  Isotopic effects observed in fragmentation reactions induced by protons,
deuterons, and alpha particles of incident energies between 660 MeV and 15.3
GeV on 112-Sn and 124-Sn targets are discussed. The exponential scaling of the
yield ratios with the third component of the fragment isospin (N-Z)/2 is
observed in all reactions, with scaling parameters that depend on the incident
energy. Breakup temperatures for these reactions are deduced from double ratios
of isotopic yields and tested for their relation with the isoscaling
parameters. The quantum statistical (QSM) and the statistical
multifragmentation (SMM) models are used for interpreting the results. The
observed isoscaling can be understood as a consequence of a statistical origin
of the emitted fragments in these reactions. The SMM analysis shows that the
exponent describing the isoscaling behavior is proportional to the strength of
the symmetry term of the fragment binding energy. Using this result, a
symmetry-term coefficient (approximately 22.5 MeV) for fragments at breakup is
deduced from the experimental data. This is close to the standard value and
supports SMM assumptions for the breakup configuration. An alternative method
of determining the symmetry-energy coefficient, by using isotope distribution
widths, is also discussed.
