Revisiting the Even-odd Staggering in Fission-fragment Yields

The even-odd staggering observed in the experimental fission-fragment nuclear-charge yields is investigated over a wide systematics of fission fragments measured at Lohengrin in direct kinematics and at GSI in inverse kinematics. The general increase of the even-odd staggering in the fission-fragment charge yields towards asymmetric charge splits is explained by the absorption of the unpaired nucleons by the heavy fragment. As a consequence, the well established trend of evenodd staggering in the fission fragment charge yields to decrease with the fissility is attributed in part to the asymmetry evolution of the charge distribution. This interpretation is strongly supported by the data measured at GSI, which cover the complete charge distribution and include precise yields at symmetry. They reveal that the even-odd effect around symmetry remains constant over a large range of fissility.