[Show abstract][Hide abstract] ABSTRACT: Background: [elided for arXiv character count] Purpose: With the advancement
of computational power it is now possible to undertake TDHF calculations
without any symmetry assumptions and incorporate the major strides made by the
nuclear structure community in improving the energy density functionals used in
these calculations. In particular, time-odd and tensor terms in these
functionals are naturally present during the dynamical evolution, while being
absent or minimally important for most static calculations. The parameters of
these terms are determined by the requirement of Galilean invariance or local
gauge invariance but their significance for the reaction dynamics have not been
fully studied. This work addresses this question with emphasis on the tensor
force. Method: The full version of the Skyrme force, including terms arising
only from the Skyrme tensor force, is applied to the study of collisions within
a completely symmetry-unrestricted TDHF implementation. Results: We examine the
effect on fusion thresholds with and without the tensor force terms and find an
effect on the fusion threshold energy of the order several MeV. Details of the
distribution of the energy within terms in the energy density functional is
also discussed. Conclusions: Terms in the energy density functional linked to
the tensor force can play a non-negligible role in dynamic processes in nuclei,
including those in which the terms do not affect ground state properties.
[Show abstract][Hide abstract] ABSTRACT: The role of the tensor terms in the Skyrme interaction is studied for
their effect in dynamic calculations where non-zero contributions to the
mean-field may arise, even when the starting nucleus, or nuclei are
even-even and have no active time-odd potentials in the ground state. We
study collisions in the test-bed 16O-16O system,
and give a qualitative analysis of the behaviour of the time-odd
tensor-kinetic density, which only appears in the mean field Hamiltonian
in the presence of the tensor force. We find an axial excitation of this
density is induced by a collision.
Journal of Physics Conference Series 09/2012; 381(1):2105-. DOI:10.1088/1742-6596/381/1/012105
[Show abstract][Hide abstract] ABSTRACT: The nuclear time-dependent Hartree-Fock model formulated in the
three-dimensional space,based on the full Skyrme energy density functional and
complemented with the tensor force,is presented for the first time. Full
self-consistency is achieved by the model. The application to the isovector
giant dipole resonance is discussed in the linear limit, ranging from spherical
nuclei (16O, 120Sn) to systems displaying axial or triaxial deformation (24Mg,
28Si, 178Os, 190W, 238U).
Particular attention is paid to the spin-dependent terms from the central
sector of the functional, recently included together with the tensor. They turn
out to be capable of producing a qualitative change on the strength
distribution in this channel. The effect on the deformation properties is also
discussed. The quantitative effects on the linear response are small and,
overall, the giant dipole energy remains unaffected.
Calculations are compared to predictions from the (quasi)-particle random
phase approximation and experimental data where available, finding good
agreement.
Physical Review C 05/2012; 86(4). DOI:10.1103/PhysRevC.86.044303 · 3.73 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: The nuclides 157W and 161Os have been discovered in reactions of 58Ni ion beams with a 106Cd target. The 161Os α-decay energy and half-life were 6890±12 keV and 640±60 μs. The daughter 157W nuclei β-decayed with a half-life of 275±40 ms, populating both low-lying α-decaying states in 157Ta, which is consistent with a 7/2− ground state in 157W. Fine structure observed in the α decay of 161Os places the lowest excited state in 157W with Iπ=9/2− at 318±30 keV. The branching ratio of 5.5−2.2+3.1% indicates that 161Os also has a 7/2− ground state. Shell-model calculations analysing the effects of monopole shifts and a tensor force on the relative energies of 2f7/2 and 1h9/2 neutron states in N=83 isotones are presented.
