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Many-body theory of positron interactions with atoms and molecules

正电子与原子和分子相互作用的多体理论

基本信息

批准号：
EP/N007948/1
负责人：
Dermot Green
金额：
$ 34.71万
依托单位：
Queen's University Belfast
依托单位国家：
英国
项目类别：
Fellowship
财政年份：
2015
资助国家：
英国
起止时间：
2015 至无数据
项目状态：
已结题

来源：
https://gtr.ukri.org/projects?ref=EP%2FN007948%2F1
关键词：
Many body theory positron interactions

项目摘要

Positrons are the antiparticles of electrons. They are produced in abundance in our Galaxy, and are readily obtained on Earth using accelerators or radioactive isotopes. When positrons come into contact with their matter counterparts, the pair annihilate in a pyrotechnic flash, releasing all their energy as pure light. This emitted light is detectable, and is strongly characterised by the environment the electron was in immediately prior to annihilation, making positrons a unique probe. As such, they have important use in medical imaging in PET (Positron Emission Tomography) scans, diagnostics of industrially important materials, and understanding the distribution of antimatter in the Universe.When low-energy positrons interact with normal matter, such as atoms, they pull strongly on the electrons and may even cause one of the electrons to `dance' around the positron, forming so-called positronium (as the positron and electron may annihilate, this may ultimately be a `dance to the death'). Such effects are known collectively as `correlations'. Correlations have a very strong effect on positron collisions with atoms and molecules. In particular, they can enhance the rate of positron annihilation by many orders of magnitude. They also make the accurate description of the positron-atom system a challenging theoretical problem. Proper interpretation of material science experiments, however, rely heavily on calculations that must fully account for the correlations. For example, to accurately interpret Positron Induced Auger Electron Spectroscopy, a powerful technique used to study defects and corrosion in materials, one requires the exact relative probabilities of annihilation with core electrons of various atoms. Moreover, accurate description of the positron-molecule system is required to help explain the origin of the strong annihilation signal from the galactic centre; to develop new spectroscopic PET-scanning methods for medical imaging, drug development and industrial diagnostics; and to advance antimatter-matter chemistry. Crucial in all cases is the ability of theory to accurately calculate the response of the atomic and molecular structure to the positron.A powerful method of describing the positron-atom or molecule system, which allows for the study and inclusion of correlations in a natural, transparent and systematic way, is many-body theory. In this method, complicated mathematical expressions that describe processes of interest, e.g., positron annihilation with an atomic electron, are replaced by series of relatively simple and intuitive diagrams, each of which represents a distinct correlation process. This programme of research proposes to develop new state-of-the-art diagrammatic many-body theory, and recently emerged revolutionary computational methods for high-precision calculations of positron annihilation with individual electrons in complex atoms and molecules. These computational methods will allow for the summation of millions of diagrams, completely unfeasible using the best existing brute-force methods, providing a powerful framework that can yield precision calculations in addition to keen insight. Moreover, the application of the methods will naturally extend to other important atomic and molecular properties and processes, required for tests of fundamental physics and development of quantum technologies.The unique and unrivalled calculational capability that this programme will develop will enable the most accurate interpretation of industrially important materials science experiments at recently launched international facilities; help provide fundamental insights into antimatter in the Galaxy; explain existing experimental results that remain crying out for theoretical explanation; advance Positron Emission Tomography technology and antimatter-matter chemistry; and overall, illuminate this intricate dance of matter and antimatter.

正电子是电子的反粒子。它们在我们的银河系中大量产生，并且很容易在地球上使用加速器或放射性同位素获得。当正电子与它们的物质对应物接触时，这对正电子在一个烟火般的闪光中湮灭，释放出它们所有的能量作为纯粹的光。这种发射的光是可检测的，并且强烈地表征了电子在湮灭之前所处的环境，使正电子成为独特的探针。因此，它们在PET中的医学成像中具有重要用途（正电子发射断层扫描）扫描，诊断工业上重要的材料，并了解反物质在宇宙中的分布。当低能量正电子与正常物质（如原子）相互作用时，它们强烈地吸引电子，甚至可能导致其中一个电子在正电子周围“跳舞”，形成所谓的正电子素（正电子和电子可能会湮灭，这可能最终是一场“死亡之舞”）。这些效应统称为“相关性”。关联对正电子与原子和分子的碰撞有很强的影响。特别是，它们可以将正电子湮灭的速率提高许多数量级。这也使得正电子-原子系统的精确描述成为一个具有挑战性的理论问题。然而，材料科学实验的正确解释在很大程度上依赖于必须充分考虑相关性的计算。例如，为了准确地解释正电子感应俄歇电子能谱，一种用于研究材料中缺陷和腐蚀的强大技术，人们需要各种原子的核心电子湮灭的精确相对概率。此外，需要准确描述正电子分子系统，以帮助解释来自银河系中心的强烈湮灭信号的起源;开发新的光谱PET扫描方法用于医学成像，药物开发和工业诊断;并推进反物质化学。在所有情况下，理论的关键是精确计算原子和分子结构对正电子的响应的能力。描述正电子-原子或分子系统的一种强有力的方法是多体理论，它允许以自然、透明和系统的方式研究和包含相关性。在该方法中，描述感兴趣的过程的复杂数学表达式，例如，正电子与原子电子的湮灭，被一系列相对简单和直观的图表所取代，每一个图表都代表了一个不同的相关过程。该研究计划提出开发新的最先进的图解多体理论，以及最近出现的革命性计算方法，用于复杂原子和分子中单个电子的正电子湮灭的高精度计算。这些计算方法将允许对数百万个图表进行求和，使用现有的最佳蛮力方法是完全不可行的，提供了一个强大的框架，除了敏锐的洞察力之外，还可以产生精确的计算。此外，这些方法的应用将自然扩展到基础物理测试和量子技术发展所需的其他重要原子和分子性质和过程，该方案将开发的独特和无与伦比的计算能力将能够最准确地解释最近启动的国际设施中的重要工业材料科学实验;帮助提供对银河系中反物质的基本见解;解释现有的实验结果，仍然迫切需要理论解释;推进正电子发射断层扫描技术和反物质化学;总体而言，照亮物质和反物质的复杂舞蹈。