Concentrated Particle-Hole Strength Observed in0ℏωStretched-State Excitations

The wide-angle spectra of the 134-MeV ($p$, $n$) reaction on ${}_{}{}^{48}{}_{}{}^{}\mathrm{Ca}$, ${}_{}{}^{54}{}_{}{}^{}\mathrm{Fe}$, ${}_{}{}^{88}{}_{}{}^{}\mathrm{Sr}$, and ${}_{}{}^{208}{}_{}{}^{}\mathrm{Pb}$ are each dominated by the excitation of a single state at low excitation energy. These excitations correspond to the $``0\mathrm{}\hslash \omega "$ stretched states and are seen to be fragmented much less than $``1\mathrm{}\hslash \omega "$ stretched states in medium- and heavy-mass nuclei. The normalization factors required for comparison with distorted-wave impulse-approximation calculations are >0.50 and indicate that these are the purest particle-hole states known in these nuclei.