Direct measurements of neutron emission in complete and incomplete /sup 12/C-induced fusion reactions

The multiplicity of neutron emission in /sup 12/C-induced nuclear reactions with /sup 197/Au, /sup 209/Bi, /sup 232/Th, and /sup 238/U was measured directly on-line using a Gd-loaded scintillation neutron multiplicity counter with 1 m diameter recording single neutrons with a registration efficiency of about 80%. Using a well-focused carbon beam one could measure up to about 30 neutrons per nuclear interaction directly, when the neutron multiplicity counter was triggered with a prompt fission fragment. For /sup 197/Au and /sup 209/Bi targets, fission was observed to follow compound-nucleus formation, whereas in the cases of /sup 232/Th and /sup 238/U, fission following incomplete fusion was seen to contribute also. An average multiplicity of nu-bar = (4 +- 1) neutrons was measured for incomplete fusion, while for complete fusion, nu-bar varied between 8 and 12, depending on target and bombarding energy. The results complement measurements of Viola et al. on fragment-angular correlations and agree with them