Investigating the astrophysical rp-process through atomic mass measurements

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Clark, Jason A
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The Canadian Penning Trap (CPT) mass spectrometer at the Argonne National Laboratory makes precise mass measurements of both stable and unstable nuclides. To date, more than 60 radioactive isotopes having half-lives as short as one second have been measured with the CPT with a mass precision approaching 10 ppb. This thesis will present measurements made of nuclides along the rp-process path, which describes a process resulting from a series of rapid proton-capture reactions in an astrophysical environment. One possible site for the rp-process mechanism is an x-ray burst which results from the rapid accretion of hydrogen and helium from one star onto the surface of its neutron star binary companion. Mass measurements are required as key inputs to network calculations used to describe the rp-process in terms of the abundances of the nuclides produced, the light-curve profile of the x-ray bursts, and the energy produced. This thesis will describe the CPT apparatus, explain the method used to make precise mass measurements, and present the masses of the "waiting-point" nuclides <sup>68</sup>Se and <sup>64</sup>Ge. The mass measurement results, when used in x-ray burst models, confirm both <sup>68</sup>Se and <sup>64</sup>Ge as waiting-point nuclides which delay the rp-process by approximately 30 s and 7 s respectively.
rp-process, Penning trap, x-ray burst, mass measurement