Bulletin of the American Physical Society
APS April Meeting 2019
Volume 64, Number 3
Saturday–Tuesday, April 13–16, 2019; Denver, Colorado
Session J04: Radionuclide AstronomyInvited
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Sponsoring Units: DAP DNP Chair: Catherine Deibel, Louisiana State University Room: Sheraton Plaza F |
Sunday, April 14, 2019 1:30PM - 2:06PM |
J04.00001: Learning from gamma-ray lines of cosmic radionuclei. Invited Speaker: Roland L Diehl Gamma ray lines from cosmic sources reveal the results of nuclear reactions in cosmic sites. Following radioactive decays, characteristic lines from excited daughter nuclei can be measured with space-borne gamma ray telescopes which address the MeV energy range of the electromagnetic spectrum. High-energy collisions with excitation of nuclei, and the 511 keV line and its associated special continuum from the annihilation of positrons falls into the same energy window, although of different origin. We review astronomical gamma-ray telescopes and cosmic gamma ray spectrometry, with their concepts and corresponding instruments and missions. Recent results and the challenges and open issues for the future are summarised. Among these are the diffuse\ radioactive afterglow of massive-star nucleosynthesis in 26Al and 60Fe gamma rays, addressing the cycle of matter driven by massive stars and their supernovae. Then, the complex processes making stars explode as either thermonuclear or core-collapse supernovae are enlightened through gamma-ray lines from shortlived radioactivities, 56Ni and 44Ti. Positron annihilation gamma ray emission throughout our Galaxy is an interesting side note here. |
Sunday, April 14, 2019 2:06PM - 2:42PM |
J04.00002: Astrophysical Radionuclides: Where are they and what can they tell us? Invited Speaker: Aimee Hungerford Radionuclides provide for a unique probe into some of the most |
Sunday, April 14, 2019 2:42PM - 3:18PM |
J04.00003: Nuclear Physics of Astrophysical Radionuclide Production Invited Speaker: Bradley S Meyer 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. |
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