Low-lying structures in the Gamow-Teller strength functions for the double-beta-decaying nuclei sup 76 Ge, sup 82 Se, sup 128 Te, and sup 130 Te

Excitation-energy distributions of transition strength to 1{sup +} states excited via the ({ital p},{ital n}) reaction at 134.4 MeV on targets of {sup 76}Ge, {sup 82}Se, {sup 128}Te, and {sup 130}Te were measured for excitation energies up to 25 MeV. Structures observed in the neutron spectra with forward-peaked ({Delta}{ital L}=0) angular distributions were identified as 1{sup +} states, except for the isobaric analog transitions. The total 1{sup +} strength in these reactions was extracted by normalizing the intensity in the 1{sup +} peaks to the Fermi transition strength observed in the isobaric analog state. The Gamow-Teller strength observed in 1{sup +} peaks above a fitted polynomial background is typically 55% of the sum rule obtained by assuming that the strength of {beta}{sup +} transitions is negligible. The portion of this strength found at excitation energies less than that of the Gamow-Teller giant resonance varied from 15% for {sup 128}Te to 38% for {sup 76}Ge. Experimental results are compared with predictions of a shell model that includes a pairing force and a long-range Gamow-Teller force in both parent and daughter nuclei. A comparison of the strength functions of the tellurium isotopes is made; this comparison is relevant in determining whether double-betamore » decay without neutrino emission (0{nu} decay) is observed in these isotopes.« less