Discrimination between roles of fissioning nucleus and asymmetry degree of freedom on the even-odd structure in fission-fragment yields

TL;DR

This study investigates how the even-odd staggering in fission-fragment yields depends on both the fissioning system and the asymmetry of the charge distribution, revealing a systematic relationship supported by comprehensive experimental data.

Contribution

It demonstrates that the variation in the even-odd effect is primarily linked to the asymmetry evolution of charge distribution, not just dissipated energy, providing a new interpretation of fission fragment yields.

Findings

The global even-odd effect varies systematically with mean asymmetry.

The increase of even-odd staggering with asymmetry depends on the fissioning system.

Inverse kinematics data support the link between asymmetry and even-odd effect.

Abstract

Based on a wide systematics of fission-fragment distributions measured in low-energy fission, the even-odd staggering in the fission-fragment element yields is investigated. The well-established evolution of the global even-odd effect with the fissioning system is found to be only a partial aspect of the even-odd structure. Indeed, it is shown that the global even-odd effect is varying systematically with the mean asymmetry of the fission-fragment distribution, and that the general increase of the even-odd staggering with asymmetry is depending on the fissioning system. Thus, the dependency of the even-odd effect with the fissioning system is accredited in part to the asymmetry evolution of the charge distribution, and not solely related to the dissipated energy as it has been done earlier. This interpretation is strongly supported by data measured in inverse kinematics, which cover the complete charge distribution and include precise yields at symmetry. The relevance of the order parameter to describe the even-odd effect in fission-fragment yields as a general property is explored.