Study of angular momentum effects in fission

Abstract

Background: The role of angular momentum in fission has long been discussed but the observable effects are difficult to quantify. Purpose: We discuss a variety of effects associated with angular momentum in fission and present quantitative illustrations. Methods: We employ the fission simulation model $\mathtt{FREYA}$ which is well suited for this purpose because it obeys all conservation laws, including linear and angular momentum conservation at each step of the process. We first discuss the implementation of angular momentum in $\mathtt{FREYA}$ and then assess particular observables, including various correlated observables. We also study potential effects of neutron-induced fission of the low-lying isomeric state of ${}^{235}$U relative to the ground state. Results: The fluctuations inherent in the fission process ensure that the spin of the initial compound nucleus has only a small influence on the fragment spins which are therefore nearly uncorrelated. There is a marked correlation between the spin magnitude of the fission fragments and the photon multiplicity. We also consider the dynamical anisotropy caused by the rotation of an evaporating fragment and study especially the distribution of the projected neutron-neutron opening angles, showing that while it is dominated by the effect of the evaporation recoils, it is possible to extract the signal of the dynamical anisotropy by means of a Fourier decomposition. Finally, we note that the use of an isomeric target, ${}^{235\mathrm{m}}$U($n_{\mathrm{th}}$,f), may enhance the symmetric yields and can thus result in higher neutron multiplicities for low total fragment kinetic energy.

11 pages, 9 figures

References in corpus (8)

• Origin of the Heaviest Elements: the Rapid Neutron-Capture Process
• Review on the progress in nuclear fission
• Future of Nuclear Fission Theory
• Calculation of fission observables through event-by-event simulation
• The contrasting fission potential-energy structure of actinides and mercury isotopes
• Correlations of neutron multiplicity and gamma multiplicity with fragment mass and total kinetic energy in spontaneous fission of 252Cf
• Correlation studies of fission fragment neutron multiplicities
• Improved modeling of photon observables with FREYA

Cited by in corpus (20)

• Theory of Nuclear Fission
• Generation of fragment angular momentum in fission
• Fission fragments intrinsic spins and their correlations
• Angular Momentum of Fission Fragments from Microscopic Theory
• Nucleosynthesis and observation of the heaviest elements
• 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
• 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
• 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
• A critical assessment of the current implementations of the Generator Coordinate Method
• Restoring Broken Symmetries for Nuclei and Reaction Fragments
• Generalization of the Maier-Leibniz Doppler-Shift Method for Gamma-Ray Correlations in Fission