[en] Exposure reconstructions for radionuclides are inherently difficult. As a result, most reconstructions are based primarily on mathematical models of environmental fate and transport. These models can have large uncertainties, as important site-specific information is unknown, missing, or crudely estimated. Alternatively, surrogate environmental measurements of exposure can be used for site-specific reconstructions. In cases where environmental transport processes are complex, well-chosen environmental surrogates can have smaller exposure uncertainty than mathematical models. Because existing methodologies have significant limitations, the development or improvement of methodologies for reconstructing exposure from environmental measurements would provide important additional tools in assessing the health effects of chronic exposure. As an example, the direct measurement of tritium atoms by accelerator mass spectrometry (AMS) enables rapid low-activity tritium measurements from milligram-sized samples, which permit greater ease of sample collection, faster throughput, and increased spatial and/or temporal resolution. Tritium AMS was previously demonstrated for a tree growing on known levels of tritiated water and for trees exposed to atmospheric releases of tritiated water vapor. In these analyses, tritium levels were measured from milligram-sized samples with sample preparation times of a few days. Hundreds of samples were analyzed within a few months of sample collection and resulted in the reconstruction of spatial and temporal exposure from tritium releases

[en] The application of ultra-sensitive heavy isotope measurements continues to expand in a variety of fields relevant to the management of nuclear materials, including nuclear isotope forensics and radiobioassay. We have developed a heavy isotope accelerator mass spectrometry (AMS) system at Lawrence Livermore National Laboratory's (LLNL) Center for Accelerator Mass Spectrometry (CAMS). The system was designed particularly for the measurement of actinide concentrations and isotopic ratios, but also allows the measurement of other heavy isotopes such as ¹²⁹I. The system includes a fast isotope switching capability that allows flexibility in isotope selection and for the quasi-continuous normalization to a reference isotope spike. Current background levels for ²³⁹Pu and ²⁴⁰Pu are equivalent to <10⁶ atoms and measurements of known materials indicate that our ²³⁹Pu and ²⁴⁰Pu measurements are accurate and precise for samples containing from ∼10¹² atoms down to the Bq level (∼10⁶ atoms). Recent exploitation of the fast isotope switching capability has allowed the quasi-simultaneous measurement of several Pu isotopes in individual samples. Our AMS measurement capability has been extended to U isotopes, with particular emphasis on ²³⁶U. Our current ²³⁶U background level is equivalent to ∼10⁶ atoms and the linear measurement range is 5-6 orders of magnitude. We have also utilized our Heavy Isotope AMS system for the measurement of ¹²⁹I. Initial measurements of available low level samples show that background contributions for 1 mg I samples are below ¹²⁹I/¹²⁷I levels of ∼10^-14, and measurements of prepared standard samples demonstrates linear measurement response to ¹²⁹I/¹²⁷I levels greater than 10^-10. The AMS technique provides high rejection of interferences, including molecular interferences, and low susceptibility to matrix components, both of which are of particular relevance to the measurement of complex sample matrices. The attendant significant reductions of demands on sample preparation chemistry allow relatively simple, cost-effective procedures to be employed. When such sample preparation improvements are combined with the high sample throughput capabilities of our AMS system, the result is a rapid and cost-effective measurement technique for heavy isotopes in a wide range of studies

[en] We report on the development of an accelerator mass spectrometry (AMS) system for the measurement of actinides at Lawrence Livermore National Laboratory. This AMS system is centered on a recently completed heavy isotope beam line that was designed particularly for high sensitivity, robust, high-throughput measurements of actinide concentrations and isotopic ratios. A fast isotope switching capability has been incorporated in the system, allowing flexibility in isotope selection and for the quasi-continuous normalization to a reference isotope spike. Initially, our utilization of the heavy isotope system has concentrated on the measurement of Pu isotopes. Under current operating conditions, background levels equivalent to ∼1 x 10⁵ atoms are observed during routine ²³⁹Pu and ²⁴⁰Pu measurements. Measurements of samples containing ∼10¹³²³⁸U atoms demonstrate that the system provides a ²³⁸U rejection factor during ²³⁹Pu measurements of ∼10⁷. Measurements of known materials, combined with results from an externally organized inter-comparison program, indicate that our ²³⁹Pu measurements are accurate and precise down to the (micro)Bq level (∼10⁶ atoms). Recently, we have investigated the performance of our heavy isotope AMS system in measurements of ²³⁷Np and ²³⁶U. Results of these investigations are discussed. The sensitivity shown by our Pu measurements, combined with the high throughput and interference rejection capabilities of our AMS system, demonstrate that AMS can provide a rapid and cost-effective measurement technique for actinides in a wide variety of studies

[en] 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