Shadowing of sequential α-emission in deep-inelastic 32S + 93Nb collisions: A new probe of fragment lifetimes

Abstract

Abstract Energy and angular distributions of products with 3⩽Z⩽22 from 32S + 93Nb reactions at 10 MeV/N were measured and the cross section for deep-inelastic reactions was deduced. Energy and angular correlations between α-particles and deep-inelastic fragments were measured and analysed in terms of sequential emission from the detected projectile-like fragment ( M α = 0.30± 0.06) and sequential emission from the target-like fragment α = 0.90±0.10). For sequential emission from the target-like fragment shadowing was observed due to the proximity of the two fragments at the time of emission. Three-body Coulomb trajectory (TBCT) calculations give a lifetime of (1–3)×10 −21 s for the target-like fragment, in good agreement with statistical-model calculations. It is shown that the shadow effect is sensitive to the charge/size of the projectile-like fragment as predicted by the TBCT calculations. In the forward hemisphere nonsequential emission of beam-velocity α-particles is observed α = 0.20±0.06). At backward angles another component is observed α = 0.05±0.01) which appears to be emission from the neck region of the scissioning fragments. It is shown that the two nonsequential emission processes have a different dependence on the exit-channel mass split.