16O(p,γ)17F
PI: Rosanna Depalo
Astrophysical Motivation
Oxygen isotopic rations, and in particular 17O/16O, are used as indicators of the structure and nucleosynthesis in Asymptotic Giant Branch (AGB) stars, and track an additional process named Hot Bottom Burning (HBB). HBB states that in massive (M > 4 M⊙) AGB stars, the base of the star’s envelope can become hot enough to trigger hydrogen burning. The success of these HBB models in recreating the observed oxygen isotopic ratios depends sensitively on the rate of the 16O(p,γ)17F reaction (Q = 600 keV) at centre of mass energies of 10 – 100 keV.
Experimental Aims
Recent measurements of the 16O(p,γ)17F reaction have been performed at LUNA using both the prompt-gamma ray detection and activation methods. This non-resonant reaction was measured at energies between Ecm = 200 keV and Ecm = 375 keV. The use of two different techniques allows us to determine the reaction branching ratios (direct capture to ground state and first excited state of 17F) and the total cross section, as well as account for possible systematic effects related to the measurement technique.
Experimental setup
For the activation method measurements a 4π BGO detector was used, while the prompt gamma measurements were taken using a HPGe detector at 55o and two CeBr3 scintillators at 0o and 90o. In both cases the detectors were contained within thick lead shielding to reduce the background level as far as possible.
The targets for both the activation and prompt gamma measurements were tantalum backings anodised in ultra-pure water with a small enrichment in 18O. The 18O allowed the targets to be analysed in situ using Nuclear Resonant Reaction Analysis (NRRA) on the Ecm = 143 keV resonance of the 18O(p,γ)19F reaction.