Generation of fragment angular momentum in fission

Abstract

A recent analysis of experimental data [J. Wilson $et.al$, Nature $590$, 566 (2021)] found that the angular momenta of nuclear fission fragments are uncorrelated. Based on this finding, the authors concluded that the spins are therefore determined only $after$ scission has occurred. We show here that the nucleon-exchange mechanism, as implemented in the well-established event-by-event fission model $\mathtt{FREYA}$, while agitating collective rotational modes in which the two spins are highly correlated, nevertheless leads to fragment spins that are largely uncorrelated. This fact invalidates the reasoning of those authors. Furthermore, it was reported [J. Wilson $et.al$, Nature $590$, 566 (2021)] that the mass dependence of the average fragment spin has a sawtooth structure. We demonstrate that such a behavior naturally emerges when shell and deformation effects are included in the moments of inertia of the fragments at scission.

5 pages, 2 figures

References in corpus (6)

• Nuclear Ground-State Masses and Deformations
• Calculation of fission observables through event-by-event simulation
• Fission fragments intrinsic spins and their correlations
• Event-by-event study of neutron observables in spontaneous and thermal fission
• Study of angular momentum effects in fission
• Correlation studies of fission fragment neutron multiplicities

Cited by in corpus (26)

• Theory of Nuclear Fission
• Physically Interpretable Machine Learning for nuclear masses
• Angular Momentum of Fission Fragments from Microscopic Theory
• Energy and pairing dependence of dissipation in real-time fission dynamics
• The angular correlation between the fission fragment intrinsic spins
• Coupled fission fragment angular momenta
• Spatial orientation of the fission fragment intrinsic spins and their correlations
• Generation, dynamics, and correlations of the fission fragments' angular momenta
• Microscopic description of the torque acting on fission fragments
• Structure in the Event-by-Event Energy-Dependent Neutron-Gamma Multiplicity Correlations in ${}^{252}\text{Cf}$(sf)
• Directional-dependence of the event-by-event neutron-$\gamma$ multiplicity correlations in ${}^{252}$Cf(sf)
• Correlations between energy and $\gamma$-ray emission in ${}^{239}\mathrm{Pu}(n,\mathrm{f})$
• New developments in fission studies within the time-dependent density functional theory framework
• Microscopic Study of Spin Transfer in Near-Barrier Nuclear Reactions
• Disentangling the influence of excitation energy and compound nucleus angular momentum on fission fragment angular momentum
• Meaurement of spin vs. TKE of ${}^{144}$Ba produced in spontaneous fission of ${}^{252}$Cf
• Instrumentation for correlated prompt $n$-$\gamma$ emission studies in coincidence with fission fragments
• Quantum-mechanical description of angular motion of fission fragments at scission
• Intrinsic spin distributions in multinucleon transfer reactions
• Fragment Intrinsic Spins and Fragments' Relative Orbital Angular Momentum in Nuclear Fission
• Microscopic theory of angular momentum distributions across the full range of fission fragments
• Restoring Broken Symmetries for Nuclei and Reaction Fragments
• A critical assessment of the current implementations of the Generator Coordinate Method
• Angular momentum removal by neutron and $\gamma$-ray emissions during fission fragment decays
• Two-center harmonic oscillator basis for Skyrme-DFT calculations (I): formalism and Proof of Principle
• Quantification of spin alignment in fission by simultaneous treatment of gamma and conversion electron angular distributions