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Angular momentum generation in nuclear fission
J N Wilson1, D Thisse2, M Lebois2
1Université Paris-Saclay, CNRS/IN2P3, IJC Laboratory, Orsay, France. jonathan.wilson@ijclab.in2p3.fr.
Nature
|February 25, 2021
Summary
Nuclear fission fragments gain angular momentum after splitting, not before. This post-scission spin generation, driven by nucleon motion in the neck, challenges prior theories and impacts nuclear reactor physics and super-heavy element research.
Area of Science:
- Nuclear Physics
- Nuclear Fission
- Quantum Mechanics
Background:
- Heavy atomic nuclei emerging with significant angular momentum after fission has been a long-standing mystery.
- Existing theories suggest angular momentum is generated before nuclear splitting (pre-scission) via collective vibrational modes.
- Lack of experimental data has prevented definitive validation of competing theories for angular momentum generation.
Purpose of the Study:
- To investigate the mechanism of angular momentum generation in nuclear fission fragments.
- To determine whether spin is generated pre-scission or post-scission.
- To propose a new model for angular momentum generation in nuclear fission.
Main Methods:
- Comprehensive experimental analysis of fragment spins in nuclear fission.
- Correlation analysis between the spins of fragment partners.
- Mass and charge dependence studies of fragment spin.
Main Results:
- No significant correlation was found between the spins of fission fragment partners.
- Fragment spin is strongly mass-dependent, exhibiting saw-tooth distributions.
- Fragment spin showed no notable dependence on the partner nucleus's mass or charge.
Conclusions:
- Angular momentum in nuclear fission is generated after the nucleus splits (post-scission).
- A proposed model suggests independent torques generated by nucleon motion in the ruptured neck.
- Findings have implications for nuclear reactor physics, neutron-rich isotope structure, and super-heavy element synthesis.
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