The underlying physics of the resonance ionization mass spectrometric technique in association with laser desorption measurements remains under-explored, and the application to isotopic measurements largely untested when compared with other approaches. When the technique was first implemented, lasers were expensive and balky to use, limiting the ultimate application of the method. Since that time, lasers have evolved significantly, resulting in lower cost, size, power, and increased ease of use, enabling measurements using laser desorption as the basis for the mass spectrometer. Because of these advances, secondary ionization approaches can approach 100% efficiency, enabling sub-parts per billion detection limits, and significantly increased measurement precision. This proposal expands the basic physical understanding of the underlying atomic processes, in addition to exploring methods that could enable real-time in-situ isotopic measurements of trace isotopic and elemental systems. Initial results show that the laser and mass spectrometer systems could be made portable for real-time field use, while maintaining sufficient precision and accuracy for enabling geo-chronology, geo-location, forensics, archeology, food tracking, and studying nuclear processes. The team will engage students in the geologic science, physics, and engineering of geo-chronology, resonance ionization, and mass spectrometry in order to support this effort.

Project Report

This NSF supported work has shown for the first time that sophisticated isotopic measurements such as geolocation and Rb-Sr geochronology, traditionally requiring months of sample preparation and analysis in a laboratory, can be rapidly completed in field settings, albeit at lower precision. For the first time, decades old physics have been used to implement a Laser Desorption Resonance Ionization Mass Spectrometer (LDRIMS), has been demonstrated for geochronology in a bench-top form (Fig.1), and miniaturized to function in a portable form (Fig. 2). The underlying physics of the RIMS technique in association with laser desorption measurements remains under-explored, and the application to isotopic measurements largely untested when compared with more traditional Thermal Ionization Mass Spectrometry (TIMS) and Secondary Ionization Mass Spectrometry (SIMS) approaches. By using LDRIMS instead of TIMS or SIMS, our results show that the laser and mass spectrometer systems could be made portable for real-time field use, while maintaining sufficient precision and accuracy for enabling geochronology, geolocation, forensics, archeology, food tracking, and studying nuclear processes. We have completed the research on optimizing isotope measurement and miniaturizing the LDRIMS prototype, and found: A) We can simultaneous measure of strontium and rubidium without isobars with LDRIMS; B) Can regularly obtain inter-isotope ratios with precision of better than 0.5% in under 5 minutes, and under 0.1% in 15 minutes; C) Have determined that LDRIMS' ultimate sensitivity is ~200-300 parts-per-trillion; D) Have determined the optimal resonance ionization timing for maximizing signals from strontium and rubidium, both individually and simultaneously; E) Have established that we can measure elemental chemistry and isotopes using laser ablation mass spectrometry; F) Have demonstrated difficult isotope measurements, such as repeatable dates on local granites, with errors < 100 Ma in a few hours (Fig. 3), as well shown initial sample preparation and measurement of foods and hair. G) Have demonstrated that a portable, fast, isobar-free, high sensitivity isotope measurement instrument can be made. This effort was sufficiently audacious that Nature recently ran a four page feature news feature on this effort.

Agency
National Science Foundation (NSF)
Institute
Division of Information and Intelligent Systems (IIS)
Type
Standard Grant (Standard)
Application #
1045679
Program Officer
Sylvia Spengler
Project Start
Project End
Budget Start
2010-10-01
Budget End
2012-09-30
Support Year
Fiscal Year
2010
Total Cost
$2,229,873
Indirect Cost
Name
Southwest Research Institute
Department
Type
DUNS #
City
San Antonio
State
TX
Country
United States
Zip Code
78238