Prevalence of Fission and Evaporation in the Decay of Heavy Nuclei Excited up to 1000 MeV with Energetic Antiprotons

Abstract

Annihilation of 1.2 GeV antiprotons has been explored as a means to generate high thermal excitation in heavy nuclei (U, Au, Ho) and to observe their decay with a minimal contribution from dynamical distortion. Conventional fission and heavy residue formation are found to dominate the decay up to ${E}^{*}\ensuremath{\approx}1000\mathrm{MeV}$. Both modes are increasingly accompanied by a modest emission of intermediate-mass fragments (up to 1 on average), but true multifragmentation is not observed. These features are in agreement with the predictions of the statistical model with no need for a fission delay ${\ensuremath{\tau}}_{f}>0.5\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}21}\mathrm{s}$.