MRI: Development of a 3-D Imaging for Vibrationally Resolved Cross Section Measurements

MRI：开发用于振动分辨横截面测量的 3D 成像

• 批准号: 1530944
• 负责人: Vola Andrianarijaona
• 金额: $ 18.95万
• 依托单位: Pacific Union College
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2015
• 资助国家: 美国
• 起止时间: 2015-10-01 至 2019-09-30
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=1530944&HistoricalAwards=false
• 关键词: MRI; Development; Imaging; Vibrationally; Resolved

The goal of this project is to develop a versatile device that probes quantum properties of small diatomic molecular ions (particles composed of two atoms that have lost one or more electrons). The singly charged hydrogen molecular ion (two protons, bound together by a single electron) is a simple but fundamental example of such an ion. Diatomic molecular ions are important because they are abundantly found in space, and might also briefly exist in other settings, including living organisms. The mechanism binding the two atoms is very similar to a coiled spring, allowing the atoms to move one with respect to the other without going astray. According to the basics of Quantum Mechanics, a diatomic molecular ion is continually vibrating in a range of discrete quantum states at different temperatures, which are defined by integers that state the degree of vibration on a given scale for which the bigger the integer, the stronger the pulsation. The proposed device probes these discrete states and is comparable to a thermometer reading a low temperature for a cold object and high temperature for hot one. It will also provide data that will help to understand how the vibrational states affect their environment during interaction with other particles. Not well understood, these slow interactions, technically called low energy interactions, are known to play important roles in the interstellar medium, in the cold part of nuclear fusion plasmas, and in the processes of DNA strand breaks, etc. Thus, this project will promote the progress of science and may have implications to a broad spectrum of areas of importance to society; at the same time, it will give participating undergraduate students the opportunity to take part in the development of a sophisticated 3-D imaging device at their own institution.The charge transfer in collisions between hydrogen and diatomic molecular ions touches a variety of disciplines spreading from physical science to life science. First of all, it is of foremost importance in fundamental physics because it involves the smallest atom. It is also one of the dominant reactions in environments such as the cold divertor plasma regions of a fusion tokamak or in interstellar clouds where the main constituents are neutral H, the positive hydrogen ion, and H-molecules. Moreover, understanding of this simplest fundamental system is a key for mastering more complex systems which exist in, e.g., biophysics where radical attacks on biomolecules such as DNA potentially involve charge transfer at very low energy. However, it is often almost impossible to compare laboratory measured cross sections to existing theories and calculations because the vibrational state distribution of the molecules is not known. The proposed 3-D imaging device will ultimately improve previously measured absolute cross section measurements by making them vibrationally resolved, enabling a more detailed comparison between theoretical and experimental results. In this 3-D imaging technique, the molecular ion undergoes a resonant dissociative charge exchange with an alkali atom and releases its vibrational energy in the form of kinetic energy of the two fragments. The detection of the positions of the daughter particles and their flight time differences made possible with the detectors allows the reconstruction of the molecular ion's initial vibrational energy via simple dynamics. This detection technique is equivalent to taking a time resolved snapshot picture of the molecular ion fragments (thus the name 3-D imaging). The whole 3-D imaging apparatus is envisioned to be a portable device which could be easily transported to and used at a variety of research facilities.

该项目的目标是开发一种多功能设备，用于探测小双原子分子离子(由失去一个或多个电子的两个原子组成的粒子)的量子性质。单电荷氢分子离子(两个质子，由一个单电子结合在一起)是这种离子的一个简单但基本的例子。双原子分子离子很重要，因为它们在太空中大量存在，也可能短暂地存在于其他环境中，包括活的有机体。结合这两个原子的机制非常类似于螺旋弹簧，允许原子相对另一个移动，而不会迷失方向。根据量子力学的基本原理，双原子分子离子在不同温度下在一系列离散的量子态中持续振动，这些态由整数定义，这些整数表示给定标度上的振动程度，整数越大，脉动越强。所提出的装置探测这些离散状态，可与温度计相媲美，读出冷物体的低温和热物体的高温。它还将提供有助于理解振动状态在与其他粒子相互作用期间如何影响环境的数据。这些缓慢的相互作用，在技术上被称为低能相互作用，已知在星际介质、核聚变等离子体的冷部分以及DNA链断裂等过程中发挥重要作用。因此，该项目将推动科学进步，并可能对社会重要领域产生广泛影响；同时，它将给参与的本科生提供机会，在他们自己的机构参与复杂的三维成像设备的开发。氢与双原子分子离子之间的碰撞中的电荷转移涉及从物理科学到生命科学的各种学科。首先，它在基础物理学中是最重要的，因为它涉及最小的原子。在聚变托卡马克的冷偏滤器等离子体区域或星际云中，它也是主要的反应之一，在这些环境中，主要成分是中性H、正氢离子和H分子。此外，理解这个最简单的基本系统是掌握更复杂的系统的关键，这些系统存在于生物物理学中，在生物物理学中，对DNA等生物分子的自由基攻击可能涉及非常低能量的电荷转移。然而，将实验室测量的截面与现有的理论和计算进行比较几乎是不可能的，因为分子的振动态分布是未知的。建议的三维成像设备最终将通过振动分辨来改进先前测量的绝对横截面测量，从而能够在理论和实验结果之间进行更详细的比较。在这种三维成像技术中，分子离子与碱原子发生共振解离电荷交换，并以两个碎片的动能的形式释放其振动能量。探测器能够检测子粒子的位置和它们的飞行时间差，从而可以通过简单的动力学重建分子离子的初始振动能量。这种探测技术相当于拍摄分子离子碎片的时间分辨快照照片(因此而得名3D成像)。整个3D成像设备被设想为一种便携式设备，可以很容易地运输到各种研究设施并在其上使用。