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Title:
Impacts of Accelerator Mass Spectrometry on the Earth Sciences
Authors:
Stone, J. O.; Caffee, M. W.
Affiliation:
AA(Department of Earth and Space Sciences, Box 351310, University of Washington, Seattle, WA 98195-1310 United States ; ), AB(PRIME Lab, Physics Department, Purdue University, West Lafayette, IN 47907-1396 United States ; )
Publication:
American Geophysical Union, Fall Meeting 2002, abstract #U12A-11
Publication Date:
12/2002
Origin:
AGU
AGU Keywords:
3630 Experimental mineralogy and petrology, 6344 System operation and management, 7294 Instruments and techniques
Abstract Copyright:
(c) 2002: American Geophysical Union
Bibliographic Code:
2002AGUFM.U12A..11S

Abstract

Accelerator Mass Spectrometry (AMS) provides a means of detecting rare radionuclides with half-lives in the range 103 - 107 years, at relative isotopic abundances down to 10-15. AMS combines high sensitivity and efficiency with low backgrounds, giving detection limits of 104 - 105 atoms for many nuclides. Due to the cost, complexity and scale of the technology, most AMS analyses are performed at shared, multi-purpose facilities. Recent growth in the availability of AMS analyses has led to major developments in: (i) Radiocarbon dating and related areas of Quaternary climatic and environmental research. Many thousands of geological C-14 measurements are now performed annually, on samples containing ~ 1 mg of carbon. (ii) Chronology of the Earth's surface, and the quantitative study of geomorphic processes, using cosmic-ray-produced nuclides. The ability to measure cosmogenic Be-10, Al-26 and Cl-36 in surficial rocks and minerals has given rise to methods for dating and correlating glacial, fluvial and marine deposits, determining earthquake recurrence patterns and displacement rates on faults, among many other applications. Analogous methods have been developed to study the geomorphic evolution of eroding and aggrading surfaces, at scales ranging from outcrops to drainage basins. Results from these studies complement recent developments in thermochronology, and have helped to advance our understanding of the interplay between tectonic and surficial processes in the evolution of mountain belts. (iii) Radioisotopic tracing of oceanic, hydrologic and atmospheric flows. AMS measurements of natural and man-made nuclides, such as H-3, C-14, Cl-36 and I-129, are contributing to large-scale ocean circulation studies and estimation of the recharge rates and residence times of groundwater. Technological improvements continue to increase efficiency and sample throughput at AMS facilities. Future developments are likely to reduce the size and operating voltage of AMS accelerators. Smaller instruments are already making significant contributions in C-14 analysis, but cannot yet match the ability of large accelerators to analyse heavy-ions such as Cl-36. No competing atom-counting technique seems likely to reach the level of practicality of AMS in the foreseeable future.
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