Our knowledge of the interaction of pions with complex nuclei is rather limited. A number of experiments carried out with stopped negative pions, primarily on light targets, have provided some information on the pion-absorption process; in addition we have some knowledge of elastic scattering and total cross sections at higher energies. 1 For nuclei heavier than 12 C almost nothing is known of how much of the total cross section corresponds to the pion suffering an inelastic collision and maintaining its identity, and how much to the pion disappearing altogether. ; J. J.Auberte* al" Phys. Rev. Lett. 35, 416 (1975).whether larger clusters play a role. We have investigated the distribution of residual nuclides produced by the bombardment of 58 » 60 Ni with -n ± and also with protons; such results can provide substantial constraints on the gross features of possible models of the pion-nucleus interaction. The residual nuclides were identified by measuring prompt y-ray spectra. In contrast to activation measurements, this technique is sensitive to stable residual nuclei, where most of the total cross section is concentrated, y rays are seen when a given residual nuclide is left with insufficient excitation energy for particle emission; this technique cannot distinguish whether y-ray spectra have been observed following the interaction of 220-MeV 7r + and if and 200-MeV protons with b8 Ni and 60 Ni and 100-MeV 7r + with 58 Ni. Product nuclides have been identified from characteristic y-ray lines corresponding to total cross sections of ~ 500 mb. The systematic trends with projectile and energy are explored; rather substantial differences are found between pions and protons.
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