电子束辐照烟气脱硫脱氮反应器中的剂量分布的模拟计算

采用Monte-Carlo程序EGSnrcMP对能量为0.8MeV的电子束辐照烟气脱硫脱硝反应器中的剂量分布进行了模拟计算,将计算的结果运用MATLAB数学分析软件进行了数据处理,对能量为0.5MeV的电子束辐照烟气脱硫脱硝反应器中的剂量分布进行了模拟计算,并与文献中实验测量值进行了比较。结果表明:采用EGSnrcMP程序计算所得到的剂量与实验结果吻合。     

电子束在弯曲螺线管中的运动

 为研究HIRFL-CSR电子冷却装置中电子束穿过电子冷却装置中弯曲螺线管后电子横向能量的变化,用POISSON程序计算出弯曲螺线管的磁场分布,考虑了空间电荷效应,用数值方法模拟计算了电子在弯曲螺线管中的运动情况,得到了电子束横向能量变化最小时磁场各分量与电子束能量和弯曲螺线管几何尺寸之间的关系,并获得了电子束横向能量在束流截面的空间分布。     

基于蒙特卡罗方法的XHA600D医用电子直线加速器的入射电子束参数研究

使用蒙特卡罗方法研究入射电子束参数对XHA600D医用电子直线加速器产生的剂量分布的影响,并确定优化的入射电子束参数。根据厂商提供的XHA600D加速器治疗头的几何、材料参数,使用蒙特卡罗程序EGSnrc对不同的入射电子束参数进行模拟并记录其在水模体中产生的剂量分布,将模拟结果与测量结果进行比较。模拟的入射电子束参数包括平均能量、径向强度分布、角度展宽和能量展宽;实验测量数据包括4 cm×4 cm、10 cm×10 cm、30 cm×30 cm射野条件下的百分深度剂量与离轴剂量。结果表明当入射电子束的平均能量为6 MeV、径向强度的半高宽(Full Width at Half Maximum, FWHM)为0.25 cm、角度展宽为0.15°时,模拟结果和测量结果吻合非常好。这些参数可以作为建立适用于XHA600D加速器的TPS(Treatment Planning System)剂量计算模型的基础参数。     

低能电子束曝光中的Monte Carlo方法及沉积能分布

建立一个低能电子在多元多层介质中散射Ｍｏｎｔｅ Ｃａｒｌｏ模拟计算方法，低能在多元介质中弹性散射用Ｍｏｔｔ截面描述并应用作者提出的平均散射截面方法进行模拟计算；给出多元介质中修正的Ｂｅｔｈｅ方程计算低能电子非弹性散射能量损失。计算了低能电子在电子束曝光胶中能量沉积分布。     

电子束和β射线两用外推电离室

电子束辐照在辐射加工、新材料研制、放射治疗和模拟空间辐射环境的各种科学实验中应用日益广泛.实践表明,在上述应用中,被照物体吸收剂量是决定成功与失败的关键.因此,近年来准确测定电子束在各种材料中的剂量分布已成为迫切需要解决的问题. 由于电子束和β射线在物质中的迁移和能量沉积行为十分复杂,所以至今也难以从理论上给出准确的吸收剂量率随深度变化的统一解析式.目前,各种解析、模拟和半经验的计算电子剂量分布的方法已经产生,但具体给出准确的电子剂量分布仍然要靠实验测定.一般来讲,对不同加速器,即使具有相同的标称能量(加速器…     

1．2MV大功率直流高压电源研制

随着工业辐照加速器技术的发展，电子加速器应用范围已经扩展到环保领域，利用大功率电子束治理燃煤烟气的污染就是其中比较成功的例子。工业加速器的束功率通常约在100kW，而电子束烟气治理技术的束功率达到1MW以上，能量0．8～1．5MeV。大功率直流高压电源是此类加速器最重要的关键技术，是整个加速器能量转换效率的决定因素，是加速器稳定性、可靠性的基础，是决定加速器制造成本的关键。     

