Spectroscopy of positive parity states in 26Mg and 26Al via the ( alpha,3He) and ( alpha,t) reactions.

Abstract

The (\ensuremath{\alpha}${,}^{3}$He) and (\ensuremath{\alpha},t) reactions on $^{25}\mathrm{Mg}$ were measured at ${\mathit{E}}_{\mathrm{\ensuremath{\alpha}}}$=50 MeV. Cross sections obtained for 57 positive parity states in $^{26}\mathrm{Mg}$ and $^{26}\mathrm{Al}$ were analyzed within the framework of the exact-finite-range distorted-wave Born approximation and compared to the full s-d shell model predictions. Reasonable agreement between the experimental strengths and the theory was obtained for the low lying states. Deviations of factors of 2 or more were found for some high lying ${2}^{+}$, ${3}^{+}$, and ${4}^{+}$ states in $^{26}\mathrm{Al}$ and especially for the ${1}_{1}^{+}$ state in $^{26}\mathrm{Mg}$. The spectroscopic factors for the transitions to the analog states in $^{26}\mathrm{Mg}$ and $^{26}\mathrm{Al}$ were compared between these reactions. The same strength was obtained for the ${6}_{1}^{\mathrm{\ensuremath{-}}}$, T=1 state in $^{26}\mathrm{Mg}$ and $^{26}\mathrm{Al}$, whereas an enhancement of about 30% was observed for the ${0}_{1}^{+}$ and ${3}_{1}^{+}$, T=1 states in $^{26}\mathrm{Al}$. Further, ${1}^{+}$ states in $^{26}\mathrm{Mg}$ proposed around ${\mathit{E}}_{\mathit{x}}$=10 MeV through the (p,p') reaction were also observed in the $^{25}\mathrm{Mg}$(\ensuremath{\alpha}${,}^{3}$He) reaction without the special enhancement for the 10.6 MeV ${1}^{+}$ state seen in the (p,p') reaction. The total observed strengths for neutron stripping to the positive-parity states in the region of ${\mathit{E}}_{\mathit{x}}$=0--11 MeV almost attained the limit of the pure j-j coupling scheme. Those for the proton stripping were 70% of the limit in the region of ${\mathit{E}}_{\mathit{x}}$=0--8 MeV.