New Progresses in Dynamics of Heavy-ion Collisions at Intermediate Energies
The characteristic properties of the fragmenting source and the mass dependence of the transverse flow in heavy-ion collisions at intermediate energies have been investigated by researchers of Nuclear Data Group at the Institute of Modern Physics, Chinese Academy of Sciences (IMP) in collaboration with the Cyclotron Institute, Texas A&M University. A new method to correct the system size effect of the temperature is proposed.
For the first time the primary hot isotope distributions are experimentally reconstructed for the reaction system 64Zn + 112Sn at 40 MeV/nucleon. The detailed process of the reconstruction method is presented. Using the self-consistent method, the density ρ/ρ0 = (0.63 ± 0.03), temperature T = (4.9 ± 0.2) MeV and symmetry energy coefficient asym = (24.7 ± 1.9) MeV are extracted. The results have been published in Phys. Rev. C 90, 044603 (2014).
An improved method is applied to the multifragmentation events calculated by using AMD model for 40Ca + 40Ca at 35 MeV/nucleon. In this method, the volume, surface, Coulomb and paring terms are removed from the free energy and only the symmetry and chemical potential are remained. The symmetry energy coefficient is then extracted by using the whole available isotopes which lead to more precise results. The temperature extracted with the improved method shows the mass dependence of fragments and is regarded as the final size effect. A method to correct the system size effect is proposed and a constant temperature is obtained after the correction. The results have been published in Phys. Rev. C90, 014605 (2014).
The mass dependence of the transverse flow in the reactions of 40Ca + 40Ca at 35 MeV/nucleon has been determined for emitted isotopes with Z =1 to 9. The observed flow is compared with that calculated by using a constrained molecular dynamics (CoMD) simulation. With the application of the appropriate experimental filter, the general trend of the experimental mass-dependent flow is well reproduced. The origin of mass dependence of the transverse flow is then studied with the collective thermal-interplay model (CTIM) by comparison with and without momentum conservation. The drastic difference between the results with and without momentum conservation strongly indicates that the momentum conservation plays an important role in the generation of the mass-dependent flow. The results have been published in Phys. Rev. C 90, 014604 (2014).
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Fig 1. Isotopic multiplicity distributions of experimental cold fragments (filled circles), reconstructed hot fragments (filled squares), and AMD primary hot fragments as a function of fragment mass number A for a given charge Z, which is indicated. AMD results are from the g0AS interaction.
Fig 2. Extracted T0 values as a function of Z. Open symbols are for the first round (k = 0) and closed symbols are for the final round (k = 0.007). Different symbols represent results with g0 (circles), g0AS (squares), and g0ASS (triangles) interactions.
Fig 3. Flow from unfiltered CoMD data at 300 fm/c as a function of particle mass number A. Circles and squares are results derived from the CTIM fits of CoMD flow with and without momentum conservation, respectively.