DIFFERENTIAL ION ENERGY-LOSS IN MULTIPLY IONIZING COLLISIONS M. Schulz1,5, R. Moshammer1, W. Schmitt1, H. Kollmus1, R. Mann2, S. Hagmann3, H. Rothard4, R.E. Olson5, J. Ullrich1 1Fakult=E4t f=FCr Physik, Universit=E4t Freiburg, 79104 Freiburg, Germany 2Gesellschaft f=FCr Schwerionenforschung (GSI), 64291 Darmstadt, Germany 3JRM, Kansas State University, Manhattan, USA 4CIRIL, 14040 Caen, France 5University of Missouri, Rolla, USA A kinematically complete experiment for single, double, and triple ionization in 3.6 MeV/amu Au53+ --> Ne collisions was performed. A new method to determine ion energy-loss spectra with unprecedented resolution is introduced. With this method it is possible for the first time to determine the energy loss separately for different collision processes. Our studies represent a crucial step in modelling stopping powers of dense matter on a microscopic level.