Compound nucleus first excited state

Nonequilibrium phenomena are distinguished by two principal features. First, they occur on a time scale much shorter than the typical equilibration time for statistical decay of a compound nucleus (t 10 s). Second, they produce multiparticle final states that are subsequently followed by statistical decay of the excited heavy product. In normal kinematics (Ap < At), the energetic light particles or clusters are forward-peaked and form a distinct exponential tail (area B in Fig. 3.41) on the Maxwellian spectra produced in later evaporation stages (area A in O Fig. 3.41). The preequilibrium component for the nucleon channels is as in by early stage emissions of the multistep compound model, as in by the FKK model for example. At the extreme of nonequilibrium emissions are the discrete peaks (labeled C), which correspond to direct reactions, or the first step in a multistep compound model. 

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