[Show abstract][Hide abstract] ABSTRACT: The nuclides 157W and 161Os have been discovered in reactions of 58Ni ion beams with a 106Cd target. The 161Os α-decay energy and half-life were 6890±12 keV and 640±60 μs. The daughter 157W nuclei β-decayed with a half-life of 275±40 ms, populating both low-lying α-decaying states in 157Ta, which is consistent with a 7/2− ground state in 157W. Fine structure observed in the α decay of 161Os places the lowest excited state in 157W with Iπ=9/2− at 318±30 keV. The branching ratio of View the MathML source indicates that 161Os also has a 7/2− ground state. Shell-model calculations analysing the effects of monopole shifts and a tensor force on the relative energies of 2f7/2 and 1h9/2 neutron states in N=83 isotones are presented.
[Show abstract][Hide abstract] ABSTRACT: The effect of the tensor component of the Skyrme effective nucleon-nucleon interaction on the single-particle structure in superheavy elements is studied. A selection of the available Skyrme forces has been chosen and their predictions for the proton and neutron shell closures investigated. The inclusion of the tensor term with realistic coupling strength parameters leads to a small increase in the spin-orbit splitting between the proton 2f7/2 and 2f5/2 partners, opening the Z=114 shell gap over a wide range of nuclei. The Z=126 shell gap, predicted by these models in the absence of the tensor term, is found to be stongly dependent on neutron number with a Z=138 gap opening for large neutron numbers, having a consequent implication for the synthesis of neutron-rich superheavy elements. The predicted neutron shell structures remain largely unchanged by inclusion of the tensor component.
[Show abstract][Hide abstract] ABSTRACT: This conference paper outlines the operation and some of the preliminary physics results using the GSI RISING active stopper. Data are presented from an experiment using combined isomer and beta‐delayed gamma‐ray spectroscopy to study low‐lying spectral and decay properties of heavy‐neutron‐rich nuclei around A ∼ 190 produced following the relativistic projectile fragmentation of 208Pb primary beam. The response of the RISING active stopper detector is demonstrated for both the implantation of heavy secondary fragments and in‐situ decay of beta‐particles. Beta‐delayed gamma‐ray spectroscopy following decays of the neutron‐rich nucleus 194Re is presented to demonstrate the experimental performance of the set‐up. The resulting information inferred from excited states in the W and Os daughter nuclei is compared with results from Skyrme Hartree‐Fock predictions of the evolution of nuclear shape.
[Show abstract][Hide abstract] ABSTRACT: This paper outlines some of the physics opportunities available with the GSI RISING active stopper and presents preliminary results from an experiment aimed at performing beta-delayed gamma-ray spectroscopic studies in heavy-neutron-rich nuclei produced following the projectile fragmentation of a 1 GeV per nucleon 208Pb primary beam. The energy response of the silicon active stopping detector for both heavy secondary fragments and beta-particles is demonstrated and preliminary results on the decays of neutron-rich Tantalum (Ta) to Tungsten (W) isotopes are presented as examples of the potential of this technique to allow new structural studies in hitherto experimentally unreachable heavy, neutron-rich nuclei. The resulting spectral information inferred from excited states in the tungsten daughter nuclei are compared with results from axially symmetric Hartree-Fock calculations of the nuclear shape and suggest a change in ground state structure for the N = 116 isotone 190W compared to the lighter isotopes of this element.