S波段6 MeV边耦合电子直线加速器的设计研究（英文）北大核心CSCD

近年来,对紧凑、稳定及可靠型电子直线加速器的需求越来越多,其能量主要分布在几百keV到十几个MeV的范围内,其中需求最多的则是能量在MeV量级的微波电子直线加速器。在这种形势下,中国科学院高能物理研究所正在研制一台S波段6 MeV的边耦合电子直线加速器,本文对基于该加速器的模拟计算研究进行了介绍。EGUN和HFSS分别用来设计电子枪和边耦合加速结构。通过将EGUN计算得到的电子束流参数和HFSS计算得到的三维电磁场分布数据引入到PARMELA中,完成了对该加速器的多粒子动力学研究。模拟结果显示,所设计的加速器完全能够满足设计指标的要求。最终,在考虑束流负载效应的因素后,完成了边耦合加速结构的微波结构设计。     

S波段6 MeV边耦合电子直线加速器的设计研究（英文）

近年来,对紧凑、稳定及可靠型电子直线加速器的需求越来越多,其能量主要分布在几百keV到十几个MeV的范围内,其中需求最多的则是能量在MeV量级的微波电子直线加速器。在这种形势下,中国科学院高能物理研究所正在研制一台S波段6 MeV的边耦合电子直线加速器,本文对基于该加速器的模拟计算研究进行了介绍。EGUN和HFSS分别用来设计电子枪和边耦合加速结构。通过将EGUN计算得到的电子束流参数和HFSS计算得到的三维电磁场分布数据引入到PARMELA中,完成了对该加速器的多粒子动力学研究。模拟结果显示,所设计的加速器完全能够满足设计指标的要求。最终,在考虑束流负载效应的因素后,完成了边耦合加速结构的微波结构设计。     

95 MeV射频电子直线加速器辐射防护分析

应相关建设安评、环评、稳评以及职业健康评估的要求,电子加速器设计过程中即应对其辐射情况进行分析。针对电子能量为40～95 MeV可调的光阴极微波电子枪直线加速器,对其辐射源项进行分析,并讨论了可能的辐射防护措施的效果。采用蒙特卡罗软件FLUKA对电子束流和加速器进行建模,通过模拟计算发现,加速器产生的等效剂量分布主要位于废束桶中,废束桶以外辐射剂量迅速下降,在电子加速器实验大厅四周设置混凝土墙体的情况下辐射等效剂量率将随墙体厚度迅速下降。若混凝土墙体厚度设置为1 m,则墙体外工作人员所在区域辐射等效剂量率不高于1 μSv/h量级,能够有效屏蔽加速器产生的电离辐射,给工作人员提供有效防护。研究方法及结果对同能区同类型加速器建设中的辐射分析及辐射防护评估具有一定的参考价值。     

TRIUMF ARIEL 电子直线加速器设计

 TRIUMF 的三期升级工程(ARIEL) 计划建造一个 50 MeV 平均流强为10 mA的电子直线加速器作为注入器,通过光裂反应生成放射性核素。电子直线加速器包括两个主要部分：注入器和后加速器,注入器完成电子能量从100 keV到10 MeV的转换,随后的后加速器将电子能量从10 MeV加速到50 MeV。电子源拟采用重复频率为650 MHz的热电子枪提供初始能量为100 keV,束长为 171 ps的电子束。束流动力学模拟了几种不同的设计方案以获得最优化的设计,模拟显示通过对腔体以及聚焦元件的仔细设计以及电子枪出射电子的参数选择, 电子束能量在达到50 MeV时束长可以被聚焦到 11.75 ps (对应于1.3 GHz 频率下5.5°) ,并且可以使电子束在超导低温柜中的尺寸保持在1.26 cm以下。     

