基于真实细胞模型的低能α粒子辐照模拟研究

本文以人体上皮细胞为模版,利用Geant4、ROOT模拟α粒子能量沉积的微观过程和空间行为,对次级电子的产生及相互作用事件等进行描述,并针对细胞形态结构特异性,对不同能量、不同生物学分布、特定源 靶组合下α粒子在真实细胞体元模型中的微观剂量特征进行研究,获取了低能α粒子物理径迹结构、次级电子作用点的径向空间分布、次级电子能谱分布、单次事件比能分布、亚细胞S值等特征量。结合计算结果分析了α粒子在亚细胞水平上的微剂量学特征变化及影响规律,实现了对特定结构亚细胞水平微观剂量特征的定量描述。     

宇宙线μ用于反应堆燃料元件成像的尝试性模拟研究

建立了用于Monte-Carlo模拟的μ抽样模型。使用此模型,采用Geant4程序和Root软件,对核燃料元件的μ成像进行模拟研究。模拟成像结果显示,基于将多次库伦散射等效为单次散射的径迹重建方法,可实现核燃料元件的μ成像。     

单细胞模型微观剂量学的Monte Carlo模拟研究

研究电离辐射在生物体内的能量沉积及相应的生物效应时,有必要研究单个细胞或部分细胞中能量吸收的统计特性。本工作利用蒙特卡罗软件Geant4,开发了计算单细胞微观剂量学程序,依据微观剂量学理论,对α释放子211At在单细胞模型中的微剂量学特征进行了研究。分析了不同大小细胞中单事件比能与存活分数的特点,并对真实细胞模型中微剂量学特征进行了分析。通过与简单数学模型结果对比,分析了细胞不同材料及形状对模拟结果的影响。本工作建立的体元单细胞模型为单细胞微剂量学研究提供了工具,同时也很易于扩展到真实组织模型。     

高纯锗谱仪探测效率的实验刻度与MC模拟

利用低本底高纯锗谱仪测量了标准源(~(133)Ba、~(137)Cs和~(60)Co)的各特征γ射线,得到了各特征能量下的探测效率,并通过拟合给出了高能端的探测效率曲线。同时,利用MC模拟工具包Geant4,模拟了各单能γ射线在高纯锗探测器组件中的输运过程,得到了不同能量下的模拟探测效率。比对结果发现:实验值与模拟值能很好地符合,可为开展相关产品的设计和制造提供参考。     

大型工业电子束脱硫脱硝装置辐射等效剂量场模拟与系统参数优化

为优化大型工业电子束脱硫脱硝装置和配套大功率电子加速器工程参数,应用Geant4模拟分析了不同出射能量的单能电子束在烟气中的径迹和偏转后电子束在烟气中的等效剂量场。计算得到1.75 MeV电子束更符合1 000 MWe级火电机组烟气系统工程设计需要,计算结果将为工业化设计提供参考。     

提高塑料闪烁体n/γ甄别能力的一种新途径

在强脉冲束中子、γ混合辐射场中,一般使用塑料闪烁体探测器测量中子注量,为了尽可能地减少γ辐射的干扰,需要提高塑料闪烁体的n/γ甄别能力.利用电子与质子在磁场中的偏转半径不同,提出一种提高塑料闪烁体n/γ甄别能力的新途径,并采用Geant4输运程序探讨了该探测方法的可行性,模拟结果表明:该方法使用较薄的闪烁体和磁铁构成探...     

电子的比能和细胞S值的Monte-Carlo计算

电离辐射往往通过它们产生的次级电子将能量传递给生物介质。在核医学以及BNCT等放射诊断和治疗中，放射性核素在细胞尺度上的分布是不均匀的，为了解电离辐射与生物介质直接作用，需对电子的细胞微剂量学进行研究。运用多种Monte—Carlo方法程序MOCA15、TRAX和Geant4，在同一细胞模型的情况下，计算了电子细胞S值和单次事件比能分布。     

运用Geant4模拟闪烁光纤辐照效率与光纤长度及射线能量的关系

利用Geant4系统对闪烁光纤中的γ粒子进行跟踪,模拟粒子与光纤的相互作用,给出粒子径迹,并计算出在闪烁光纤中的能量沉积,从而得到能量沉积效率与光纤长度及射线能量的关系,此工作对研究闪烁光纤的性质以及利用闪烁光纤进行实时成像有着重大的意义。     

