The spectrum of high-energy gamma rays following the capture of negative pions in ${}_{}{}^{12}{}_{}{}^{}\mathrm{C}$ was measured with high resolution. The observed structure in the giant resonance region is the first direct experimental proof of the influence of collective excitations in radiative pion capture. This supports recent theories concerning the analogy between this process and muon capture.

• Received 8 June 1970

DOI:https://doi.org/10.1103/PhysRevLett.25.689