Astrophysically important Si states studied with the Si(p,t)Si reaction

The production of the Al radioisotope in astrophysical environments is not understood, in part, because of large uncertainties in key nuclear reaction rates. The Al(p, γ)Si reaction is one of the most important, but its rate is very uncertain as a result of the lack of information on the Si level structure above the proton threshold. To reduce these uncertainties, we have measured differential cross sections for the Si(p,t)Si reaction and determined excitation energies for states in Si. A total of 21 states in Si were observed, including ten above the proton threshold. One new state at 7019 kev was observed, the excitation energies of several states were corrected, and the uncertainties in the excitation energies of other states were significantly reduced. Spins and parities of several states above the proton threshold were determined for the first time through a distorted-wave Born approximation analysis of the angular distributions. These results substantially clarify the level structure of Si.