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Title: Studies of states in 19Ne about the 18F + p threshold and the 18Ne(α,p) HCNO breakout reaction
Authors: Josephides, Alexis Noel
Supervisor(s): Davinson, Thomas
Issue Date: 2009
Publisher: The University of Edinburgh
Abstract: The rate of destruction of 18F via the 18F + p reactions is of importance in both novae and X-ray burster explosive scenarios. The rate of the competing destructive reactions, 18F(p,γ)19Ne and 18F(p,α)15O, depend upon the level structure of the compound nucleus 19Ne. The first experiment in this thesis examines the level structure of 19Ne about the 18F + p threshold via elastic 15O(α,α)15O scattering. The experiment was performed at the CRC Louvain-la-Neuve. A radioactive 15O beam bombarded a thick 4He gaseous target with elastically scattered alpha particles detected using segmented silicon detectors. An R-matrix approach was used to analyse the data and extract the resonance parameters Er and Ѓα. Particular emphasis was placed on extracting information regarding the possible 3/2+ doublet, the parameters of which, to date, have been inferred from the mirror nucleus 19F. The nominal values for the doublet taken from the mirror are Er = 8 and 38 keV, with Ѓα = 0.27 and 1.3 keV respectively. Following this new analysis it has been found that the doublet straddles the threshold at Er = -22 and 3 keV, with Ѓα = 0.15 and 3.3 keV respectively. S-factor calculations and interference effects were also examined. The 18Ne(α,p)21Na reactions is believed to be a key process in X-ray bursters. It is thought to be a possible HCNO-breakout reaction; the mechanism responsible for producing energy to drive the X-ray burster. To date the reaction has been studied both directly and indirectly. The results from each previous experiment show su cient discrepancies to warrant a re-examination of the reaction rate. As such, the second experiment presented in this thesis revolves around a new direct measurement of 18Ne(α,p). The experiment was undertaken at the CRC Louvain-la-Neuve, where, a radioactive 18Ne beam impinged upon a thin gaseous 4He target. The beam energy was chosen to provide data points in common with previous experiments at Er = 1.7 and 2.5 MeV. Reaction protons were detected via a segmented silicon detector telescope system. The total cross section calculated at Er = 2.5 MeV is 1.22 0.151 mb. An upper limit for the cross-section of 0.0208 mb was evaluated at Er = 1.7 MeV
Sponsor(s): Engineering and Physical Sciences Research Council (EPSRC)
Keywords: HCNO-breakout reaction
Reaction protons
Appears in Collections:Physics thesis and dissertation collection

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