Fission of excited nuclei with Z(2)/A=20-33: Mass-energy distributions of fragments, angular momentum, and liquid-drop model

The mass-energy distributions of fission fragments in the reactions Ne-20 + Ru-99, Cd-106,Cd-110, Sn-112.118.124 are measured by means of a two-arm time-of-flight spectrometer DEMAS. The fission of Ba-124 in two ion-target combinations C-12 + Sn-112 and Mg-25 + (99)RU is also studied. Global analysis of data obtained in this study and data reported by other authors made it possible to determine the variances sigma(M)(2) and sigma(E)(2) of mass and energy distributions as functions of the angular momentum I of the compound nucleus and nucleon composition. It is found that, for nuclei with Z(2)/A less than or equal to 30 (in contrast to heavier nuclei), an increase in the angular momentum introduced into a nucleus undergoing fission leads to the narrowing of the mass distributions of fragments. The stability of nuclei to mass-asymmetric deformation is studied, and it is shown that the Sierk liquid-drop model with finite-range nuclear forces provides the closest description of experimental data in the region Z(2)/A similar to 20 - 30. The Businaro-Gallone point at which the nucleus is absolutely unstable to mass-asymmetric deformations is found to be (Z(2)/A)(BG) = 22.0 +/- 0.6.