33 research outputs found
Islands of shape coexistence from single-particle spectra in covariant density functional theory
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 to 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 3-dimensional isotropic harmonic oscillator (3D-HO)
magic numbers N=112 and N=70, which correspond to the beginning of the
participation of the opposite parity orbitals 1i13/2 and 1h11/2 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.Comment: 21 pages, 17 figure
Shape coexistence in even-even nuclei: A theoretical overview
The last decade has seen a rapid growth of our understanding of the
microscopic origins of shape coexistence, assisted by the new data provided by
the modern radioactive ion beam facilities built worldwide. Islands of the
nuclear chart in which shape coexistence can occur have been identified, and
the different microscopic particle-hole excitation mechanisms leading to
neutron-induced or proton-induced shape coexistence have been clarified. The
relation of shape coexistence to the islands of inversion, appearing in light
nuclei, to the new spin-aligned phase appearing in N=Z nuclei, as well as to
shape/phase transitions occurring in medium mass and heavy nuclei, has been
understood. In the present review, these developments are considered within the
shell model and mean field approaches, as well as by symmetry methods. In
addition, based on systematics of data, as well as on symmetry considerations,
quantitative rules are developed, predicting regions in which shape coexistence
can appear, as a possible guide for further experimental efforts, which can
help in improving our understanding of the details of the nucleon-nucleon
interaction, as well as of its modifications occurring far from stability.Comment: 80 pages, 14 figures, 837 reference
Microscopic origin of shape coexistence in the N=90, Z=64 region
A microscopic explanation of the nature of shape coexistence in the N=90,
Z=64 region is suggested, based on calculations of single particle energies
through standard covariant density functional theory. It is suggested that
shape coexistence in the N=90 region is caused by the protons, which create
neutron particle-hole (p-h) excitations across the N=112 3-dimensional
isotropic harmonic oscillator (3D-HO) magic number, signaling the start of the
occupation of the 1i13/2 intruder orbital, which triggers stronger
proton-neutron interaction, causing the onset of the deformation and resulting
in the shape/phase transition from spherical to deformed nuclei described by
the X(5) critical point symmetry. A similar effect is seen in the N=60, Z=40
region, in which p-h excitations across the N=70 3D-HO magic number occur,
signaling the start of the occupation of the 1h11/2 intruder orbital.Comment: 6 pages, 7 figure