Development of a Simplified Cavity Thermal Ionization Source for Geoscience Applications

用于确定材料化学和同位素组成的仪器的改进为从材料科学到医学的各种领域提供了关键的进步。 通常，天然材料，如岩石和环境样品，被证明是最难分析的，因为它们是周期表中每种元素的复杂混合物。 任何元素最显著的特征是它的质量和同位素组成。 这导致了质谱仪在20世纪20年代的发明，并导致了这种类型仪器的能力的逐渐扩展，使得现在大量不同类型的质谱仪构成了每当需要化学分析，特别是同位素分析时最广泛使用的仪器。 质谱仪的灵敏度取决于待分析元素转化为带电离子的效率，称为电离效率。 该项目将以橡树岭国家实验室开发的基本仪器为基础，扩大空腔离子源的使用范围，用于地球科学的化学和同位素测量。 腔离子源由一个狭窄的（1毫米直径）管，其中放置样品。 然后将空腔加热到极端温度（高达3000 C），导致样品蒸发。 单个样品原子在到达腔开口的途中反复地撞击腔壁。 每当原子接触到腔的热金属表面时，它就有有限的概率被电离。 一旦它这样做了，在腔的开口处施加的电场提取离子并将其加速进入质谱仪。 腔离子源的电离效率比传统的热电离质谱仪高10-50倍。 空腔离子源电离效率的提高将使分析能够扩展到比目前可能的小10-50倍的样品大小，或者使大样品的同位素组成分析精度更高。 该项目应用增强灵敏度的腔离子源，重点研究固体地球形成的过程和时间尺度，以及它如何以及何时分离成地核、地幔、和地壳导致的可居住的环境和集中的资源，使生命在地球上生存和繁荣。这笔赠款将允许开发一个简化的腔热离子源，这将大大提高一种广泛用于地球科学研究的质谱仪的灵敏度。 近世纪来，热电离质谱（TIMS）一直是地球科学中的重要工具，广泛应用于放射性年代学、同位素示踪和高灵敏度化学分析等领域。腔热离子源，如在核实验室中使用的那些，对于在地球科学中有用的各种元素（例如，Cr、Sr、Nd、Pb）。 这种幅度的灵敏度改进转化为样本量的类似幅度减少，以在当前精度水平下进行同位素测量，或者替代地允许对与当前使用的样本量类似的样本量进行更高精度的同位素比分析。 该项目的目标是设计一种腔体离子源，可以很容易地适应地球科学中常用的商业TIMS类型，以提供大大提高的电离效率，同时保持现代TIMS仪器的简单性，清洁度和易用性。 同位素比测量解决了地球科学中的许多一级问题，从提供放射性地质年代学的基础，到追踪许多改变地球表面和内部的主要化学过程。 一个离子源，可以提供10倍或更多的增加灵敏度超过现有的来源，但保留了简单性，易用性，和清洁的现有仪器将发现迅速采用地球科学界和商业仪器制造商，服务于该社区。该项目还将包括培训一名早期职业科学家，他不仅要学习按计算机上的哪些按钮来告诉仪器产生数据，还要学习质谱仪的基本物理学。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。

Improvements in the instrumentation used to determine the chemical and isotopic composition of materials have provided critical advances across a wide variety of fields from material science to medicine. Often, natural materials, such as rocks and environmental samples, prove to be the most difficult to analyze as they are complex mixtures of every element in the periodic table. The most distinguishing characteristic of any element is its mass and isotopic composition. This gave rise to the invention of the mass spectrometer in the 1920's and to the gradual expansion of the capabilities of this type of instrument so that now a vast array of different types of mass spectrometers constitute the most widely used instrument whenever chemical, and particularly isotope, analyses are needed. The sensitivity of the mass spectrometer depends on how efficiently the element(s) to be analyzed can be turned into electrically charged ions, termed ionization efficiency. This project will build on basic instrumentation developments done at Oak Ridge National Laboratory to extend and expand the use of a cavity ion source for chemical and isotopic measurements applied to the geosciences. The cavity ion source consists of a narrow (1 mm diameter) tube into which the sample is placed. The cavity is then heated to extreme temperatures (up to 3000 C) causing the sample to evaporate. Individual sample atoms repeatedly bounce against the walls of the cavity on their way to the cavity opening. Whenever an atom touches the hot metal surface of the cavity, it has a finite probability of becoming ionized. Once it does, the electric field applied at the opening of the cavity extracts the ion and accelerates it into the mass spectrometer. Cavity ion sources have demonstrated ionization efficiencies 10-50 times greater than that of the conventional instruments, known as thermal ionization mass spectrometers. The improvement in ionization efficiency in cavity ion sources will allow analyses to be extended to sample sizes 10-50 times smaller that currently possible, or allow the isotopic composition of large samples to be analyzed to much higher precision. This projects application of the enhanced sensitivity of the cavity ion source will focus on study of the processes and timescales by which the solid Earth formed, and how and when it separated into core, mantle, and crust leading to the habitable environments and concentrating the resources that allow life to survive and prosper on Earth.This grant will allow development of a simplified cavity thermal ion source that will dramatically improve the sensitivity of a type of mass spectrometer widely used for geoscience studies. Thermal ionization mass spectrometry (TIMS) has been a critical tool in geosciences for almost a century, on a wide range of topics that depend on radioactive chronology, isotope tracing, and high-sensitivity chemical analyses. Cavity thermal ion sources, like those used in nuclear laboratories, can offer up to a factor of 10-50 increase in ionization efficiency over conventional TIMS for a variety elements that are useful in the geosciences (e.g., Cr, Sr, Nd, Pb). Sensitivity improvements of this magnitude translate to similar magnitude reductions in sample size to make isotopic measurements at current levels of precision, or alternatively allow much higher precision isotope ratio analyses for sample sizes similar to those used currently. The goal of the project is to design a cavity ion source that can be readily adapted to the type of commercial TIMS commonly used in the geosciences to provide greatly enhanced ionization efficiencies while retaining the simplicity, cleanliness, and ease of use of the modern TIMS instrument. Isotope ratio measurements address many first order questions in the geosciences, from providing the basis for radiometric geochronology, to tracing of many of the main chemical processes that act to modify Earth's surface and interior. An ion source that can offer factors of 10 or more increased sensitivity over existing sources, but retains the simplicity, ease of use, and cleanliness of existing instruments would find rapid adoption by the geoscience community and the commercial instrument manufacturers that serve that community. The project also will involve the training of an early career scientist who will learn not only which buttons on the computer to push to tell the instrument to produce data, but the basic physics of the mass spectrometer.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.