科研之友
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摘要
Angular distributions of fragments have been studied for Au-197 + Au-197 ternary reactions at bombarding energy 15 A MeV by an improved quantum molecular dynamics model. The calculated results are qualitatively in agreement with the experimental data. Through analyzing the angular distributions of fragments, it is shown that in semi-peripherals collisions Au-197 + Au-197 interacting system often reseparates into three massive fragments which are almost aligned in space along the separation axis. The anisotropic distribution in azimuthal angle phi shows that the projectile-like fragment (PLF) or target-like fragment (TLF) breaks up violently, reflecting nonequilibrium effects in the consecutive reseparation. The time scale elapsing from the scission of the binary PLF+TLF system to the secondary scission of PLF or TLF is estimated to be of about 80 fm/c. It is found that the distribution in Theta(cm) depends on the impact parameter, and its peak seems to be moving and narrowing with increasing impact parameter. Its asymptotic peak value is in agreement with the grazing angle. The shift of the peak value of Theta(cm) implies that the collective energy dissipation depends on impact parameter and decreases with impact parameter increasing since the exchange nucleons becomes less frequent during the reaction process.
