Effect of shell structure on the fission of sub-lead nuclei

Abstract

Fission of atomic nuclei often produce mass asymmetric fragments. However, the origin of this asymmetry was believed to be different in actinides and in the sub-lead region [A. Andreyev et al., Phys. Rev. Lett. 105, 252502 (2010)]. It has recently been argued that quantum shell effects stabilising pear shapes of the fission fragments could explain the observed asymmetries in fission of actinides [G. Scamps and C. Simenel, Nature 564, 382 (2018)]. This interpretation is tested in the sub-lead region using microscopic mean-field calculations of fission based on the Hartree-Fock approach with BCS pairing correlations. The evolution of the number of protons and neutrons in asymmetric fragments of mercury isotope fissions is interpreted in terms of deformed shell gaps in the fragments. A new method is proposed to investigate the dominant shell effects in the pre-fragments at scission. We conclude that the mechanisms responsible for asymmetric fissions in the sub-lead region are the same as in the actinide region, which is a strong indication of their universality.

Quasifission Dynamics in Microscopic Theories

“…For this system the Z = 82 shell effect does not seem to play a major role contrary to previous TDHF observations for the Ca+U target projectile combinations. We also point out that mass-angle correlations could be used to experimentally isolate the fragments influenced by N = 56 octupole shell gaps [100,101,54]. We also find that more peripheral collisions are centered about the proton number Z = 40 confirming similar observations from past calculations [37] that the 100 Zr region plays an important role in determining the lighter fragments due to the existence of strongly bound highly deformed Zr isotopes in this region [102].…”

Nucleon localization function in rotating nuclei

“…The spatial electron localization function (ELF) was originally introduced in the context of electronic Hartree-Fock (HF) studies to characterize shell structure in atoms and chemical bonds in molecules [9][10][11][12][13][14]. In nuclear structure research, the nucleon localization function (NLF) turned out to be a useful tool for the identification of clusters in light nuclei [15][16][17] and nuclear reactions [18]; formation of fragments in fission [19][20][21][22][23]; and nuclear pasta phases in the inner crust of neutron stars [16]. Compared with nucleonic distributions that are fairly constant in the nuclear interior, the NLF more effectively quantifies nuclear configurations through its characteristic oscillating pattern due to shell effects.…”

Effect of Octupole Correlations on Fission of Light Nuclei

“…However, due to strong Coulomb interaction, and the presence of a neck between the fragments in which strong interaction between the fragments is still present, both pre-fragments are deformed with a strong quadrupole shape or a strong octupole deformation. As a result, deformed shell effects are expected to dominate [3,4].…”

“…To test the universality of the effect of octupole shell structure on the asymmetry of fission, neutron-rich mercury isotopes have been studied with a similar approach [4]. The 180 Hg case is particular since it was expected to fission symmetrically leading to two 90 Zr which is a magic nuclei with N = 50.…”

“…Nevertheless, the light fragment is found to be strongly elongated. Then the Z = 34 gap is due to a more complex deformation [4].…”