Production of26Al in stellar hydrogen-burning environments: Spectroscopic properties of states in27Si

Abstract

Model predictions of the amount of the radioisotope ${}^{26}$Al produced in hydrogen-burning environments require reliable estimates of the thermonuclear rates for the ${}^{26\mathrm{g}}$Al($p$,\ensuremath{\gamma}) ${}^{27}$Si and ${}^{26\mathrm{m}}$Al($p$,\ensuremath{\gamma})${}^{27}$Si reactions. These rates depend upon the spectroscopic properties of states in ${}^{27}$Si within about 1 MeV of the ${}^{26\mathrm{g}}$Al + $p$ threshold (${S}_{p}$ = 7463 keV). We have studied the ${}^{28}$Si(${}^{3}$He,\ensuremath{\alpha})${}^{27}$Si reaction at 25 MeV using a high-resolution quadrupole-dipole-dipole-dipole magnetic spectrograph. For the first time with a transfer reaction, we have constrained ${J}^{\ensuremath{\pi}}$ values for states in ${}^{27}$Si over ${E}_{x}$ = 7.0--8.1 MeV through angular distribution measurements. Aside from a few important cases, we generally confirm the energies and spin-parity assignments reported in a recent \ensuremath{\gamma}-ray spectroscopy study. The magnitudes of neutron spectroscopic factors determined from shell-model calculations are in reasonable agreement with our experimental values extracted using this reaction.