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Abstract
In 1944 Los Alamos National Laboratory (LANL) instituted a program for the collection and analyses of urine samples from individuals working with plutonium. This program has operated continuously for over 60 years. During that time the plutonium bioassay program incorporated advances in urine sample collection, radiochemical separation techniques, alpha-spectroscopy and thermal ionization mass spectrometry measurement techniques as well as cleanroom technology. All of these advances have produced incremental improvements in plutonium detection limits. A chronological description is given of the methodologies used in the plutonium bioassay program at Los Alamos.
Abstract
Identifying both physical and chemical characteristics of Special Nuclear Material (SNM) production processes is the corner stone of nuclear forensics. Typically, processing markers are based on measuring an interdicted sample’s bulk chemical properties, such as the elemental or isotopic composition, or focusing on the chemical and physical morphology of only a few particles. Therefore, it is imperative that known SNM processes be fully characterized from bulk to trace level for each particle size range. This report outlines a series of particle size measurements and fractionation techniques that can be applied to a bulk SNM powders, categorizing both chemical and physical properties in discrete particle size fractions. This will be demonstrated by characterizing the process signatures of a series of different depleted uranium oxides prepared at increasing firing temperatures (350–1100 °C). Results will demonstrate how each oxides’ material density, particle size distribution, and morphology varies.
Knowledge of the weed seedbank composition, dynamics and relationships with the emergent weed community, is necessary to improve weed management practices. Field research was made over three years in a maize (Zea mays L.)-soybean (Glycine max (L.) Merr.) crop rotation under two contrasting tillage regimes [conventional (CT) and no-till (NT)] to evaluate (i) changes in the weed seedbank and in the emerged community and (ii) to determine if the soil seedbank composition has any predictive value for the composition of the emergent weed community. The experiment was a randomised complete block design. Each year, after crop planting, samples of the seedbank were taken, then the seeds were extracted by washing soil samples through a sieve. Weed emergence was recorded during the first month after planting. Data were analysed with Principal Components Analysis and diversity was estimated using the Shannon index. Although the most abundant species found in the seedbank were always present in the above-ground community, percentage recruitment varied markedly between tillage regimes and years. The degree of soil disturbance, timing of tillage practices, crop rotation and planting date act as filters which allow or prevent the germination and emergence of weeds. The results indicated that knowledge of soil seedbank composition alone has relatively little predictive value for the composition of the emergent weed community.
The River Paraná is the second largest river of South America and its flood plain is covered by different kinds of forests and herbaceous vegetation. It is subject to an annual pulse of flooding; floods larger than the normal annual ones at irregular periods of few year and catastrophic extraordinary floods few times in a century. The last catastrophic flood was in 1983, followed by a short lived high flood in 1992. The catastrophic flood destroyed almost completely the herbaceous vegetation. Our hypotheses are, on the one hand, that the plant communities of this area will be restored rapidly, and on the other, that there will be a succession process which will produce a shift of communities so that, those on the higher part of the elevation gradient will encroach the ones at its lower part. We analyse, by means of the floristic composition, the effect of disturbance induced by catastrophic floods on the vegetation stability and dynamic processes, in an internal depression and pond of the riparian plant communities in an island of the River Paraná valley. The results strongly support the first hypothesis.
Abstract
Utilization of thermal ionization mass spectrometry as a routine analytical service provided to the Los Alamos National Laboratory Bioassay Program has evolved significantly since its implementation just over three years ago. Converting this unique research tool designed to support nuclear weapons testing to a quasi-production mode for the routine analysis of ~300 urine samples/year for ultra-low levels of plutonium has required resolution of numerous practical issues. These issues include clean-room sample preparation, adequate tracer recovery, customer specified turn-around times, throughput, water and urine blank values, statistical data reduction, and quality control and performance evaluation sample requirements.
Abstract
The goal of nuclear forensics is to establish an unambiguous link between illicitly trafficked nuclear material and its origin. The Los Alamos National Laboratory (LANL) Nuclear Materials Signatures Program has implemented a graded “conduct of operations” type analysis flow path approach for determining the key nuclear, chemical, and physical signatures needed to identify the manufacturing process, intended use, and origin of interdicted nuclear material. This analysis flow path includes both destructive and non-destructive characterization techniques and has been exercized against different nuclear materials from LANL’s special nuclear materials archive. Results obtained from the case study will be presented to highlight analytical techniques that offer the critical attribution information.
