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

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*≈1000MeV. 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 τf>0.5×10^-21s.