The Role of Fission in Neutron Star Mergers and Its Impact on the r-Process Peaks

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Datum
15.07.2015Autorin/Autor
Metadata
Zur LanganzeigeType
01 - Zeitschriftenartikel, Journalartikel oder Magazin
Primary target group
Science
Created while belonging to FHNW?
Yes
Zusammenfassung
Comparing observational abundance features with nucleosynthesis predictions of
stellar evolution or explosion simulations can scrutinize two aspects: (a) the conditions
in the astrophysical production site and (b) the quality of the nuclear physics input utilized.
We test the abundance features of r-process nucleosynthesis calculations for
the dynamical ejecta of neutron star merger simulations based on three different nuclear
mass models: The Finite Range Droplet Model (FRDM), the (quenched version
of the) Extended Thomas Fermi Model with Strutinsky Integral (ETFSI-Q), and the
Hartree-Fock-Bogoliubov (HFB) mass model. We make use of corresponding fission
barrier heights and compare the impact of four different fission fragment distribution
models on the final r-process abundance distribution. In particular, we explore the
abundance distribution in the second r-process peak and the rare-earth sub-peak as a
function of mass models and fission fragment distributions, as well as the origin of a
shift in the third r-process peak position. The latter has been noticed in a number of
merger nucleosynthesis predictions. We show that the shift occurs during the r-process
freeze-out when neutron captures and β-decays compete and an (n,γ)-(γ,n) equilibrium
is not maintained anymore. During this phase neutrons originate mainly from fission
of material above A = 240. We also investigate the role of β-decay half-lives from
recent theoretical advances, which lead either to a smaller amount of fissioning nuclei
during freeze-out or a faster (and thus earlier) release of fission neutrons, which can
(partially) prevent this shift and has an impact on the second and rare-earth peak as
well.