Isobaric analog impurities from neutron capture and transmission by magnesium

Abstract

Resonance neutron interactions with the stable isotopes of magnesium were measured at the Oak Ridge electron linear accelerator time-of-flight facility. The transmission of a natural metal sample (78.7% $^{24}\mathrm{Mg}$) was measured at 200 m and capture by natural metal and by enriched isotope samples was measured at 40 m. Twenty-six resonances in $^{24}\mathrm{Mg}+n$ up to 1.8 MeV were fitted with Breit-Wigner multilevel parameters. The data were sufficient to assign spin and parity to 19 of these. The capture data were analyzed for resonances up to 850 keV for $^{24}\mathrm{Mg}+n$, 265 keV for $^{25}\mathrm{Mg}+n$ (${17}^{+}$ resonances), and 440 keV for $^{26}\mathrm{Mg}+n$ (4 resonances). Average capture at stellar interior temperatures was calculated. The $^{24}\mathrm{Mg}+n$ data serve to assess the isospin impurities in three isobaric analog states. Three other states exhibit reduced neutron widths each several percent of the Wigner limit which may be understood in terms of simple shell model configurations.NUCLEAR REACTIONS $\mathrm{Mg}(n,x)^{24,25,26}\mathrm{Mg}(n,\ensuremath{\gamma})$, $E=0.1\ensuremath{-}1800$ keV; measured $T(E)$ and ${\ensuremath{\sigma}}_{n,\ensuremath{\gamma}}(E)$; deduced $^{25,26,27}\mathrm{Mg}$ level parameters, isobaric analog isospin impurities, shell model configurations, average capture in stars as a function of temperature.