Experimental investigations of the nuclear level density by using heavy ion reactions

The transition of the level density parameter aeff from the low excitation energy value aeff = A/8 MeV-1 to the Fermi gas value aFG to approximately A/15 MeV-1 was discovered a few years ago studying particle spectra evaporated from hot compound systems of A to approximately 160. A number of experiments have been recently performed to confirm the earlier findings and extend the investigation to other mass regions and to higher excitation energies. Furthermore, precision coincidence experiments have been done in the lead region in which evaporation residues are tagged by low energy gamma-rays. Those experiments open the possibility of a detailed study of the level densities in nuclei where the shell effects are important.