Neutron emission for the fusion of Ar40+Ni, Mo92, Sn122 reactions at E/A=26 MeV

In order to study the properties of hot nuclei, neutrons emitted in the Ar40+Ni, Mo92, Sn122 reactions at E/A=26 MeV were measured in coincidence with fusion residues. The neutron spectra obtained for different residue velocities were analyzed with the moving source model. The spectra are well reproduced with two sources; one corresponds to preequilibrium emission and the other to the decay of fusion nuclei. The extracted neutron multiplicity and initial temperature of the fusion nuclei indicate the formation of thermally equilibrated nuclei with excitation energy up to 5.0 MeV/nucleon. The extracted relation between the temperature and the excitation energy shows that the level densities of the hot nuclei are well described with the level density parameter a=A/(91) for excitation energies from 2.5 to 5.0 MeV/nucleon.