The excitation of a Δ-isobar in a finite nucleus in charge--exchange
(3He,t) reaction is discussed in terms of a nuclear response function. The
medium effects modifying a Δ- and a pion propagation were considered for
a finite size nucleus. The Glauber approach has been used for distortion of a
3He and a triton in the initial and the final states. The effects
determining the peak positions and its width are discussed. Large displacement
width for the Δ - h excitations and considerable contribution of
coherent pion production were found for the reaction on 12C.Comment: 29 pages including 8 figures, IU/NTC 92-3