Mechanisms of non-equilibrium light-particle emission in ³²S + Ag reactions at 30 A · MeV

Energy spectra of light charged particles (Z = 1,2) observed at θ_LP = 5°-150° in coincidence with fragments of Z = 5-14 at θ_F = ±9° are examined. The fragment-energy spectra show two components, one with a projectile-like velocity and another with a much lower velocity. Light particles in coincidence with fragments of projectile-like velocity show a very strong left-right asymmetry in the forward hemisphere. At very forward angles the asymmetry is essentially dominated by a recoil effect of the ejectile emitted from the fragment. The asymmetry at intermediate angles (27°≤ θ ≤ 60°) shows a strong dependence on the charge of the fragments and the asymmetry is similar among those for the composite particles, whereas the asymmetry is much smaller for protons. Light particles in coincidence with the lower-energy component of the fragment spectra show much less asymmetry. For such fragments α-particle energy spectra are reproduced without an intermediate-velocity source of high apparent temperature, whereas this high temperature source is needed for the proton spectra. These facts may indicate that the dominant emission mechanism of the intermediate-velocity protons and α-particles is different. Possible mechanisms for the production of these particles are discussed.