Date of Award

12-2018

Document Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Physics and Astronomy

Committee Member

Bradley S. Meyer, Committee Chair

Committee Member

Sean D. Brittain

Committee Member

Dieter H. Hartmann

Committee Member

Jeremy R. King

Committee Member

Chad E. Sosolik

Abstract

A proper accounting for the inferred abundances of the roughly 10 short-lived radioactivities in the early Solar System requires a comparison to their expectations from an appropriate model of Galactic chemical evolution (GCE) (e.g., [115]). Because the timescale for mixing between phases in the interstellar medium (ISM) is comparable to the lifetime of many of the short-lived radioactivities, the GCE model should follow different ISM phases and the mixing between them. The model must also account for the long temporal distance between the rare astrophysical events that produce many of the short-lived species, such as mass transfer from a low-mass star to its white-dwarf companion leading to a thermonuclear supernova or a binary neutron-star collision that may lead to production of r-process isotopes. In this work, we present expectations for the abundances of short-lived radioactivities in the early Solar System with a detailed GCE model inclusive of these effects. Our model, as discussed in chapter 6 with a star-formation rate consistent with the current Galactic-disk gas fraction and mixing time for ejecta into star-forming regions of ∼107 yr, provides abundances of 53Mn and 60Fe in Solar-mass stars forming at the time of the Sun’s birth that are in reasonable agreement with the inferred values [115][245]. Corroborated by many studies, the 26Al/27Al ratio is too low and requires special injection (e.g., [84]). In our model, as the 41Ca ratio abundance varies widely, the observed value [151] cannot be accommodated, although this species may be injected along with 26Al [27]. The model has difficulty accounting for the abundance of 36Cl, which may be produced by irradiation in the early Solar System [270]. We can account for the abundances of the r-process radioactivities, 107Pd and 129I, as products of binary neutron-star mergers and interpret the abundance of 182Hf via production in the shells of massive stars, which also contribute to the abundances of 107Pd and 129I.

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