Reaction dynamics at the barrier for heavy compound systems

Abstract

To investigate basic properties of the fusion reaction dynamics for heavy compound systems, the partial wave distribution σl extracted from measured γ multiplicities can be employed as an alternative to the classically used fusion/fission excitation functions. A variety of reactions leading to compound nuclei in the Pb region can be used to investigate features like the fusion-fission competition, the role of deformation in the fusion of heavy systems, and a possible effect of the Z=82 shell on the enhancement of evaporation residue production. The measured spin distribution can provide information on the single partial wave cross sections, which is hidden in the integral fusion cross section. Moreover, it can reveal signatures in the high-spin region, which could be an indication of a stabilization due to an increase in the potential hole by shell correction energies Eshell in the vicinity of a closed shell. The systematic investigation and understanding of the fusion-fission reaction dynamics, together with the understanding of the structure of transfermium nuclei, which are stabilized only via shell effects, are essential for a successful program aiming at the synthesis of new elements at GSI, Dubna, or elsewhere. We started a series of experiments to measure those properties for the reactions at the Laboratori Nazionali di Legnaro, Italy. In order to extract the compound nucleus spin distribution, γ multiplicities are measured using the γ-detector array GASP and its inner ball in the multiplicity filter mode.