A study on beam profile of an industrial electron accelerator

Experimental evaluation of electron beam profile of a recently upgraded industrial electron accelerator has been carried out to study characteristics of the beam required for the irradiation of various industrial products. Calibrated cellulose triacetate (CTA) film strip dosimeters were used for the measurement of dose profile along and transverse to the scanning direction at different distances in air under the beam extraction window in dynamic (conveyor) and static mode of operation. Two-dimensional dose distribution mapping under the beam has also been measured by using a large number of CTA strip dosimeters. The obtained result shows that the electron beam emerging out from scanning horn has a good uniformity along the scanning direction within 90% of the average maximum dose. Also, the paper reports depth dose distribution in unit density material under the 4.5?MeV beam. Using this study, area affecting dose to the product is controlled within the limit for the irradiation.     

Electron beam irradiation induced changes in the dielectric and electro-optical properties of a room temperature nematic display material 4-(trans-4′-n-hexylcyclohexyl) isothiocyanatobenzoate (6CHBT)

Dielectric and electro-optical studies of a pure and electron beam irradiated liquid crystalline compound 4-(trans-4′-n-hexylcyclohexyl) isothiocyanatobenzoate have been carried out. Dielectric anisotropy, relaxation frequency, activation energy and distribution parameter of an observed non-collective mode corresponding to the molecular rotation about the short axes have been determined as a function of temperature and irradiation dose whereas threshold and switching voltages, splay elastic constant are determined as a function of irradiation dose. The relaxation frequencies initially decrease up to an irradiation dose of 40 kGy but thereafter increase due to irradiation. The activation energies are increased up to irradiation dose of 40 kGy but around 60 kGy dose of irradiation, we found decrease in the activation energy. Electro-optical measurements show the lowering of the threshold voltage with sufficient improvement in the steepness of the transmission voltage curves due to irradiation. The observed changes in the dielectric and electro-optical properties are related with the cis–trans isomerization due to electron beam irradiation.     

Dosimetric evaluation of an indigenously developed 10 MeV industrial electron beam irradiator

The high dose rate electron beams are increasingly being used for radiation processing of various products worldwide. A comprehensive dosimetric evaluation of an in-house developed 10 MeV industrial electron beam irradiator was carried out in static as well as in dynamic mode of irradiations. Radiochromic B3 film and graphite calorimeter were used for dosimetric measurements. The dose rate from the electron beam was also calculated using the empirical relation prescribed in the ASTM report E2232-02. The measured electron beam profile indicates the dose rate variation within 8% in the irradiated product boxes. The most probable energy determined from the depth dose distribution in PMMA, Al and water was found in agreement with the intended energy of the electron beam. Measured dose rate using radiochromic film and graphite calorimeter were found in good agreement with each other and also found comparable with the theoretically estimated dose rates. Experimentally measured dose rates were considered for the trial irradiation of medical and industrial products. Dosimetric data obtained through this study confirms the suitability of the irradiator for routine radiation processing of various products.     

Effects of F2 Color Center Spatial Distribution on the Emission Properties of Optical Microcavities Based on LiF Films

Highly stable F₂ color centers are very efficiently produced in lithium fluoride (LiF) by electron beam irradiation at room temperature. We have fabricated optical microcavities in which the active medium is a low-energy electron beam irradiated LiF film, whose optical thickness is comparable with the peak wavelength (～668nm) of the F₂ broad photoluminescence band. By selecting the proper electron beam energy, one can control the F₂ color center depth distribution. This distribution influences the photoemission angular distribution of the microcavity, whose resonance properties are determined by the coupling of the depth profile of the defects with the pump electromagnetic field and microcavity modes.     

