Ion and photon beam interactions with atoms and materials: fundamental physics and inter-disciplinary applications including chemical analysis of the Martian surface

我们工作的基础是原子物理学，我们在原子物理学中对涉及内电子动力学的过程进行了许多测量，目的是测试当前的理论计算。我们的测量包括粒子加速器、X射线光谱仪，以及能量分散的X射线光谱的复杂计算机处理。作为支持，我们致力于X射线探测器的特性和光谱拟合方法。我们最近的重点有点转移到特定基本参数(FP)的研究上，这些参数是基于X射线激发和发射的材料分析技术的基础。这些方法包括X射线荧光、电子探针和质子诱导X射线发射(PIXE)，它们可以相对于认证的标准进行元素分析，也可以采取无标准的方法，然后要求准确了解必要的FP。新的人造材料的出现速度如此之快，以至于许多紧急分析都没有标准可用，因此对更准确的FP的需求最近有所增长。需要新的实验方法。我们目前的重点是低能X射线穿过物质时的光电吸收；吸收系数对于准确的X射线发射分析是至关重要的，但目前广泛使用的理论和实验表格显示，轻元素如硅的X射线存在很大差异。我们介绍了一种基于PIXE的新方法，并计划扩展该方法。**这项基础工作支持了我们对PIXE分析发展的广泛贡献，PIXE分析使用相同的硬件和类似的计算方法。利用微束(MICRO-PIXE)测量样品表面的元素分布情况，我们的很多工作都是用Guelph扫描核微探头完成的，该探头是开展大量跨学科合作的基础，涵盖了矿藏化学、城市和农村地区气溶胶以及北极和大西洋鱼类物种的迁徙等不同主题。我们用于PIXE分析的GUPIX软件已经供应给世界各地的170个离子束分析实验室，包括卢浮宫博物馆的Aglae实验室。我们现在计划扩展GUPIX，以支持与质子诱导伽马射线发射和质子背向散射等其他离子束技术同时部署PIXE的测量方法。**以PIXE和GUPIX为起点，我们创建了新的方法和新的软件，用于分析由火星漫游者勇气号、机遇号和好奇号上的阿尔法粒子X射线光谱仪(APXS)记录的火星岩石和土壤的X射线光谱。这使我们能够校准火星科学实验室APXS以测量元素浓度，并了解样品矿物学对不同岩石类型(如玄武岩、粗面岩等)元素分析的影响程度。这项涉及物理、矿物学和地球化学的工作真正是跨学科的。我们设计了一种新的方法来处理火星的部分数据--所谓的“X射线散射峰”--这使得我们首次对火星赤道附近地下土壤中的水进行了现场定量测量；这种方法正在进行改进，以降低其检测下限。我们研究的主要部分现在致力于扩展APXS作为加拿大未来行星和月球任务的独特仪器的能力。例如，我们开发了一种蒙特卡罗方法来模拟给定样品的APXS响应，这可能构成将APXS数据与X射线衍射结果相结合的新方法的基础。

The foundations of our work lie in atomic physics, where we have made many measurements on processes involving inner-electron dynamics for the purpose of testing current theoretical calculations. Our measurements involve particle accelerators, X-ray spectrometers, and sophisticated computer processing of energy-dispersed X-ray spectra. In support, we work on X-ray detector properties and spectrum fitting methodology. Our focus has recently shifted somewhat towards the study of specific fundamental parameters (FPs) which underpin materials analysis techniques that are based on X-ray excitation and emission. These methods, which include X-ray fluorescence, electron microprobe and proton-induced X-ray emission (PIXE), can conduct elemental analysis relative to certified standards or they can take a standard-less approach which then demands accurate knowledge of the necessary FPs. The rate of emergence of new human-made materials is such that standards are not available for many urgent analyses and so the demand for more accurate FPs has grown recently. New experimental approaches are needed. Our present focus is on photo-electric absorption of low-energy X-rays as they traverse matter; the absorption coefficients are crucial to accurate X-ray emission analysis, but current widely-used theoretical and experimental tabulations show large differences for the X-rays of light elements such as silicon. We have introduced a new method based on PIXE and plan to expand this approach. * *This fundamental work has supported our extensive contributions to the development of PIXE analysis, which employs the same hardware and similar computational methods. Using microbeams (micro-PIXE) gives the option of mapping sample surfaces for element distributions Much of our work has been done with the Guelph scanning nuclear microprobe, which has been the basis for a large number of inter-disciplinary collaborations covering diverse topics such as chemistry of mineral deposits, urban and rural aerosols, and migration of Arctic and Atlantic fish species. Our GUPIX software for PIXE analysis has been supplied to 170 ion beam analysis labs around the world, including the Louvre Museum's AGLAE lab. We plan now to expand GUPIX to support measurement approaches which deploy PIXE simultaneously with other ion beam techniques such as proton-induced gamma-ray emission and proton backscattering.**With PIXE and GUPIX as the starting points, we have created new methodology and new software for analysis of X-ray spectra of Martian rocks and soils recorded by the alpha-particle X-ray spectrometers (APXS) on the Mars Rovers Spirit, Opportunity and Curiosity. This enabled us to calibrate the Mars Science Laboratory APXS for measurement of element concentrations, and to understand the degree to which sample mineralogy can affect element analysis in different rock types, e.g. basalts, trachytes etc. This work, at the interface of physics, mineralogy and geochemistry, is truly inter-disciplinary. We have devised a new approach to part of the Martian data - the so-called "X-ray scatter peaks" - which resulted in our making the first quantitative in situ measurement of water within subsurface soils near the Martian equator; this method is undergoing refinement to lower its detection limits. A major part of our research is now devoted to extending the capabilities of the APXS as a unique Canadian instrument for future planetary and lunar missions. For example, we have developed a Monte Carlo method for modeling APXS response to a given sample, and this may form the basis of a new approach which combines APXS data with X-ray diffraction results.