Manifestation of clustering in the 252Cf(sf) and 249Cf(nth,f) reactions

A comparative analysis of the high-statistics mass-energy distributions of the fission fragments formed in the 252Cf(sf) and 249Cf(nth,f) reactions is performed on the basis of the potential energy surface calculations. The available experimental and theoretical results provide evidence for the existence of fission modes due to the clustering of the fissioning nucleus. In 252Cf one of the modes can be treated as a heavy-cluster decay involving the formation of two fragments close to the magic nuclei of Sn. A sharp drop of the proton odd-even effect is observed at an excitation energy above E*∼40 MeV at the scission point, which is presumably associated with the complete clusterization of the fissioning nucleus. (orig.)