出版社：SISSA, Scuola Internazionale Superiore di Studi Avanzati
摘要：15O(a,g ) is the critical breakout reaction from the hot CNO cycles, which triggers the thermonuclear
runaways or X-ray bursts occurring in accreting neutron stars. Recent studies have shown
that this reaction is critical for the burst amplitude and periodicity of X-ray bursters. However,
a direct measurement of this reaction rate at astrophysically relevant temperatures is not feasible
yet due to the lack of very high intensity radioactive 15O beams. There has been considerable
effort in the past to investigate this reaction rate indirectly by obtaining gamma and alpha decay
widths of the alpha-unbound states in 19Ne. While this approach has been successful for investigating
higher energy resonances, the critical level at 4.03 MeV remains unknown. This leaves
the reaction rate largely uncertain since previous attempts have only provided limits on its gamma
width and its alpha decay branching ratio. We present new experimental work conducted at the
University of Notre Dame. Lifetimes of the 4.03 MeV state and other relevant states in 19Ne have
been measured successfully using the 17O(3He,n-g ) reaction. We will also present the results of
our recent measurement of the alpha-decay branching ratios. Alpha-unbound states in 19Ne were
populated via the reaction 19F(3He,3H-a) and triton-alpha coincidences were observed using a
low energy particle detection Silicon array and the TWINSOL facility. The first experimental
reaction rate is proposed and its astrophysical implications will be discussed.
