  The influence of the transient thermal effects on the partition of the energy
of selfrecoils in germanium and silicon into energy eventually given to
electrons and to atomic recoils respectively is studied. The transient effects
are treated in the frame of the thermal spike model, which considers the
electronic and atomic subsystems coupled through the electron - phonon
interaction. For low energies of selfrecoils, we show that the corrections to
the energy partition curves due to the energy exchange during the transient
processes modify the Lindhard predictions. These effects depend on the initial
temperature of the target material, as the energies exchanged between
electronic and lattice subsystems have different signs for temperatures lower
and higher than about 15 K. Many of the experimental data reported in the
literature support the model.
