397 research outputs found
Microscopic description of octupole shape-phase transitions in light actinides and rare-earth nuclei
A systematic analysis of low-lying quadrupole and octupole collective states
is presented, based on the microscopic energy density functional framework. By
mapping the deformation constrained self-consistent axially symmetric
mean-field energy surfaces onto the equivalent Hamiltonian of the
interacting boson model (IBM), that is, onto the energy expectation value in
the boson condensate state, the Hamiltonian parameters are determined. The
study is based on the global relativistic energy density functional DD-PC1. The
resulting IBM Hamiltonian is used to calculate excitation spectra and
transition rates for the positive- and negative-parity collective states in
four isotopic chains characteristic for two regions of octupole deformation and
collectivity: Th, Ra, Sm and Ba. Consistent with the empirical trend, the
microscopic calculation based on the systematics of -
energy maps, the resulting low-lying negative-parity bands and transition rates
show evidence of a shape transition between stable octupole deformation and
octupole vibrations characteristic for -soft potentials.Comment: 18 pages, 18 figures, 1 tabl
Potential energy surfaces of actinide and transfermium nuclei from multi-dimensional constraint covariant density functional theories
Multi-dimensional constrained covariant density functional theories were
developed recently. In these theories, all shape degrees of freedom
\beta_{\lambda\mu} deformations with even \mu are allowed, e.g., \beta_{20},
\beta_{22}, \beta_{30}, \beta_{32}, \beta_{40}, \beta_{42}, \beta_{44}, and so
on and the CDFT functional can be one of the following four forms: the meson
exchange or point-coupling nucleon interactions combined with the non-linear or
density-dependent couplings. In this contribution, some applications of these
theories are presented. The potential energy surfaces of actinide nuclei in the
(\beta_{20}, \beta_{22}, \beta_{30}) deformation space are investigated. It is
found that besides the octupole deformation, the triaxiality also plays an
important role upon the second fission barriers. The non-axial
reflection-asymmetric \beta_{32} shape in some transfermium nuclei with N =
150, namely 246Cm, 248Cf, 250Fm, and 252No are studied.Comment: 7 pages, 6 figures; invited talk at the International Conference on
Nuclear Structure and Related Topics, Jul 02-July 7, 2012, Dubn
Precise determination of lattice phase shifts and mixing angles
We introduce a general and accurate method for determining lattice phase
shifts and mixing angles, which is applicable to arbitrary, non-cubic lattices.
Our method combines angular momentum projection, spherical wall boundaries and
an adjustable auxiliary potential. This allows us to construct radial lattice
wave functions and to determine phase shifts at arbitrary energies. For coupled
partial waves, we use a complex-valued auxiliary potential that breaks
time-reversal invariance. We benchmark our method using a system of two
spin-1/2 particles interacting through a finite-range potential with a strong
tensor component. We are able to extract phase shifts and mixing angles for all
angular momenta and energies, with precision greater than that of extant
methods. We discuss a wide range of applications from nuclear lattice
simulations to optical lattice experiments.Comment: 7 pp, 4 figs, 1 tabl
Breaking and restoration of rotational symmetry for irreducible tensor operators on the lattice
We study the breaking of rotational symmetry on the lattice for irreducible
tensor operators and practical methods for suppressing this breaking. We
illustrate the features of the general problem using an cluster model
for Be. We focus on the lowest states with non-zero angular momentum and
examine the matrix elements of multipole moment operators. We show that the
physical reduced matrix element is well reproduced by averaging over all
possible orientations of the quantum state, and this is expressed as a sum of
matrix elements weighted by the corresponding Clebsch-Gordan coefficients. For
our cluster model we find that the effects of rotational symmetry
breaking can be largely eliminated for lattice spacings of fm, and
we expect similar improvement for actual lattice Monte Carlo calculations.Comment: 8 pages, 4 figure
Multidimensionally-constrained relativistic mean-field study of spontaneous fission: coupling between shape and pairing degrees of freedom
Studies of fission dynamics, based on nuclear energy density functionals,
have shown that the coupling between shape and pairing degrees of freedom has a
pronounced effect on the nonperturbative collective inertia and, therefore, on
dynamic (least-action) spontaneous fission paths and half-lives.
Collective potentials and nonperturbative cranking collective inertia tensors
are calculated using the multidimensionally-constrained relativistic mean-field
(MDC-RMF) model. Pairing correlations are treated in the BCS approximation
using a separable pairing force of finite range. Pairing fluctuations are
included as a collective variable using a constraint on particle-number
dispersion. Fission paths are determined with the dynamic programming method by
minimizing the action in multidimensional collective spaces.
The dynamics of spontaneous fission of Fm and Fm are
explored. Fission paths, action integrals and corresponding half-lives computed
in the three-dimensional collective space of shape and pairing coordinates,
using the relativistic functional DD-PC1 and a separable pairing force of
finite range, are compared with results obtained without pairing fluctuations.
Results for Fm are also discussed in relation with those recently
obtained using the HFB model.
The inclusion of pairing correlations in the space of collective coordinates
favors axially symmetric shapes along the dynamic path of the fissioning
system, amplifies pairing as the path traverses the fission barriers,
significantly reduces the action integral and shortens the corresponding SF
half-life.Comment: 10 pages, 8 figures. arXiv admin note: text overlap with
arXiv:1511.0568
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