β-delayed Fission in r-process Nucleosynthesis

M. R. Mumpower1, T. Kawano1, T. M. Sprouse2, N. Vassh2, E. M. Holmbeck2, R. Surman2, and P. Möller1
Astrophysical Journal 869, 14 Link to Article [DOI: 10.3847/1538-4357/aaeaca]
1Theoretical Division, Los Alamos National Laboratory Los Alamos, NM 87545, USA
2Department of Physics, University of Notre Dame Notre Dame, IN 46556, USA

We present β-delayed neutron emission and β-delayed fission (βdf) calculations for heavy, neutron-rich nuclei using the coupled Quasi-Particle Random Phase Approximation plus Hauser-Feshbach (QRPA+HF) approach. From the initial population of a compound nucleus after β-decay, we follow the statistical decay, taking into account competition between neutrons, γ-rays, and fission. We find a region of the chart of nuclides where the probability of βdf is ~100%, which likely prevents the production of superheavy elements in nature. For a subset of nuclei near the neutron dripline, neutron multiplicity and the probability of fission are both large, leading to the intriguing possibility of multi-chance βdf, a decay mode for extremely neutron-rich heavy nuclei. In this decay mode, β-decay can be followed by multiple neutron emission, leading to subsequent daughter generations that each have a probability to fission. We explore the impact of βdf in rapid neutron-capture process (r-process) nucleosynthesis in the tidal ejecta of a neutron star–neutron star merger and show that it is a key fission channel that shapes the final abundances near the second r-process peak.

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