Angular momentum effects on mass division in actinide fission

Angular momentum (I) effects on mass yield curves were studied for the fission from the same compound nucleus (CN) ²³⁹Np of the same excitation energy but with different angular momenta, produced by the ⁷Li+²³²Th and p+²³⁸U reactions. The effects were examined only for the complete fusion-fission 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 ⁷Li+²³²Th fission at the same excitation energy (E_x) of the CN, the former value increases while the latter ratio decreases with E_x. Statistical model calculations incorporating angular momentum dependent fission barriers were made to reproduce the observed cross section data of evaporation residues and fission. The observations can well be explained if the angular momentum dependence of fission barriers is taken into account in the competition process of fission and neutron evaporation in the decay of a compound nucleus except the observed trend of the width of the mass yield curve which could not be explained straightforwardly.