Spin-isospin strength distributions forfpshell nuclei: Results for theMn55(n,p),Fe56(n,p), andNi58(n,p) reactions at 198 MeV

Cross sections for the reactions ${}_{}{}^{55}{}_{}{}^{}\mathrm{Mn}$(n,p), ${}_{}{}^{56}{}_{}{}^{}\mathrm{Fe}$(n,p), and ${}_{}{}^{58}{}_{}{}^{}\mathrm{Ni}$(n,p) have been measured at an incident energy of 198 MeV, with protons observed over a range of energies corresponding to excitations of up to about 35 meV in the residual nuclei ${}_{}{}^{55}{}_{}{}^{}\mathrm{Cr}$, ${}_{}{}^{56}{}_{}{}^{}\mathrm{Mn}$, and ${}_{}{}^{58}{}_{}{}^{}\mathrm{Co}$, respectively. Measurements were carried out at center-of-mass angles between 1.6° and 19.9°. A multipole analysis of the results yielded the distribution of Gamow-Teller (GT) and spin-dipole strength for each target. The total GT strength below an excitation energy of 8.5 MeV was 1.7 units for ${}_{}{}^{55}{}_{}{}^{}\mathrm{Mn}$, 2.8 units for ${}_{}{}^{56}{}_{}{}^{}\mathrm{Fe}$, and 3.8 units for ${}_{}{}^{58}{}_{}{}^{}\mathrm{Ni}$. Shell model calculations of the GT strength distribution, carried out in a restricted vector space, show fair to good agreement with the data up to an excitation energy of 8.5 MeV, but overestimate the total strength by a factor of between 3 and 4.