β− decay of Tz=+112 isotopes Al37 and Si39 : Understanding Gamow-Teller strength distribution in neutron-rich nuclei

Abstract

${\ensuremath{\beta}}^{\ensuremath{-}}$ decay of ${T}_{z}=+\frac{11}{2}$ nuclei $^{37}\mathrm{Al}$ and $^{39}\mathrm{Si}$ was studied to obtain information about excited states in the daughter and granddaughter nuclei. New information on excited states has been obtained for $^{37,39}\mathrm{P}$, whereas level schemes for $^{37}\mathrm{Si}$ and $^{37,39}\mathrm{S}$ were confirmed and expanded on as compared to the most recent investigations. For the nuclei studied, the valence proton and neutron occupy different major shells with opposite parities, hence, the ${\ensuremath{\beta}}^{\ensuremath{-}}$ decay preferentially and primarily populates core-excited $1p1h$ intruder states with a parity opposite to the ground state of the daughter nucleus. These low-lying intruder states shed light on the $N=20$ shell gap and its evolution with neutron number. The ${\ensuremath{\beta}}^{\ensuremath{-}}$ decay of very neutron-rich nuclei also illustrates how the Gamow-Teller (GT) strength distribution changes with neutron excess. Comparing ${\ensuremath{\beta}}^{\ensuremath{-}}$ decay of $^{37,39}\mathrm{Si}$ presented here with $^{38,40}\mathrm{Si}$ from a previous study, we clearly see an even-odd effect in the GT strength distribution with the decay from even-even nuclei showing strong low-lying strength whereas for the odd $A$ being very fragmented. Configuration interaction shell-model calculations with the state-of-art SDPFSDG-MU effective interaction were performed to understand the structure of the $1p1h$ states and explore the GT strength distribution.