The masses and kinetic energies of coincident heavy fragments emitted from a ${}_{}{}^{239}{}_{}{}^{}\mathrm{U}$ target bombarded with 11.5-GeV protons were measured as a function of the angle between the fragments. Fragments with nearly equal and opposite laboratory momenta are observed with a total mass as low as ∼ ½ that of the target and higher kinetic energy than expected from fission, providing evidence for a new reaction mechanism.

• Received 23 July 1979

DOI:https://doi.org/10.1103/PhysRevLett.43.1080