Studies of 4He/1H emission in fission and deeply inelastic reactions of 485-MeV 56Fe with 197Au

Emission of 4He and 1H has been studied in reactions of 485-MeV 56Fe + 197Au. The light charged particles were measured both in singles and in coincidence with heavy products of deeply inelastic and fission reactions. Experimental detection capabilities were greatly enhanced through the use of two five-detector arrays for light charged particles, and two heavy fragment trigger detectors placed at symmetrically opposite angles with respect to the beam direction. Statistical model analyses of the data show that nearly all 4He/1H intensity is due to evaporation from energy equilibrated reaction products both in deeply inelastic and fission reactions. In deeply inelastic reactions, the observed 4He/1H emission can be attributed to evaporation from the post-scission reactant-like products, while in fusion-like fission reactions 4He/1H evaporation from pre- and post-scission sources are observed in roughly equivalent amounts. Angle-integrated multiplicities for 4He and 1H are deduced for each source of emission, and are compared with results from similar systems. The 4He/1H multiplicity ratios show no strong dependence on emitter spin, in contrast to simple expectations. Particle evaporation times are evaluated semi-quantitatively, based on relationships between estimated emitter lifetimes and experimental observations, and are compared to other characteristic timescales. Apparent reductions in 4He evaporation barriers can be explained by shape deformation of the composite system in fusion-like reactions, but for 1H emission the barrier lowering is too large to be reasonably characterized in this manner