电子束辐照对GaN基LED发光性能的影响

研究了不同能量的电子束辐照对GaN基发光二极管(Light emitting diode,LED)发光性能的影响。利用实验室提供的电子束模拟空间电子辐射,对GaN基LED外延片进行1.5,3.0,4.5 MeV电子束辐照实验,并应用光致发光(Photoluminescence,PL)谱测试发光性能。结果表明:在1.5 MeV电子束辐照下,采用10 kGy剂量辐照时,LED的发光强度增加约25%;而在100 kGy剂量辐照时,LED的发光强度降低约16%。3 MeV的电子束辐照可使原来色纯度不高的LED的色纯度变好,而更高能量的辐照将会引起器件失效。     

Electron emission and charging of natural diamond under irradiation with medium-energy electrons

The processes of charging of a natural diamond crystal irradiated by an electron beam with primary electron energies in the range 1–30 keV have been experimentally investigated. The charging kinetics has been studied as a function of the irradiation dose and the electron-emission properties of the crystal. The following fundamental characteristics have been determined: the second crossover equilibrium energy of the beam electrons and the values of high-voltage surface potentials and accumulated charges.     

Effect of electron beam irradiation on the structural,thermal and optical properties of poly(vinyl alcohol) thin film

Poly(vinyl alcohol) (PVA) polymer was prepared using the casting technique. The obtained PVA thin films have been irradiated with electron beam doses ranging from 20 to 300 kGy. The resultant effect of electron beam irradiation on the structural properties of PVA has been investigated using X-ray diffraction (XRD) and Fourier transform infrared spectroscopy (FTIR), while the thermal properties have been investigated using thermo-gravimetric analysis and differential thermal analysis (DTA). The onset temperature of decomposition T ₀ and activation energy of thermal decomposition E _a were calculated, results indicate that the PVA thin film decomposes in one main weight loss stage. Also, the electron beam irradiation in dose range 95–210 kGy led to a more compact structure of the PVA polymer, which resulted in an improvement in its thermal stability with an increase in the activation energy of thermal decomposition. The variation of transition temperatures with electron beam dose has been determined using DTA. The PVA thermograms were characterized by the appearance of an endothermic peak due to melting. In addition, the transmission of the PVA samples and any color changes were studied. The color intensity Δ E was greatly increased with increasing electron beam dose, and was accompanied by a significant increase in the blue color component.     

放疗绝对剂量的数学算法模型

本文提出一种通过物理模型计算放疗过程中每一个组织深度处绝对剂量的算法,它可代替蒙特卡罗仿真的部分工作且耗费时间更少.这个算法是基于对照射野内X射线产生电子的能量注量的积分运算,并考虑了射线的能谱及二次散射线,得到了后向散射对表面剂量的贡献比例,同时得到前向散射、后向散射及原射线剂量贡献的关系.比较了二次光子和二次电子的三维能谱,得出该能谱是粒子注量关于粒子能量和粒子运动方向的函数.为了得到每一深度处的光子注量,计算了有连续能谱的X射线的期望质量衰减系数.上述算法计算得到的绝对剂量与蒙特卡罗方式仿真的结果趋势一致,两者的差异在于算法未考虑高于二次的散射线.最后将算法应用到非均匀模体剂量计算,能准确反映其中剂量分布特点且具有较小的误差.     

Investigations of electron beam induced conductivity in silicon oxide thin films

Silicon oxide thin film conductivity under electron beam irradiation is studied. An induced current in the films is varied in a range from a few tenths to a few values of the beam current. The dependence of the current normalized to a product of the applied voltage and the beam current on the beam energy is found to have a maximum determined by the film thickness, beam energy, and sign of the applied voltage. For the negative voltage applied to the metal electrode deposited on the film, this maximum is observed at the beam energy, at which the depth generation function is smaller by several tens of nanometers than the film thickness. For the positive voltage on the metal electrode, the maximum is observed at higher beam energies. The obtained result could be qualitatively explained under the assumption that a stationary excess carrier distribution is formed under the electron beam. This distribution is shifted with respect to the generation function due to diffusion and drift of excess carriers. A value of this shift is of about a few tens of nanometers, and its sign indicates that the majority carriers providing the induced conductivity in the films studied are electrons.