International Journal of Modern Physics E 12/2008; 17:8-20. DOI:10.1142/S0218301308011719 · 1.34 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: The energy of the vh{sub 9/2} orbital in nuclei above N = 82 drops rapidly in energy relative to the vf{sub 7/2} orbital as the occupancy of the {pi}h{sub 11/2} orbital increases. These two neutron orbitals become nearly degenerate as the proton drip line is approached. In this work, we have discovered the new nuclides {sup 161}Os and {sup 157}W, and studied the decays of the proton emitter {sup 160}Re in detail. The {sup 161}Os and {sup 160}Re nuclei were produced in reactions of 290, 300 and 310 MeV {sup 58}Ni ions with an isotopically enriched {sup 106}Cd target, separated in-flight using the RITU separator and implanted into the GREAT spectrometer. The {sup 161}Os{alpha} a decays populated the new nuclide {sup 157}W, which decayed by {beta}-particle emission. The {beta} decay fed the known {alpha}-decaying 1/2{sup +} and 11/2{sup -} states in {sup 157}Ta, which is consistent with a vf{sub 7/2} ground state in {sup 157}W. The measured {alpha}-decay energy and half-life for {sup 161}Os correspond to a reduced {alpha}-decay width that is compatible with s-wave {alpha}-particle emission, implying that its ground state is also a vf{sub 7/2} state. Over 7000 {sup 160}Re nuclei were produced and the {gamma} decays of a new isomeric state feeding the {pi}d{sub 3/2} level in {sup 160}Re were discovered, but no evidence for the proton or a decay of the expected {pi}h{sub 11/2} state could be found. The isomer decays offer a natural explanation for this non-observation and provides a striking example of the influence of the near degeneracy of the vh{sub 9/2} and vf{sub 7/2} orbitals on the properties of nuclei in this region.
[Show abstract][Hide abstract] ABSTRACT: Abstract The basic concepts of nuclear structure theory were reviewed, including the Hartree-Fock approximation method for the solution of the energy eigenstates of even-even nuclei. The construction of the density function for the efiective Skyrme interaction with the Hartree- Fock-Bogolyubov approach was considered, along with the inclusion of the tensor part of the Skyrme force in the HFB equations. Two pieces of computer code were utilised in order to investigate the single-particle spectra of neutron-rich nuclei. The efiect of the various Skyrme force parameters and the tensor component on these spectra were studied. Evidence for shell and magic number evolution was investigated. Nuclides ,Ca were used as starting points before removing protons in steps of two for computation of the single-particle spectra of the subsequent chains of nuclei as they approached the neutron drip-line. Solution of the HFB plus Skyrme equations provided no evidence for shell or magic
[Show abstract][Hide abstract] ABSTRACT: Abstract The influence of the tensor component of the eective,nucleon-nucleon interaction has been inves- tigated for the single-particle structure of superheavy nuclei within the spherical Skyrme Hartree- Fock plus BCS model. Inclusion of this term into the model generally leads an increase in spin- orbit splitting between the proton 2f7/2 and 2f5/2 spin-orbit partners, opening the Z=114 shell gap, which is shown to remain a stable closure across several isotopic chains in the neutron range N=160-200. The single-proton structure around Z=126 is found to be strongly dependent on nu- cleon number, where a possible new shell closure is opened at Z=138 for the more neutron-rich superheavy nuclei when the tensor term is added. The predictions for the neutron shell structure remain unchanged after the inclusion of the tensor force in the model, however there are discrep- ancies between the dierent parameterisations, with some forces predicting the magic number in neutrons to occur at N=164 and others predicting N=184. Calculations on the quadrupole deformation and charge radius properties across the zirconium isotopes (in the neutron-rich A»100 region) have been performed using an axially-deformed Skyrme Hartree-Fock plus BCS model. The observed trends in mean-square charge radius for the strongly deformed, neutron-rich isotopes are well reproduced by the selected Skyrme forces, however, the discontinuity in the trend going from the spherical to the deformed nuclei are not well reproduced. Although several of the parameterisations predict a jump in the mean-square charge radius due to a sudden onset of quadrupole deformation, the observed magnitude and location (i.e. N=60) of this feature are not predicted by the model. These nuclei are shown to be soft with respect to shape fluctuations and their calculated energy surfaces change rapidly as a function of nucleon number, suggesting that beyond mean-field techniques such as particle number,and angular momentum projection are essential ingredients for a better description of the nuclei in this region. Particle number projection after variation has been studied according to the Fomenko formalism as a first step towards incorporating such projection techniques into the mean-field models. The expression for the particle number projected energy with respect to the many-body wavefunctions of BCS-type has been derived and investigated within a simple BCS model. i Contents