Measurement of the decay branching ratios of theα-unbound states inNe19and theO15(α,γ)reaction rate

Abstract

The breakout reaction {sup 15}O({alpha},{gamma}){sup 19}Ne from the hot CNO cycle is critical to understanding explosive astrophysical phenomena such as x-ray bursts. In spite of considerable past experimental effort via indirect methods, this reaction rate remained mostly uncertain until our recent measurement [Phys. Rev. Lett. 98, 242503 (2007)] of the eluding {alpha}-decay branching ratios of the near-threshold states in {sup 19}Ne, particularly the critical level at 4.03 MeV. In this paper, we present more details of and deeper insights into the measurement and the uncertainties of the experimental results. The {alpha}-unbound states in {sup 19}Ne were populated via the reaction {sup 19}F({sup 3}He,t), and the {alpha}-decay branch was observed from t-{alpha} coincidences using a low-energy particle detection array and the TWINSOL facility at the University of Notre Dame. In particular, the measured branching ratio of the 4.03-MeV state is 2.9{+-}2.1x10{sup -4}. In combination with previous measurements of the lifetimes of these states, a new experimental reaction rate of {sup 15}O({alpha},{gamma}){sup 19}Ne is proposed and discussed in the astrophysical scenario. Further experimental investigations are necessary to reduce the remaining uncertainties.