多能复合谱电子束与X射线能量沉积剖面的等效性

以模拟等效核爆X射线热-力学效应为目标,从能量沉积剖面着手,对给定多能复合谱电子束的入射角度进行了设计计算.给出了不同靶材、不同温度黑体谱X射线的等效设计计算结果.对比表明,该设计方法适用于多种靶材、多种目标X射线的等效设计,并且设计后的电子束能够提高模拟目标X射线的热-力学效应的逼真度.     

强流电子束轫致辐射复合薄靶设计

针对目前脉冲硬X射线源能谱硬、辐照面积小、辐射场电子份额高无法开展系统电磁脉冲效应实验研究的技术难题,提出了采用复合薄靶软化脉冲硬X射线能谱、降低电子份额的方法。采用MCNP程序数值模拟了电子和光子在不同材料中的输运规律,分析了复合靶结构和材料厚度对X射线能谱、电子份额的影响。以闪光二号加速器为电子束源,设计了复合薄靶、X射线窗。实验得到的X射线参数:平均能量121 keV;均匀性2∶1情况下,700 cm2平均剂量40 rad（Si）,500 cm2平均剂量170 rad（Si）;光子数与电子数的比值大于103,可以开展系统电磁脉冲效应初步实验研究。     

电子束放射照相的特性与参数优化

短脉冲强激光产生的电子束具有源尺寸小、脉宽窄、准单能谱等特点, 在放射照相诊断中具有独特作用. 本文通过分析电子在材料中散射并采用蒙特卡罗方法数值模拟, 研究了100 keV到几百MeV能量电子束对有厚度起伏或存在界面的靶的透视, 并与质子、X射线束透视结果比较, 给出了电子束放射照相的特性与参数优化: 基于电子在材料中非弹性散射或能量损失, 选用能量使其射程与靶厚度接近的电子束来诊断靶厚度不均匀性; 基于电子在材料中的弹性散射, 选用射程超过靶厚度的电子束来诊断靶界面.     

不同入射角度下强流脉冲电子束能量沉积剖面和束流传输系数模拟计算

 强流脉冲电子束在材料中的能量沉积剖面、能量沉积系数和束流传输系数受其入射角的影响很大，理论计算了0.5~2.0MeV的电子束以不同的入射角在Al材料中的能量沉积剖面和能量沉积系数，并且还计算了0.4~1.4MeV电子束以不同入射角穿透不同厚度C靶的束流传输系数。计算结果表明，随着入射角的增大，靶材表面层单位质量中沉积的能量增大，电子在靶材料中穿透深度减小，能量沉积系数减小，相应的束流传输系数也减小；能量为0.5~2.0MeV的电子束当入射角在60°~70°时在材料表面层单位质量中沉积的能量较大。     

高能电子束对抗蚀剂曝光的Monte Carlo模拟

利用分段散射模型, 借助Monte Carlo方法模拟了具有高斯分布特征的 高能入射电子束(50keV≤E₀≤100keV)在抗蚀剂中的 散射过程, 分别得到了不同曝光条件下的电子背散射系数和能量沉积分布, 模拟结果与实验结果很好地符合. 在这一能量段, 当电子束能量越高、抗蚀剂 越薄、基片材料的原子序数越低时, 邻近效应越弱. 本文的模拟结果不仅能为高能电子束光刻工艺优化曝光条件、降低邻近效应提供理论指导, 而且能为进一步的邻近效应的校正提供更精确的数据.     

低能质子辐照对ZnO白漆光学性能退化的影响

 通过光致荧光光谱解谱和X射线光电子能谱（XPS）分析,研究了ZnO白漆经受能量低于200 keV低能质子辐照过程中氧空位缺陷的形成与演化过程。XPS解析表明质子辐照后晶格氧减少,光致荧光光谱解析表明锌空位减少,说明ZnO白漆中氧空位数量增加,且双电离氧空位能够捕获价带中的电子转变为单电离氧空位,使单电离氧空位逐渐成为辐照产生的主要缺陷。质子辐照使ZnO白漆中氧空位数量增加,而氧空位易捕获电子形成色心,从而导致光学性能下降。     

α-LiIO_3晶体的电子辐照效应

用透射电子显微镜观察了电子辐照对α-LiIO_3晶体结构的影响。α-LiIO_3经100keV能量中等强度的电子束辐照后,最初转变为γ-LiIO_3继而转变为Li_2O和另一种新的、可能是非化学比的Li—O化合物,称之新产物X。若用强电子束进行辐照,则α-LiIO_3迅速熔化。此时减弱电子束或停止辐照,均能使熔融物质凝固成上述新产物X,新产物X在电子束辐照下逐渐转变为Li_2O和金属锂。从新产物X转变为Li_2O的相变有一定程度的可逆性。此外发现,在电子束辐照下,α-LiIO_3单晶的结构变化有明显的各向异性。     

