The reaction 15 O(alpha; gamma) 19 Ne is one of the potential breakout reactions from
the Hot CNO cycle to the rpprocess. As such, it may play an important
role in nuclear astrophysics for the understanding of energy generation rates
and the synthesis of protonrich nuclei in sites of explosive hydrogen burning,
such as novae and Xray bursters.
Experiments were performed at the radioactive ion beam facility, at
LouvainlaNeuve, Belgium, to test the validity of measuring indirectly the
15 O(alpha; gamma) 19 Ne reaction rate. The method utilised was the population of ex
cited states in 19 Ne and the observation of their ffdecay. Information on the
alpha branching ratios of the states of astrophysical interest, just above the alpha
threshold, allows the reaction rate to be calculated, provided other resonance
properties, i.e. T , ER and J , are known.
Excited states in 19 Ne were populated via an inverse 18 Ne(d,p) reac
tion on a deuterated polyethylene target. The reaction and decay products
were measured in an experimental set up that comprised three silicon strip
detector arrays, with a total of 320 detector elements. Two experiments were
performed at E lab = 44.1 MeV and E lab = 54.3 MeV. The recoiling protons
tagged the populated state and the detection of a coincident ffparticle and
heavy residue pair identified its decay.
Branching ratios for several states in 19 Ne were determined, showing the
viability of this experimental approach. Optical model parameters were de
termined from 18 Ne elastic scattering on deuterons. DWBA calculations were
performed and compared with experimental angular distributions to yield
spectroscopic factors. The results were comparable with a previous meas
urement using a stable beam, despite the significantly lower beam intensity,
and indicated that, provided the necessary beam intensity was available, this
method would allow the measurement of the alpha branching ratio of the reson
ance of most astrophysical interest at 504 keV and thus the determination of
the 15 O(alpha; gamma) 19 Ne reaction rate