Low-lying resonances in Si26 relevant for the determination of the astrophysical Al25(p,γ)Si26 reaction rate

Abstract

The $^{25}\mathrm{Al}(p,\ensuremath{\gamma})^{26}\mathrm{Si}$ reaction plays a key role in accurately modeling and understanding the nucleosynthesis of the long-lived radioisotope $^{26}\mathrm{Al}$ observed throughout the galaxy by $\ensuremath{\gamma}$-ray telescopes via the detection of its 1.809 MeV $\ensuremath{\gamma}$-ray line. The $^{25}\mathrm{Al}(p,\ensuremath{\gamma})^{26}\mathrm{Si}$ reaction is responsible for redirecting the flux of nuclear material away from the ground state of the long-lived radioisotope $^{26}\mathrm{Al}$ ($^{26}\mathrm{Al}^{g}$) in favor of its short-lived isomer ($^{26}\mathrm{Al}^{m}$) which bypasses the emission of the 1.809 MeV $\ensuremath{\gamma}$ ray, but is observed in, for example, an excess of the isotopic abundance of $^{26}\mathrm{Mg}$ in meteorites. Uncertainties in the $^{25}\mathrm{Al}(p,\ensuremath{\gamma})^{26}\mathrm{Si}$ reaction rate are dominated by the nuclear properties of low-lying proton-unbound states in $^{26}\mathrm{Si}$. A high-sensitivity spectroscopic study of $^{26}\mathrm{Si}$ was performed at the John D. Fox Accelerator Laboratory at Florida State University, using a neutron/$\ensuremath{\gamma}$-ray coincidence measurement with the $^{24}\mathrm{Mg}(^{3}\mathrm{He},n\ensuremath{\gamma})^{26}\mathrm{Si}$ reaction. The present measurement solves previous discrepancies in the existence and location of the relevant resonances in $^{26}\mathrm{Si}$. Furthermore, the high sensitivity of the study allowed for a direct estimate of the 3${}_{3}^{+}\phantom{\rule{4pt}{0ex}}\ensuremath{\gamma}$-partial width. The present experimental information combined with previous works provide an updated rate of the $^{25}\mathrm{Al}(p,\ensuremath{\gamma})^{26}\mathrm{Si}$ reaction at nova temperatures.