Fission of heavy nuclei induced by energetic pions

Fission of ${}_{}{}^{238}{}_{}{}^{}\mathrm{U}$, ${}_{}{}^{209}{}_{}{}^{}\mathrm{Bi}$, and ${}_{}{}^{197}{}_{}{}^{}\mathrm{Au}$ induced by both positive and negative pion beams at incident energies of 60 to 100 MeV is examined. Energy and mass spectra and angular correlations of coincident fission fragments are compared to theoretical calculations and to other data. Excitation energies of the fissioning system in excess of 100 MeV are deduced, implying that the fission examined in this study is caused primarily by true absorption of the pion. The masses of the coincident fission fragments are found to have a wider distribution than those from fissioning systems of similar excitation energy induced by nucleon beams. The fission cross sections are close to the reaction cross sections for ${}_{}{}^{238}{}_{}{}^{}\mathrm{U}$ and scale with the fissility for the other nuclei studied.