Pions offer a unique possibility as probes of nuclear structure since they can exchange two units of electrical charge unaccompanied by other quantum numbers. We have calculated the double-charge-exchange cross section for the reaction ${\pi }^{-}+{\mathrm{He}}^3\to {\pi }^{+}+3n$ in the impulse approximation using the Chew-Low model for the pion-nucleon interaction. Only the dominant 3-3 channel is retained. For incident pions in the energy region of several hundred MeV, values of the differential cross section of $\frac{d^2\sigma }{d\Omega \mathrm{dE}}\approx 1-10$ μb/MeV are obtained for forward angles. Triple-scattering terms are also calculated and found to introduce corrections of <10% in $\frac{d^2\sigma }{d\Omega \mathrm{dE}}$. Similar results are obtained when the work is extended to the reaction ${\pi }^{+}+{\mathrm{O}}^{18}\to {\pi }^{-}+{\mathrm{Ne}}^{18}$ using shell-model wave functions.

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