Gamow-Teller and M1 strength in the 32S(p,n)32Cl reaction at 135 MeV.

Abstract

The $^{32}\mathrm{S}$(p,n${)}^{32}$Cl reaction was studied at 135 MeV by the time-of-flight technique. The overall energy resolution obtained was about 270 keV. 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 ${1}^{+}$ spectrum is described well by distorted-wave Born approximation calculations with full S-D shell-model wave functions and a normalization factor of 0.60. The strengths of the ${1}^{+}$ excitations are interpreted as being equivalent to Gamow-Teller strengths excited in beta decay. The (p,n) cross sections are converted to reduced transition probabilities, B(GT), by means of a ``universal'' relationship obtained from other nuclei where analog beta decay measurements are available. The general distribution and total strength so obtained are represented well by full S-D shell-model calculations with Gamow-Teller matrix elements adjusted to reproduce the strengths of Gamow-Teller beta decays of S-D shell nuclei. The ${1}^{+}$ (p,n) cross sections are interpreted also in terms of magnetic-dipole (M1) strength and compared with inelastic-electron scattering measurements of such strength in $^{32}\mathrm{S}$. The strength observed in individual states is seen to vary considerably between the two reactions; these differences are ascribed to orbital-current contributions in the electron-scattering reaction not present in the (p,n) reaction. The (p,n) measurements extend to higher excitation energies than the electron-scattering measurements.