We have measured the reactions ${}_{}{}^{3,4}{}_{}{}^{}\mathrm{He}({\pi }^{-}, n){}_{}{}^{2,3}{}_{}{}^{}\mathrm{H}$ at $T_{\pi }=285, 428, 525, \mathrm{and} 575$ MeV over an angular range ${\theta }_n=18\mathrm{}°-134\mathrm{}°$ in the center-of-momentum frame, and the reaction ${}_{}{}^3{}_{}{}^{}\mathrm{He}({\pi }^{-}, {\pi }^0){}_{}{}^3{}_{}{}^{}\mathrm{H}$ at $T_{\pi }=285, 428, \mathrm{and} 525$ MeV over an angular range ${\theta }_{{\pi }^0}=60\mathrm{}°-140\mathrm{}°$. The pion absorption is found to proceed by a two-nucleon mechanism, with an energy dependence consistent with the formation of an $I=\frac{1}{2}$ resonance in the intermediate state. The pion single-charge exchange is discussed within the framework of the optical and Glauber models, and the dependence on the ${}_{}{}^3{}_{}{}^{}\mathrm{He}$ electromagnetic form factors is discussed. We also examine the isospin dependence of the $\pi$-nuclear Hamiltonian.

NUCLEAR REACTIONS ${}_{}{}^{3,4}{}_{}{}^{}\mathrm{He}({\pi }^{-}, n){}_{}{}^{2,3}{}_{}{}^{}\mathrm{H}$, $T_{\pi }=285-575\mathrm{}$ MeV, ${\theta }_n=18\mathrm{}°-134\mathrm{}°$; and ${}_{}{}^3{}_{}{}^{}\mathrm{He}({\pi }^{-}, {\pi }^0){}_{}{}^3{}_{}{}^{}\mathrm{H}$,, $T_{\pi }=285-525\mathrm{}$ MeV, ${\theta }_{{\pi }^0}=60\mathrm{}°-140\mathrm{}°$; measured $\frac{d\sigma }{d\Omega }$; discussed reaction mechanism, effects of form factors.

• Received 22 April 1982

DOI:https://doi.org/10.1103/PhysRevC.26.2111