Roles of Coulomb Interaction on Isospin Fractionation in Intermediate Energy Heavy Ion Collisions

As we know that in fact, nuclei offer an interesting isospin situation, where symmetry potential, Coulomb interaction and isospin dependent in-medium nucleon-nucleon collisions are simultaneously present. But, in general, the isospin effects of Coulomb interaction is not studied separately in more detail, even though the studies for the isospin effect of the isospin dependent mean field in the heavy ion collisions include automatically the role of Coulomb term. However the Coulomb interaction is an important asymmetry term, which can bring important isospin effect into the observable in the intermediate energy heavy ion collisions. The study for the role of Coulomb interaction on the isospin effects of observable in intermediate energy heavy ion collisions, is important for exploring isospin physics and setting up the equation of state for the isospin asymmetry nuclearmatter.

Effect of System Mass on Isospin Fractionation in Heavy Ion Collisions at Intermediate Energies

Based on the isospin dependent quantum molecular dynamics model(IQMD) we investigated the dependence of isospin fractionation degree (N/Z)n / (N/Z)Nfrag on the mass of system. The (N/Z)n and (N/Z)Nfrag are the neutron proton ratio of nucleon emission (gas phase) and that of fragment emission (liquid phase) respectively. We found that the isospin fractionation degree is a scnsitive function of system mass. The (N/Z)n/ (N/Z)Nfrag, reduces with increasing the mass of colliding system when neutron proton ratio of colliding system is fixed.

Isospin Effect of Coulomb Interaction on Nuclear Stopping in Intermediate Energy Heavy Ion Collisions

Nuclei offer an interesting isospin situation where symmetry potential, Coulomb term and isopin dependent nucleon-nucleon collisions are simultaneously present. However, in general, Coulomb potential is not studied in the heavy ion collisions. As we know that the Coulomb potential is an important asymmetry term which can bring important isospin effect into the observable in the intermediate energy heavy ion collisions. Recently extensions by Colonna et al.[1] to finite nuclei show that Coulomb and surface effects reduce instability regions. So in this paper the isospin effects of Coulomb term and symmetry potential on the nuclear stopping at intermediate energy heavy ion collisions are studied by using isospin-dependent quantum molecular dynamics model (IQMD).

Chemical Instability in Heavy Ion Collisions at Intermediate Energies

With the establishment of secondary beam facilities at many laboratories around the world, one can investi-gate the properties of nuclei very far from the β stability line and isospin degrees of freedom in nuclear reactions at wide energy ranges. It is also possible to explore the chemical instability of hot and isospin-asymmetric nuclear matter. A better agreement with the experimental data has been found in our recent study by means of an isospin dependent quantum molecular dynamics (IQMD) mode. Recently experiments really reported the isospin dependence of multifragment production in reactions of ^58Fe+^58Fe and ^58Ni+^58Ni at higher incident energ.y; These phenomena may be related to the chemical instability in HIC induced by neutron-rich nuclei and therefore it is a challenge for theoretical and experimental nuclear physicists to investigate the chemical instability in heavv ion collisions.

Effects of Impact Parameter on Isospin Fractionation in Heavy Ion Collision at Intermediate Energies

We calculated the degree of isospin fractionation (N/Z)n/(N/Z)Nfrag by using the isospin dependent quantum molecular dynamics model (IQMD), where (N/Z)n and (N/Z)Nfrag are the saturated neutron to proton ratio of nucleon emissions and that of the fragment emissions respectively. In general, the observable in nuclear reaction is very sensitive to impact parameter. So it is interesting to investigate the dependence of (N/Z)n/(N/Z)Nfrag on the impact parameter b. Fig.1 shows the value of (N/Z)n/(N/Z)Nfrag as a function of impact parameter b for four different cases:

Dependence of Isospin Fractionation on Beam Energy in Heavy Ion Collisions at Intermediate Energies

We investigated the dependence of isospin fractionation degree (N/Z)n/ (N/Z)Nfrag on the beam energy by using the isospin dependent quantum molecular dynamics model (IQMD). The (N/Z)n and (N/Z)Nfrag are the neutron proton ratio of nucleon emission (gas phase) and that of fragment emission (liquid phase) respectively. The calculated results show that (N/Z)n / (N/Z)Nfrag enhances with increasing the beam energy due to the increase of excitation energy of colliding system. But above properties is only occurred in the definiteenergy region.

Extension of Isospin Dependent Quantum Molecular Dynamics

Isospin dependent molecular dynamics (IQMD) has been used with success for studying isospin effects in heavy ion collisions at intermediate energies[1,2]. However, this model meets difficulty to study heavy ion collisions at low energies near Coulomb barrier since unsuitable dealing with the deformation, such as surface term induced by deformation during approaching projectile and target, which is not important at high energies, and it results in the calculated cross sections with IQMD which are much smaller than the experimental data at low energies. In this report, we propose a new method in which the surface term in the mean field is included in a proper way, the switch function method.

Isospin Effect of Charged Particle Multiplicity in Intermediate Energy Heavy Ion Collisions

The dependences of He and intermediate mass fragments (IMF) production rates in the reactions 55 MeV/u ^40Ar+^58,64 Ni on the isospin, impact parameter and primary excitation energy of the reaction nuclear system were studied by using the 4π charged particle multi-detector array system (MUDAL). For the mentioned two reaction systems, the measured He particle contribution in the total charged particle multiplicity increases with increasing the total charged particle multiplicity but for the contribution of IMFs in the total charged particle multiplicity increases with increasing the total charged particle multiplicity at lower total charged particle multiplicities, and latter on it drops down with further increasing of the total charged particle multiplicities (see Fig.l). The experimental results of these two reaction systems with the same nuclear charge indicate that the contribution of He and IMFs in the total charged particle multiplicities are obviously isospin dependent.