Observation of Delayed Nuclear Fission in the Region of180Hg

The formation of nuclides undergoing delayed fission with half-lives in the range of T1/2 1 s has been observed in fusion-evaporation reactions induced by 230 MeV 40Ca and 40Ar projectiles on isotopically enriched targets of 144Sm, 147Sm and 150Sm. The fission activity with T1/2 = 0.70+0.12-0.09 s produced in the 144Sm + 40Ca reaction has been found to be the most striking one. The origin of this activity is explained as being due to the β-delayed fission occurring in the chain . The discovery of β-delayed fission in the Hg region opens up valuable prospects for extending low-energy (E* ≤ Qβ+(EC)) fission studies to neutron-deficient nuclei of many elements belonging to the translanthanide part of the Mendeleev periodic table.