Particle-hole strength excited in the 48Ca(p,n)48Sc reaction at 134 and 160 MeV: ( pi f7/2, nu f7/2-1) band.

Abstract

The $^{48}\mathrm{Ca}$(p,n${)}^{48}$Sc reaction was studied at 134 and 160 MeV. Neutron energy spectra were measured by the time-of-flight technique with resolutions from 320 to 460 keV at 11 angles from 0\ifmmode^\circ\else\textdegree\fi{} to 60\ifmmode^\circ\else\textdegree\fi{} spaced approximately 6\ifmmode^\circ\else\textdegree\fi{} apart. The neutron spectra reveal strong excitation of the (\ensuremath{\pi}${f}_{7/2}$,\ensuremath{\nu}${f}_{7/2}^{\mathrm{\ensuremath{-}}1}$) band of states at low excitation energies; five of the known eight members of the band are excited strongly, generally consistent with distorted-wave-impulse-approximation calculations with 1f-2p shell-model wave functions. The normalization of the distorted-wave-impulse-approximation calculations to the extracted angular distributions at 135 MeV vary from 0.40 for the ${5}^{+}$ state to 0.93 for the ${0}^{+}$, isobaric analog state. The normalization factor of 0.60 required for the ${7}^{+}$, stretched-state transition is significantly larger than those required for similar distorted-wave-impulse-approximation calculations of various stretched-state excitations observed in inelastic proton scattering, which involve promoting a nucleon up into the next major shell (a ``1 \ensuremath{\Elzxh}\ensuremath{\omega}'' excitation). The larger normalization factor required for the (\ensuremath{\pi}${f}_{7/2}$,\ensuremath{\nu}${f}_{7/2}^{\mathrm{\ensuremath{-}}1}$) ${7}^{+}$ excitation (a ``0 \ensuremath{\Elzxh}\ensuremath{\omega}'' excitation) indicates that this strength is more highly concentrated in a single state. The ${4}^{+}$ and ${6}^{+}$ states of this band are observed to be only weakly excited, consistent with predictions that transitions dominated by the tensor term of the nucleon-nucleon interaction will predominantly excite non-normal parity states. The excitation of the ${2}^{+}$ member of this band shows both \ensuremath{\Delta}l=0 and \ensuremath{\Delta}l=2 contributions to the angular distribution and may indicate significant two-step processes for this transition.