31 research outputs found
Solution of the Skyrme HF+BCS equation on a 3D mesh. II. A new version of the Ev8 code
We describe a new version of the EV8 code that solves the nuclear
Skyrme-Hartree-Fock+BCS problem using a 3-dimensional cartesian mesh. Several
new features have been implemented with respect to the earlier version
published in 2005. In particular, the numerical accuracy has been improved for
a given mesh size by (i) implementing a new solver to determine the Coulomb
potential for protons (ii) implementing a more precise method to calculate the
derivatives on a mesh that had already been implemented earlier in our
beyond-mean-field codes. The code has been made very flexible to enable the use
of a large variety of Skyrme energy density functionals that have been
introduced in the last years. Finally, the treatment of the constraints that
can be introduced in the mean-field equations has been improved. The code Ev8
is today the tool of choice to study the variation of the energy of a nucleus
from its ground state to very elongated or triaxial deformations with a
well-controlled accuracy.Comment: 24 pages, 3 figure
Finite-temperature mean-field approximations for shell model Hamiltonians: the code HF-SHELL
We present the code HF-SHELL for solving the self-consistent mean-field
equations for configuration-interaction shell model Hamiltonians in the
proton-neutron formalism. The code can calculate both ground-state and
finite-temperature properties in the Hartree-Fock (HF),
HF+Bardeen-Cooper-Schrieffer (HF+BCS), and the Hartree-Fock-Bogoliubov (HFB)
mean-field approximations. Particle-number projection after variation is
incorporated to reduce the grand-canonical ensemble to the canonical ensemble,
making the code particularly suitable for the calculation of nuclear state
densities. The code does not impose axial symmetry and allows for triaxial
quadrupole deformations. The self-consistency cycle is particularly robust
through the use of the heavy-ball optimization technique and the implementation
of different options to constrain the quadrupole degrees of freedom.Comment: 18 pages, 5 figures, source code repository can be found at
http://github.com/wryssens/hf-shel
The mass of odd-odd nuclei in microscopic mass models
Accurate estimates of the binding energy of nuclei far from stability that
cannot be produced in the laboratory are crucial to our understanding of
nuclear processes in astrophysical scenarios. Models based on energy density
functionals have shown that they are capable of reproducing all known masses
with root-mean-square error better than 800 keV, while retaining a firm
microscopic foundation. However, it was recently pointed out in [M. Hukkanen et
al., arXiv:2210.10674] that the recent BSkG1 model fails to account for a
contribution to the binding energy that is specific to odd-odd nuclei, and
which can be studied by using appropriate mass difference formulas. We analyse
here the (lacking) performance of three recent microscopic mass models with
respect to such formulas and examine possibilities to remedy this deficiency in
the future.Comment: 6 pages, 2 figures; Contribution to the proceedings of INPC 2022,
Cape Town, South Afric
Binding energies of ground and isomeric states in neutron-rich ruthenium isotopes: measurements at JYFLTRAP and comparison to theory
We report on precision mass measurements of Ru performed with
the JYFLTRAP double Penning trap mass spectrometer at the Accelerator
Laboratory of University of Jyv\"askyl\"a. The phase-imaging
ion-cyclotron-resonance technique was used to resolve the ground and isomeric
states in Ru and enabled for the first time a measurement of the
isomer excitation energies, Ru keV and
Ru keV. The ground state of Ru was measured
using the time-of-flight ion-cyclotron-resonance technique. The new mass-excess
value for Ru is around 36 keV lower and 7 times more precise than the
previous literature value. With the more precise ground-state mass values, the
evolution of the two-neutron separation energies is further constrained and a
similar trend as predicted by the BSkG1 model is obtained up to the neutron
number .Comment: 12 pages, 9 figures, submitted to Physical Review
De-excitation of the strongly coupled band in 177Au and implications for core intruder configurations in the light Hg isotopes
Excited states in the proton-unbound nuclide 177Au were populated in the 92Mo(88Sr, p2n) reaction and identified using the Jurogam-II and GREAT spectrometers in conjunction with the RITU gas-filled separator at the University of Jyväskylä Accelerator Laboratory. A strongly coupled band and its decay path to the 11/2− α-decaying isomer have been identified using recoil-decay tagging. Comparisons with cranked HartreeFock-Bogoliubov (HFB) calculations based on Skyrme energy functionals suggest that the band has a prolate deformation and is based upon coupling the odd 1h11/2 proton hole to the excited 0+ 2 configuration in the 178Hg core. Although these configurations might be expected to follow the parabolic trend of core Hg(0+2 ) states as a function of neutron number, the electromagnetic decay paths from the strongly coupled band in 177Au are markedly different from those observed in the heavier isotopes above the midshell. This indicates that a significant change in the structure of the underlying A+1Hg core occurs below the neutron midshell
Shape staggering of midshell mercury isotopes from in-source laser spectroscopy compared with density-functional-theory and Monte Carlo shell-model calculations
Neutron-deficient 177−185Hg isotopes were studied using in-source laser resonance-ionization spectroscopy at the CERN-ISOLDE radioactive ion-beam facility in an experiment combining different detection methods tailored to the studied isotopes. These include either α-decay tagging or multireflection time-of-flight gating for isotope identification. The endpoint of the odd-even nuclear shape staggering in mercury was observed directly by measuring for the first time the isotope shifts and hyperfine structures of 177−180Hg. Changes in the mean-square charge radii for all mentioned isotopes, magnetic dipole, and electric quadrupole moments of the odd-A isotopes and arguments in favor of I=7/2 spin assignment for 177,179Hg were deduced. Experimental results are compared with density functional theory (DFT) and Monte Carlo shell model (MCSM) calculations. DFT calculations using Skyrme parametrizations predict a jump in the charge radius around the neutron N=104 midshell, with an odd-even staggering pattern related to the coexistence of nearly degenerate oblate and prolate minima. This near-degeneracy is highly sensitive to many aspects of the effective interaction, a fact that renders perfect agreement with experiments out of reach for current functionals. Despite this inherent difficulty, the SLy5s1 and a modified UNEDF1SO parametrization predict a qualitatively correct staggering that is off by two neutron numbers. MCSM calculations of states with the experimental spins and parities show good agreement for both electromagnetic moments and the observed charge radii. A clear mechanism for the origin of shape staggering within this context is identified: a substantial change in occupancy of the proton πh9/2 and neutron νi13/2 orbitals
Towards symmetry-unrestricted Skyrme-HFB in coordinate-space representation: the example of rotational bands of the octupole-deformed nucleus Th
International audienceWe report on cranked Skyrme-HFB calculations of rotational bands of the octupole-deformed nucleus Th. A sudden change in configuration is observed, with the shape of the yrast state jumping from large octupole deformation at low spin to small octupole deformation at high spin