Novel shape evolution in exotic Ni isotopes and configuration-dependent shell structure

Abstract

The shapes of neutron-rich exotic Ni isotopes are studied. Large-scale shell model calculations are performed by advanced Monte Carlo Shell Model (MCSM) for the pf -g 9/2 -d 5/2 model space. Experimental energy levels are reproduced well by a single fixed Hamiltonian. Intrinsic shapes are analyzed for MCSM eigenstates. Intriguing interplays among spherical, oblate, prolate and γunstable shapes are seen, including shape fluctuations, E(5)-like situation, the magicity of doublymagic 56,68,78 Ni, and the coexistence of spherical and strongly deformed shapes. Regarding the last point, strong deformation and change of shell structure can take place simultaneously, being driven by the combination of the tensor force and changes of major configurations within the same nucleus.

Characterization of the low-lying0+and2+states inNi68Flavigny1, Pauwels2, Radulov3 et al. 2015Phys. Rev. C462420View full textAdd to dashboardCite

“…Theoretical values for MCSM calculations using the revised A3DA interaction (see Ref. [6] for details) and SM calculations using the LNPS interaction from Ref. [8] are compared to experimental values.…”

“…Contrary to these suppressed transitions, it is crucial to stress that the 2 + 2 → 0 + 3 transition is a truly collective one in the theoretical calculations, as illustrated in the shape coexistence picture of Refs. [6,7]. While this transition is of paramount interest to explore unknown rich collectivities of nuclei around 68 Ni, a lack of sensitivity on its relative B(E2) ratio (2σ upper limit of 9 × 10 4 ) comes mainly from the energy factor (2743/232) 5 and avoids an experimental test of this high degree of collectivity.…”

“…[6,7] using the A3DA effective interaction with minor revisions and from shell model (SM) calculations using the LNPS effective interaction from Ref. [8] are summarized in Table II.…”

“…Experimentally, Dijon et al [18] proposed a candidate at this energy for such a highly deformed π (2p-2h) proton intruder state using a multinucleon transfer reaction but no supporting evidence was found for this state in a subsequent study [12]. Importantly, only shell model calculations including proton excitations predict a third 0 + state between 2.5 and 3 MeV but its configuration involves both π (2p-2h) and ν(4p-4h) excitations [5][6][7][8].…”

“…6(6) keV. According to shell model calculations, the structure of this 0 + 2 state consists basically in 2p-2h excitations from the Z = 28 and N = 40 closed shells with more weight of neutron excitations [4,[6][7][8][9]. This hypothesis has just been confirmed by a 66 Ni(t,p) 68 Ni reaction study performed at REX-ISOLDE on the basis of the relative cross sections to the 0 + 1 and 0 + 2 states [10].…”