Fragment distributions have been measured for Au + Au collisions at $\frac{E}{A}=100\mathrm{} \mathrm{and} 1000$ MeV. A high detection efficiency for fragments was obtained by combining the ALADIN spectrometer and the MSU-Miniball/WU-Miniwall array. At both energies the maximum multiplicity of intermediate mass fragments (IMF) normalized to the size of the decaying system is about one IMF per 30 nucleons but the element distributions show significant differences. Within a coalescence picture the suppression of heavy fragments in central collisions at $\frac{E}{A}=100\mathrm{}$ MeV may be related to a reduction of the density in momentum space which is caused by the collective expansion.

• Received 9 August 1994

DOI:https://doi.org/10.1103/PhysRevLett.74.38