Particle-particle coincidence measurements for 1,2,3H and 4He in the reaction 480 MeV 56Fe+natAg.

Particle-particle coincidence measurements have been made between light charged particles (/sup 1,2,3/H and /sup 4/He) produced in the reaction (8.5 MeV/nucleon) /sup 56/Fe+/sup nat/Ag. This coincidence requirement emphasizes central collisions leading to evaporation residues. Average multiplicities are found to be approximately three alphas and approximately four protons per evaporation residue; these values imply that approximately (1/2 the initial excitation energy of about 211 MeV is evacuated from the evaporation residues by these particles. This fractional energy evacuation by charged particles is considerably larger than that found for the similar reaction (8.5 MeV/nucleon) /sup 40/Ar+/sup nat/Ag. In both reactions the effective emission barriers for /sup 1/H and /sup 4/He (as deduced from the energy spectra) are found to be significantly lower than corresponding empirical fusion barriers between cold nuclei. This is particularly surprising for emitter nuclei that survive fission.