Acta Phys. Hung. A 19/1–2 (2004) 1–6 HEAVY ION PHYSICS Reaction Dynamics at the Barrier for Heavy Compound Systems D. Ackermann 1,2 1 Gesellschaft f¨ ur Schwerionenforschung GSI Planckstr. 1, D-64291 Darmstadt, Germany 2 Institut f¨ ur Physik, Johannes Gutenberg-Universit¨ at, D-55099 Mainz, Germany Received 20 January 2003 Abstract. To investigate basic properties of the fusion reaction dynamics for heavy compound systems the partial wave distribution σ ℓ extracted from mea- sured γ multiplicities can be employed as an alternative to the classically used fusion/fission excitation functions. A variety of reactions leading to compound nuclei (CN) 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 (ER) production. The measured spin distribution (SD) can provide informa- tion on the single partial wave cross sections which is hidden in the integral fusion cross section. We started a series of experiments to measure those prop- erties for the reactions at the Laboratori Nazionali di Legnaro, Italy. In order to extract the CN spin distribution, γ multiplicities are measured by using the γ -detector array GASP and its inner ball in the multiplicity filter mode. Keywords: heavy ion reactions, HI fusion, fusion/fission, spin distribution, superheavy elements, partial wave cross sections, fusion barrier distribution PACS: 24.75.+i, 25.70.Gh, 25.70.Jj, 27.70.+q, 27.80.+w, 27.90.+b, 29.30.Kv 1. Introduction The assumption that shell effects in the CN could favour the survival probability of the ER could not be confirmed for the N = 126 neutron shell [1]. Nevertheless, in particular with respect to the recent results for the elements 114 [2] and 116 [3] in Dubna, the possibility is discussed that the shell stabilisation close to the next higher proton shell could favour the survival of heavy nuclei in its vicinity. Here various observed decay chains for 48 Ca induced reactions on 244 Pu and 248 Cm were interpreted as 3n or 4n reactions leading to isotopes of element 114 and 116. The 1219-7580/04/ $ 20.00 c  2004 Akad´ emiai Kiad´o, Budapest