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

Early maturation processes in coal. Part 1: Pyrolysis mass balances and structural evolution of coalified wood from the Morwell Brown Coal seam

In this work, we develop a theoretical approach to evaluate maturation process of kerogen-like material, involving molecular dynamic reactive modeling with a reactive force field to simulate the thermal stress. The Morwell coal has been selected to study the thermal evolution of terrestrial organic matter. To achieve this, a structural model is first constructed based on models from the literature and analytical characterization of our samples by modern 1-and 2-D NMR, FTIR, and elemental analysis. Then, artificial maturation of the Morwell coal is performed at low conversions in order to obtain, quantitative and qualitative, detailed evidences of structural evolution of the kerogen upon maturation. The observed chemical changes are a defunctionalization of the carboxyl, carbonyl and methoxy functional groups coupling with an increase of cross linking in the residual mature kerogen. Gaseous and liquids hydrocarbons, essentially CH4, C4H8 and C14+ liquid hydrocarbons, are generated in low amount, merely by cleavage of the lignin side chain

Distribution of 99Tc and 129I in the Vicinity of Underground Nuclear Tests at the Nevada Test Site

{sup 99}Tc and {sup 129}I are important contributors to risk assessment due to their long half-lives and high mobility as aqueous anionic species. We analyzed {sup 99}Tc and {sup 129}I in groundwater samples in and near 11 underground nuclear tests and in melt glass and rock samples retrieved from the Chancellor test cavity, Nevada Test Site. The {sup 129}I/{sup 127}I ratio ranges from 10{sup -3} to 10{sup -6} in cavity water and 10{sup -4} to 10{sup -9} in satellite wells. The {sup 99}Tc concentration ranges from 3 to 10{sup -4} Bq/L in cavity waters and from 0.3 to 10{sup -4} Bq/L in satellite wells. Downstream migration is apparent for both radionuclides. However, it is affected by both retardation and initial distribution. In-situ {sup 99}Tc and {sup 129}I K{sub d}s calculated using rubble and water concentrations are 3 to 22 mL/g and 0 to 0.12 mL/g, respectively and are suggestive of mildly reducing conditions. {sup 129}I distribution in the melt glass, rubble and groundwater of the Chancellor test cavity is 28%, 24% and 48%, respectively; for {sup 99}Tc, it is 65%, 35% and 0.3%, respectively. Our partitioning estimates differ from those of underground tests in French Polynesia, implying that fission product distribution may vary from test to test. Factors that may influence this distribution include geologic conditions (e.g. lithology, water and CO{sub 2} content) and the cooling history of the test cavity

Editorial

The Tenth International Conference on Accelerator Mass Spectrometry (AMS-10) was held from September 5-10 at the University of California, Berkeley campus. The conference attracted 305 attendees from 26 countries who gave 144 platform presentations and presented a total of 170 posters. The conference opened with a special tribute to the late Roy Middleton, which was followed by a companion session on 'ion sourcery'. A plenary talk by Wally Broecker on his '53 years in the Radiocarbon Trenches', provided thought-provoking challenges to commonly accepted paradigms. A workshop on issues in the estimation of isotopic ratios and evaluations of activities from AMS measurements preceded the conference and a workshop on AMS in low-dose bioscience concluded it. Conference attendees had ample opportunity to sample local sights and mid-week excursions to the Napa Valley wine region and the Monterey Bay Aquarium were well attended. The social highlight of the conference was a dinner cruise on San Francisco Bay aboard the San Francisco Belle, which toured the bay on a clear evening and afforded spectacular views of the city front as well as the Bay and Golden Gate bridges. The proceedings of AMS-10 contain 140 peer-reviewed papers that detail recent developments in AMS technology and a broad range of scientific applications. The editors worked to ensure that these contributions represent original research that has not been published elsewhere. We are grateful to the many outside reviewers who provided thoughtful consideration and suggestions in their reviews of these manuscripts. The staff of the Center for Accelerator Mass Spectrometry at the Lawrence Livermore National Laboratory wishes to thank the many members of the international AMS community in allowing us to organize this conference. We are particularly grateful to the University of California's Toxic Substances Research Program, which provided key assistance with conference administration

Hydrologic Resources Management Program and Underground Test Area Project FY2005 Progress Report

This report describes FY 2005 technical studies conducted by the Chemical Biology and Nuclear Science Division (CBND) at Lawrence Livermore National Laboratory (LLNL) in support of the Hydrologic Resources Management Program (HRMP) and the Underground Test Area Project (UGTA). These programs are administered by the U.S. Department of Energy, National Nuclear Security Administration, Nevada Site Office (NNSA/NSO) through the Defense Programs and Environmental Restoration Divisions, respectively. HRMP-sponsored work is directed toward the responsible management of the natural resources at the Nevada Test Site (NTS), enabling its continued use as a staging area for strategic operations in support of national security. UGTA-funded work emphasizes the development of an integrated set of groundwater flow and contaminant transport models to predict the extent of radionuclide migration from underground nuclear testing areas at the NTS. The report is organized on a topical basis and contains five chapters that highlight technical work products produced by CBND. However, it is important to recognize that most of this work involves collaborative partnerships with the other HRMP and UGTA contract organizations. These groups include the Energy and Environment Directorate at LLNL (LLNL-E&E), Los Alamos National Laboratory (LANL), the Desert Research Institute (DRI), the U.S. Geological Survey (USGS), Stoller-Navarro Joint Venture (SNJV), and Bechtel Nevada (BN)

