22 research outputs found
Towards microscopic studies of survival probabilities of compound superheavy nuclei
The microscopic approach of fission rates and neutron emission rates in
compound nuclei have been applied to No and Cn. The microscopic
framework is based on the finite-temperature Skyrme-Hartree-Fock+BCS
calculations, in which the fission barriers and mass parameters are
self-consistently temperature dependent. The fission rates from low to high
temperatures can be obtained based on the imaginary free energy method. The
neutron emission rates are obtained with neutron gases at surfaces. Finally the
survival probabilities of superheavy nuclei can be calculated microscopically.
The microscopic approach has been compared with the widely used statistical
models. Generally, there are still large uncertainties in descriptions of
fission rates.Comment: 9 pages,7 figures, accepted for Physica Scripta Special Issu
Microscopic description of neutron emission rates in compound nuclei
The neutron emission rates in thermal excited nuclei are conventionally
described by statistical models with a phenomenological level density parameter
that depends on excitation energies, deformations and mass regions. In the
microscopic view of hot nuclei, the neutron emission rates can be determined by
the external neutron gas densities without any free parameters. Therefore the
microscopic description of thermal neutron emissions is desirable that can
impact several understandings such as survival probabilities of superheavy
compound nuclei and neutron emissivity in reactors.
To describe the neutron emission rates microscopically, the external thermal
neutron gases are self-consistently obtained based on the Finite-Temperature
Hartree-Fock-Bogoliubov (FT-HFB) approach. The results are compared with the
statistical model to explore the connections between the FT-HFB approach and
the statistical model.
The Skyrme FT-HFB equation is solved by HFB-AX in deformed coordinate spaces.
Based on the FT-HFB approach, the thermal properties and external neutron gas
are properly described with the self-consistent gas substraction procedure.
Then neutron emission rates can be obtained based on the densities of external
neutron gases.
The thermal statistical properties of U and U are studied in
detail in terms of excitation energies. The thermal neutron emission rates in
U and superheavy compound nuclei Cn and
Fl are calculated, which agree well with the statistical model by
adopting an excitation-energy-dependent level density parameter.
The coordinate-space FT-HFB approach can provide reliable microscopic
descriptions of neutron emission rates in hot nuclei, as well as microscopic
constraints on the excitation energy dependence of level density parameters for
statistical models.Comment: 6 pages, 5 figures, revised and accepted for PR
Extension and parameterization of high-order density dependence in Skyrme forces
The three-body force is indispensable in nuclear energy density functionals
which leads to a density dependent two-body term in the Hartree-Fock approach.
Usually a single factional power of density dependency has been adopted. We
consider the possibility of an additional higher-order density dependence in
extended Skyrme forces. As a result, new extended Skyrme parametertizations
based on the SLy4 force are obtained and the improvements in descriptions of
global nuclei have been demonstrated. The higher-order term can also
substantially affect nuclear properties in the high density region in general
ways.Comment: 6 pages, 5 figure
Study of weakly-bound odd-A nuclei with quasiparticle blocking
The coordinate-space Hartree-Fock-Bogoliubov (HFB) approach with
quasiparticle blocking has been applied to study the odd-A weakly bound nuclei
B and Mg, in which halo structures have been reported in
experiments. The Skyrme nuclear forces SLy4 and UNEDF1 have been adopted in our
calculations. The results with and without blocking have been compared to
demonstrate the emergence of deformed halo structures due to blocking effects.
In our calculations, B and Mg have remarkable features of
deformed halos.Comment: 7 pages, 4 figures, 1 tabl
Fission Dynamics of Compound Nuclei: Pairing versus Fluctuations
Energy dependence of fission observables is a key issue for wide nuclear
applications. We studied real-time fission dynamics from low-energy to high
excitations in the compound nucleus Pu with the time-dependent
Hartree-Fock+BCS approach. It is shown that the evolution time of the later
phase of fission towards scission is considerably lengthened at finite
temperature. As the role of dynamical pairing is vanishing at high excitations,
the random transition between single-particle levels around the Fermi surface
to mimic thermal fluctuations is indispensable to drive fission. The obtained
fission yields and total kinetic energies with fluctuations can be divided into
two asymmetric scission channels, namely S1 and S2, which explain well
experimental results, and give microscopic support to the Brosa model. With
increasing fluctuations, S2 channel takes over S1 channel and the spreading
fission observables are obtained.Comment: 5 pages, 4 figure
Speed of Sound and Phase Transitions in Neutron Stars Indicated by the Thick Neutron Skin of Pb
The speed of sound is a novel probe of equation of state and phase
transitions in dense cores of neutron stars. Recently nuclear experiments
extracted a surprising thick neutron skin of Pb, causing tensions to
reproduce the tidal deformability in gravitational-wave observations. This work
finds that exotic structures in the speed of sound with a small softening slope
followed by a steep-rising peak are required to reconcile the thick neutron
skin of Pb with astronomical observations of neutron stars.
Furthermore, the peak of speed of sound is narrowly constrained around two
times the nuclear saturation density with the thick neutron skin. Consequently
early and strong first-order phase transitions are comparatively more
favorable.Comment: 5 pages 4 figures, submitte
Hartree-Fock-Bogoliubov Theory of Polarized Fermi Systems
Condensed Fermi systems with an odd number of particles can be described by
means of polarizing external fields having a time-odd character. We illustrate
how this works for Fermi gases and atomic nuclei treated by density functional
theory or Hartree-Fock-Bogoliubov (HFB) theory. We discuss the method based on
introducing two chemical potentials for different superfluid components,
whereby one may change the particle-number parity of the underlying
quasiparticle vacuum. Formally, this method is a variant of non-collective
cranking, and the procedure is equivalent to the so-called blocking. We present
and exemplify relations between the two-chemical-potential method and the
cranking approximation for Fermi gases and nuclei.Comment: 11 RevTeX pages, 4 figures, submitted to Physical Review A, extended
versio
MADNESS: A Multiresolution, Adaptive Numerical Environment for Scientific Simulation
MADNESS (multiresolution adaptive numerical environment for scientific
simulation) is a high-level software environment for solving integral and
differential equations in many dimensions that uses adaptive and fast harmonic
analysis methods with guaranteed precision based on multiresolution analysis
and separated representations. Underpinning the numerical capabilities is a
powerful petascale parallel programming environment that aims to increase both
programmer productivity and code scalability. This paper describes the features
and capabilities of MADNESS and briefly discusses some current applications in
chemistry and several areas of physics