DOUBLE GIANT-DIPOLE RESONANCE IN THE (PI-, PI+) REACTION

The double isovector giant dipole state has been observed in the (pi-, pi+) DELTA-T(z) = +2 double-charge-exchange reaction on C-13, Al-27, Ca-40, Fe-56, Co-50, and Nb-93. The resonances observed in the (pi-, pi+) reaction are closely related via Coulomb displacement energy and isospin symmetry to the resonances measured in the inverse (pi+, pi-) reaction on the same nuclei. The new observations provide a direct determination of the upper isospin component of the double giant dipole state, which is generally very weak in the (pi+, pi-) reaction. The comparison between the double dipole in the two double-charge-exchange modes gives valuable information on the isospin splitting and the Pauli-blocking effects for isotensor transitions.