Quantum Fluctuations Drive Angular Momenta in Nuclear Fission

Abstract

Quantum fluctuations are ubiquitous and play crucial roles across various scales and systems, such as the Big Bang, black hole dynamics, quantum phase transitions in microscopic many-body systems, and so on. Nuclear fission manifests as a complex nuclear shape stretching until it splits into fragments with substantial angular momenta, also exhibiting complex quantum fluctuations and specifically shape fluctuations. For over 40 years, researchers have puzzled how the fission fragment angular momenta are generated dynamically from (almost) zero spin, as well as the particular role played by quantum fluctuations. Here, for the first time, we report the quantum shape fluctuations that drive fragment angular momenta during nuclear fission, based on a global, microscopic, and dynamical simulation. The calculated probability distributions of fragment angular momenta are in good agreement with the experimental measurements, and the sawtooth-like mass dependence of average angular momenta is reproduced very well. It is noteworthy to find that the shape fluctuations -- multiple rotations, vibrations, and their couplings -- drive the generation and chaotic evolution of fragment angular momenta during fission fragment formation and induce strong correlations between angular momentum orientations of partner fragments at small, medium, and large opening angles ($\phi_{LH}\approx 30^\circ, 90^\circ, 160^\circ$). Our work not only deepens the fundamental understanding of the nuclear fission mechanism but also has implications for the $\gamma$-ray heating problem in nuclear reactors and the synthesis of superheavy elements.