Neutron dominance in excited states of Mg26 and Be10 probed by proton and α 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.