【作者】 马云志；

【导师】 周宏余； 卓益忠；

【作者基本信息】 北京师范大学 ， 凝聚态物理， 2005， 博士

【摘要】 三维径迹结构(3DTS)是当前辐射生物效应研究的主要立足点。近些年来,径迹结构研究及其应用呈现如下趋势和特点:1)研究表明能量为几个电子伏特的电子能使DNA链断裂,该类电子的径迹模拟是3DTS研究的新方向;2)利用3DTS所提供的信息,建立面向机制的生物物理模型;3)模拟生物等效介质中的3DTS;4)旁观者效应以及相关研究。本学位论文所报告的工作就是围绕这几个方面展开的。 第一章介绍了与径迹结构方法有关的放射生物效应的概念和理论。 第二章根据近年报道的<100 eV电子与水介质相互作用的截面数据,将原有的径迹结构模型推广到0～10 eV能区,并在计算机上实现了对<10 eV电子的径迹模拟。运用这一工具我们研究了低能电子在径迹结构中的分布、低能电子射程分布等物理内容。同时,这一工作提供了进一步研究辐射生物效应的理论工具。 第三章提出了集群簇(clustering clusters)的概念—辐射品质的一种更细致的描述。在纳米级电离簇谱和集群簇概念的基础上,我们提出了ICC(Ionization Clustering Cluster)模型。经过刻度的ICC模型,能够更好地描述GI/S期和晚S期V79细胞存活率的实验数据,因此该模型能够提供对重带电粒子导致细胞增殖死亡机制的更富洞察力的解释。同时,我们证明了唯象动力学模型、线性二次模型和ICC模型的近似等价性,并从动力学的角度探讨了ICC模型参数的物理意义。 第四章探讨了历史凝聚算法(CH)用于微观尺度径迹模拟的可行性,并提出了一个相应的判据:截断电子穿透射程R远小于问题特征尺度l。通过与事件跟踪算法的比较,发现CH算法能够应用于特征尺度在100纳米以上的微观径迹结构模拟。由于CH算法在相同计算精度的要求下对碰撞截面的依赖程度较轻,因而能够对更多的辐射材料进行研究,同时可以成量级地缩短计算时间。 第五章应用CH算法研究了电子微束装置的微观剂量分布,得到的一次事件谱与文献中用精细算法得到的结果符合良好。邻靶比的计算表明,采用60～70keV电子具有最大的邻靶比,因而实验中要尽量避免应用该能量的电子。本文还研究了有限束宽的影响,发现束流宽度对细胞核、细胞质和邻居细胞中的授予能分布均有一定的连续变化的影响。邻靶比随着束流宽度的增加而呈两段线更多还原

【Abstract】 The 3-dimensional track structure(3DTS) is the main starting point of theoretical work in the study of radiation biological effect. In recent years, the new features and trends in this field of research include: 1) electrons with energy of several electron-volts(ESEV) were confirmed as a new mechanism inducing DNA strand breaks, and the track simulation of ESEV became a new direction of 3DTS; 2) to establish mechanism-oriented model on the basis of 3DTS; 3) the 3DTS generation in tissue-equivalent (TE) materials; 4) the bystander-effect and the relevant studies. Works reported in this dissertation were carried out around the points stated above.Some 3DTS-related concepts and theories were retrospected in chapter 1.Based on the cross section data reported in literature, we generalized the 3DTS model to 0~10 eV energy region and implemented the simulation code in chapter 2. With this code we studied the spatial distribution of low-energy electron (LEE) in track structure and the range distribution of LEE. Further theoretical work can be done with the tool.Chapter 3 proposed the concept of clustering clusters, which is a more meaningful description of quality factor. Using this concept and the concept of nanometer ionization spectrum, we proposed the Ionization Clustering Cluster model (ICC). The calibrated ICC model can give better description for the experimental data of Gl/S and Late-S V79 cell irradiated by protons and α-particles of different energies. Furthermore, we verified the approximate equivalence of the dynamics model, the linear quardratic (LQ) model and the ICC model. Then the physical meanings of the model parameters were analyzed in terms of dynamics.In chapter 4, the applicability of the condensed-history (CH) algorithm in problems of microscopic scale was explored. A criterion was proposed to determine whether the CH algorithm can be used: the penetration range R is much smaller than the characteristic length / of the problem. We found that the CH method can be used in the problem of characteristic length larger than 100 nm. Because the CH algorithm is less dependent on cross section data, it can simulate the experimental environment of actual materials. And the calculating time is reduced by more than an order of magnitude.In chapter 5 the dose distribution of Electron Microbeam (EMB) device was calculated with the 3DTS code of CH type. The single event size distribution agrees well with the results of event-by-event code reported in the literature. The calculated neighbor-to-target ratio, Ryvr. attains a maximum value around 60-70 keV , which indicates that electrons of these energies should be avoided in the experiments. Furthermore, the effect of finite beam-width were studied and it was found thatthe single event size distribution in HeLa cell nucleus, in cytoplasm and in neighbors shift continuously with the beam-width. And Rnt increases with the beam-width. The results are useful for the design and calibration of EMB.更多还原