Hashimoto, Masa-aki | Engineering Papers

DOE OSTI2019

Catching Element Formation In The Act

Gamma-ray astronomy explores the most energetic photons in nature to address some of the most pressing puzzles in contemporary astrophysics. It encompasses a wide range of objects and phenomena: stars, supernovae, novae, neutron stars, stellar-mass black holes, nucleosynthesis, the interstellar medium, cosmic rays and relativistic-particle acceleration, and the evolution of galaxies. MeV gamma-rays provide a unique probe of nuclear processes in astronomy, directly measuring radioactive decay, nuclear de-excitation, and positron annihilation. The substantial information carried by gamma-ray photons allows us to see deeper into these objects, the bulk of the power is often emitted at gamma-ray energies, and radioactivity provides a natural physical clock that adds unique information. New science will be driven by time-domain population studies at gamma-ray energies. This science is enabled by next-generation gamma-ray instruments with one to two orders of magnitude better sensitivity, larger sky coverage, and faster cadence than all previous gamma-ray instruments. This transformative capability permits: (a) the accurate identification of the gamma-ray emitting objects and correlations with observations taken at other wavelengths and with other messengers; (b) construction of new gamma-ray maps of the Milky Way and other nearby galaxies where extended regions are distinguished from point sources; and (c) considerable serendipitous science of scarce events -- nearby neutron star mergers, for example. Advances in technology push the performance of new gamma-ray instruments to address a wide set of astrophysical questions.

Fryer, Chris L↗

DOE OSTI2019

Supernova Neutrino Process of Li and B Revisited

In this work, we reinvestigate effects of neutrino oscillations on the production of 7 Li and 11 B in core-collapse supernovae (SNe). During the propagation of neutrinos from the proto–neutron star, their flavors change, and the neutrino reaction rates for spallation of 12 C and 4 He are affected. In this work, corrected neutrino spallation cross sections for 4 He and 12 C are adopted. Initial abundances involving heavy s-nuclei and other physical conditions are derived in a new calculation of the SN 1987A progenitor in which the effects of the progenitor metallicity are included. A dependence of the SN nucleosynthesis and final yields of 7 Li and 11 B on the neutrino mass hierarchy are shown in several stellar locations. In the normal hierarchy case, the charged-current (CC) reaction rates of ${\nu }_{e}$ are enhanced, and yields of proton-rich nuclei, along with 7 Be and 11 C, are increased. In the inverted hierarchy case, the CC reaction rates of ${\bar{\nu }}_{e}$ are enhanced, and yields of neutron-rich nuclei, along with 7 Li and 11 B, are increased. We find that variation of the metallicity modifies the yields of 7 Li, 7 Be, 11 B, and 11 C. This effect is caused by changes in the neutron abundance during SN nucleosynthesis. Therefore, accurate calculations of Li and B production in SNe should take into account the metallicity of progenitor stars.

79 ASTRONOMY AND ASTROPHYSICS↗