Excitation functions of pion single charge exchange reactions in /sup 27/Al, /sup 45/Sc, and /sup 65/Cu

The cross sections for the pion single charge exchange reactions /sup 27/Al(..pi../sup -/,..pi../sup 0/) /sup 27/Mg, /sup 45/Sc(..pi../sup +/,..pi../sup 0/) /sup 45/Ti, and /sup 65/Cu(..pi../sup -/,..pi../sup 0/) /sup 65/Ni were measured at pion kinetic energies from 80 to 400 MeV by activation techniques. The excitation functions measured for these target nuclei do not show any structure near the (3,3) resonance, but rather, all exhibit a monotonic decrease in cross section over this energy range, proportional to T/sub ..pi..//sup -1/. Theoretical predictions based on the impulse approximation with the Fermi gas model show a minimum near the (3,3) resonance, in disagreement with these experimental results.