超短超强激光产生正电子的蒙特卡罗模拟

通过理论分析，建立了超短超强激光与固体靶作用产生正电子的蒙特卡罗模拟模型及Geant4模拟程序。模拟研究了靶材料、靶厚度及超热电子温度等对正电子产额的影响，结果表明:对铝、铜、锡、钽、金、铅6种靶材料，金靶的正电子产额最高，是优秀的正电子产生靶；不同超热电子温度下存在不同的最佳靶厚度，在最佳靶厚度以下，正电子产额随靶厚度增长而增大，靶厚度取3 mm较为合适；超热电子温度越高，正电子产额也越高，提高激光强度是增加正电子产额的有效途径。模拟研究给出了正电子角分布及其能谱，结果显示，正电子发射明显前倾，从大于90方向范围发射的正电子数量极少，且超热电子温度越高前倾特点越明显，能量呈类麦克斯韦分布，靶背法线方向出射的正电子的温度随超热电子温度升高而升高。

Monte Carlo simulation on positron production by ultrashort ultraintense laser

The Monte Carlo model and simulation code based on Geant4 for positron production in the interactions of ultraintense laser and solid target are set up by theoretically analyses. The influence of the temperature of hot electrons and target parameters for positron production is investigated. Simulation results show that the gold target is the optimal choice among the six targets of different materials under investigation. The best thickness of the target for generating abundant positrons exists for a certain temperature of hot electrons. The positron yield will increase when the temperature of hot electrons increases. The positron angular distributions and energy spectra are presented. Most positrons are ejected in the normal direction at the back of the target and the positron energy spectra show quasi-Maxwell distributions. Finally, the dependence of the positron temperature on the temperature of hot electrons is presented.