Gamow-Teller strength inFe54andFe56

Through a sequence of large scale $0\hslash \omega$ shell model calculations, Gamow-Teller strengths ($S_{+}$ and $S_{-}$) in ${}_{}{}^{54}{}_{}{}^{}\mathrm{Fe}$ and ${}_{}{}^{56}{}_{}{}^{}\mathrm{Fe}$ are obtained. They reproduce the experimental values by quenching the $\sigma \tau$ operator through the standard factor of 0.77. Comparisons are made with recent shell model Monte Carlo calculations. Results are shown to depend critically on the interaction. It is argued that the experimental data contain enough strength in the region above the resonance to make them consistent with the $3(N-Z)\mathrm{}$ sum rule.