  Within our fission model, the Coulomb and proximity potential model (CPPM)
cluster formation probabilities are calculated for different clusters ranging
from carbon to silicon for the parents in the trans-tin and trans- lead
regions. It is found that in trans-tin region the 12^C, 16^O, 20^Ne and 24^Mg
clusters have maximum cluster formation probability and lowest half lives as
compared to other clusters. In trans-lead region the 14^C, 18, 20^O, 23^F,
24,26^Ne, 28,30^Mg and 34^Si clusters have the maximum cluster formation
probability and minimum half life, which show that alpha like clusters are most
probable for emission from trans-tin region while non-alpha clusters are
probable from trans-lead region. These results stress the role of neutron
proton symmetry and asymmetry of daughter nuclei in these two cases.
