First application of Markov chain Monte Carlo-based Bayesian data analysis to the Doppler-shift attenuation method

Motivated primarily by the large uncertainties in the thermonuclear rate of the ³⁰P^{(p , γ) 31}S 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) 31}S 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 J^π = 3 /2⁺, 260-keV ³⁰P^{(p , γ) 31}S resonance with an excitation energy of E_x = 6390.2 (7) keV in ³¹S has also been observed, although strong constraints on the lifetime will require better statistics.