Hard photon production from neutron-proton bremsstrahlung in intermediate energy heavy-ion reactions is examined as a probe of the in-medium pn scattering cross section within a transport model. Uncertainty of photon production probability pn-pngamma is cancelled out by using the ratio of hard photon spectra R_{12C+12C/p+n}(gamma) from two reactions. The in medium pn scattering cross section is constrained by using the ratio of hard photon production cross sections of proton-induced reactions p+12C and p+2H. A reduction factor sigma_pn^medium/sigma_pn^free of about 0.5 ~ 0.7 around saturation density is obtained by comparing with the existing experimental data.Comment: 9 pages, 3 figures, accepted by PL

Using a transport model coupled with a phase-space coalescence afterburner, we study the triton-3 He (t-3 He) ratio with both relative and differential transverse flows in semicentral 132 Sn + 124 Sn reactions at a beam energy of 400 MeV/nucleon. The neutron-proton ratios with relative and differential flows are also discussed as a reference. We find that similar to the neutron-proton pairs, the t-3 He pairs also carry interesting information regarding the density dependence of the nuclear symmetry energy. Moreover, the nuclear symmetry energy affects more strongly the t-3 He relative and differential flows than the π − /π + ratio in the same reaction. The t-3 He relative flow can be used as a particularly powerful probe of the high-density behavior of the nuclear symmetry energy.

Based on the isospin-dependent Boltzmann-Uehling-Uhlenbeck transport model plus the Skyrme force parameters, initialization effect is studied in heavy-ion collision at intermediate energies. We find that there are moderate initialization effects in the observables of free neutron to proton ratio (n/p), π − /π + ratio, as well as neutron to proton differential flow (F x n−p ). Effects of initialization are larger for charged π − /π + ratios than n/p ratios. And the effects of initialization are more evident in nuclear reactions at lower incident beam energies. We do not see large effects of initialization for light reaction systems or large asymmetric (neutron-richer) reaction systems. We also see relatively large effects of initialization on the neutron to proton differential flow at relatively lower incident beam energies or with large impact parameters. These results may be useful for the delicate studies of Equation of Sate (EoS) of asymmetric nuclear matter.