Fragment Production in Intermediate Energy Heavy Ion Reactions.
The emission of fragments with A (LESSTHEQ) 14 has been studied in intermediate energy argon and neon -induced reactions. The energy spectra were observed to be approximately Maxwellian and the high energy region was fitted assuming emission from a single moving source. The source was found to move with a velocity intermediate between that of the projectile and the target, and its temperature was approximately independent of the mass of the emitted fragment, suggesting that complex fragments as well as light particles are emitted from a thermalized subsystem in the reaction. A quantum statistical model of the disassembly of the thermalized region was used to infer information about the entropy of the system from the observed fragment distribution. This method yields lower values for the entropy per nucleon than derived from the production of protons and deuterons alone. The entropy extracted from target-like fragments observed in other experiments was found to be lower than the entropy from intermediate rapidity fragments, and was independent of the projectile energy. The complex fragment spectra through nitrogen were also well described by the coalescence model, yielding source radii of 4.5-5.5 fm, in agreement with experiments measuring two-proton correlations. The light particle data were used to test two models for the collision dynamics. A solution of the Boltzmann equation, incorporating a mean field and Pauli blocking as well as two-nucleon collisions, described the proton spectra from Ar + Ca for bombarding energies as low as 42 MeV/A. A conventional intranuclear cascade model, developed for high energy collisions, was unable to reproduce the data, underlining the importance of nuclear mean field and Pauli blocking effects in this energy regime. Nuclear fluid dynamical calculations were also compared with the data. The agreement was fair above 100 MeV/nucleon, but the model did not describe the lower energy data.
- Pub Date:
- Physics: Nuclear