Effect of non-axial octupole shapes in heavy and superheavy nuclei

Abstract

We search for effects of tetrahedral deformation β32 over a range of ∼ 3000 heavy and superheavy nuclei, 82 ≤ Z ≤ 126, using a microscopic-macroscopic model based on the deformed Woods-Saxon potential, well tested in the region. We look for the energy minima with a non-zero tetrahedral distortion, both absolute and conditional -with the quadrupole distortion constrained to zero. In order to assure reliability of our results we include 10 most important deformation parameters in the energy minimization. We could not find any cases of stable tetrahedral shapes. The only sizable -up to 0.7 MeV -lowering of the ground state occurs in superheavy nuclei Z ≥ 120 for N = 173−188, as a result of a combined action of two octupole deformations: β32 and β30, in the ratio β32/β30 ≈ 3/5. The resulting shapes are moderately oblate, with the superimposed distortion β33 with respect to the oblate axis, which makes the equator of the oblate spheroid slightly triangular. Almost all found conditional minima are excited and not protected by any barrier; a handful of them are degenerate with the axial minima.

Colloquium : Superheavy elements: Oganesson and beyond

“…The transition towards spherical shapes happens around N = 184. In-between located is a transitional region of deformation-soft and triaxial nuclei, exhibiting rich shape isomerism (Agbemava et al, 2015;Bürvenich et al, 1998;Ćwiok et al, 2005;Heenen et al, 2015;Jachimowicz et al, 2017b;Prassa et al, 2012;Ren, 2002). The softness of the potential energy surface (PES) generally grows with the level density at the Fermi level, due to reduced shell effects.…”

“…III, such a situation is typical to superheavy nuclei due to the diffused shell structure (Bender et al, 2001). In any case, reflection asymmetric ground-states are expected to appear in certain regions of superheavy nuclei and can potentially impact their lifetimes (Erler et al, 2012b;Jachimowicz et al, 2017b;Warda and Egido, 2012).…”

First observation of high-$K$ isomeric states in $^{249}$Md and $^{251}$Md

“…Fig. 10 and Table III in [53]). One can also see a significant effect of freezing the high-K configuration: the saddle points for 249,251 Md (Fig.…”

“…On the other hand, effect of the non-axiality (not included here) on the first saddle point is considerable in the region of Z = 100 − 104 (see Fig. 7 of [53]) and one can expect that K is not conserved in fission. Still, even the barriers reduced by non-axiality make fission of 249,251 Md very rare.…”

Spontaneous fission half-lives of actinides and superheavy elements

“…[34] for an extensive review) and are currently used to investigate all kinds of nuclear properties. One of the most widely used (see, e.g., [35][36][37][38]) such parametrization is the one Lord Rayleigh proposed already towards the end of the 19th century [39]. Among other more recent shape parametrizations which have been used to describe the fission process, we mention the quadratic surfaces of revolution (QSR) [40] of Nix, the Cassini ovals [41,42] of Pashkevich, the famous funny-hills parametrization [28] of the Copenhagen group and its improved version [43], as well as the expansion of the nuclear surface in Legendre polynomials [44] of Trentalange, Koonin, and Sierk.…”