Collisions involving {112Sn} and {124Sn} nuclei have been simulated with the improved quantum molecular dynamics transport model. The results of the calculations reproduce isospin diffusion data from two different observables and the ratios of neutron and proton spectra. By comparing these data to calculations performed over a range of symmetry energies at saturation density and different representations of the density dependence of the symmetry energy, constraints on the density dependence of the symmetry energy at subnormal density are obtained. The results from the present work are compared to constraints put forward in other recent analyses.

%B Physical Review Letters %V 102 %P 122701 %8 03/2009 %G eng %0 Journal Article %J Physical Review Letters %D 2009 %T Survey of Excited State Neutron Spectroscopic Factors for Z=8-28 Nuclei %A M. B. Tsang %A Jenny Lee %A S. C. Su %A J. Y. Dai %A M. Horoi %A H. Liu %A W. G. Lynch %A S. Warren %XWe have extracted 565 neutron spectroscopic factors of sd and fp shell nuclei by systematically analyzing more than 2000 measured (d, p) angular distributions. We are able to compare 125 of the extracted spectroscopic factors to values predicted by large-basis shell-model calculations and evaluate the accuracies of spectroscopic factors predicted by different shell-model interactions in these regions. We find that the spectroscopic factors predicted for most excited states of sd-shell nuclei using the latest {USDA} or {USDB} interactions agree with the experimental values. For fp shell nuclei, the inability of the current models to account for the core excitation and fragmentation of the states leads to considerable discrepancies. In particular, the agreement between data and shell-model predictions for Ni isotopes is not better than a factor of 2 using either the {GXPF1A} or the {XT} interaction.

%B Physical Review Letters %V 102 %P 062501 %8 01/2009 %G eng %0 Journal Article %J Physics Letters B %D 2008 %T The influence of cluster emission and the symmetry energy on neutron-proton spectral double ratios %A Yingxun Zhang %A P. Danielewicz %A M. Famiano %A Li, Z. %A W. G. Lynch %A M. B. Tsang %XThe emissions of neutrons, protons and bound clusters from central {124Sn} + {124Sn} and {112Sn} + {112Sn} collisions are simulated using the Improved Quantum Molecular Dynamics model for two different density-dependent symmetry-energy functions. The calculated neutron-proton spectral double ratios for these two systems are sensitive to the density dependence of the symmetry energy, consistent with previous work. Cluster emission increases the double ratios in the low energy region relative to values calculated in a coalescence-invariant approach. To circumvent uncertainties in cluster production and secondary decays, it is important to have more accurate measurements of the neutron-proton ratios at higher energies in the center of mass system, where the influence of such effects is reduced.

%B Physics Letters B %V 664 %P 145–148 %8 02/2008 %G eng %0 Journal Article %J Physical Review C %D 2008 %T Transport Model Simulations of Projectile Fragmentation Reactions at 140 {MeV/nucleon} %A M. Mocko %A M. B. Tsang %A D. Lacroix %A A. Ono %A P. Danielewicz %A W. G. Lynch %A R. J Charity %K Nuclear Experiment %K Nuclear Theory %XThe collisions in four different reaction systems using {\$ˆ{40,48}\$Ca} and {\$ˆ{58,64}\$Ni} isotope beams and a Be target have been simulated using the Heavy Ion Phase Space Exploration and the Antisymmetrized Molecular Dynamics models. The present study mainly focuses on the model predictions for the excitation energies of the hot fragments and the cross sections of the final fragments produced in these reactions. The effects of various factors influencing the final fragment cross sections, such as the choice of the statistical decay code and its parameters have been explored. The predicted fragment cross sections are compared to the projectile fragmentation cross sections measured with the A1900 mass separator. At {\$E/A=140\$} {MeV,} reaction dynamics can significantly modify the detection efficiencies for the fragments and make them different from the efficiencies applied to the measured data reported in the previous work. The effects of efficiency corrections on the validation of event generator codes are discussed in the context of the two models.

%B Physical Review C %V 78 %8 08/2008 %G eng %N 2