RUI: Positronium Scattering By Atoms, Molecules and Surfaces

正电子(Ps)是电子和正电子的束缚状态。在这个项目中，PI将研究Ps原子与各种原子和分子的相互作用，通过建立这些相互作用的模型，然后计算与这些目标的散射截面。电子和正电子散射已经得到了广泛的研究，而Ps散射的研究相对较少。这在一定程度上是因为Ps是一个复合体，这使得理论和实验都更加困难。最近的实验表明，在很大的射速范围内，电子和Ps的散射是惊人的相似。在很低的ps速度下，实验和理论之间存在一些差异，基本问题仍有待回答。这项工作有助于理解较高速度下的相似性，并解决较低速度下的差异。这些研究可以提供对物质和反物质之间的基本相互作用的洞察，并有助于更好地了解涉及正电子发射断层扫描(PET)和探测材料缺陷的技术。本科生参与了这项研究，目的是为他们提供一个应用数学方法解决现实世界物理问题的机会。在这个项目中，PI将研究Ps与原子、分子和表面的碰撞。该计划将计算各种原子和分子目标的弹性散射截面和电离(Ps分裂)截面。为了描述Ps与目标原子或分子之间的相互作用，PI将使用自由电子气模型，该模型已被成功地用于描述Ps与稀有气体原子和分子氮碰撞中的交换和关联效应。PI还将使用正交化赝势模型来考虑泡利不相容原理的排斥效应。重点将是将这些模型扩展到分子，以及除了稀有气体之外的原子目标。PI还将寻求通过改进模型中固有的近似来更好地理解Ps原子/分子相互作用。PI以前已经开发了一个用于计算电离截面的二元相遇模型，该模型将允许计算新的原子和分子靶的总截面。PI还计划扩展模型，以研究P与LiF等表面的散射。这一奖项反映了NSF的法定使命，并通过使用基金会的智力优势和更广泛的影响审查标准进行评估，被认为值得支持。

Positronium (Ps) is the bound state of an electron and positron. In this project the PI will study the interaction of the Ps atom with a variety of atoms and molecules, by developing models of these interactions and then calculating scattering cross sections with these targets. Electron and positron scattering has been studied quite extensively while Ps scattering has been studied relatively little in comparison. This is partly because Ps is a composite object which makes both theory and experiment more difficult. Recently, experiments have shown that electron and Ps scattering are surprisingly similar over a wide range of projectile velocities. At very low Ps velocities there is some discrepancy between experiment and theory, and fundamental questions remain to be answered. This work can help to understand the similarity at higher velocities and to resolve the discrepancy at low velocities. These studies can provide insight into the fundamental interactions between matter and anti-matter and help to provide a better understanding of technologies that involve Ps such as Positron Emission Tomography (PET) and the probing of defects in materials. Undergraduate students are involved in this research with the goal of providing them with an opportunity to apply mathematical methods to solve real world physical problems. In this project the PI will study Ps collisions with atoms, molecules and surfaces. The plan is to calculate elastic scattering cross sections as well as ionization (Ps break-up) cross sections for a variety of atomic and molecular targets. To describe the interaction between Ps and the target atom or molecule the PI will use a free electron gas model that has been previously successfully used to describe the exchange and correlation effects in Ps collisions with rare-gas atoms and molecular nitrogen. The PI will also employ an orthogonalizing pseudopotential model to take account of the repulsive effect of the Pauli exclusion principle. The focus will be on extending these models to molecules, as well as to atomic targets besides the rare-gases. The PI will also seek to better understand the Ps-atom/molecule interaction by seeking to improve the approximations inherent in the models. The PI has previously developed a binary encounter model for calculation of the ionization cross section which will allow calculation of total cross sections for new atomic and molecular targets. The PI also plans to extend the models to study the scattering of Ps with surfaces such as LiF.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.