Lifetime Measurements of Excited States in 19-Neon

In novae and x-ray bursts, the 15O(alpha,gamma)19Ne reaction is a potential breakout path from the hot-CNO cycle and into the rp-process. The dominance of this reaction depends on the decay properties of the levels in 19Ne above the alpha threshold. The 4.033 MeV state in $^{19}$Ne, with its low spin (3/2+), is thought to be the main contributor to the reaction rate. The astrophysical rate of the 15O(alpha,gamma)19Ne reaction can be calculated using the branching ratios and radiative widths or level lifetimes of states in 19Ne. Three experiments were done at the University of Notre Dame's Nuclear Structure Laboratory from 1999--2002 using the Doppler shift attention method (DSAM) to measure the lifetime of the 4.03 MeV state in 19Ne via the 3He(17O,n)19Ne and 19F(3He,t)19Ne reactions. Two independent measurements of the lifetime were made placing a limit of 14 fs < t < 24 fs on the lifetime and therefore a limit on the gamma width of 27 meV < Gamma < 47 meV. These values agree with currently accepted values for the lifetime and support the belief that the 15O(alpha,gamma)19Ne reaction is not a probable breakout path from the HCNO cycle into the rp-process in novae, but may have an impact on breakout in x-ray bursts.