Iodine-129 AMS for Earth Science, Biomedical, and National Security Applications
This Laboratory Directed Research and Development project created the capability to analyze the radionuclide iodine-129 ({sup 129}I) by accelerator mass spectrometry (AMS) in the CAMS facility at LLNL, and enhanced our scientific foundation for its application through development of sample preparation technology required for environmental, biomedical, and national security applications. The project greatly improved our environmental iodine extraction and concentration methodology, and developed new techniques for the analysis of small quantities of {sup 129}I. The project can be viewed as having two phases, one in which the basic instrumental and chemical extraction methods necessary for general {sup 129}I analysis were developed, and a second in which these techniques were improved and new techniques were developed to enable broader and more sophisticated applications. The latter occurred through the mechanism of four subprojects that also serve as proof-of-principle demonstrations of our newly developed {sup 129}I capabilities. The first subproject determined the vertical distribution of bomb-pulse {sup 129}I ({sup 129}Iv distributed globally as fallout from 1950's atmospheric nuclear testing) through 5 meters in the upper vadose zone in the arid southwestern United States. This characterizes migration mechanisms of contaminant {sup 129}I, or {sup 129}I released by nuclear fuel reprocessing, as well as the migration of labile iodine in soils relative to moisture flux, permitting a determination of nutrient cycling. The second subproject minimized the amount of iodine required in an AMS sample target. Because natural iodine abundances are very low in almost all environments, many areas of research had been precluded or made extremely difficult by the demands of sample size. Also, certain sample types of potential interest to national security are intrinsically small - for example iodine on air filters. The result of this work is the ability to measure the {sup 129}I/{sup 127}I ratio at the 2E-07 level or higher in a sample as small as a single raindrop. The third subproject tested the feasibility of using bomb-pulse {sup 129}I in shallow groundwaters in the Sierra Nevada to determine the source of waters entering into the Merced River. The sources of water and their time (age) within the hydrologic system is crucial to understanding the effects of climate change on California waters. The project is in collaboration with faculty and students at the University of California - Merced, and is now the subject of a follow-on Ph.D. dissertation project funded by the LLNL-URP University Education Participation Program. The fourth subproject examined the requirements for using the decay of {sup 129}I to date pore waters associated with continental shelf methane hydrate deposits. Understanding the age of formation and the historical stability of these hydrates is important in determining their response to climate change. Thawing of the world's methane hydrates would quickly and dramatically increase greenhouse gases in the atmosphere. The calculations and testing performed on this project have led to a follow on project that selectively implants {sup 127}I to the exclusion of {sup 129}I, creating an analytical iodine carrier with a substantially lower {sup 129}I background than is available from natural sources. This will permit measurement of {sup 129}I/{sup 127}I ratios at sub-10-14 levels, thereby providing a method for dating hydrate pore waters that are tens of millions of years old.
- Research Organization:
- Lawrence Livermore National Lab. (LLNL), Livermore, CA (United States)
- Sponsoring Organization:
- USDOE
- DOE Contract Number:
- W-7405-ENG-48
- OSTI ID:
- 908114
- Report Number(s):
- UCRL-TR-228252; TRN: US0703622
- Country of Publication:
- United States
- Language:
- English
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