Instantaneous Shape Sampling for Calculation of the Electromagnetic Dipole Strength

Electromagnetic dipole absorption cross-sections of transitional nuclei with large-amplitude shape fluctuations are calculated in a microscopic way by introducing the concept of Instantaneous Shape Sampling, which is based on the slow shape dynamics as compared to the dipole vibrations. The dipole strength is calculated by means of RPA for the instantaneous shapes, the probability of which is obtained by means of IBA-1. Very good agreement with the experimental absorption cross sections near the nucleon emission threshold is obtained. The dipole strength in this energy region is controlled by the Landau fragmentation.