The influence of fission on the fragmentation of relativistic 208Pb and 238U projectiles in peripheral collisions

The projectile fragmentation in peripheral nuclear collisions was studied using ≈ 1 GeV·A of ²⁰⁸Pb and ²³⁸U from the SIS at GSI, impinging on a copper target. Lead and thallium isotopes from the fragmentation of ²⁰⁸Pb as well as uranium and protactinium isotopes from ²³⁸U, were selected by the fragment separator FRS. In contrast to the fragmentation of ²⁰⁸Pb, the cross sections for the production of heavy fragments from ²³⁸U are strongly reduced by fission. The measured isotopic yields may be explained quantitatively by calculations in the framework of the abrasion-ablation model, if fission is allowed to compete with particle evaporation in the deexcitation of the prefragments.