Abstract
Motivated primarily by the large uncertainties in the thermonuclear rate of the 30P(p,γ)31S reaction that limit our understanding of classical novae, we carried out lifetime measurements of 31S excited states using the Doppler Shift Lifetimes (DSL2) facility at the TRIUMF Isotope Separator and Accelerator (ISAC-II) facility. The 31S excited states were populated by the 3He(32S,α)31S reaction. The deexcitation γ rays were detected by a clover-type high-purity germanium detector in coincidence with the α particles detected by a silicon detector telescope. We have applied modern Markov chain Monte Carlo-based Bayesian statistical techniques to perform lineshape analyses of Doppler-shift attenuation method γ-ray data for the first time. We have determined the lifetimes of the two lowest-lying 31S excited states. First experimental upper limits on the lifetimes of four higher-lying states have been obtained. The experimental results were compared to shell-model calculations using five universal sd-shell Hamiltonians. Evidence for γ rays originating from the astrophysically important Jπ=3/2+, 260-keV 30P(p,γ)31S resonance with an excitation energy of Ex=6390.2(7) keV in 31S has also been observed, although strong constraints on the lifetime will require better statistics.