Realistic fission models, new beta-decay half-lives and the r-process in neutron star mergers

Abstract

Abstract.Almost half of heavy nuclei beyond iron are considered to be produced by rapid neutron capture process (r-process). This process occurs in the neutron-rich environment such as core-collapse supernovae or neutron star mergers, but the main production site is still unknown. In the r-process of neutron star mergers, nuclear fission reactions play an important role. Also beta-decay half-lives of magic nuclei are crucial for the r-process. We have carried out r-process nucleosynthesis calculations based upon new theoretical estimates of fission fragment distributions and new beta-decay half-lives for N=82 nuclei measured at RIBF-RIKEN. We investigate the effect of nuclear fission on abundance patterns in the matter ejected from neutron star mergers with two different fission fragment mass distributions. We also discuss how the new experimental beta-decay halflives affect the r-process.

R-Process Nucleosynthesis in Neutron Star Merger With New Fission Model

“…One possible interpretation of this is that binary neutron star mergers do not contribute to the production of the solar r-process elements at all. Here, however, we propose [7] another possible interpretation: neutron star mergers produce only a part of the solar r-process elements. In order to confirm this hypothesis, we have summed the elemental abundances of three candidates for the r-process, i.e.…”

“…This code has been updated with a new nuclear mass model [9], along with new beta-decay rates, beta-delayed neutron emission probabilities, beta-delayed fission probabilities, fission fragment distributions [10,11], and alpha-decay rates [12]. As summarized in [7,10], this model predicts that nuclei become unstable to fission in a region of higher nuclear masses than other nuclear models. This feature is crucial to the termination point of the r-process path as discussed below.…”

“…Weight factors for the neutron star merger and the neutrino driven wind relative to the magnetorotational supernova are introduced to match the solar r-process abundances. These parameters were determined [7] by a χ 2 minimization to the solar r-process abundances. The solar r-process abundances are normalized to fit the resulting sum of the three r-process components at A = 153.…”

“…Previous studies of neutron star mergers have indicated that the nuclear fission of neutron-rich nuclei is crucial to determining resulting nuclear abundances after the rprocess [5,6]. In this paper, we report on r-process nucleosynthesis simulations [7] of binary neutron star mergers based upon a new nuclear reaction network code. We have added new nuclear data for nuclear masses, nuclear fission probabilities, fission distributions, etc.…”

Beta-Decay Rates for Exotic Nuclei and R-Process Nucleosynthesis

“…This implies that the dynamical ejecta of NS-NS mergers can be an origin of the solar r-process nuclei. Note, however, that the different model suggests in completely different abundance pattern due to asymmetric fission recycling at such a low Y e < 0.1 [11].…”