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超短超强激光与物质相互作用产生的高能带电粒子束在放射照相中具有重要应用. 当几十到几百MeV能量的高能带电粒子束穿过薄膜靶时，能量损失可忽略，主要发生小角散射. 由于这个散射效应，高能带电粒子束对具有横向陡峭密度梯度区的靶照相，透射束在探测面上的通量密度分布中会出现靶密度梯度区散射产生的调制现象，有可能反过来诊断出陡峭密度梯度区信息. 以往对带电粒子束发生散射和产生调制现象的理论分析采用蒙特卡罗方法数值计算，不仅很消耗计算机时，计算的参数范围也有限. 本文发展了一个解析模型，用来处理带电粒子束在靶中传输的散射效应以及在探测面上产生的调制现象，能够快速给出结果，而且和蒙特卡罗方法数值计算的结果符合很好. 使用这一解析模型，对带电粒子束照相密度梯度靶产生散射调制现象的特征进行了分析. 提出了一个与照相条件有关的无量纲参量，其取值范围决定了散射调制信号特征以及诊断陡峭密度梯度区的可能性.Energetic charged-particle beams produced from ultrashort ultra-intense laser plasma interactions play a vital role in charged-particle radiography. When such an energetic beam penetrates through a foil target, its energy loss is negligible, and the main physics process is small-angle scattering. Due to this scattering effect, charged-particle radiography of a target with a transversely distributed steep density gradient region will produce a modulation structure in the fluence distribution on the detection plane, which could be used to diagnose the steep density gradient region. In the past theoretical work on the scattering effect and the resulting modulation structure was done with Monte-Carlo simulations, which cost a lot of computing time and the studied parameter range was limited. In the present work an analytical model is developed to deal with the scattering effect inside the target and the modulation structure on the detection plane in radiography, which gives results quickly and coincides with Monte-Carlo simulations very well. By using this analytical model, the characteristics of modulation structures are analyzed. A dimensionless characteristic parameter related to radiography conditions is put forward, its range determines different modulation structures and also the probability of diagnosing a steep density gradient region of width ⪝μm
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Keywords:
- scattering /
- radiography /
- charged-particle beam
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