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

Journal Article · Wed May 21 04:00:00 EDT 2008 · AIP Conference Proceedings

DOI:https://doi.org/10.1063/1.2943565· OSTI ID:21143460

Moeller, P; Sierk, A J ^[1]; Bengtsson, R ^[2]; Ichikawa, T ^[3]; Iwamoto, A ^[4]

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1. Theoretical Division, Los Alamos National Laboratory, Los Alamos, New Mexico 87545 (United States)
2. Department of Mathematical Physics, Lund Institute of Technology, Box 118, SE--22100 Lund (Sweden)
3. RIKEN Nishina Center, RIKEN, Wako, Saitama, 351-0198 (Japan)
4. Japan Atomic Energy Agency (JAEA), Tokai-mura, Naka-gun, Ibaraki, 319-1195 (Japan)

The FRDM(1992) mass model [1] 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 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 ({epsilon}{sub 2}, {epsilon}{sub 3}, {epsilon}{sub 4}, {epsilon}{sub 6},) 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 {sup 70}Se 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.

• OSTI ID: 21143460
• Journal Information: AIP Conference Proceedings, Journal Name: AIP Conference Proceedings Journal Issue: 1 Vol. 1016; ISSN APCPCS; ISSN 0094-243X
• Country of Publication: United States
• Language: English

Related Subjects

73 NUCLEAR PHYSICS AND RADIATION PHYSICS
ACCURACY
ACTINIDES
ASTROPHYSICS
ASYMMETRY
DEGREES OF FREEDOM
FISSION
FISSION BARRIER
FOUR-DIMENSIONAL CALCULATIONS
GROUND STATES
HALF-LIFE
MASS
MEV RANGE
NEUTRONS
NUCLEAR MODELS
NUCLEAR STRUCTURE
PROTONS
SELENIUM 70