6 MV医用加速器电子对效应的蒙特卡罗模拟研究

以Geant4编程构建6 MV医用加速器机头和照射条件,并通过实测数据比对验证模型的正确性,模拟加速器粒子输运过程,获取不同射野和不同层面的粒子相空间文件,以正电子和湮没光子为指标研究射野及各机头部件对电子对效应产生的影响,模拟电子对效应对加速器射束及水模中剂量沉积的影响。结果表明：射野面积越小,电子对效应产生越多;在靶、均整器及次级准直器处均会有较明显的电子对效应发生,其中次级准直器是主要的发生部件;电子对效应使射束中污染电子增加了约4%,降低了射束的平均能量,使射束粒子分布更加分散,增加了模体表面剂量及射野外剂量。     

固体径迹探测器在辐射剂量学、环境和生命科学中的应用

本文主要介绍固体径迹探测器在辐射剂量学、环境和生命科学中的一些应用,着重描述利用塑料径迹探测器测量热中子和快中子剂量。热中子剂量测量通常需要使用“转换屏”,例如~(235)U、~6Li和~(10)B,以产生能在塑料内留下可蚀径迹的带电粒子,而快中子除了利用转换屏(例如~(237)Np、~(232)Th等)外,还可以通过与探测器材料自身的组分的相互作用,直接在塑料内     

High energy electron beam generation during interaction of a laser accelerated proton beam with a gas-discharge plasma

The study of the interaction between ion beam and plasma is very important to the areas of inertial fusion energy and high energy density physics. With detailed one-dimensional electromagnetic particle-in-cell simulations, we investigate here the interaction of a laser-accelerated proton beam assuming an ideal monoenergetic beam with a gas-discharge plasma. After the saturation stage of the two-stream instability excited by the proton beam, significant high energy electrons are observed, with maximum energy approaching 2 MeV, and a new two-stream instability occurs between the high energy electrons and background electrons. The trajectories of plasma electrons are studied, showing the process of electron trapping and de-trapping from the wakefield.     

单能电子诱发DNA损伤的理论计算

利用径迹结构的方法模拟了单能电子从入射DNA水溶液到最终产生DNA损伤的早期物理和化学变化过程。着重研究了直接能量沉积导致碱基损伤的判断方法、DNA损伤穷举分类的定义及计算机实现方法,以及确定自由基产生位置的随机抽样方法。结果表明：物理、化学径迹与DNA的反应主要以NB（nobreak）的形式存在,而在链断裂中,主要也以易修复的单链断裂(SSB)为主;在为数不多的双链断裂（DSB）中,复杂DSB占到相当数量的份额。验证了DNA是辐射作用主要“靶”的假定。     

The Degradation of Solar Cells under Van Allen Radiation

The electrons and protons of the Van Allen Belt cause radiation damage to silicon solar cells which results in a gradual reduction of the power output of solar power plants on satellites passing through the Belt. The study of the radiation damage caused by monoenergetic electrons and by monoenergetic protons of various energy indicates that N on P solar cells are substantially more radiation resistant than the commonly used P on N cells. From such studies and a knowledge of the composition of the Van Allen Belt, a flux of, for example, 1 Mev electrons can be determined that will cause the same radiation damage per unit time to a bare solar cell as the Van Allen Belt spectrum would produce under a given shielding. Observations of radiation damage on satellites are also conveniently expressed in terms of such an equivalent flux. Measurements of solar cell short circuit current changes and changes in the current gain of specially designed highly radiation sensitive transistors have been performed on the Telstar satellite. The results are in general agreement with the radiation damage expected from the observed particle flux and they indicate that solar power is practical for long-life satellites passing through the Van Allen Belt, particularly if N on P solar cells are used.     

辐射流体力学数值模拟中的隐式蒙特卡罗方法

研究了一种模拟辐射流体力学问题的隐式蒙特卡罗方法,该方法考虑了相对论效应的影响。采用算子分裂思想将问题分为3步：1） 计算不含辐射与物质相互作用项的流体力学方程组;2） 采用隐式蒙特卡罗方法模拟辐射输运过程,通过追踪粒子历史,采用统计的方法给出粒子在1个时间步的能量和动量沉积,在此过程中考虑了相对论效应对辐射输运的影响;3） 更新流体能量和动量。在整个计算过程中,流体力学过程和蒙特卡罗粒子在介质中的运动过程均在实验室坐标系下进行模拟,但粒子的碰撞事件在局部的流体静止系下进行模拟。最后针对辐射流体力学的几个典型问题开展数值实验,计算结果验证了算法的适用性和程序的正确性。     

The design of “multiple energies from one source” in D-T neutron tube

To obtain multiple monoenergetic neutron sources and realize the on-site calibration of radiation monitoring equipment for nuclear-involved places,the structural characteristics and neutron source features of D-T neutron tube were analyzed;Monte Carlo method was adopted to simulate the effect of interaction between typical materials and different energy neutrons;multilayered shielding materials were combined and optimized to acquire the optimal scheme to shield the neutron sources from the neutron tube.On the base,a tapered alignment filtration construction was designed and Monte Carlo method was employed to simulate the effect of alignment construction.The result showed that the tapered alignment filtration construction can create monoenergetic neutrons including14.1 MeV,0.18 MeV and thermal neutrons and demonstrated good monochrome performance which provides multiple monoenergetic sources for the on-site calibration.     

