{2}}^{+}$ states suggest strongly that the ${\frac{7}{2}}^{+}$ is excited primarily by a multiple-excitation process, while interference effects between the simple single-nucleon transfer and multiple excitation may be more important in the ${\frac{9}{2}}^{+}$.