Structure of krypton isotopes calculated with symmetry-conserving configuration-mixing methods

Abstract

Shape transitions and shape coexistence in the 70−98 Kr region are studied in a unified view with state-of-the-art beyond self-consistent mean field methods based on the Gogny D1S interaction. Beyond mean field effects are taken into account through the exact angular momentum and particle number restoration and the possibility of axial and non-axial shape mixing. The results of the low-lying properties of these isotopes are in good agreement with the experimental data when the triaxial degree of freedom is included. Shape transitions from axial-oblate ( 70−72 Kr) to triaxialprolate ( 74−78 Kr) and from spherical-triaxial ( 86−92 Kr) to axial-oblate ( 94−98 Kr) ground states are obtained. Additionally, low-lying 0 + excited states and quasi-gamma bands are found showing the richness of the collective structure in this region.

Toward global beyond-mean-field calculations of nuclear masses and low-energy spectra

“…The inclusion of additional degrees of freedom such as triaxiality, time-reversal symmetry-breaking, and quasiparticle excitations, which are more relevant in the excited states than in the ground state, allows a variational description of these excited states and the excitation energies can be reduced. For example, local studies with a GCM method including triaxial angular momentum projection [38,[55][56][57] or pairing fluctuations [54] have already shown this effect. However, quantum number projections and GCM can modify significantly both the equilibrium deformation of the system ( 32 Mg is the paradigm for this effect [37]) and the collective masses.…”

“…[9,22,25,27]). These tasks are highly demanding, both the refit of the interaction and the inclusion of, for example, pairing fluctuations [54], triaxial [38,[55][56][57] and/or octupole [58,59] shapes with the corresponding symmetry restorations and configuration mixing. However, it is possible that the central, spin-orbit, and density-dependent terms of the starting Gogny interaction have to be modified, including, for instance, explicit tensor terms [60,61].…”

Kr369660 –Low- Z Boundary of the Island of Deforma

“…For this nucleus, Delaroche et al [31] show the best agreement with the experimental data. Figure 4 shows the deviation of the calculated R 4=2 ratio (in percent) from various theoretical works for the isotonic chains N ¼ 58, 60, and 62 as a function of the proton number [18,[28][29][30][31]43]. Positive values refer to theoretically underestimated R 4=2 and could be interpreted as an insufficient degree of collectivity, while negative values indicate a toostrong degree of collectivity.…”

“…Several theoretical approaches attempted to describe the structure of Kr isotopes. An oblate shape was proposed for 96 Kr, and the possibility of prolateoblate shape coexistence was argued [28][29][30][31]. However, the sharp transitions at N ¼ 60 and between Kr and Sr are not well reproduced simultaneously by those theories as well as the excited states beyond the first 2 þ state, highlighting that the underlying mechanisms remain to be understood.…”

“…To understand these differences from a theoretical point of view, it is necessary to reproduce the sudden transition observed for Sr, Zr, and Mo at N ¼ 60, the very abrupt transition observed at Z ¼ 36, and the relation between R 4=2 and BðE2Þ. Different theoretical approaches performed for the 96 Kr nucleus are available in the literature [25,[29][30][31]. The right panel in Fig.…”