Definitive measurements of negative 〈${\mathit{p}}_{\mathit{L}}$〉 in the projectile rest frame are carried out for isotopes produced by fragmentation of relativistic ${}_{}{}^{16}{}_{}{}^{}\mathrm{O}$ and ${}_{}{}^{12}{}_{}{}^{}\mathrm{C}$ nucleus projectiles. They are analyzed for the evidence of the dominant two-step diffractive excitation processes during the fragmentation. Average energies in the range of 100 MeV or less are explored and the decays of the excited states with lifetimes longer than ${10}^{\mathrm{-}21}$ s are investigated.

• Received 24 March 1992

DOI:https://doi.org/10.1103/PhysRevC.46.1495