Degree

Doctor of Philosophy (PhD)

Department

Physics & Astronomy

Document Type

Dissertation

Abstract

Type I X-Ray bursts (XRB’s) are a site of nucleosynthesis for some proton-rich elements up to A=100. These stellar explosions occur on the surface of a neutron star in a Low- Mass X-ray Binary accreting H- and He-rich material. During accretion nuclear burning occurs through stable processes such as the hot CNO (HCNO) cycles, but at some critical accretion condition the the HCNO cycles are bypassed through a breakout reaction. This triggers the thermonuclear runaway of the XRB. During the burst, nucleosynthesis on certain proton-rich nuclei, called (α, p) waiting points, can stall which could stall the energy generation and diminish the light curve. These waiting-point nuclei, such as 34 Ar, are in (p, γ) − (γ, p) equilibrium due to their low Q(p,γ) values, and do not immediately β+ decay due to long half lives, but the (α, p) reaction may provide a path to break out of the waiting point. We performed proton elastic scattering by 37 K to study the compound nucleus 38Ca, at the National Superconducting Cyclotron Laboratory using a 4.448 MeV/u beam of 37 K incident on a 30 μm-thick polypropylene target. This was done over 13 days with detector equipment designed and built at Louisiana State University. Scattered protons were measured in telescopes of Si strip detectors, while heavy recoils were detected in a gas-filled ionization chamber. An R-matrix analysis of the measured scattering cross section calculated properties of resonances in 38 Ca that are important for determining the 34 Ar(α, p)37 K reaction rate. This analysis found spin assignments for 11 resonances, of varying levels of confidence. Four states were identified as 2+ with high confidence, along with an additional resonance not discovered by previous work. The quantities determined by this analysis were used to calculate a reaction rate. This rate was input in stellar evolution models built with the software MESA. A 1D model mimicking the “Clocked Burster” GS 1826-24 was evolved using the standard vi REACLIB reaction rate and the rate factor found in this work. The observables were then compared with a baseline and to observational results.

Date

10-23-2017

Committee Chair

Deibel, Catherine

Included in

Nuclear Commons

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