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1. chinaXiv:201707.00932 [pdf]

Non-Gaussian Fluctuation and Non-Markovian Effect in the Nuclear Fusion Process: Langevin Dynamics Emerging from Quantum Molecular Dynamics Simulations

Kai Wen; Fumihiko Sakata; Zhu-Xia Li; Xi-Zhen Wu; Ying-Xun Zhang; Shan-Gui Zhou
Subjects: Physics >> Nuclear Physics

Macroscopic parameters as well as precise information on the random force characterizing the Langevin type description of the nuclear fusion process around the Coulomb barrier are extracted from the microscopic dynamics of individual nucleons by exploiting the numerical simulation of the improved quantum molecular dynamics. It turns out that the dissipation dynamics of the relative motion between two fusing nuclei is caused by a non-Gaussian distribution of the random force. We find that the friction coefficient as well as the time correlation function of the random force takes particularly large values in a region a little bit inside of the Coulomb barrier. A clear non-Markovian effect is observed in the time correlation function of the random force. It is further shown that an emergent dynamics of the fusion process can be described by the generalized Langevin equation with memory effects by appropriately incorporating the microscopic information of individual nucleons through the random force and its time correlation function.

submitted time 2017-07-30 Hits1586Downloads921 Comment 0

2. chinaXiv:201707.00921 [pdf]

Energy-Dependence of Nucleus-Nucleus Potential and Friction Parameter in Fusion Reactions

Kai Wen; Fumihiko Sakata; Zhu-Xia Li; Xi-Zhen Wu; Ying-Xun Zhang; Shan-Gui Zhou
Subjects: Physics >> Nuclear Physics

Applying a macroscopic reduction procedure on the improved quantum molecular dynamics (ImQMD) model, the energy dependences of the nucleus-nucleus potential, the friction parameter, and the random force characterizing a one-dimensional Langevin-type description of the heavy-ion fusion process are investigated. Systematic calculations with the ImQMD model show that the fluctuation-dissipation relation found in the symmetric head-on fusion reactions at energies just above the Coulomb barrier fades out when the incident energy increases. It turns out that this dynamical change with increasing incident energy is caused by a specific behavior of the friction parameter which directly depends on the microscopic dynamical process, i.e., on how the collective energy of the relative motion is transferred into the intrinsic excitation energy. It is shown micro- scopically that the energy dissipation in the fusion process is governed by two mechanisms: One is caused by the nucleon exchanges between two fusing nuclei, and the other is due to a rearrangement of nucleons in the intrinsic system. The former mechanism monotonically increases the dissipative energy and shows a weak dependence on the incident energy, while the latter depends on both the relative distance between two fusing nuclei and the incident energy. It is shown that the latter mechanism is responsible for the energy dependence of the fusion potential and explains the fading out of the fluctuation-dissipation relation.

submitted time 2017-07-30 Hits1232Downloads708 Comment 0

3. chinaXiv:201703.00575 [pdf]

Effect of annealing on Cu precipitates in H ion irradiated Fe–0.6%Cu studied by positron annihilation

Shuoxue Jin; Peng Zhang; Eryang Lu; Baoyi Wang; Daqing Yuan; Long Wei; Xingzhong Cao
Subjects: Physics >> Condensed Matter: Structural, Mechanical and Thermal Properties

Fe–0.6%Cu alloy was irradiated with H ions to 0.1 dpa, and then annealed for 30 min from 150 oC to 500 oC. We focused the evolution of Cu precipitates in irradiated Fe–0.6%Cu alloy after the isochronal annealing from the perspective of positron annihilation. The ΔW parameters after thermal annealing (400 oC and 500 oC) were much larger than that induced by 0.1 dpa H irradiation. Annealing could promote the aggregation of the Cu-vacancy complexes, and form the Cu cluster–vacancies complexes. When the vacancy-like defects recovered around 500 oC, it meant the formation and growing of the defect-free Cu precipitates.

submitted time 2017-03-26 Hits2177Downloads1190 Comment 0

4. chinaXiv:201703.00512 [pdf]

Effect of annealing on VmHn complexes in hydrogen ion irradiated Fe and Fe-0.3%Cu alloys

Peng Zhang; Shuoxue Jin; Eryang Lu; Baoyi Wang; Yongnan Zheng; Daqing Yuan; Xingzhong Cao
Subjects: Physics >> Condensed Matter: Structural, Mechanical and Thermal Properties

The effect of annealing on VmHn complexes and Cu precipitate behaviors in hydrogen ion irradiated Fe and Fe-0.3%Cu alloys was investigated by positron annihilation spectroscopy using a slow positron beam. The results of S parameters indicated that the room temperature irradiation was benefit for the formation of the VmHn complex compared to the elevated temperature irradiation. The S-W results confirmed the formation of Cu precipitates in Fe-0.3%Cu even at the irradiation dose of 0.1 dpa. The formation of the evident S value peaks in the damage region after annealing treatment suggested that the VmHn complexes were broken and a larger of hydrogen atoms were escaping. The residual vacancy defects would migrate towards both the surface region and the opposite direction with the increasing annealing temperature.

submitted time 2017-03-23 Hits1387Downloads783 Comment 0

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