ENTRANCE CHANNEL EFFECTS IN THE FUSION-FISSION TIME SCALES FROM STUDIES OF PRESCISSION NEUTRON MULTIPLICITIES

Prescission neutron multiplicities in fusion-fission reactions of B-11 +Np-237, B-11+Th-232, C-12+Th-232, and O-16+Th-232, lying on either si de of the Businaro-Gallone mass asymmetry (alpha(BG)), have been measu red. The present data along with those available in literature for com pound systems spanning the fissility range from 0.70 to 0.84 were anal yzed in a consistent manner to deduce fusion-fission time scales for a ll systems. From the systematic behavior of all the data, the three co mponents of total dynamical fusion-fission delay, namely, transient de lay, saddle-to-scission delay, and formation delay, have been deduced. It is found that the formation delay depends on the entrance channel mass asymmetry relative to Businaro-Gallone point. The variations of t he fusion-fission time scales with fissility, ratio of fission barrier to temperature, and entrance channel mass asymmetry have been studied .