Asymmetric fission around lead: The case of Po198

Asymmetric low-energy fission of neutron-deficient nuclei around lead is addressed with the measurement of fragment mass and total kinetic energy properties for the fissioning system Po-198 produced in heavy-ion fusion. Interpretation of the measurement for such a transitional nucleus at finite excitation energy is challenging. The presence of asymmetric partitions is suggested by the observed weak dependence of the total kinetic energy on mass and by the nonmonotonic evolution of the fragment-mass distribution width with excitation energy. The interpretation is supported by microscopic model calculations as well as by the results of an advanced semiempirical code. Combined with previous experiments in the region, the present measurement contributes to establish the evolution of the fragment-mass distribution as a function of the fissioning system. The connection between the "new" and the "old" islands of asymmetric fission is discussed.