Forward-angle spectra of $\alpha$ particles inelastically scattered from heavy nuclei at incident energies up to 90 MeV are found to exhibit a broad but conspicous plateau. The integrated cross section of this plateau constitutes about 25% of the total ($\alpha ,{\alpha }^{\prime }$) cross section at an incident energy of 65 MeV. The total ($\alpha ,{\alpha }^{\prime }$) cross section is, in turn, about $\frac{1}{6}$ of the total reaction cross section. It is suggested that nucleon pickup (to form the unstable nuclei${}_{}{}^5{}_{}{}^{}\mathrm{He}$ and ${}_{}{}^5{}_{}{}^{}\mathrm{Li}$) may be responsible for a portion of the plateaulike structure in the observed spectra.

• Received 10 May 1971

DOI:https://doi.org/10.1103/PhysRevLett.27.434