High-spin states in Al29 and Mg27

Abstract

The structure of $^{29}\mathrm{Al}$ and $^{27}\mathrm{Mg}$ was investigated using the reactions $^{18}\mathrm{O}$($^{14}\mathrm{C},p2n$) and $^{18}\mathrm{O}$($^{14}\mathrm{C},\ensuremath{\alpha}\phantom{\rule{0.16em}{0ex}}n$) at 40 MeV. The charged particles were detected and identified with a $\mathrm{\ensuremath{\Delta}}E\ensuremath{-}E$ telescope in coincidence with $\ensuremath{\gamma}$ radiation detected in the Florida State University Compton suppressed $\ensuremath{\gamma}$ detector array. The level and decay schemes of both nuclei have been expanded at higher spins and excitation energies. The positive-parity states up to 3.5\char21{}4.5 MeV agree well with shell model calculations using the USDA interaction. The negative-parity states in $^{27}\mathrm{Mg}$ are reproduced relatively well by one-particle\char21{}one-hole calculations with the WBP-a interaction. Three $^{27}\mathrm{Mg}$ states unbound by 0.4\char21{}1.4 MeV to neutron decay were observed to decay radiatively. One of these states had been previously observed to $\ensuremath{\gamma}$ decay in a ($d,p\ensuremath{\gamma}$) experiment along with a surprising 16 other neutron unbound states. The competition between neutron and $\ensuremath{\gamma}$ decay in these states is discussed in terms of angular momentum barriers and spectroscopic factors.