  We have applied the Giessen BUU (GiBUU) transport model to the description of
the double charge exchange (DCX) reaction of pions with different nuclear
targets at incident kinetic energies of 120-180 MeV . The DCX process is highly
sensitive to details of the interactions of pions with the nuclear medium and,
therefore, represents a major benchmark for any model of pion scattering off
nuclei at low and intermediate energies. The impact of surface effects, such as
the neutron skins of heavy nuclei, is investigated. The dependence of the total
cross section on the nuclear mass number is also discussed. We achieve a good
quantitative agreement with the extensive data set obtained at LAMPF.
Furthermore, we compare the solutions of the transport equations obtained in
the test-particle ansatz using two different schemes - the full and the
parallel ensemble method.
