Study of isovector resonances with pion charge exchange

Studies with the pion charge exchange reactions (..pi../sup +-/,..pi../sup 0/) at 164 MeV using the LAMPF ..pi../sup 0/ spectrometer are yielding new results on the existence and systematic features of isovector resonances in nuclei. These experiments possess an unusually high signal/background ratio for isovector resonances of low-multipolarity. Results obtained to date are: (1) observation and angular disribution measurement of the giant dipole resonance in nuclei /sup 12/C, /sup 40/Ca, /sup 90/Zr, and /sup 120/Sn; and (2) observation and angular distribution measurements in the (..pi../sup -/,..pi../sup 0/) reaction on /sup 90/Zr and /sup 120/Sn of large signals possessing the expected angular distribution shapes and magnitudes for the isovector monopole resonance. Excitation energies are near the hydrodynamical model values 170 A/sup -//sup 1/3/ MeV. Differential cross sections are approximately 0.7 J/sub 1//sup 2/(qR) mb/sr. An overview of this experimental program, with emphasis on new results and how they correlate with existing knowledge on the isovector resonances, is presented