Masters Theses

Date of Award

12-2001

Degree Type

Thesis

Degree Name

Master of Science

Major

Physics

Major Professor

Mike Guidry

Committee Members

Marianne Breinig, W. Rapheal Hix, Michael S. Smith, Kermit Duckett

Abstract

The rate of the 17F(p,γ)18Ne reaction has a profound effect on the abundances of several isotopes produced during a nova outburst. In 1999 a new rate for 17F(p,γ)18Ne was determined from a measurement of the excitation function for the 1H(17F,p)17F reaction at Oak Ridge National Laboratory's (hereafter ORNL) Holifield Radioactive Ion Beam Facility[1]. This experiment yielded the first definite evidence of a Jπ =3+ state in 18Ne. This state provided a new resonance in the 17F +p capture, which could, depending on its properties, dominate the rate of 17F(p,γ)18Ne at stellar explosive temperatures. The new rate for 17F(p,γ) 18Ne was determined from these parameters and several other resonance parameters that had been previously determined [2].

A nuclear reaction network was used to calculate abundances produced during a nova outburst. The network required the input of an initial abundance profile, a reaction rate library and a set of hydrodynamic trajectories for each nova. The reaction network was run with the new 17F(p,γ)18Ne rate placed in the reaction rate library and also with three previous determination of the rate by Wiescher et al., Sherr et al. and Garcia et al. [3][4][5]. Abundances for 169 isotopes from hydrogen to chromium were calculated. The final abundances produced by each earlier rate were compared to the final abundances produced by the new ORNL rate. This was done for simulations of novae occurring on a 1.35 M ⊙ ONeMg white dwarf, a 1.25 M⊙ ONeMg white dwarf, and a 1.00 M⊙ CO white dwarf.

The hotter 1.35 M⊙ white dwarf nova simulation showed the greatest variation in the abundance patterns produced by the four rates. In this simulation, the new ORNL rate changed the abundances of some nuclei, such as 17O, that are synthesized in the hottest zones of the nova by up to 15,000 times, when compared to the network results with the Wiescher rate and up to 4 times, when compared to the network results with the Wiescher rate when all zones of the nova were considered. Similar results were achieved for the ORNL to Wiescher rate comparisons for the l.25 M⊙ WD nova nucleosynthesis calculations, with differences of up to 600 times for the hottest zones and up to 2 times when all zones of the nova were considered.

For both the 1.35 M⊙ and 1.25 M⊙ white dwarf nova nucleosynthesis calculations the abundance patterns produced by the networks with the Sherr and Garcia rates were similar to those of the network with the new ORNL rate, with the exception of small differences for a few key isotopes such as 17O and 15N. The 1.00 M⊙ WD nova calculations showed that there was little variation in the abundance patterns produced by the networks with the four rates, even in the hottest zones.

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