Στ+ Strength in Nuclei

The sigmatau/sub +/ strength function is studied with the quasiparticle random phase approximation. The residual interaction modifies the pairing theory strength function in two ways. The particle-hole interaction reduces the overall strength by about a factor of 2, without shifting strength between different levels. The particle-particle interaction does not affect the overall strength, but shifts part of the strength from the lowest excitation to a higher excitation energy region. By comparing the theory with the observed log(ft) values of the ..beta../sup +/ decay in medium heavy nuclei, we find that an additional quenching is required for the sigmatau/sub +/ mode, similar in magnitude to the additional quenching present in other isovector spin-flip transitions. Finally, we predict that there is a large concentration of the sigmatau/sub +/ strength at higher excitation energy which cannot be observed by the ..beta../sup +/ decay.