Probing the new island of asymmetric fission in the 180Hg region by means of fusion-fission reactions

Deby Kattikat (GANIL, France)

Nuclei in the neutron-deficient region around ¹⁸⁰Hg₁₀₀ are different from the actinides traditionally used for fission studies, from the viewpoint of their fission barriers, separation energies and proton-to-neutron ratios. Fission properties of these neutron-deficient sub-led nuclei were expected to be similar to those of their heavier isotopes around the stability line, known to fission symmetrically. The picture changed drastically in 2010, when the asymmetric fission-fragment mass distribution of the 180Hg nucleus was discovered in a beta-delayed fission of 180Tl in a dedicated experiment at ISOLDE (CERN). This much unexpected observation promptly attracted extensive attention from both theory and experiment. That led to several important conclusions, first of all regarding the importance of the microscopic (shell) effects and their dependence on the excitation energy. Moreover, existence of a new and extended region of asymmetric fission was predicted for neutron-deficient Re-Pb nuclei.

In order to investigate fission properties of nuclei in, and the extension of, this predicted region, a dedicated experimental campaign of prompt fusion-fission studies was initiated at the JAEA (Japan). In the framework of this program, we recently investigated, at different beam energies, fission properties of N=100 nuclei 176Os, 177Ir and 179Au obtained from complete fusion-fission reactions of 35Cl beam with 141Pr, 142Nd and 144Sm targets.

This talk will present some results on Fission Fragment Mass Distribution (FFMD) and Total Kinetic Energy (TKE) distribution, from the point of view of fission modes coexistence as well as their evolution with the excitation energy and isospin of the Compound Nucleus (CN).