Fragment production in intermediate energy heavy ion reactions.

Abstract

The emission of intermediate rapidity fragments with Aless than or equal to14 has been studied in 42 to 151 MeV/nucleon Ar- and Ne-induced reactions on Al, Ca, and Au targets. The energy spectra were fitted assuming emission from a single source moving with a velocity intermediate between that of the projectile and target. The extracted temperatures were independent of fragment mass, indicating that the fragments had a common source. The spectra for fragments as heavy as nitrogen were also well described using the coalescence model and the resulting coalescence radii were independent of fragment mass. The observed fragment production cross sections were fitted with a quantum statistical model from which the entropy produced was extracted. This entropy was found to be much less than that derived from d/p ratios and higher than the entropy displayed by target-like fragments. The light particle spectra were compared to a model utilizing a solution of the Boltzmann equation incorporating mean field and Pauli blocking effects to describe the proton spectra from Ar + Ca. Nuclear fluid dynamics calculations agreed reasonably well with the higher energy data but could not describe the 42 MeV/nucleon data.