Complex Fragment Emission In Dissipative Binary Decay Of Kr-74,Kr-76

The fragment emission mechanism in the binary decay of composites formed in the reactions Ne-20+Fe-56 and O-16+Ni-58 has been studied at two different excitation energies. The inclusive energy and angular distributions of the emitted fragments Li-6,Li-7, Be-7,Be-8,Be-9, B-10,B-11, and C-11,C-12,C-13,C-14 have been measured in the laboratory angles ranging from 15 degrees to 35 degrees (corresponding angles in center of mass ranging from 20 degrees to 50 degrees). The energy distributions of the fragments are found to be Gaussian and peaked at energies higher than those expected from fusion-fission-type reactions. The center-of-mass angular distributions of all the fragments have been found to fall faster than approximate to 1/sin theta(c.m.)-like dependence and the average Q values of the fragments are found to decrease with increasing the center-of-mass angle of the emitted fragment for both the systems. The above characteristics of fragments signify that they were emitted from nonequilibrium sources, produced in a highly energy damped deep-inelastic-type reaction. The lifetimes of the dinuclear composites estimated from the angular distributions of these fragments are found to be in the range of approximate to(0.5-2.7)x10(-22) s, which are smaller than the respective compound-nuclear lifetimes [approximate to(1.0-2.0)x10(-21) s]. The angular-momentum dissipations estimated from the average kinetic energies of the fragments are found to be, for lighter fragments in particular, greater than those predicted by the empirical sticking limit.