Study of isovector resonances with pion charge exchange

Studies with the pion charge exchange reactions (π/sup +-/,π0) at 164 MeV using the LAMPF π0 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 12C, 40Ca, 90Zr, and 120Sn; and (2) observation and angular distribution measurements in the (π-,π0) reaction on 90Zr and 120Sn 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 1/3/ MeV. Differential cross sections are approximately 0.7 J12(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