Using symmetric 112Sn+112Sn, 124Sn+124Sn collisions as references, we probe isospin diffusion in peripheral asymmetric 112Sn+124Sn, 124Sn+112Sn systems at an incident energy of E/A=50 MeV. Isoscaling analyses imply that the quasiprojectile and quasitarget in these collisions do not achieve isospin equilibrium, permitting an assessment of isospin transport rates. We find that comparisons between isospin sensitive experimental and theoretical observables, using suitably chosen scaled ratios, permit investigation of the density dependence of the asymmetry term of the nuclear equation of state.
Isotope, isotone and isobar yield ratios are utilized to obtain an estimate of the isotopic composition of the gas phase, i.e., the relative abundance of free neutrons and protons at breakup. Within the context of equilibrium calculations, these analyses indicate that the gas phase is enriched in neutrons relative to the liquid phase represented by bound nuclei.
Collisions of112 Sn and 124 Sn nuclei, which differ in their isospin asymmetry, provide information about the rate of isospin diffusion and equilibration. While several different probes can provide accurate diffusion measurements, the ratios of the mirror nuclei may be the simplest and most promising one. Ratios of the mass seven mirror nuclei yields are analyzed to show the rapidity, transverse momentum and impact parameter dependence of isospin diffusion. [4][5][6][7] for its determination. Recently, constraints on the density dependence of the symmetry energy were obtained from measurements of isospin diffusion in peripheral nuclear collisions [6,8]. In this paper, we identify a set of experimental observables, specifically observables constructed with yield ratios of mirror nuclei, that provide consistent measures of the isospin diffusion and extend those experimental investigations to a wider range of rapidity, transverse momentum and impact parameter.In a heavy ion collision involving a projectile and a target with different proton fractions, Z/A, the symmetry energy tends to propel the system towards isospin equilibrium so that the difference between neutron and proton densities is minimized [7].The isospin asymmetry A Z N − = δ of a projectile-like residue produced in a peripheral collision reflects the exchange of nucleons with the target; significant diffusion rates should lead to larger isospin asymmetries for collisions with neutron-rich targets and smaller isospin asymmetries for collisions with proton-rich targets [6].To isolate the isospin diffusion effects from similar effects caused by preequilibrium emission, Coulomb or sequential decays, relative comparisons involving different targets are important. In recent studies, isospin diffusion has been measured by "comparing" A+B collisions of a neutron-rich (A) nucleus and a proton-rich (B) nucleus to symmetric collisions involving two neutron-rich nuclei (A+A) and two proton-rich (B+B) nuclei under the same experimental conditions [6]. Non-isospin diffusion effects such as preequilibrium emission from a neutron-rich (A) projectile should be approximately the same for asymmetric A+B collisions as for symmetric A+A collisions. 2Similarly, non-isospin diffusion effects from a proton-rich (B) projectile in B+A collisions and B+B collisions should be the same.The degree of isospin equilibration can be quantified by rescaling the isospin asymmetry δ of a projectile-like residue from a specific collision according to the isospin transport ratio R i (δ) [6,9] given by ( )In the absence of isospin diffusion, the asymmetry B A+ δ of a residue of a neutron-rich projectile following a collision with a proton-rich target has the limiting values 1 ) (. On the other hand, if isospin equilibrum is achieved for roughly equal sized projectile and. By focusing on the differences in isospin observables between mixed and symmetric systems, R i (δ) largely removes the sensitivity to preequilibrium emission and enhances the sensitivity to isospin diffusion.Id...
Simultaneous measurement of both neutrons and charged particles emitted in the reaction 64 Zn + 64 Zn at 45 MeV/nucleon allows comparison of the neutron to proton ratio at midrapidity with that at projectile rapidity. The evolution of N/Z in both rapidity regimes with increasing centrality is examined. For the completely re-constructed midrapidity material one finds that the neutron-to-proton ratio is above that of the overall 64 Zn + 64 Zn system. In contrast, the re-constructed ratio for the quasiprojectile is below that of the overall system. This difference provides the most complete evidence to date of neutron enrichment of midrapidity nuclear matter at the expense of the quasiprojectile.
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