A Progress Report Testing and improvements of gamma-ray strength functions for nuclear model calculations of nuclear data

Testing and improvements of gamma-ray strength functions for nuclear model calculations of nuclear data Kiev SUMMARY A closed-form thermodynamic pole approach, TPA, is developed for average description of the E1 radiative strength functions using the microcanonical ensemble for initial states. The method can be applied to calculate the dipole strengths in heated and cold nuclei for processes of the gamma-decay as well as photoabsorption in a unified way. A semiclassical description of the collective excitation damping in the TPA method is based on modern physical notion on the relaxation processes in Fermi systems. The strengths within TPA approach depends on the excitation energy, i.e. Brink hypothesis is violated in this method. The TPA calculations were compared with experimental data and calculations within the EGLO method which is recommended by the IAEA as the best practical model for calculation of the E1 strength. It is shown that the TPA model is able to cover a relatively wide energy interval, ranging from zeroth gamma-ray energy to values above GDR peak energy. It gives rather accurate means of simultaneous description of the γ-decay and photoabsorption strength functions in the medium and heavy nuclei. The results obtained by EGLO and TPA approaches are almost the same at low energies ǫ γ < ∼ 3MeV. In this range the EGLO and TPA models describe experimental data much better than the standard Lorentzian model, SLO, and give a non-zero temperature-dependent limit of the strength function for vanishing gamma-ray energy. For gamma-ray energies near neutron binding energies the calculations within the TPA model describe experimental data somewhat better for heavy nuclei with A > ∼ 150 as compared to other closed-form approaches. The set of the best parameters for TPA calculations of the E1 strengths in heavy nuclei is determined. The further investigations are important to refine dependence of the collisional and fragmentation components of the strength function width on gamma-ray energy and mass number. The computer codes were created for the calculations and plotting of the radiative strength functions. The E1 strength are calculated within framework of the SLO, EGLO and TPA models as a function of gamma-ray energies or mass number. The codes made under MS-DOS and Windows 3.1X/9X operating systems are written in Fortran and Del-phi programming languages. An option of visual comparison between the calculations and experimental data is included.