Electron Scattering from Fundamental Gaseous Targets

基本气体目标的电子散射

• 批准号: 1606905
• 负责人: Murtadha Khakoo
• 金额: $ 40.24万
• 依托单位: CSU Fullerton Auxiliary Services Corporation
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2016
• 资助国家: 美国
• 起止时间: 2016-09-01 至 2021-08-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=1606905&HistoricalAwards=false
• 关键词: Electron; Scattering; Fundamental; Gaseous; Targets

Electrons scattering from matter are responsible for a host of phenomena, including the light emitted from planetary atmospheres (including that of the Earth), the sparks in gasoline engines, and the fragmentation of DNA in biological tissues exposed to radiation. These processes can be understood by the theory of quantum mechanics. The present experimental project involves setting up controlled collisions between a well-defined beam of electrons and gas atoms or molecules placed in their path. The aim is to carefully investigate how these electrons are deflected by the target gas atoms or molecules and how they change the physical and chemical state of these targets for a given energy of the electrons. The experiments are conducted for a wide range of electron energies and will look at the dynamic interaction between the electrons and the targets and delve into the physics which controls how the electrons are scattered in various directions at these controlled energies. The targets include simple atoms such as neon, argon, krypton, and xenon, molecular hydrogen and nitrogen, and more complex molecules such as water, alcohols and benzene-type aromatic molecules. The experimental results are used to test detailed quantum scattering models to promote our understanding of the interaction of these electrons with targets. The project continues prior work in the same lab which has advanced the modeling of industrial processes. A benefit from this project will be the exposure of undergraduates to world-wide PhD programs as a result of their engagement in this project.A new electron time-of-flight spectrometer will be able to handle very slow electrons emerging from scattering events. The electron beam is pulsed and the scattered electrons are separated in velocity by the amount of time they take to reach the detector. The scattering of low energy electrons with kinetic energies ranging from 0.5 eV to 100 eV is studied using electron energy loss spectroscopy where the incident energy of a 1 mm collimated beam of high energy resolution crosses a tenuous beam of pure atoms or molecules in a vacuum chamber. The energy separation of electrons (produced from a tungsten filament source) is made at high resolution (30-50 meV full-with at half maximum) using electrostatic lenses combined with hemispherical analyzers. The measurements consist of differential scattering cross sections and polarization correlations for electron scattering from rare gas atoms and simple diatomic molecules (H2 and N2). The data provide tests for models of electron scattering and shed light on the quantum dynamics of the scattering process which involves details of Coulomb interactions, electron spin processes (spin-exchange, spin-orbit), and resonant interactions. Models to date have been evolving to handle more complex targets as computational power is rapidly increasing. The present project will look at the polarization of emitted vacuum ultraviolet radiation and, perpendicular to the scattering plane, in coincidence with differentially scattered electrons whose energy loss coincides with the excitation energy of the radiation. Importantly, it will measure the circular polarization of the radiation in the vacuum ultraviolet, a parameter which is related to the angular momentum imparted to the target by the scattered electron, and provides valuable physical insights to the collision process. In addition, the development of a new time-of-flight spectrometer (using a fast 1 nanosecond pulsed electron beam) will enable absolute calibration of scattering cross sections as well as be able to handle slow emergent electrons in the energy range of 0.5eV to 20eV, and add to the range and accuracy of the overall ongoing measurements. This project aims to continue its productive supply of accurate collision data involving undergraduates in laboratory research.

从物质中散射的电子是一系列现象的原因，包括行星大气（包括地球大气）发出的光，汽油发动机中的火花，以及暴露于辐射的生物组织中DNA的碎片。这些过程可以用量子力学理论来理解。目前的实验项目包括在一束定义明确的电子和置于其路径上的气体原子或分子之间建立受控碰撞，目的是仔细研究这些电子如何被目标气体原子或分子偏转，以及对于给定的电子能量，它们如何改变这些目标的物理和化学状态。这些实验是针对各种电子能量进行的，将研究电子与目标之间的动态相互作用，并深入研究控制电子如何在这些受控能量下向各个方向散射的物理学。目标包括简单的原子，如氖、氩、氪和氙，分子氢和氮，以及更复杂的分子，如水、醇和苯型芳族分子。实验结果被用来测试详细的量子散射模型，以促进我们的理解这些电子与目标的相互作用。该项目继续在同一实验室进行先前的工作，该实验室已经推进了工业过程的建模。该项目的一个好处是，由于参与该项目，本科生将接触到世界范围的博士课程。一种新的电子飞行时间谱仪将能够处理从散射事件中出现的非常慢的电子。 电子束是脉冲的，并且散射的电子在速度上被它们到达检测器所花费的时间量分开。本文用电子能量损失谱研究了低能电子的散射，其动能范围为0.5 ~ 100 eV，入射能量为1 mm的高能量分辨率准直电子束与真空室中的纯原子或分子束相交。电子的能量分离（从钨丝源产生）是在高分辨率（30-50毫电子伏全与半最大值）使用静电透镜结合半球形分析仪。测量包括微分散射截面和极化相关的电子散射稀有气体原子和简单的双原子分子（H2和N2）。这些数据提供了电子散射模型的测试，并揭示了散射过程的量子动力学，其中涉及库仑相互作用，电子自旋过程（自旋交换，自旋轨道）和共振相互作用的细节。随着计算能力的迅速提高，迄今为止的模型一直在发展，以处理更复杂的目标。本项目将着眼于发射的真空紫外线辐射的偏振，垂直于散射平面，与差分散射电子的能量损失与辐射的激发能量一致。重要的是，它将测量真空紫外线中辐射的圆偏振，这是一个与散射电子赋予目标的角动量有关的参数，并为碰撞过程提供了有价值的物理见解。此外，新的飞行时间光谱仪（使用快速1纳秒脉冲电子束）的开发将能够绝对校准散射截面，并能够处理0.5eV至20 eV能量范围内的慢速出射电子，并增加整体测量的范围和准确性。该项目的目的是继续有效地提供涉及实验室研究的大学生的准确碰撞数据。