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

Abstract

Cross sections for the reactions [sup 55]Mn([ital n],[ital p]), [sup 56]Fe([ital n],[ital p]), and [sup 58]Ni([ital n],[ital 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 [sup 55]Cr, [sup 56]Mn, and [sup 58]Co, respectively. Measurements were carried out at center-of-mass angles between 1.6[degree] and 19.9[degree]. 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 [sup 55]Mn, 2.8 units for [sup 56]Fe, and 3.8 units for [sup 58]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.