Evidence for Nucleon Clustering from High-Energy Reactions

The telescope method was used with solid-state detectors for measuring angular and energy distributions of complex particles emitted in nuclear reactions induced by 157-MeV protons on heavy nuclei (Ag, Au, Bi, Th). Both an isotropic and a forward-peaked emission of ${}_{}{}^4{}_{}{}^{}\mathrm{He}$, tritons, and deuterons were observed. Yields of ${}_{}{}^3{}_{}{}^{}\mathrm{He}$ were found to be very low at the back angles. The components of the above particle spectra emitted at forward angles are interpreted in terms of a direct-interaction mechanism on "$\alpha$ clusters" in the surface, and a Monte Carlo calculation was performed to compute the yield of "$\alpha$ clusters" knocked out by prompt cascade nucleons. The tritons and ${}_{}{}^3{}_{}{}^{}\mathrm{He}$ particles might partly be ejected by a double pickup process, partly by a stripping mechanism on "$\alpha$ clusters."