New Global Calculation of Nuclear Masses and Fission Barriers for Astrophysical Applications

P. Möller and A. J. Sierk Theoretical Division, Los Alamos National Laboratory, New Mexico 87545, USA
R. Bengtsson Department of Mathematical Physics, Lund Institute of Technology, SE-22100 Lund, Sweden
T. Ichikawa RIKEN Nishina Center, Riken, Wako, Saitama, 351-0198, Japan
A. Iwamoto Japan Atomic Energy Agency (JAEA),
Tokai-mura, Naka-gun, Ibaraki, 319-1195, Japan
This paper was presented at the
OMEG07, The 10th International Symposium on Origin of Matter and Evolution of Galaxies: From the Dawn of Universe to the Formation of Solar System,
Sapporo, Japan 4-7 December 2007.
It appears in the proceedings published in
AIP Conference Proceedings vol. 1016 (2008) p. 150-155.
It has been assigned Los Alamos National Laboratory Preprint No LA-UR-08-0322,

Abstract:

The FRDM(1992) mass model has an accuracy of 0.669 MeV in the region where its parameters were determined. For the 529 masses that have been measured since, its accuracy is 0.46 MeV, which is encouraging for applications far from stability in astrophysics. We are developing an improved mass model, the FRDM (2008). The improvements in the calculations with respect to the FRDM(1992) are in two main areas. (1) The macroscopic model parameters are better optimized. By simulation (adjusting to a limited set of now known nuclei) we can show that this actually makes the results {\it more} reliable in new regions of nuclei. (2) The ground-state deformation parameters are more accurately calculated. We minimize the energy in a four-dimensional deformation space (

ε

₂,ε₃,ε₄, and ε₆) using a grid interval of 0.01 in all 4 deformation variables. The (non-finalized) FRDM (2008-a) has an accuracy of 0.596 MeV with respect to the 2003 Audi mass evaluation before triaxial shape degrees of freedom are included (in progress). When triaxiality effects are incorporated preliminary results indicate that the model accuracy will improve further, to about 0.586 MeV. We also discuss very large-scale fission-barrier calculations in the related FRLDM (2002) model, which has been shown to reproduce very satisfactorily known fission properties, for example barrier heights from ⁷⁰Se to the heaviest elements, multiple fission modes in the Ra region, asymmetry of mass division in fission and the triple-humped structure found in light actinides. In the superheavy region we find barriers consistent with the observed half-lives. We have completed production calculations and obtain barrier heights for 5254 nuclei heavier than A=170 for all nuclei between the proton and neutron drip lines. The energy is calculated for 5009325 different shapes for each nucleus and the optimum barrier between ground state and separated fragments is determined by use of an ``immersion'' technique.
Figures 1,2 and 4, are in color, so the paper should be printed on a color printer.

The complete manuscript in color is available for download.

Peter Moller

Created: June 4 2008 --> Last modified: Thu Jul 5 2012