Collective effects in the level density are not well understood, and including these effects as enhancement factors to the level density does not produce sufficiently consistent predictions of observables. Therefore, collective effects are investigated in the level density parameter instead of treating them as a final factor in the level density. A new Laplacelike formula is proposed for the energy dependence of the level density parameter, including collective effects. A significant improvement has been achieved in agreement between observed and predicted energy levels. This new model can also be used in both structure and reaction calculations of the nuclei far from stability, especially near the drip lines.

No abstract

The new definition of the energy dependence for the level density parameter including collective effects depends strongly on the semi-classical approach. For this method, defining an accurate single-particle potential is of great importance. The effect of the single-particle potential terms, which are central, spinorbit, harmonic oscillator, Woods-Saxon and Coulomb potential, both for spherical and deformed cases, on the level density parameter was investigated by examining the local success of the global parameterizations of eight different combinations of these terms. Among these combinations, the sum of the central, spinorbit, harmonic oscillator and Coulomb potentials, gives the most accurate predictions compared with experimental data. The local selections of the global parameterizations show that the single-particle models, which are based on Woods-Saxon potential as the main term, are more suitable candidates than the models based on harmonic oscillator potential to extrapolate away far from stability. Also it can be concluded that the contribution of the Coulomb interaction, both around the closed and open shells is not neglectable.

No abstract

No abstract