Radionuclide Partitioning in an Underground Nuclear Test Cavity

In 2004, a borehole was drilled into the 1983 Chancellor underground nuclear test cavity to investigate the distribution of radionuclides within the cavity. Sidewall core samples were collected from a range of depths within the re-entry hole and two sidetrack holes. Upon completion of drilling, casing was installed and a submersible pump was used to collect groundwater samples. Test debris and groundwater samples were analyzed for a variety of radionuclides including the fission products {sup 99}Tc, {sup 125}Sb, {sup 129}I, {sup 137}Cs, and {sup 155}Eu, the activation products {sup 60}Co, {sup 152}Eu, and {sup 154}Eu, and the actinides U, Pu, and Am. In addition, the physical and bulk chemical properties of the test debris were characterized using Scanning Electron Microscopy (SEM) and Electron Microprobe measurements. Analytical results were used to evaluate the partitioning of radionuclides between the melt glass, rubble, and groundwater phases in the Chancellor test cavity. Three comparative approaches were used to calculate partitioning values, though each method could not be applied to every nuclide. These approaches are based on: (1) the average Area 19 inventory from Bowen et al. (2001); (2) melt glass, rubble, and groundwater mass estimates from Zhao et al. (2008); and (3) fission product mass yield data from England and Rider (1994). The U and Pu analyses of the test debris are classified and partitioning estimates for these elements were calculated directly from the classified Miller et al. (2002) inventory for the Chancellor test. The partitioning results from this study were compared to partitioning data that were previously published by the IAEA (1998). Predictions of radionuclide distributions from the two studies are in agreement for a majority of the nuclides under consideration. Substantial differences were noted in the partitioning values for {sup 99}Tc, {sup 125}Sb, {sup 129}I, and uranium. These differences are attributable to two factors: chemical volatility effects that occur during the initial plasma condensation, and groundwater remobilization that occurs over a much longer time frame. Fission product partitioning is very sensitive to the early cooling history of the test cavity because the decay of short-lived (t{sub 1/2} < 1 hour) fission-chain precursors occurs on the same time scale as melt glass condensation. Fission product chains that include both volatile and refractory elements, like the mass 99, 125, and 129 chains, can show large variations in partitioning behavior depending on the cooling history of the cavity. Uranium exhibits similar behavior, though the chemical processes are poorly understood. The water temperature within the Chancellor cavity remains elevated (75 C) more than two decades after the test. Under hydrothermal conditions, high solubility chemical species such as {sup 125}Sb and {sup 129}I are readily dissolved and transported in solution. SEM analyses of melt glass samples show clear evidence of glass dissolution and secondary hydrothermal mineral deposition. Remobilization of {sup 99}Tc is also expected during hydrothermal activity, but moderately reducing conditions within the Chancellor cavity appear to limit the transport of {sup 99}Tc. It is recommended that the results from this study should be used together with the IAEA data to update the range in partitioning values for contaminant transport models at the Nevada National Security Site (formerly known as the Nevada Test Site)

Comparative genome analysis of lignin biosynthesis gene families across the plant kingdom

<p>Abstract</p> <p>Background</p> <p>As a major component of plant cell wall, lignin plays important roles in mechanical support, water transport, and stress responses. As the main cause for the recalcitrance of plant cell wall, lignin modification has been a major task for bioenergy feedstock improvement. The study of the evolution and function of lignin biosynthesis genes thus has two-fold implications. First, the lignin biosynthesis pathway provides an excellent model to study the coordinative evolution of a biochemical pathway in plants. Second, understanding the function and evolution of lignin biosynthesis genes will guide us to develop better strategies for bioenergy feedstock improvement.</p> <p>Results</p> <p>We analyzed lignin biosynthesis genes from fourteen plant species and one symbiotic fungal species. Comprehensive comparative genome analysis was carried out to study the distribution, relatedness, and family expansion of the lignin biosynthesis genes across the plant kingdom. In addition, we also analyzed the comparative synteny map between rice and sorghum to study the evolution of lignin biosynthesis genes within the <it>Poaceae </it>family and the chromosome evolution between the two species. Comprehensive lignin biosynthesis gene expression analysis was performed in rice, poplar and <it>Arabidopsis</it>. The representative data from rice indicates that different fates of gene duplications exist for lignin biosynthesis genes. In addition, we also carried out the biomass composition analysis of nine <it>Arabidopsis </it>mutants with both MBMS analysis and traditional wet chemistry methods. The results were analyzed together with the genomics analysis.</p> <p>Conclusion</p> <p>The research revealed that, among the species analyzed, the complete lignin biosynthesis pathway first appeared in moss; the pathway is absent in green algae. The expansion of lignin biosynthesis gene families correlates with substrate diversity. In addition, we found that the expansion of the gene families mostly occurred after the divergence of monocots and dicots, with the exception of the C4H gene family. Gene expression analysis revealed different fates of gene duplications, largely confirming plants are tolerant to gene dosage effects. The rapid expansion of lignin biosynthesis genes indicated that the translation of transgenic lignin modification strategies from model species to bioenergy feedstock might only be successful between the closely relevant species within the same family.</p