Isospin fractionation in the nucleon emissions and fragment emissions in the intermediate energy heavy ion collisions
Abstract The degree of isospin fractionation is measured by ( N / Z ) n /( N / Z ) N imf , where ( N / Z ) n and ( N / Z ) N imf are the saturated neutron–proton ratio of nucleon emissions (gas phase) and that of fragment emissions (liquid phase) in heavy ion collision at intermediate energy. The calculated results by using the isospin-dependent quantum molecular dynamics model show that the degree of isospin fractionation is sensitive to the neutron–proton ratio of colliding system but insensitive to the difference between the neutron–proton ratio of target and that of projectile. In particular, the degree of isospin fractionation sensitively depends on the symmetry potential. However, its dependences on the isospin dependent in-medium nucleon–nucleon cross section and momentum dependent interaction are rather weak. The nucleon emission (gas phase) mainly determines the dynamical behavior of the degree of isospin fractionation in the isospin fractionation process, compared to the effect of fragment emission. In this case, we propose that ( N / Z ) n /( N / Z ) N imf or ( N / Z ) n can be directly compared with the experimental data so that the information about symmetry potential can be obtained.
CONSTRAINING THE SKYRME EFFECTIVE INTERACTIONS AND THE NEUTRON SKIN THICKNESS OF NUCLEI USING ISOSPIN DIFFUSION DATA FROM HEAVY ION COLLISIONS
Recent analysis of the isospin diffusion data from heavy-ion collisions based on an isospin- and momentum-dependent transport model with in-medium nucleon-nucleon cross sections has led to the extraction of a value of L = 88 ± 25 MeV for the slope of the nuclear symmetry energy at saturation density. This imposes stringent constraints on both the parameters in the Skyrme effective interactions and the neutron skin thickness of heavy nuclei. Among the 21 sets of Skyrme interactions commonly used in nuclear structure studies, the 4 sets SIV, SV, Gσ, and Rσ are found to give L values that are consistent with the extracted one. Further study on the correlations between the thickness of the neutron skin in finite nuclei and the nuclear matter symmetry energy in the Skyrme Hartree-Fock approach leads to predicted thickness of the neutron skin of 0.22 ± 0.04 fm for 208Pb, 0.29 ± 0.04 fm for 132Sn, and 0.22 ± 0.04 fm for 124Sn.
Influence of electric fields on friction electrification between metals and borosilicate glass
Abstract In a cylindrical geometry, electric fields were applied through the entire contact area between the sliding metal and the glass surface. The maximum electric charges developed on the metal were measured and plotted against the applied voltage producing the field. The metals were high-purity nickel and gold. The borosilicate glass was Pyrex, brand 7740. The experiments with nickel, which has a work function greater than that of the glass, were performed in 10 −7 mm Hg vacuum. The experiments with gold, with a work function smaller than that of glass, were carried out in air at atmospheric pressure. The results show that: 1. 1) There is both asymmetry and a reversed slope portion in the charge vs. voltage plot. 2. 2) For a certain range of reversing fields, the electric charge developed on the nickel is always negative and the charge on gold is always positive.