We measured the energies, widths, and cross sections of the isovector monopole and dipole resonances in various nuclei between ${}_{}{}^{40}{}_{}{}^{}\mathrm{Ca}$ and ${}_{}{}^{208}{}_{}{}^{}\mathrm{Pb}$ with the reactions (${\pi }^{\pm }$,${\pi }^0$). Both resonances exhaust approximately the same substantial fraction of the cross section calculated in a random-phase-approximation–distorted-wave-impulse-approximation model. The excitation energies and widths of the monopole and dipole are in good agreement with random-phase-approximation calculations and for the dipole they are also in agreement with other data. No isovector quadrupole resonance was observed, and the upper limits for the cross sections for the light elements are well below the sum rule strength for the isovector monopole and giant dipole resonance.

• Received 24 April 1986

DOI:https://doi.org/10.1103/PhysRevC.34.1822