Isospin Dependent Nucleon-nucleon Cross Section Research Articles

Covariance analysis of an isospin-dependent probe**Supported by National Natural Science Foundation of China (10905041) and the Hujiang Foundation of China (B14004)

Based on a modified quantum molecular dynamics model, we calculate the neutron-proton ratio and the nuclear stopping of reaction systems with different symmetry potentials and collision cross sections. We perform correlations of several probes using the covariance data processing method. It is shown that the correlation between the nuclear stopping and the isospin-dependent nucleon-nucleon cross sections is strong, but the nuclear stopping and symmetry potentials have a weak correlation. The correlation between neutron-proton ratio and symmetry potentials in the case of low energy is stronger. The correlation between neutron-proton ratio and isospin-dependent collision cross sections is enhanced with the increase of energy, but remains weak. In addition, the correlations of the emission numbers of the deuteron with the symmetry potentials and collision cross sections at different beam energies are not obvious compared to two prior physical quantities. In this paper, we define a parameter to quantitatively describe the sensitivity of isospin-dependent probes. By analyzing this parameter, one can extract more information about the isospin effects of the physical quantity.

Nucleon Emission Number as a Probe of Isospin-Dependent N—N Cross Section in Photonuclear Reactions

Based on the modified isospin-dependent quantum molecular dynamics model, the number of emitted nucleons in a photonuclear reaction is studied with different symmetry potentials and different isospin-dependent nucleon-nucleon (N—N) collision cross sections. It is found that the number of emitted nucleons is sensitive to the isospin-dependent nucleon-nucleon cross section when the photon's energy is higher than 150MeV, while it is insensitive to symmetry potential. The number of emitted neutrons is more sensitive to N—N collision cross sections than that of protons. It is realized that the number of emitted neutrons can be used as a sensitive probe to extract the information of the isospin-dependent N—N cross section at high energy photonuclear reactions.

Symmetry energy and nucleon-nucleon cross sections

The extension of the Boltzmann-Uehling-Uhlenbeck model of nucleus-nucleus collision is presented. The isospin-dependent nucleon-nucleon cross sections are estimated using the proper volume extracted from the equation of state of the nuclear matter transformed into the form of the Van der Waals equation of state. The results of such simulations demonstrate the dependence on symmetry energy which typically varies strongly from the results obtained using only the isospin-dependent mean-field. The evolution of the n/p multiplicity ratio with angle and kinetic energy, in combination with the elliptic flow of neutrons and protons, provides a suitable set of observables for determination of the density dependence of the symmetry energy. The model thus provides an environment for testing of equations of state, used for various applications in nuclear physics and astrophysics.

Isospin-dependent nucleon-nucleon cross section and the collective flow of nucleons in heavy-ion collision at intermediate energy

In this paper, the influences of the different forms of nucleon-nucleon (NN) cross sections on the rapidity distributions and the in-plane flows of nucleons in reactions 60Ca+60Ca and 60Ni+60Ni are studied by using IBUU04 transport model with the moment-dependent symmetry potential. The calculation results indicate that (1) the discrepancies of the rapidity distributions and in-plane flows corresponding to different forms of NN cross sections are large, (2) the sensitivity of the in-plane flow to the NN cross section still holds when the new form of moment-dependent symmetry energy is adopted, and (3) the influence of the N/P ratio of reaction systems on the transverse flow calculated with a certain NN cross section is more obvious when the incident energy is near the balance energy.

Isospin effect of nucleon-nucleon cross section on the isoscaling parameter α

The isospin effects of isoscaling parameter α on the nucleon-nucleon cross section are investigated for two couples of central nuclear reactions 40C+ 40Ca with 60Ca + 40Ca and 112Sn+ 112Sn with 124Sn+ 124Sn within an isospin dependent quantum molecular dynamics. It is found that the isospin effect of isoscaling parameter α on the isospin dependent nucleon-nucleon cross section σmedNN(αm) compared with that on the isospin independent nucleon-nucleon cross sections σ1NN(αm) is very obvious. However, the isospin effect of isoscaling parameter α on σmedNN(αm) compared with that on the isospin independent nucleon-nucleon cross section σ2NN(αm) is small. The mechanisms for the above difference are investigated in detail.

Medium Influence of the Nucleon-Nucleon Cross Section on theFragmentation

Based on an isospin-dependent quantum molecular dynamics model westudied the influence of a medium correction of an isospin-dependentnucleon-nucleon cross section on the fragmentation at the intermediateenergy heavy-ion collisions. We found that the medium correction froman isospin-dependent nucleon-nucleon cross section increases thedependence of the fragmentation on the isospin effect of in-mediumnucleon-nucleon cross section, at the same time, the momentum-dependentinteraction also produces an important role for enhancing theinfluence of the medium correction on the isospin effect of two-bodycollisions in the fragmentation process.