Physics of even-even superheavy nuclei with 96<Z<110 in the quark-meson-coupling model

The quark-meson-coupling (QMC) model has been applied to the study of the properties of even-even superheavy nuclei with 96≤Z≤110, over a wide range of neutron numbers. The aim is to identify the deformed shell gaps at N=152 and N=162, predicted in macroscopic-microscopic (macro-micro) models, in a model based on the mean-field Hartree-Fock+BCS approximation. The predictive power of the model has been tested on proton and neutron spherical shell gaps in light doubly closed (sub)shell nuclei Ca40, Ca48, Ni56, Ni56, Ni78, Zr90, Sn100, Sn132, Gd146, and Pb208, with results in a full agreement with experiment. In the superheavy region, the ground-state binding energies of 98≤Z≤110 and 146≤N≤160 differ, in the majority of cases, from the measured values by less than ±2.5MeV, with the deviation decreasing with increasing Z and N. The axial quadrupole deformation parameter, β2, calculated over the range of neutron numbers 138≤N≤184, revealed a prolate-oblate coexistence and shape transition around N=168, followed by an oblate-spherical transition towards the expected N=184 shell closure in Cm, Cf, Fm, and No. The closure is not predicted in Rf, Sg, Hs, and Ds as another shape transition to a highly deformed (β2≈0.4) shape in Sg, Hs, and Ds for N>178 appears, while Rf288 (N=184) remains oblate. The bulk properties predicted by QMC, such as ground-state binding energy, two-neutron separation energy, the empirical shell-gap parameter δ2n and Qα values, are found to have a limited sensitivity to the deformed shell gaps at N=152 and 162. However, the evolution of the neutron single-particle spectra with 0≤β2≤0.55 of Cm244, Cf248, Fm252, No256, Rf260, Sg264, Hs268, and Ds272, as representative examples, gives a (model-dependent) evidence for the location and size of the N=152 and 162 gaps as a function of Z and N. In addition, the neutron number dependence of neutron pairing energies provides supporting indication for existence of the energy gaps. Based on these results, the mean-field QMC and macro-micro models and their predictions of deformed shell structure of superheavy nuclei are compared. Clearly the QMC model does not give results as close to the experiment as the macro-micro models. However, considering that it has only four global variable parameters (plus two parameters of the pairing potential), with no local adjustments, the results are promising.