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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

基本信息

批准号：
2010699
负责人：
Clifford Surko
金额：
$ 62.52万
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：
2020
资助国家：
美国
起止时间：
2020-09-01 至 2023-08-31
项目状态：
已结题

来源：
https://www.nsf.gov/awardsearch/showAward?AWD_ID=2010699&HistoricalAwards=false
关键词：
Interaction Low Energy Positrons Atoms

项目摘要

General audience abstract: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. They also have many technological applications such as new techniques for mass spectroscopy, the characterization of materials using positrons, and positron emission tomography (PET) to study metabolic processes and for drug design. While aspects of positron interactions with matter are well understood, there are many outstanding questions. When positrons and electrons collide, they can annihilate with the energy converted to gamma rays. Such processes are important facets in gaining an understanding of the physics and chemistry of the interaction of matter and antimatter. This research group has shown that positrons bind to many molecules (lifetimes before annihilation less than one hundred millionth of a second). The positron binding studies the group will be doing are relevant to positron surface states on materials and the fate of positrons in PET. In terms of scientific education and training, the research will actively involve 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 will be communicated broadly, not only to physics audiences but also to those involved in plasma, chemical, and materials science, and gaseous electronics research. Antimatter in the laboratory is an important new frontier of science. It is regarded with considerable fascination by lay audiences; and as such, it aids in helping broader segments of society to appreciate basic research in the physical sciences.Technical audience abstract:In previous research, the group showed that positrons bind to molecules. Two important intellectual challenges related to this phenomenon, and the modes of annihilation that result from it, are to develop methods to treat electron-positron correlations and to better understand the role of molecular dynamics in positron annihilation processes when a positron is in the proximity of neutral matter. The research being conducted under this award speaks to both of these issues. One focus of the project is gaining a better understanding of positron binding to molecules, the magnitudes of these binding energies, and what they depend upon. A second objective is gaining a better understanding of mechanisms for positron annihilation in molecules, which proceeds by a resonant process in which annihilation rates can be orders of magnitude greater than expected on the basis of simple collisions. While it is appreciated that molecular vibrations play an important role in this enhancement, the details are not understood. The experiments will be conducted with a state-of-the-art, tunable, high-energy-resolution positron beam that was developed recently by the research team and is now coming to full capability. The excellent energy resolution of this new beam is expected to play an important role in making detailed annihilation spectral measurements as a function of incident positron energy. This can provide much more precise measurements of positron binding energies and key insights into the critical role molecular dynamics plays in producing greatly enhanced annihilation rates.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.

摘要：本研究项目主要研究正电子（电子的反粒子）科学。正电子在原子、等离子体和天体物理学、生物学和医学等基础科学中发挥着重要作用。它们也有许多技术应用，如质谱的新技术，使用正电子表征材料，正电子发射断层扫描（PET）研究代谢过程和药物设计。虽然正电子与物质相互作用的各个方面已被很好地理解，但仍有许多悬而未决的问题。当正电子和电子碰撞时，它们会湮灭，能量转化为伽马射线。这些过程是理解物质和反物质相互作用的物理和化学的重要方面。这个研究小组已经证明，正电子与许多分子结合（湮灭前的寿命不到一亿分之一秒）。该小组将进行的正电子结合研究与材料上的正电子表面态和正电子在PET中的命运有关。在科学教育和培训方面，从实验的规划到研究成果的传播，各级学生和青年研究人员将积极参与研究。该项目涉及小型实验，是科学和技术人员的极好训练场。这项工作将广泛传播，不仅对物理观众，而且对那些参与等离子体，化学，材料科学，和气体电子研究。实验室中的反物质是一个重要的新前沿科学。它被外行观众认为具有相当的魅力；因此，它有助于帮助更广泛的社会阶层欣赏物理科学的基础研究。技术观众摘要：在之前的研究中，该小组表明正电子与分子结合。与这一现象相关的两个重要的智力挑战，以及由此产生的湮灭模式，是开发处理电子-正电子相关关系的方法，以及更好地理解当正电子靠近中性物质时，分子动力学在正电子湮灭过程中的作用。在这个奖项下进行的研究说明了这两个问题。该项目的一个重点是更好地理解正电子与分子的结合，这些结合能的大小，以及它们依赖于什么。第二个目标是更好地理解分子中正电子湮灭的机制，这是通过共振过程进行的，其中湮灭速率可以比基于简单碰撞的预期大几个数量级。虽然人们认识到分子振动在这种增强中起着重要作用，但细节尚不清楚。实验将使用最先进的、可调谐的、高能量分辨率的正电子束进行，该正电子束是研究小组最近开发的，目前正在全面发挥作用。这种新光束具有优异的能量分辨率，有望在进行详细的湮灭光谱测量（作为入射正电子能量的函数）方面发挥重要作用。这可以提供更精确的正电子结合能测量，并对分子动力学在产生大大提高的湮灭率方面所起的关键作用有重要的见解。该奖项反映了美国国家科学基金会的法定使命，并通过使用基金会的知识价值和更广泛的影响审查标准进行评估，被认为值得支持。