Data of the (${\pi }^{+}, {\pi }^{-}$) reaction on ${}_{}{}^{128}{}_{}{}^{}\mathrm{Te}$ and ${}_{}{}^{130}{}_{}{}^{}\mathrm{Te}$ at $T_{\pi }=48\mathrm{}$ MeV are presented, which constitute also the first observation of pionic double charge exchange (DCX) on heavy nuclei at energies below the (3,3) resonance. For the ground state transitions in these isotopes we find very small cross sections of about 15 nb/sr only at 30° and a ratio of $\frac{\sigma \left({}_{}{}^{130}{}_{}{}^{}\mathrm{Te}\right)}{\sigma \left({}_{}{}^{128}{}_{}{}^{}\mathrm{Te}\right)}={1.5}_{-0.8\mathrm{}}^{+1.8\mathrm{}}$. The experimental results and their impact on the understanding of the $\beta \beta$ decay of the Te isotopes are discussed within the framework of recent proton-neutron quasiparticle random phase approximation calculations. For the transitions to the double isobaric analog states in ${}_{}{}^{128}{}_{}{}^{}\mathrm{Xe}$ and ${}_{}{}^{130}{}_{}{}^{}\mathrm{Xe}$ we obtain cross sections in the range 1 μb/sr which fit very well into a systematics, that is in accordance with a dominance of the short-range part of the DCX operator in analog transitions at low pion energies.

• Received 21 November 1995

DOI:https://doi.org/10.1103/PhysRevC.53.R2033