【作者】 方美华；

【导师】 魏志勇；

【作者基本信息】 南京航空航天大学 ， 材料加工工程， 2011， 博士

【摘要】 随着探月工程、火星探险等深空探测任务的提出、实施,航天活动在时间上的延长、空间上的延伸,尤其是载人航天工程的开展,深空辐射带来的辐射危险和防护问题日益突出。本文围绕着深空辐射损伤和防护问题,系统地研究了深空辐射模型、粒子输运、辐射效应和材料屏蔽,重点研究了高能重离子在介质中的输运过程、能量转移和能量沉积,研发了重粒子剂量计算软件HID和深空辐射分析软件PSR,研究了重离子在高聚物材料中损伤形成的径迹结构及其微剂量学实验特征。本文分析研究了深空辐射场粒子的特点和模型,采用CREME-96模型得到了GCR的各种粒子谱分布,以特大太阳粒子事件的拟合谱代表SPE质子谱,获得了不同来源空间辐射粒子的注量、谱分布。采用蒙特卡罗方法,运用Geant4软件工具包进行程序编制,对粒子输运问题进行了深入研究;通过扩充数据库、纳入新的相互作用模型、建立新的功能模块实现了粒子输运的能量沉积、能量转移、等效剂量等辐射剂量学量的模拟计算、分析。采用软件移植、封装手段和操作界面优化设计,形成了两个粒子输运软件HID和PSR。HID软件中引入了核碎裂模型,改进了计算结果,实现了重离子能量沉积、剂量等的准确计算,通过对比高能碳离子和铁离子在等效介质中的能量沉积行为,发现碎裂核反应对射线品质因子有重要影响,并研究了次级粒子的剂量学特性。PSR经过数据库扩充和完善,实现了行星表面的辐射环境、粒子在大气或行星磁场中的运动模拟,可为火星任务等深空探测提供辐射环境预估。这两个软件均实现了windows界面的操作方式,同时也可在Linux下操作,满足多层次任务的需求。通过基于Linux和MPI的并行模拟计算平台,从次级碎片、人体关键器官剂量、中子场三个辐射防护量对典型空间辐射屏蔽材料的屏蔽性能进行评价,从三个方面得到了一致的结论:富氢元素材料在深空辐射防护中具有较好的屏蔽效果,对于深空中的重离子,厚度增加对提高屏蔽效率已经不再具有优势,对于长时间的深空探测,深空辐射防护问题十分严峻。从微观层次对重离子的径迹结构进行了研究,以高聚物CR-39为介质材料,利用中国原子能院提供重离子微束进行实验,用光学和原子力显微镜(AFM)研究重离子的径迹结构。研究了纳米和微米尺度蚀刻径迹,得到了微观辐射损伤参数,发现了传统模型在蚀刻初始时的不适用性,同时在传统模型适用的微观尺度提出了新的蚀刻速率比参量来建立蚀刻动力学模型,并通过观测分析得到了100MeV硅离子的径迹半径、微观局部剂量等微剂量学量。更多还原

【Abstract】 With the development of deep exploration, the hazards of space radiation to crews in traveling to moon and mars play the dominant role. In case of mars mission, in which crews spend most of the time outside the earth’s magnetic field, galactic cosmic rays(GCR) and solar particle event(SPE) are main exposure concerns. The accumulation of exposures to GCR ions can significantly increase the risk of cancer to astronaut and the SPE can deliver a potentially lethal dose in a few hours’time. So radiation protection is essential and central significance in exploration scenario.The topics of this paper include deep space radiation environment modeling, radiation transport, material protection and damage, which have been recognized as four critical issues in space radiation protection system.First, GCR model which is CREME-96 and SPE model which is a data fitting model are used for deep space radiation analysis. Thereafter, two space radiation transport codes, Heavy Ion Dosimetry(HID) and Deep Space Radiation Analysis(PSR), are developed based on Geant4 Monte Carlo toolkit. Nuclear reaction model– abrasion-ablation model is adopted in HID code which refines the calculation results as dose, energy deposition, et al. Heavy ion induced fragments is analyzed in case of high energy heavy ion pass through biological material and space protection materials. PSR code is aim to deal with space radiation transport in atmosphere and magnet of the planet. It can be used for planet radiation analysis in deep space by renewing the database of the planet and particle transport data. These two codes are encapsulated and windows operating interface and can operated under both Linux and windows system to meet the need of different people.Heavy ion fragments, organ dose and neutron flux are considered as three main aspect in space radiation protection material assessment. All the evaluation aspects do claim and verify that liquid hydrogen is the optimal material among typical space radiation protection materials as water, polyethylene and aluminum. And in deep space, protection efficiency decreases as shielding thickness increases for heavy ions.Heavy ion track is connected to radiation damage. A kind of polymer material called CR-39 is chosen as protection and biological equivalent material. The experiment is done in china institute of atomic energy in which silicon ion with the energy of 100 MeV is supplied. After irradiation, heavy ion tracks is displayed by chemical etching and observed under atomic force microscope (AFM). AFM is a relatively new and fine tool to get the images of tracks in nanometer size. As a result, a new track etch rate parameter is defined to model the track development. The track core size is determined after second etching. And then local dose in the track core is calculated by theδ-ray theory. Track etch rate and etch rate are derived after minute etching from three dimensional track structure. In addition, it is found that the micro-track development model violets the traditional model. And it is the micro-track development model that can explain the relationship between micro-track and material damage.更多还原