衍射辐射及其在电子束诊断中的应用

衍射辐射是由于运动的带电粒子遇到随空间变化的电介质而由感应电流产生的一种辐射. 衍射辐射由于其非阻拦性, 多参数性, 可在线性, 非常适合下一代对撞机和第四代光源的电子束诊断. 简要介绍了其物理机制, 系统的讨论了其在电子束诊断中的应用.     

高能闪光照相对电子束参数的要求

对高能闪光机光源性能用Monte-Carlo方法模拟研究发现：并非击靶电子束半径越小、发射度越低, 闪光机的照相性能就会越好. 研究结果表明：为了使闪光照相图像视面上照射量分布比较均匀, 对束半径与电子束归一发射度有一个联合限制, 对于20MeV闪光机, 如果击靶电子束有效半径是0.12cm, 那么仅当束归一发射度≥550cm.mrad时,在2°内的照射量不均匀性才小于5%.     

用^60Co放射源检测油垢厚度的初步实验研究

本文用石蜡模拟油垢，用^60Co放射源的1．25MeV平均能量的γ射线垂直入射，以一定的散射角和不同的探测立体角接收散射γ光子敫．发现散射γ计数与被测石蜡厚度之间存在不同的线性关系．结果发现，放射源与探测器之间屏蔽的好坏和合理的探测距离对提高线性度有很大关系．本实验测得最佳线性相关系数平方值为0．9981，平均测量精度为1．26mm．这对研究散射法检测油垢厚度和选择合适的探测距离提供了实验基础．     

70 GHz二次谐波倍频回旋速调管研究

 对70 GHz二次谐波倍频回旋速调管高频结构和电子与波互作用进行了研究。研究了TE02模腔体绕射品质因数及模式转化，解决了二次谐波倍频回旋速调管漂移段不能截止70 GHz的TE01模而引起的腔体间高频串扰的问题。分析了注电流、输入功率、电子横纵速度比和电子注引导中心半径等参数对输出功率、增益和效率的影响。针对二次谐波回旋速调管放大器工作频带窄、效率低，进行了高频结构优化设计，显著地展宽了工作频带，提高了互作用效率。在理论分析和高频计算的基础上，建立了注-波互作用PIC（粒子模拟）模型，进行了粒子模拟计算和优化，得到了70 GHz 的二次谐波倍频四腔回旋速调管放大器设计方案。粒子模拟结果表明：在工作电压70 kV，注电流13 A，电子注横向速度与纵向速度比为1.5时，中心频率69.81 GHz输出功率256 kW，带宽160 MHz，电子效率28%，饱和增益大于44 dB。     

重离子治疗计划系统的构想

对重离子柬治癌的优势进行简要的回顾，并着重介绍了用于重离子放射治疗的治疗计划系统。治疗计划系统是一套软件系统，不同的硬件设施应有与其相匹配的软件系统，即治疗计划系统。在此基础上，针对兰州重离子加速器的特点提出一些关于治疗计划系统方面的构想。After a brief review concerning the advantages of heavy ions in radiotherapy, more interests are concentrated on treatment planning system （TPS） for heavy ion radiotherapy. Compared to the hardware devices such as accelerator and beam delivery system, the TPS is a set of software system, and different therapy facilities require their corresponding TPSs. Based on the specialities of the Heavy Ion Research Facility in Lanzhou （HIIRFL）, some suggestions on the TPS for tumor therapy at HIRFL finally are given.     

复杂像散椭圆光束的轨道角动量的实验研究

提出一种直接测量光束的轨道角动量的方法，其原理是把具有轨道角动量的光束照射到一个金属靶上，使其在光束的角动量作用下发生转动. 通过测量靶转动的角度来计算光束的角动量值. 对几种不同参数的光束的轨道角动量进行了测量，获得了轨道角动量与光束参数之间的关系，实验结果与理论分析较好地符合. 关键词： 复杂像散椭圆光束 轨道角动量 测量     

Slow positron beam study of corrosion-related defects in pure iron

Corrosion-related defects of pure iron were investigated by measuring Doppler broadening energy spectra (DBES) of positron annihilation and positron annihilation lifetime (PAL). Defect profiles of the S-parameter from DBES as a function of positron incident energy up to 30 keV (i.e. ∼1 μm depth) were analyzed. The DBES data show that S-parameter increases as a function of positron incident energy (mean depth) after corrosion, and the increase in the S-parameter is larger near the surface than in the bulk due to corrosion. Furthermore, information on defect size from PAL data as a function of positron incident energy up to 10 keV (i.e. ∼0.2 μm depth) was analyzed. In the two-state trapping model, the lifetime τ₂ = 500 ps is ascribed to annihilation of positrons in voids with a size of the order of nanometer. τ₁, which decreases with depth from the surface to the bulk, is ascribed to the annihilation of positrons in dislocations and three-dimensional vacancy clusters. The corroded samples show a significant increase in τ₁ and the intensity I₂, and near the surface the corroded iron introduces both voids and large-size three-dimensional vacancy clusters. The size of vacancy clusters decreases with depth.     

Surface reconstructions of InGaAs alloys

The surface reconstructions of In_xGa_1−xAs alloys grown by molecular beam epitaxy on the (0 0 1) surfaces of GaAs and InAs have been studied by reflection high-energy electron diffraction and scanning tunnelling microscopy. A surface phase diagram is presented for the nominally strain-free alloy as a function of substrate temperature and alloy composition, and structural models for the commonly observed 3× reconstructions are discussed. Two new, electronically stable structural models are described that account for the transition of the In_xGa_1−xAs surface alloy from a c(4 × 4) to an asymmetric 3× reconstruction and that are fully consistent with all current experimental evidence.     

An efficient calculation algorithm for focusing by plane ultrasonic transducers

In the present paper, we simulate focused wave fields generated by a system of plane transducers used in an immersion ultrasonic technique. The ultrasonic beam penetrates into the elastic medium through the fluid-solid boundary. A real-time computer algorithm is proposed to calculate stress components in the solid medium. It is shown that a good focusing wave structure can be provided by a pair of plane rectangular transducers, inclined with respect to each other and to the beam acoustic axis.     

单分子光子源光子统计的非平衡探测

研究了在Hanbury Brown Twiss探测方式下，非平衡探测系统对光子统计测量的影响。通过记录2个单光子计数器响应的单分子光子源输出的每一个事件，分析具有泊松统计背景的实际单分子光子源的光子统计特性，讨论并给出了非平衡探测系统的单分子光子源Mandel参数。研究表明：非理想的50／50分束器、非理想的线性传输效率和非理想的探测器都会使单分子光子源Mandel参数的实际测量结果小于平衡系统的Mandel参数，最后给出了单分子光子源Mandel参数的非理想探测的校正表达式。