Speaker
Description
A quantitative understanding of nuclear fission is important in nuclear physics, astrophysics, and nuclear applications. However, its full physical description remains unresolved because fission is a complex multistage process. We investigate the fission properties of neutron-rich uranium isotopes relevant to r-process nucleosynthesis, focusing on fragment mass distributions and prompt neutron emission in the postfission stage, while also discussing the role of multi-chance fission and prefission neutron emission. We employ a hybrid framework [1], in which fission dynamics are described by a Langevin approach and prompt neutron emission is treated with a Hauser-Feshbach statistical model code, CCONE [2]. In the Langevin calculation, the neck parameter $\varepsilon$ is introduced as an adjustable quantity, and we examine how different treatments of $\varepsilon$ affect the predicted observables. We calculated uranium isotopes from ${}^{245}$U to ${}^{276}$U, covering a wide neutron-rich region relevant to the r-process. We find a transition from asymmetric to symmetric fission around $A \sim 250$, although the detailed behavior depends on the choice of $\varepsilon$. The prompt neutron multiplicity generally increases toward heavier isotopes, but this trend is modified by changes in the fission asymmetry. We also discuss how multi-chance fission influences the fragment mass distributions and neutron emission in the most neutron-rich isotopes. Variations in $\varepsilon$ also affect neutron emission, although the resulting uncertainty remains at the level of about 10% within a reasonable parameter range. Our results provide a systematic dynamical description of fragment mass distributions and prompt neutron emission for neutron-rich uranium isotopes and show that the evolution of the fission mode plays a key role in determining postfission neutron emission.
[1] S. Tanaka, N. Nishimura, F. Minato, and Y. Aritomo, Phys. Rev. C 108, 054607 (2023).
[2] O. Iwamoto, N. Iwamoto, S. Kunieda, F. Minato, and K. Shibata, Nuclear Data Sheets, 131:259--288 (2016).
| Category | Theory |
|---|