  The exponential scaling of isotopic yields is investigated for sources of
different sizes over a broad range of excitation energies and freeze-out
volumes, in both primary and asymptotic stages of the decay in the framework of
a microcanonical multifragmentation model. It was found that the scaling
parameters have a strong dependence on the considered pair of equilibrated
sources and excitation energy and are affected by the secondary particle
emission of the break-up fragments. No significant influence of the freeze-out
volume on the considered isotopic ratios has been observed. Deviations of
microcanonical results from grandcanonical expectations are discussed.