硅漂移电子温度测量系统的研制

在磁约束聚变装置中，对等离子体电子温度的测量一般采用电子回旋辐射法（ECE）、汤姆逊散射法以及软X射线能谱法。其中软X射线（1～20keV）能谱法是一种传统的方法，它比汤姆逊散射法的测量误差小，且有较好的时空分辨；与电子回旋辐射法（ECE）相比较，时空分辨能力相近，但可作绝对测量，并且受超热电子和逃逸电子的影响较ECE小。在软X射线能谱法的应用中，过去使用Si（Li）探测器来探测软X射线能谱，Si（Li）探测器体积大，能量分辨和量子效率低，并且需要使用液氮冷却，大体积的杜瓦（通常35L）使探测器体积庞大，     

电子能量对收集极中电子束能量沉积的影响北大核心CSCD

理论分析了收集极中运动电子的失能机制和电子能量对电子束能量沉积的影响,用蒙特卡罗方法计算了不同能量下入射电子的能量沉积分布,分析了电子能量对电子束在收集极中能量沉积的影响,并据此提出了提高收集极耐电子束轰击能力的两种途径。结果表明:激发和电离是收集极中入射电子的主要失能机制;电子的能量越高,在材料中的穿透能力越强,收集极中被收集电子束的最大能量沉积密度越低。综合考虑束流密度分布对能量沉积的影响,可通过两种途径来提高收集极耐电子束轰击的能力:一是通过结构设计增大电子束的收集面积,减小收集极上被收集电子束的束流密度;二是设计高阻抗器件,增大被收集电子束的电子能量,减小收集极上被收集电子束的束流密度。     

CsI光阴极在10-100 keV X射线能区的响应灵敏度计算

为了满足10-100 keV高能X射线光电探测器研究的需要,对CsI光阴极在该能量范围的响应灵敏度进行了研究.基于高能量X射线光子与材料相互作用的物理过程,分析了康普顿散射等效应对CsI响应灵敏度的影响.推导了CsI的响应灵敏度与二次电子平均逃逸深度和光阴极厚度的关系式和二次电子平均逃逸深度与入射光子能量的关系式,计算了CsI在10-100 keV范围内的响应灵敏度,计算结果与实验测试数据相符,验证了分析与推导的可靠性.根据计算可以获得不同入射X射线能量下CsI光阴极的最佳厚度,从而为高能X射线光电探测器的设计优化提供了理论参考.     

Thermal spike analysis of low energy ion tracks

The theoretical track diameter of low energy ions in organic materials is usually estimated through the model of dose deposition by delta rays, with results remarkably lower than the experimental values obtained via a replica method and electron microscopy. The track detector used here is Makrofol-E and the ions studied have specific energies between 1.4 and 100 keV/n. To evaluate the problem from another point of view, thermal effects for track formation, a modified version of the “liquid drop model” for insulators was applied. The electronic as well as nuclear energy deposition by an individual ion are considered and the thermal spike evolution is studied. The model allows for the formation of ion tracks in a range of energies previously considered as “forbidden”. There still exists a discrepancy between the experimental data and the track diameters predicted by the model, and although this difference is smaller than the obtained with previous calculations, it suggests the necessity of further adjustments.     

电子束和X射线双曝光制作大高宽比高分辨率的X射线波带片

介绍了利用电子束和 X射线束双曝光技术制作大高宽比高分辨率的 X射线聚焦或色散元件的新方法 (波长范围为 1～ 5 nm )。所制做的厚度为 10μm的 Au波带片具有 30个波带 ,最外环的宽度为 0 .5μm。实验表明 :对 8ke V的X射线来说 ,波带片的衬度大于 10 ,分辨率为 0 .5 5μm,焦距为 2 1.3cm。     

Nuclear Reactions under Irradiation of Deuterated Structures by X Rays

Measurements of emission from nuclear reaction products (neutrons and protons) have been carried out appearing in the deuterated structures of textured CVD diamond, palladium, titanium, and zirconium under irradiation with a beam of X rays using independent methods (neutron detector based on He-3 counters, Si surface-barrier semiconductor detectors and CR-39 track detector). The possibility of enhancement of both DD reaction and multi-particle deuterium fusion by the beam of X rays with energy ranging 20–30 keV in solid deuterated targets has been established. Analysis of X-ray fluorescence spectra of the target bombarded by beams of ions has revealed “additional” peaks, the occurrence of which cannot be related to any of the known elements, and requires separate study.

     

Multimodal hard X‐ray imaging of a mammography phantom at a compact synchrotron light source

The Compact Light Source is a miniature synchrotron producing X‐rays at the interaction point of a counter‐propagating laser pulse and electron bunch through the process of inverse Compton scattering. The small transverse size of the luminous region yields a highly coherent beam with an angular divergence of a few milliradians. The intrinsic monochromaticity and coherence of the produced X‐rays can be exploited in high‐sensitivity differential phase‐contrast imaging with a grating‐based interferometer. Here, the first multimodal X‐ray imaging experiments at the Compact Light Source at a clinically compatible X‐ray energy of 21 keV are reported. Dose‐compatible measurements of a mammography phantom clearly demonstrate an increase in contrast attainable through differential phase and dark‐field imaging over conventional attenuation‐based projections.     

