Nuclear Physics of Astrophysical Radionuclide Production

Nearly all nucleosynthetic environments produce radioactive nuclides, which may have significant observable consequences for astronomy. For example, weak decays during hydrogen burning in the Sun produce neutrinos, which have proven to be important probes of the Solar interior and our models of particle physics. At the other extreme of nuclear burning, ejecta from neutron star-neutron star mergers undergo r-process nucleosynthesis and produce light curves of kilonovae. Accurate calculation of the yields of radioactive nuclides from an astrophysical event and the consequent astronomical implications requires knowledge of the nuclear properties of those species and their precursors. A helpful rule of thumb for understanding which nuclear properties are important in the astrophysical production of radioactive nuclides is the radioactive mass fraction present. If the radioactive mass fraction is low during an event, the nuclear dynamics in the event are probably relatively far from equilibrium, and individual nuclear reaction rates are the governing quantities in the nucleosynthesis. If, on the other hand, the radioactive mass fraction is high, the nuclear dynamics are likely dominated by evolving equilibria and the key governing nuclear properties are nuclear masses and weak interaction rates. I present an illustration of this rule of thumb with the production of ¹²⁹I and ¹⁸²Hf, two short-lived radioactivities important for our understanding of the circumstances of the Sun's birth in Galactic history. I also present some open-source, freely-available computational tools for studying the nuclear physics properties governing radionuclide production in astrophysical events.