Angular momentum effects on mass division in actinide fission

Angular momentum (l) effects on mass yield curves were studied for the fiss ion from the same compound nucleus (CN) Np-239 of the same excitation energ y but with different angular momenta, produced by the Li-7+Th-232 and p+U-2 38 reactions. The effects were examined only for the complete fusion-fissio n events after careful estimation of the contribution of incomplete fusion- fission. It is found that the width of the whole mass yield curve is larger while the peak-to-valley ratio is smaller for the Li-7+Th-232 fission at t he same excitation energy (E-X) of the CN, the former value increases while the latter ratio decreases with E-X. Statistical model calculations incorp orating angular momentum dependent fission barriers were made to reproduce the observed cross section data of evaporation residues and fission. The ob servations can well be explained if the angular momentum dependence of fiss ion barriers is taken into account in the competition process of fission an d neutron evaporation in the decay of a compound nucleus except the observe d trend of the width of the mass yield curve which could not be explained s traightforwardly.