带电粒子输运的两群模型:回顾与总结

本工作系统地总结了到目前为止带电粒子输运的两群模型已经取得的进展，包括该模型的基本思想和概念，主要的数学公式和数值方法以及这个模型的各种应用。叙述了这个模型如何从描述中能电子输运中产生，逐步扩展到研究轻离子输运，任意质量的离子输运，原子级联碰撞和包括研究溅射在内的粒子表面发射而成为广泛有效的精确的带电粒子输运理论的发展过程。总计15个图给出了两群模型与已有的实验测量结果和其他理论资料所作的广泛比较，表明带电粒子输运的两群模型是一个功能很强并富有潜力的统一带电粒子输运理论，一些尚未解决的带电粒子输运问题也将在本工作末提到。     

A new tool to compare neutron and ion irradiation in materials

The slowing down of neutrons produced in nuclear plants or in spallation sources generates many defects in a material, driving this material far from its equilibrium state. This concentration of defects leads to important structural modifications of solids. To model the impact of radiation in solids, particle accelerators are useful tools. The nature and the energy of ions in accelerators must be chosen to produce similar effects to those occurring in nuclear plants. A new program, DART, based on the binary collision approximation, has been developed to optimize the choice of incident particles. In this program, the anisotropy of the neutron atom interaction is treated with a new formalism. Such a formalism allows us to compute accurate displacement cross sections and recoil spectra for all kinds of particles (ions, neutrons, or electrons). The comparison of these displacement cross sections as well as recoil spectra due to ions, electrons and neutrons permits to define the nature and the energy of ions able to simulate damages in reactors.     

15 MeV～3 GeV电子加速器90°方向光子源项研究

韧致辐射光子是电子加速器屏蔽设计中的重要源项。为研究90°方向光子源项特征以及靶体半径和厚度对90°方向光子源项的影响,采用蒙特卡罗程序MCNPX27对15 MeV～3 GeV电子束轰击铁靶后的辐射源项进行计算。分析了90°方向光子辐射剂量、光子能谱等源项随靶厚度和半径的变化。通过与0°方向光子源项以及靶体内级联电子沉积能量进行对比,进一步分析了90°方向的光子源项特点。结果表明,90°方向光子能量主要集中在10 MeV以内,光子能谱形状与入射电子能量关系较小。受级联电子在靶内能量沉积程度及靶体对光子自吸收的共同影响,靶体半径和厚度是影响90°方向光子源项的重要因素。在电子加速器的屏蔽设计中应考虑靶体尺寸差异所带来的影响,同时建议针对束流90°方向和0°方向光子源项的差异,对加速器辐射屏蔽和防护进行优化设计。     

A transition radiation detector which features accurate trackingand dE/dx particle identification

The results of a test run involving a transition radiation detector (TRD) that can distinguish electrons from pions with momenta greater than 0.7 GeV/c and simultaneously track particles passing through the detector are described. The particle identification is accomplished by a combination of the detection of transition radiation from the electron and the difference in electron and pion energy (dE/dx) in the detector. The dE/dx particle separation is most efficient below 2 GeV/c, while particle identification utilizing transition radiation is effective above 1.5 GeV/c. Combined, the electron-pion separation is better than 5×10². The single-wire, track-position resolution for the TRD is ~230 μm     

A deterministic computational procedure for space environment electron transport

A deterministic computational procedure for describing the transport of electrons in condensed media is formulated to simulate the effects and exposures from spectral distributions typical of electrons trapped in planetary magnetic fields. The primary purpose for developing the procedure is to provide a means of rapidly performing numerous repetitive transport calculations essential for electron radiation exposure assessments for complex space structures. The present code utilizes well-established theoretical representations to describe the relevant interactions and transport processes. A combined mean free path and average trajectory approach is used in the transport formalism. For typical space environment spectra, several favorable comparisons with Monte Carlo calculations are made which have indicated that accuracy is not compromised at the expense of the computational speed.