Fragment kinetic energies and modes of fragment formation

Kinetic energies of light fragments (A less than or equal to 10) from the d ecay of target spectators in Au-197 + Au-197 collisions at 1000 MeV per nuc leon have been measured with high-resolution telescopes at backward angles. Except for protons and apart from the observed evaporation components, the kinetic-energy spectra exhibit slope temperatures of about 17 MeV, indepen dent of the particle species, but not corresponding to the thermal or chemi cal degrees of freedom at breakup. Tt is suggested that these slope tempera tures may reflect the intrinsic Fermi motion and thus the bulk density of t he spectator system at the instant of becoming unstable.