Interaction of Low-Energy Positrons with Atoms and Molecules

低能正电子与原子和分子的相互作用

• 批准号: 2306404
• 负责人: Clifford Surko
• 金额: $ 74.64万
• 依托单位: University of California-San Diego
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2023
• 资助国家: 美国
• 起止时间: 2023-09-01 至 2026-08-31
• 项目状态: 未结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=2306404&HistoricalAwards=false
• 关键词: Interaction; Low; Energy; Positrons; Atoms

This research project focuses on science with positrons (the antiparticles of electrons). Positrons play an important role in basic science, including atomic, plasma and astrophysics, biology and medicine. Positrons also have many technological applications such as new techniques for mass spectroscopy, the characterization of materials, and positron emission tomography (PET), the latter to study metabolic processes and for drug design. While some aspects of positron interactions with matter are well understood, there are many outstanding questions. When positrons and electrons collide, they can ‘annihilate’ – i.e. their energy, originally in the form of mass, is converted into gamma rays. The research group has shown that positrons briefly – typically for less than one hundred millionth of a second - bind to most molecules before undergoing annihilation. The present project will carry out a more detailed study of the binding of positrons on various molecules. These positron binding studies are relevant to positron surface states on materials and the fate of positrons in PET and in the interstellar medium. In terms of scientific education and training, the research actively involves students and young researchers at all levels, from the planning of experiments to the dissemination of research results. The project involves small-scale experiments that are an excellent training ground for scientific and technical personnel. The work is communicated broadly, not only to physics audiences but also to those involved in plasma, chemical, and materials science, and gaseous electronics research. In previous research, the group showed that positrons bind to molecules. Two important intellectual challenges related to this phenomenon are to develop methods to treat electron-positron correlations and to better understand the role of vibrational dynamics in positron annihilation processes. One focus of the project is to gain a better understanding of positron binding to molecules, the magnitudes of binding energies, and what they depend upon. A second objective is to gain a better understanding of mechanisms for positron annihilation in molecules. This process proceeds by means of vibrational resonances and results in annihilation rates orders of magnitude greater than expected in simple collisions. The experiments will be conducted with a tunable, state-of-the-art, high-energy-resolution positron beam, developed by the research team, that is now coming to full capability. This device is expected to play an important role in making high-resolution measurements as a function of incident positron energy. It is expected to provide new insights into the critical role of molecular dynamics in resonant positron annihilation. The research group’s experimental work has motivated complementary theoretical work by groups around the world with the goal of gaining a more complete and fundamental understanding of resonant positron annihilation and positron-molecule binding.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.

该研究项目重点关注正电子（电子的反粒子）科学。正电子在基础科学中发挥着重要作用，包括原子、等离子体和天体物理学、生物学和医学。正电子还有许多技术应用，例如质谱新技术、材料表征和正电子发射断层扫描 (PET)，后者用于研究代谢过程和药物设计。虽然正电子与物质相互作用的某些方面已被很好地理解，但仍存在许多悬而未决的问题。当正电子和电子碰撞时，它们会“湮灭”——也就是说，它们的能量最初以质量形式转化为伽马射线。研究小组表明，正电子在湮灭之前会短暂地（通常不到亿分之一秒）与大多数分子结合。本项目将对正电子与各种分子的结合进行更详细的研究。这些正电子结合研究与材料上的正电子表面状态以及 PET 和星际介质中正电子的命运有关。在科学教育和培训方面，该研究积极让各级学生和年轻研究人员参与，从实验的规划到研究成果的传播。该项目涉及小规模实验，是培养科技人员的良好平台。 这项工作不仅向物理学读者广泛传播，而且还向那些参与等离子体、化学、材料科学以及气体电子学研究的人们传播。 在之前的研究中，该小组表明正电子与分子结合。与这种现象相关的两个重要的智力挑战是开发处理电子-正电子相关性的方法以及更好地理解振动动力学在正电子湮灭过程中的作用。该项目的重点之一是更好地了解正电子与分子的结合、结合能的大小以及它们所依赖的因素。第二个目标是更好地了解分子中正电子湮灭的机制。这个过程通过振动共振进行，并导致湮灭率比简单碰撞中预期的要大几个数量级。这些实验将使用由研究团队开发的可调谐、最先进的高能量分辨率正电子束进行，该正电子束现已完全具备能力。该设备预计将在作为入射正电子能量函数的高分辨率测量中发挥重要作用。预计它将为分子动力学在共振正电子湮灭中的关键作用提供新的见解。该研究小组的实验工作促进了世界各地团体的补充性理论工作，其目标是对共振正电子湮灭和正电子分子结合获得更完整和基本的理解。该奖项反映了 NSF 的法定使命，并通过使用基金会的智力价值和更广泛的影响审查标准进行评估，被认为值得支持。