Differential cross sections for the reaction 8 He(7r" ,7r°) 3 H at energies of 200, 250, 275, and 290 MeV over the angular region 8O°^0 ColT]t>^ 150° are presented. Comparison is made with theoretical predictions based on Glauber theory and optical-potential calculations. Neither approach gives a satisfactory description of the data; in particular, the observed energy dependence is much smaller than the theoretical predictions.Pion charge-exchange (CEX) scattering from nuclei has been studied for some time by means of decay measurements of the residual nucleus, which have provided information on the angle-integrated cross section (see the recent review articles 1 ' 2 ). The energy dependence of this total cross section has attracted particular interest. It has generally been found to be very small, and roughly flat around the energy of the (3, 3) resonance of the ir-N interaction. Current scattering theories have had difficulty in reproducing this energy behavior. While there is an apparent need to include pion-nucleus distortion effects to reproduce the magnitude of the cross section, the strong pion absorption at resonant energies gives rise to a minimum in the predicted energy dependence; i 0 e 0 , the effect of the (3,3) resonance on absorption tends to dominate over the simple resonant behavior in the CEX transition amplitude,, Various remedies for this erroneous energy dependence have been tried, and the inclusion of second-order effects seems to yield some improvemento 2 ' 3 Until now, there has been no conclusive theoretical account of the CEX scattering in complex nuclei, and data on the three-body nuclear system 3 He (or 3 H) have been desirable» The distortion effects should be smaller for this system and the theoretical difficulties should be much reduced, making detailed multiple-scattering and optical-model calculations 4 " 9 manageable. The predictions of current calculations have generally been put to a test by comparing with the extensive body of elastic-scattering data for these nuclei. 10 The amplitudes for pion elastic and CEX scattering from 3 He are simply related: The CEX amplitude is proportional to the difference between the 7i + and ir~ elastic-scattering amplitudes. Data on all of these cross sections are thus needed to help put the current scattering theories and their approximations to further test. From an experimental point of view, the 3 He(7r",77°) 3 H process presents the opportunity to detect the recoil triton, circumventing the problem of ir° detection. We have exploited this technique in the present experiment, and in this Letter we report the first differential cross section of CEX scattering to a discrete final state.The angular distributions were measured using the EPICS pion channel at LAMPF (the Clinton P. Anderson Meson Physics Facility) in the course of measurements of the (IT" ,n) reaction on 3 He and 4 He. u Briefly, the beam used had a flux varying between 1 and 3X10 6 7r"/s« The target 12