³⁰P(p,γ)³¹S reaction rate in novae: lifetimes of ³¹S states

In classical novae, the ³⁰P(p,γ)³¹S reaction acts as a nucleosynthesis bottleneck in the flow of material to heavier masses. The thermonuclear rate of the ³⁰P(p,γ)³¹S reaction is dominated by proton capture into narrow resonances just above the proton-emission threshold in ³¹S. To constrain the resonance strengths, we carried out lifetime measurements of the ³¹S resonances using the Doppler Shift Attenuation Method. The experiment was performed using the Doppler Shift Lifetimes (DSL) facility at the TRIUMF-ISAC-II facility. The ³¹S states were populated by the ³He(³²S,α)³¹S reaction. The deexcitation γ rays were detected by Clover detectors in coincidence with the α particles detected by a Si telescope. We applied a Bayesian parameter estimation method and obtained the lifetimes for the two lowest ³¹S excited states. The upper limits of the lifetimes for five higher-lying states were obtained for the first time. The γ rays originating from a key 3/2⁺ resonance were observed but with limited statistics. To further improve the sensitivity, an upgrade of the DSL facility is currently underway.