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The production of intermediate mass fragments ͑IMF's͒ from the four reactions 55A MeV 124,136 Xe ϩ 112,124 Sn is studied with an experimental apparatus which is highly efficient for the detection of both charged particles and neutrons. The IMF's are more localized in the midvelocity region than are the light charged particles, and the detected multiplicity of IMF's depends linearly on the charge lost from the projectile and increases with the neutron excess of the system. Remnants of the projectile, with very little velocity reduction, are found for most of the reaction cross section. Isotopic and isobaric fragment yields in the projectile-velocity region indicate that charge-to-mass ratio neutralization is generally not achieved but is approached when little remains of the projectile. For all systems, the fragments found in the midvelocity region are substantially more neutron rich than those found in the velocity region dominated by the emission from the projectile. This observation can be accounted for if the midvelocity source ͑or sources͒ is either more neutron rich or smaller, with the same neutron-to-proton ratio, than the source with the velocity of the projectile. Taken together, the observations of this work suggest that the intermediate mass fragments are, to a large extent, formed by multiple neck rupture of the overlap material, a process which might enhance the neutron-to-proton ratio of the primary source material and/or limit the size of the sources. This scenario is reminiscent of low-energy ternary fission and one predicted by Boltzmann-Uehling-Uhlenbeck calculations. However, these calculations predict too much velocity damping of the projectile remnant. The calculations improve, in this regard, when the in-medium nucleon-nucleon cross sections and the cost of creating low density material are reduced.

The emission of composite-particles is studied in the reaction p+Au at Ep=2.5 GeV, in addition to neutrons and protons. Most particle energy spectra feature an evaporation spectrum superimposed on an exponential high-energy, non-statistical component. Comparisons are first made with the predictions by a two-stage hybrid reaction model, where an intra-nuclear cascade (INC) simulation is followed by a statistical evaporation process.The high-energy proton component is identified as product of the fast pre-equilibrium INC, since it is rather well reproduced by the INCL2.0 intra-nuclear cascade calculations simulating the first reaction stage. The low-energy spectral components are well understood in terms of sequential particle evaporation from the hot nuclear target remnants of the fast INC. Evaporation is modeled using the statistical code GEMINI. Implementation of a simple coalescence model in the INC code can provide a reasonable description of the multiplicities of high-energy composite particles such as 2–3H and 3He. However, this is done at the expense of 1H which then fails to reproduce the experimental energy spectra