Isovector resonances in pion single-charge-exchange reactions

An experimental study of L = 0, 1, and 2 isovector resonances in pion charge-exchange reactions is reported. In these experiments well-understood, spherical, even-even nuclei were studied at 120, 165, and 230 MeV. The emphasis of the 165 MeV study was on L = 0, 1, and 2 isovector resonances as a function of the atomic mass of the target. The targets were Ca-40, Ni-60, Zr-90, Sn-120, Ce-140, and Pb-208. The 120 and 230 MeV studies were aimed at measuring the properties of the isovector resonances as function of bombarding energy for a few targets, Ca-40, Ni-60, and Sn-120. Double differential cross sections up to excitation energies of 60 MeV were measured out to angles extending well past the second maximum of the isovector quadrupole resonance angular distribution. Results of the experiments were found to be in good agreement with RPA-DWIA and other theoretical calculations as regards isovector dipole and monopole energies, widths and cross sections, and strong interaction radii. However, some problem in the distorted wave Born approximation treatment of the reaction mechanism or in the structure of the isobaric-analog state was indicated from measurements of the energy dependence of the maximum cross sections for the dipole and monopole resonances. 12 refs., 10 figs