Contrasting fission potential-energy structure of actinides and mercury isotopes

Ichikawa, Takatoshi*; Iwamoto, Akira; Mller, P.*; Sierk, A. J.*

Fission-fragment mass distributions are asymmetric in fission of typical actinide nuclei for nucelon number in the range and proton number in the range . For somewhat lighter systems it has been observed that fission mass distributions are usually symmetric. However, a recent experiment showed that fission of Hg following electron capture on HI is asymmetric. An earlier experiment has shown fission of Hg and nearby nuclei is symmetric, but with hints of asymmetric yield distributions up to about 10 MeV above the saddle-point energy. We calculate potential-energy surfaces for a typical actinide nucleus and for 12 even isotopes in the range Hg-Hg, demonstrating the radical differences between actinide and mervury potential surfaces. We discuss these differences and how the changing potential-energy structure along the mercury isotope chain affects the observed (a)symmetry of the fission fragments. We show that the mechanism of asymmetric fission is very different in proton-rich mercury isotopes compared to the actinide region.