Observation of the Repulsive Nature of the P-Wave Pion-Nucleus Interaction at Large Z

We have measured the zero-energy P-wave pion-nucleus interaction for Pd (Z=46) using the pionic-atom nuclear-resonance effect. The observed ratios of selected pionic x-ray intensities for two isotopes of Pd imply that the interaction is repulsive for this value Z, in contrast to its observed attractive nature for Z< or =30. This cahnge in the P-wave pion-nucleus interaction is in agreement with a previously untested theoretical prediction. (AIP)