A monolithic Fresnel bimirror for hard X‐rays and its application for coherence measurements

Experiments using a simple X‐ray interferometer to measure the degree of spatial coherence of hard X‐rays are reported. A monolithic Fresnel bimirror is used at small incidence angles to investigate synchrotron radiation in the energy interval 5–50 keV with monochromatic and white beam. The experimental set‐up was equivalent to a Young's double‐slit experiment for hard X‐rays with slit dimensions in the micrometre range. From the high‐contrast interference pattern the degree of coherence was determined.     

Polarization control of an X‐ray free‐electron laser with a diamond phase retarder

A diamond phase retarder was applied to control the polarization states of a hard X‐ray free‐electron laser (XFEL) in the photon energy range 5–20 keV. The horizontal polarization of the XFEL beam generated from the planar undulators of the SPring‐8 Angstrom Compact Free‐Electron Laser (SACLA) was converted into vertical or circular polarization of either helicity by adjusting the angular offset of the diamond crystal from the exact Bragg condition. Using a 1.5 mm‐thick crystal, a high degree of circular polarization, 97%, was obtained for 11.56 keV monochromatic X‐rays, whereas the degree of vertical polarization was 67%, both of which agreed with the estimations including the energy bandwidth of the Si 111 beamline monochromator.     

Experimental calculations of number,energy and dose albedos for various materials using 662 keV gamma rays

ABSTRACT

Number, energy and dose albedos are measured at a scattering angle of 180° for a broad beam of 662 keV gamma rays obtained from a radioactive source of ¹³⁷Cs (having strength in µCi; 1 Ci?=?3.7?×?10¹⁰ disintegrations per second). The gamma beam is incident on semi-infinite thick targets of variable atomic numbers. The scattering media is divided into three sets, which are pure elements, alloys and composite materials. Experiments are carried out using a 3^″?×?3^″ NaI(Tl) scintillation detector. To obtain precision in data, the response unfolding of a scintillation detector is used, which converts the observed pulse-height distribution to a true photon spectrum over the energy range of 2.5 to 640 keV. The detector response unfolding results in the true intensity of back-scattered gamma flux by shifting the events resulting from partial absorption of photons to the full energy peak of the spectrum. In the present study, albedo factors are studied as a function of target thickness and their atomic number. The experimentally calculated numbers of back-scattered gamma photon are in good agreement with theoretically generated numbers of multiple back-scattered counts by using a Monte Carlo simulation code. The experimental data on energy and intensity of 662 keV gamma photons are used to evaluate the number, energy and dose albedos for different materials under investigation.     

Towards more exoticness—X-ray spectroscopy of Ξ− atoms at J-PARC

Atoms with a doubly-strange hadron, namely Ξ^?, are really exotic and interesting objects. We are planning to measure X rays from Ξ^? atoms for the first time at J-PARC, where a high intensity and high quality kaon beam is available. Our purpose is to obtain the strength of the optical potential, and hence to provide information on the Ξ-N interaction which is currently very poorly known. We can accumulate several thousand counts of X rays and determine the level energy shift down to ~0.05 keV. This is sensitive enough to observe the expected level shift (~1 keV) with reasonable accuracy, while the sensitivities for the level width is somewhat weaker (measurable down to ~1 keV).     

电子-离子束缚态及其引发核聚变

 在文献[1]关于电子 离子束缚态的基本概念的基础上, 对电子-离子束缚态三体系统给出严格的薛定谔方程, 给出能量的近似解:(1)对pep束缚态, 释放单能E_p≈12.5keV的X射线; (2)对D⁺eD⁺束缚态, 释放单能E_D≈25keV的X射线, 同时引发少量的核聚变, 放出γ、质子、中子、氚、³He和⁴He。这是两个独立发生的过程。以Ni-H和氘气辉光放 电实验为例,用束缚态模型给出定量的解释。进而提出太阳耀斑发生过程中也包含电子-离子束缚态放射12.5keV和25keV两种X射线并引发少量核聚变的过程, 给出了观测结果验证。     

Defect engineering by synchrotron radiation X‐rays in CeO2 nanocrystals

This work reports an unconventional defect engineering approach using synchrotron‐radiation‐based X‐rays on ceria nanocrystal catalysts of particle sizes 4.4–10.6 nm. The generation of a large number of oxygen‐vacancy defects (OVDs), and therefore an effective reduction of cations, has been found in CeO₂ catalytic materials bombarded by high‐intensity synchrotron X‐ray beams of beam size 1.5 mm × 0.5 mm, photon energies of 5.5–7.8 keV and photon fluxes up to 1.53 × 10¹² photons s^?1. The experimentally observed cation reduction was theoretically explained by a first‐principles formation‐energy calculation for oxygen vacancy defects. The results clearly indicate that OVD formation is mainly a result of X‐ray‐excited core holes that give rise to valence holes through electron down conversion in the material. Thermal annealing and subvalent Y‐doping were also employed to modulate the efficiency of oxygen escape, providing extra control on the X‐ray‐induced OVD generating process. Both the core‐hole‐dominated bond breaking and oxygen escape mechanisms play pivotal roles for efficient OVD formation. This X‐ray irradiation approach, as an alternative defect engineering method, can be applied to a wide variety of nanostructured materials for physical‐property modification.