The Impact of Fission on R-Process Calculations

M Eichler,T Rauscher,A Arcones,G Martinez-Pinedo,R Käppeli,F-K Thielemann,C Winteler,I V Panov,O Korobkin,S Rosswog,M Liebendörfer

doi:10.1088/1742-6596/665/1/012054

Abstract

We have performed r-process calculations in neutron star mergers (NSM) and jets of magnetohydrodynamically driven (MHD) supernovae. In these very neutron-rich environments the fission model of heavy nuclei has an impact on the shape of the final abundance distribution and the second r-process peak in particular.We have studied the effect of different fission fragment mass distribution models in calculations of low-Ye ejecta, ranging from a simple parametrization to extensive statistical treatments (ABLA07).The r-process path ends when it reaches an area in the nuclear chart where fission dominates over further neutron captures. The position of this point is determined by the fission barriers and the neutron separation energies of the nuclei involved. As these values both depend on the choice of the nuclear mass model, so does the r-process path. Here we present calculations using the FRDM (Finite Range Droplet Model) and the ETFSI (Extended Thomas Fermi with Strutinsky Integral) mass model with the related TF and ETFSI fission barrier predictions. Utilizing sophisticated fission fragment distribution leads to a highly improved abundance distribution.

Highlights

The r-process is responsible for the production of about half of the heavy elements in our universe
There is a significant difference: While the electron fraction for the neutron star merger is very low, which allows for several fission cycles before the r-process freeze-out, its value is between 0.2 and 0.4 in the magnetohydrodynamically driven (MHD) jets
We have shown that the choice of fission fragment distribution model has a strong effect on the final abundance distribution in r-process calculations

Summary

Introduction

The r-process (rapid neutron capture process) is responsible for the production of about half of the heavy elements in our universe. The r-process reaction path in the nuclear chart proceeds in the very neutron-rich, unstable region, involving nuclei that cannot (yet) be studied in experiments. This means that r-process reaction networks need to rely on theoretically predicted nuclear data. Nuclei split into two lighter ones with roughly half the mass of the parent nucleus, while there is a possibility of several fission neutrons to be emitted.

Methods

Results

Conclusion