Nuclear structure of the spin-isospin excited states inN13studied via the(He3,t)and(He3,tp)reactions at450MeV

Abstract

Spin-isospin excitations in $^{13}\mathrm{N}$ have been studied by means of the $(^{3}\mathrm{He},t)$ and $(^{3}\mathrm{He},tp)$ reactions at a bombarding energy of $E(^{3}\mathrm{He})=450\phantom{\rule{0.3em}{0ex}}\mathrm{MeV}$. The zero-degree $(^{3}\mathrm{He},t)$ spectrum is found to be similar to those from the $(p,n)$ reactions at intermediate energies, suggesting a simple direct reaction mechanism at $E(^{3}\mathrm{He})=450\phantom{\rule{0.3em}{0ex}}\mathrm{MeV}$. The Gamow-Teller $(\mathrm{GT})$ states with ${J}^{\ensuremath{\pi}}=1∕{2}^{\ensuremath{-}}$ and $3∕{2}^{\ensuremath{-}}$ have been strongly excited at ${\ensuremath{\theta}}_{\mathrm{lab}}=0\ifmmode^\circ\else\textdegree\fi{}$. The angular distribution of cross sections for the $^{13}\mathrm{C}(^{3}\mathrm{He},t)^{13}\mathrm{N}$ reaction and the elastic $^{3}\mathrm{He}$ scattering off $^{13}\mathrm{C}$ were obtained at ${\ensuremath{\theta}}_{\mathrm{lab}}=0\ifmmode^\circ\else\textdegree\fi{}--17\ifmmode^\circ\else\textdegree\fi{}$ and at ${\ensuremath{\theta}}_{\mathrm{lab}}=2\ifmmode^\circ\else\textdegree\fi{}--22\ifmmode^\circ\else\textdegree\fi{}$, respectively. The obtained experimental results were compared with calculations performed in distorted-wave Born approximation. Microscopic structures of the states in $^{13}\mathrm{N}$ have further been studied by observing decay protons in coincidence with high-energy tritons measured at ${\ensuremath{\theta}}_{\mathrm{lab}}=0\ifmmode^\circ\else\textdegree\fi{}$. The branching ratios for proton decay from the $\mathrm{GT}$ states in $^{13}\mathrm{N}$ to the final low-lying $T=0$ states in $^{12}\mathrm{C}$ were obtained. The wave functions of the excited states in $^{13}\mathrm{N}$ are discussed on the basis of obtained experimental data and relevant theoretical calculations.