Identification of 4(-) states in the 14C(p,n)14N reaction at 135 MeV.

Abstract

Neutron time-of-flight spectra were measured for the $^{14}\mathrm{C}$(p,n${)}^{14}$N reaction at 135 MeV with the beam-swinger system at the Indiana University Cyclotron Facility. Excitation-energy spectra and differential cross sections for the observed excitations in this reaction were extracted over the momentum transfer range from 0 to 2.5 ${\mathrm{fm}}^{\mathrm{\ensuremath{-}}1}$. The goal of this work is to identify the ${4}^{\mathrm{\ensuremath{-}}}$ states in $^{14}\mathrm{N}$ and to determine the isovector transition strengths. The identification of the ${4}^{\mathrm{\ensuremath{-}}}$ states is based on comparisons of the theoretical differential cross sections, performed in a DWIA formalism, with the experimental cross sections and with information from the $^{14}\mathrm{C}$(e,e') reaction. Isospin assignments are based primarily on comparisons of the measured (p,n) and (e,e') isovector strengths. Candidate ${4}^{\mathrm{\ensuremath{-}}}$ states are identified at excitation energies of 8.49 MeV (T=0), 13.76 MeV and 19.49 MeV (T=1), and 26.61 MeV (T=2) in the $^{14}\mathrm{C}$(p,n${)}^{14}$N reaction, and the isovector strengths for the transitions leading to these states re extracted. The observed excitation energies and isovector strengths are in good agreement with the analog T=1 and T=2 ${4}^{\mathrm{\ensuremath{-}}}$ states observed in the (e,e') reaction. The experimental results are compared with results from shell-model calculations.