Core excitations and narrow states beyond the proton dripline: The exotic nucleus21Al

Abstract

We present the first predictions for the widths of resonance states in a so-far unobserved exotic isotope beyond the proton dripline, ${}^{21}$Al. For this purpose we employ mirror symmetry between the widths of low-lying resonance states and the asymptotic normalization coefficients (ANC) of their mirror analogs. The latter are extracted from a recently measured peripheral reaction ${}^{20}$O($d$,$p$)${}^{21}$O while the positions of resonances are estimated within a microscopic cluster model and a two-body potential model. We have found that ${}^{21}$Al should have two low-lying states decaying into the ${}^{20}$Mg+$p$ channel and three states at higher energy, built on the 2${}^{+}$ core excited state and decaying into the ${}^{20}$Mg(2${}^{+})+p$ channel. The widths of all these states are much smaller than their energies, which makes experimental spectroscopic studies of this isotope beyond the proton dripline possible.