Fusionlike reactions of 40Ar up to 1.36 GeV: Prethermalization and postthermalization particles and fragments.

Abstract

Heavy residual nuclei are shown to result from the most violent (i.e., central) collisions for {sup 40}Ar + Ag reactions of up to 1.36 GeV; their average velocities are {approx_gt}80{percent} of the c.m. velocity. Angular and energy distributions for {sup 1,2,3}H, {sup 3,4}He, and Li are measured in coincidence with these heavy nuclei. The dominant light particle components are nearly isotropic in a frame of reference having the velocity of the heavy residues. In addition there are forward-peaked high-energy components of the H, He, and Li emission attributable to prethermalization emission. Fractional abundances of these prethermalization components increase markedly with increasing incident energy. Mass and momentum balance preclude the presence of a projectilelike fragment and thus indicate fusionlike reactions with large but incomplete linear momentum transfer. The remainder of the momentum is carried away by the spray of forward-peaked ejectiles. For 1.36 GeV {sup 40}Ar {approximately}1/2 of the 900 MeV available is completely thermalized, and {approximately}1/2 goes into prethermalization emission after strong collisional mixing. {copyright} {ital 1996 The American Physical Society.}