LOW-ENERGY PIONIC DOUBLE-CHARGE-EXCHANGE ON THE BETA-BETA-INSTABLE NUCLEI TE-128,TE-130

Data of the (pi(+), pi(-)) reaction on Te-128 and Te-130 at T-pi = 48 MeV are presented, which constitute also the first observation of pion ic 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 degrees a nd a ratio of sigma(Te-130)/sigma(Te-128) = 1.5(-0.8)(+1/8). The exper imental results and their impact on the understanding standing of the beta beta decay of the Te isotopes are discussed within the framework of recent proton-neutron quasiparticle random phase approximation calc ulations. For the transitions to the double isobaric analog states in Xe-128 and Xe-130 we obtain cross sections in the range 1 mu b/sr whic h fit very well into a systematics, that is in accordance with a domin ance of the short-range part of the DCX operator in analog transitions at low pion energies.