Reaction Dynamics and Multifragmentation in Fermi Energy Heavy Ion Reactions

Abstract

The reaction systems, 64Zn + 58Ni, 64Zn + 92Mo, 64Zn + 197Au, at 26A, 35A and 47A MeV, have been studied both in experiments with a 4$\pi$ detector array, NIMROD, and with Antisymmetrized Molecular Dynamics model calculations employing effective interactions corresponding to soft and stiff equations of state (EOS). Direct experimental observables, such as multiplicity distributions, charge distributions, energy spectra and velocity spectra, have been compared in detail with those of the calculations and a reasonable agreement is obtained. The velocity distributions of $\alpha$ particles and fragments with Z >= 3 show distinct differences in calculations with the soft EOS and the stiff EOS. The velocity distributions of $\alpha$ particle and Intermediate Mass Fragments (IMF's) are best described by the stiff EOS. Neither of the above direct observables nor the strength of the elliptic flow are sensitive to changes in the in-medium nucleon-nucleon (NN) cross sections. A detailed analysis of the central collision events calculated with the stiff EOS revealed that multifragmentation with cold fragment emission is a common feature predicted for all reactions studied here. A possible multifragmentation scenario is presented; after the preequilibrium emission ceases in the composite system, cold light fragments are formed in a hotter gas of nucleons and stay cold until the composite system underdoes multifragmentation. For reaction with 197Au at 47A MeV a significant radial expansion takes place. For reactions with 58Ni and 92Mo at 47A MeV semi-transparency becomes prominent. The differing reaction dynamics drastically change the kinematic characteristics of emitted fragments. This scenario gives consistent explanations for many existing experimental results in the Fermi energy domain.

34 pages, 43 figures

References in corpus (7)

• Transverse momentum analysis of collective motion in relativistic nuclear collisions
• Constraint Molecular Dynamics approach to Fermionic systems
• Compatibility of localized wave packets and unrestricted single particle dynamics for cluster formation in nuclear collisions
• Proton Differential Elliptic Flow and the Isospin-Dependence of the Nuclear Equation of State
• Imaging Sources with Fast and Slow Emission Components
• A "Little Big Bang" Scenario of Multifragmentation
• Limitation of energy deposition in classical N body dynamics

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• Experimental Determination of In-Medium Cluster Binding Energies and Mott Points in Nuclear Matter
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• Bimodality as a signal of Liquid-Gas phase transition in nuclei?
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• Relevance of equilibrium in multifragmentation
• Short timescale behavior of colliding heavy nuclei at intermediate energies
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• Experimental reconstruction of primary hot isotopes and characteristic properties of the fragmenting source in the heavy ion reactions near the Fermi energy
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• Multifragmentation and the liquid-gas phase transition: an experimental overview
• Experimental determination of the quasi-projectile mass with measured neutrons
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