Gamow-Teller strength in the 54Fe(p,n)54Co reaction at 135 MeV.

Abstract

The $^{54}\mathrm{Fe}$(p,n${)}^{54}$Co reaction was studied at 135 MeV by the time-of-flight technique. Neutrons were detected with an energy resolution of 245 keV in large-volume, mean-timed counters at a flight path of 125 m. The forward-angle spectra are dominated by the excitation of ${1}^{+}$ states with characteristic \ensuremath{\Delta}l=0 angular distributions peaked at 0\ifmmode^\circ\else\textdegree\fi{}. The strengths of the ${1}^{+}$ excitations are interpreted as being equivalent to Gamow-Teller (GT) strengths excited in beta decay. This strength is observed to be highly fragmented; GT strength is identified in more than 30 states. The B(GT-) strength is obtained relative to the Fermi strength B(F) assumed to be concentrated in the ${0}^{+}$, isobaric-analog ground state. The total B(GT-) strength observed in discrete states, combined with the B(GT+) strength obtained from the (n,p) reaction, yields a lower limit of 48 percent of the 3(N-Z) sum rule. Inclusion of \ensuremath{\Delta}l=0 strength in the background and continuum above a quasifree scattering background increases this lower limit to 73 percent. If one considers the \ensuremath{\Delta}l=0 strength observed in the full background and continuum up to ${\mathit{E}}_{\mathit{x}}$=25 MeV, the entire sum rule may be satisfied. The observed distribution of GT strength is in good agreement with a truncated 1f-2p shell-model calculation.