Islands of shape coexistence from single-particle spectra in covariant density functional theory
Dennis Bonatsos, Konstantinos Karakatsanis, Andriana Martinou, T. J. Mertzimekis, N. Minkov
Abstract
Using covariant density functional theory with the DDME2 functional and labeling single-particle energy orbitals by Nilsson quantum numbers, a search for particle-hole (p-h) excitations connected to the appearance of shape coexistence is performed for $Z=38$ to 84. Islands of shape coexistence are found near the magic numbers $Z=82$ and $Z=50$, restricted in regions around the relevant neutron midshells $N=104$ and $N=66$, respectively, in accordance with the well-accepted p-h interpretation of shape coexistence in these regions, which we call neutron-induced shape coexistence, since the neutrons act as elevators creating holes in the proton orbitals. Similar but smaller islands of shape coexistence are found near $N=90$ and $N=60$, restricted in regions around the relevant proton midshells $Z=66$ and $Z=39$, respectively, related to p-h excitations across the three-dimensional isotropic harmonic-oscillator magic numbers $N=112$ and $N=70$, which correspond to the beginning of the participation of the opposite parity orbitals $1{i}_{13/2}$ and $1{h}_{11/2}$, respectively, to the onset of deformation. We call this case proton-induced shape coexistence, since the protons act as elevators creating holes in the neutron orbitals, thus offering a possible microscopic mechanism for the appearance of shape coexistence in these regions. In the region around $N=40$, $Z=40$, an island is located on which both neutron p-h excitations and proton p-h excitations are present.