Dipole response of deformed halo nuclei ${}^{31}$Ne and ${}^{37}$Mg

Abstract

We study the soft electric dipole ($E1$) response of deformed halo nuclei ${}^{31}$Ne and ${}^{37}$Mg using a deformed Woods-Saxon potential, with the potential depth adjusted to reproduce empirical separation energy of last neutron orbit, i.e., 150 keV for ${}^{31}$Ne and 220 keV for ${}^{37}$Mg. The configuration dependence of the $E1$ strength near the neutron threshold is pointed out. The halo configurations $[321]3/2$ at ${\beta }_2=0.5$ and $[330]1/2$ at ${\beta }_2=0.24$ in ${}^{31}$Ne contain large amplitudes of halo $p$-shell orbits, which significantly enhance the threshold strength by several times compared to the non-halo configuration $[202]5/2$ at ${\beta }_2=0.32$. In ${}^{37}$Mg, the last neutron configuration is assigned as $[321]1/2$ at a large deformation of ${\beta }_2=0.46$, which involves a halo $p$-shell configuration that significantly enhances the soft dipole strength. This enhancement is about 60\% larger than that of the $[321]3/2$ configuration in ${}^{31}$Ne because of large $p$-shell probability in ${}^{37}$Mg. Experimental confirmation of the soft dipole strength is highly desired to determine the deformation and the configuration of the last neutron orbits both in ${}^{31}$Ne and ${}^{37}$Mg.

Comments: 10 pages, 8 figures