$^{178}$Hg and asymmetric fission of neutron-deficient pre-actinides

TL;DR

This study investigates asymmetric fission in neutron-deficient pre-actinides using innovative inverse kinematics techniques, revealing new insights into nuclear structure effects and extending the understanding of fission mechanisms in this region.

Contribution

It introduces a novel experimental approach with enhanced detection capabilities, providing first-time access to pre-neutron mass and energy distributions in pre-actinide fission.

Findings

Access to pre-neutron mass and energy distributions achieved

Identification of an extended asymmetric-fission island

Comparison with models highlights new driving effects

Abstract

Fission at low excitation energy is an ideal playground to probe the impact of nuclear structure on nuclear dynamics. While the importance of structural effects in the nascent fragments is well-established in the (trans-)actinide region, the observation of asymmetric fission in several neutron-deficient pre-actinides can be explained by various mechanisms. To deepen our insight into that puzzle, an innovative approach based on inverse kinematics and an enhanced version of the VAMOS++ heavy-ion spectrometer was implemented at the GANIL facility, Caen. Fission of $^{178}$Hg was induced by fusion of $^{124}$Xe and $^{54}$Fe. The two fragments were detected in coincidence using VAMOS++ supplemented with a new SEcond Detection arm. For the first time in the pre-actinide region, access to the pre-neutron mass and total kinetic energy distributions, and the simultaneous isotopic identification of one the fission fragment, was achieved. The present work describes the experimental approach, and discusses the pre-neutron observables in the context of an extended asymmetric-fission island located south-west of $^{208}Pb. A comparison with different models is performed, demonstrating the importance of this "new" asymmetric-fission island for elaborating on driving effects in fission.