First application of Markov Chain Monte Carlo-based Bayesian data analysis to the Doppler-Shift Attenuation Method

Abstract

Motivated primarily by the large uncertainties in the thermonuclear rate of the 30 P(p, γ) 31 S reaction that limit our understanding of classical novae, we carried out lifetime measurements of 31 S excited states using the Doppler Shift Lifetimes (DSL) facility at the TRIUMF Isotope Separator and Accelerator (ISAC-II) facility. The 31 S excited states were populated by the 3 He( 32 S, 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 methods to perform lineshape analyses of Doppler-Shift Attenuation Method γ-ray data for the first time. We have determined the lifetimes for the two lowest-lying 31 S excited states. Upper limits on the previously unknown lifetimes of four higher-lying states have been obtained. The experimental results were compared to the shell-model calculations using five universal sd-shell Hamiltonians. The γ rays originating from the astrophysically important J π = 3/2 + , 260-keV 30 P(p, γ) 31 S resonance have also been observed, but the lifetime is expected to be better constrained with more statistics at the upgraded DSL2 facility.