Neutron dominance in excited states of ${}^{26}$Mg and ${}^{10}$Be probed by proton and alpha inelastic scattering

Abstract

Isospin characters of nuclear excitations in ${}^{26}$Mg and ${}^{10}$Be are investigated via proton($p$) and alpha($\alpha$) inelastic scattering. A structure model of antisymmetrized molecular dynamics (AMD) is applied to calculate the ground and excited states of ${}^{26}$Mg and ${}^{10}$Be. The calculation describes the isoscalar feature of the ground-band $2_1^{+}$($K^{\pi }=0_1^{+}$) excitation and predicts the neutron dominance of the side-band $2_2^{+}$($K^{\pi }=2^{+}$) excitation in ${}^{26}$Mg and ${}^{10}$Be. The $p$ and $\alpha$ inelastic scattering off ${}^{26}$Mg and ${}^{10}$Be is calculated by microscopic coupled-channel (MCC) calculations with a $g$-matrix folding approach by using the matter and transition densities of the target nuclei calculated with AMD. The calculation reasonably reproduces the observed $0_1^{+}$, $2_1^{+}$, and $2_2^{+}$ cross sections of ${}^{26}$Mg+$p$ scattering at incident energies $E_p=$24 and 40 MeV and of ${}^{26}$Mg+$\alpha$ scattering at $E_{\alpha }=$104 and 120 MeV. For ${}^{10}$Be+$p$ and ${}^{10}$Be+$\alpha$ scattering, inelastic cross sections to the excited states in the $K^{\pi }=0_1^{+}$ ground-, $K^{\pi }=2^{+}$ side-, $K^{\pi }=0_2^{+}$ cluster-, and $K^{\pi }=1^{-}$ cluster-bands are investigated. The isospin characters of excitations are investigated via inelastic scattering processes by comparison of the production rates in the ${}^{10}$Be+$p$, ${}^{10}$Be+$\alpha$, and ${}^{10}$C+$p$ reactions. The result predicts that the $2_2^{+}$ state is selectively produced by the ${}^{10}$Be+$p$ reaction because of the neutron dominance in the $2_2^{+}$ excitation as in the case of the ${}^{26}$Mg+$p$ scattering to the $2_2^{+}$ state, whereas its production is significantly suppressed in the ${}^{10}$C+$p$ reaction.

Comments: 19 pages, 12 figures