A velocity spectrum of neutral sputtered particles as well as a low resolution mass spectrum of sputtered molecular ions has been measured for4.74 MeV 19F+2 incident on UF4. The velocity spectrum is dramatically different from spectra taken with low energy (keV) bombarding ions, and is shown to be consistent with a hot plasma of atoms in thermal equilibrium inside the target. We propose a "thermalized ion explosion" model for high energy sputtering which is also expected to describe track formation in dielectric materials. The model is shown to be consistent with the observed total sputtering yield and the dependence of the yield on the primary ionization rate of the incident ion.
