  Heavy nuclei bombarded with protons and deuterons in the 1 GeV range have a
large probability of undergoing a process of evaporation and fission; less
frequently, the prompt emission of few intermediate-mass fragments can also be
observed.
  We employ a recently developed microscopic approach, based on the
Boltzmann-Langevin transport equation, to investigate the role of mean-field
dynamics and phase-space fluctuations in these reactions.
  We find that the formation of few IMF's can be confused with asymmetric
fission when relying on yield observables, but it can not be assimilated to the
statistical decay of a compound nucleus when analysing the dynamics and
kinematic observables: it can be described as a fragmentation process initiated
by phase-space fluctuations, and successively frustrated by the mean-field
resilience. As an extreme situation, which corresponds to non-negligible
probability, the number of fragments in the exit channel reduces to two, so
that fission-like events are obtained by re-aggregation processes.
  This interpretation, inspired by nuclear-spallation experiments, can be
generalised to heavy-ion collisions from Fermi to relativistic energies, for
situations when the system is closely approaching the fragmentation threshold.
