Pion double charge exchange reactions inC12andCa40,44,48

Cross sections, $\frac{d^2\sigma }{d\Omega \mathrm{dT}}$, on ${}_{}{}^{12}{}_{}{}^{}\mathrm{C}$, ${}_{}{}^{40,44,48}{}_{}{}^{}\mathrm{Ca}$ are presented for inclusive (${\pi }^{+}$,${\pi }^{-}$) and (${\pi }^{-}$,${\pi }^{+}$) reactions at an incident energy of $T_{\pi }=290\mathrm{}$ MeV with the exit pions detected over an energy range of $T_{\pi }=175-255\mathrm{}$ MeV at an angle of 60°. These cross sections are found to vary systematically with reported proton-neutron differences in nuclear radial distributions.