The effect of the tensor force on the predictions for superheavy nuclei

1
The effect of the tensor force on the predictions
for superheavy nuclei
E.B. Suckling and P.D. Stevenson
50th Anniversary Symposium on Nuclear Sizes and
Shapes 2008
2
The effect of the tensor force on the predictions
for superheavy nuclei
Outline

• Motivation
• Theoretical Challenges
• The Tensor Force
• Theoretical Framework
• Results
• Outlook

E.B. Suckling and P.D. Stevenson
50th Anniversary Symposium on Nuclear Sizes and
Shapes 2008
3
The effect of the tensor force on the predictions
for superheavy nuclei
Motivation

• The superheavy elements are a key topic of study
  for nuclear structure at the limits of stability
• The single-particle structure of superheavy
  nuclei and location of the island of stability
  pose a number of experimental and theoretical
  challenges
• Discrepancies exist between the theoretical
  models as to the predicted location of the major
  shell closures

E.B. Suckling and P.D. Stevenson
50th Anniversary Symposium on Nuclear Sizes and
Shapes 2008
4
The effect of the tensor force on the predictions
for superheavy nuclei
Theoretical Challenges

• Macroscopic-microscopic models predict shell
  closures at Z114 and N184, but mean-field
  models disagree

M.Bender et al., Phys. Rev. C 60, 034304 (1999)

• Improvements of the effective interactions are
  required to remove the deficiencies in regions of
  high single-particle level density

E.B. Suckling and P.D. Stevenson
50th Anniversary Symposium on Nuclear Sizes and
Shapes 2008
5
The effect of the tensor force on the predictions
for superheavy nuclei
The Tensor Force

• The tensor force originates from 1-p exchange and
  induces strong correlations between
  single-nucleon orbitals with different isospin

T. Otsuka et al., Phys. Rev. Lett. 95, 232502
(2005)

• This results in a contribution to binding energy
  and spin-orbit splitting
• In mean-field models the effect on spin-orbit
  splitting dominates

E.B. Suckling and P.D. Stevenson
50th Anniversary Symposium on Nuclear Sizes and
Shapes 2008
6
The effect of the tensor force on the predictions
for superheavy nuclei
Theoretical Framework

• The tensor part of the Skyrme effective
  interaction is written in terms of coupling
  strength parameters U T
• Recent attempts have been made to include this
  component

G. Colò et al., Phys. Lett. B. 646, 227-231
(2007) B.A. Brown et al., Phys. Rev. C
74, 061303 (2006)

• The influence of the tensor component on the
  predictions for the superheavy nuclei is studied
  within the spherical SHF BCS model

E.B. Suckling and P.D. Stevenson
50th Anniversary Symposium on Nuclear Sizes and
Shapes 2008
7
The effect of the tensor force on the predictions
for superheavy nuclei
Results

• Predicted shell structure for 298114

E.B. Suckling and P.D. Stevenson
50th Anniversary Symposium on Nuclear Sizes and
Shapes 2008
8
The effect of the tensor force on the predictions
for superheavy nuclei
Results

• Predicted shell structure for 310126

E.B. Suckling and P.D. Stevenson
50th Anniversary Symposium on Nuclear Sizes and
Shapes 2008
9
The effect of the tensor force on the predictions
for superheavy nuclei
Results

• Single-proton structure across Z114 isotopes for
  SLy6

E.B. Suckling and P.D. Stevenson
50th Anniversary Symposium on Nuclear Sizes and
Shapes 2008
10
The effect of the tensor force on the predictions
for superheavy nuclei
Summary

• Inclusion of the tensor term consistently leads
  to an increase in spin-orbit splitting between
  proton 2f7/2 and 2f5/2 levels
• The Z114 shell gap is opened over a large range
  of nuclei
• The Z126 shell gap is shown to be closed with
  increasing proton number, where Z114 is the more
  dominant gap in the nucleus 310126
• The tensor force introduces a dependence of shell
  structure on nucleon number
• The Z114 gap is stable over a chain of isotopes
  between N160-200
• The Z126 gap is rapidly closed over the chain,
  opening a new shell closure at Z138 for nuclei
  with Ngt200
• The neutron picture remains unchanged after
  inclusion of the tensor component
• Most forces predict N184 as the next shell
  closure
• N164 is calculated to be a closure by the Skx
  Skyrme forces

E.B. Suckling and P.D. Stevenson
50th Anniversary Symposium on Nuclear Sizes and
Shapes 2008
11
The effect of the tensor force on the predictions
for superheavy nuclei
Outlook

• Further efforts are required to understand the
  role of the tensor force in superheavy nuclei
• Refits of the Skyrme parameter sets should be
  attempted to include the tensor component
• Efforts to tune the tensor coupling parameters to
  G matrix calculations using the 1-p exchange
  potential result in a poorer overall description
  of spin-orbit splitting
• Fits including more experimental data on exotic
  nuclei and the available data for the superheavy
  region would allow more reliable predictions
• Investigations into the influence of the tensor
  force in exotic nuclei will be performed by
  including the term into deformed Skyrme
  Hartree-Fock plus pairing codes

E.B. Suckling and P.D. Stevenson
50th Anniversary Symposium on Nuclear Sizes and
Shapes 2008
12
The effect of the tensor force on the predictions
for superheavy nuclei
Thank You
E.B. Suckling and P.D. Stevenson
50th Anniversary Symposium on Nuclear Sizes and
Shapes 2008