Giant resonance decay in hot fissile nuclei

The γ-ray strength function of the Giant Dipole Resonance (GDR) in hot nuclei produced in heavy ion fusion reactions yields information about the deformation of the hot nucleus. In fissile nuclei where the GDR γ-decay competes mostly with fission the relative time scales of the two processes can be extracted from a comparison of pre- and post-fission γ-rays. A systematic study of γ-ray spectra, γ-fission coincidences and angular correlations in fusion reactions shows the existence of superdeformation in hot neutron deficient Pb isotopes. Even in hot Actinide nuclei the excited state GDR is still observed, which indicates that the fission time scale is slowed down significantly relative to that of the cold nucleus. The GDR strength function is a direct test for the formation of the compound nucleus (CN). Thus data on the CN formation for different target-projectile combinations for the same angular momentum and excitation energy can be discussed in terms of statistical CN decay and the presence of fast non-compound processes. From this an estimate can be made for the heaviest nucleus in which a CN GDR is likely to be observable