Prompt and sequential decay processes in the fragmentation of 40 MeV/nucleon Ne-20 projectiles

The fragmentation of E/A = 40 MeV Ne-20 projectiles into exit channels containing only p, d, t, He-3, alpha, He-6, Li-6, and Li-7 fragments has been investigated. Relative shifts between the average longitudinal velocity of each fragment type were measured with Sn-120 and Au-197 targets. A post-breakup Coulomb acceleration component of these shifts was isolated. Its magnitude indicates that the projectile broke up while in near contact with the target. On the other hand, correlations between projectile fragments indicate that a significant fraction of these fragments are produced by the sequential decay of long- and short-lived unstable intermediates. A fully sequential decay process, although consistent with the experimental relative angle distributions, fails to reproduce the correlation function. Thus, a picture emerges of a prompt breakup step producing stable and unstable particles with the subsequent decay of the latter extending over a long time period.