Several studies have evaluated the morphology of uranium compounds produced under controlled conditions at the laboratory scale, but it is unclear whether the morphological characteristics of these ...materials persist in commercially produced uranium ore concentrates (UOCs). To assess the morphology in “real-world” UOCs, we qualitatively evaluated the morphological profile of secondary electron images from over 100 commercial UOCs using a previously published lexicon. We observe differences between samples with differing chemical composition and samples with similar chemical composition and differing provenance. This work contextualizes morphology for commercially produced UOCs and will provide a basis for future machine learning efforts.
•Surface roughness methods were developed via profilometry and microscopy.•3D measurements provide quicker, more precise values than 2D measurements.•Digital microscopy provides higher quality ...results than profilometry.•UO2 pellet surface roughness has potential as a nuclear forensic signature.
Rapid, non-destructive nuclear forensic techniques can aid in signature development and provide valuable information for provenance assessments. Using optical profilometry and digital microscopy, we studied the surface roughness of fuel pellets to probe its usefulness as a forensic signature and its relationship to a given producer’s grinding techniques. Arithmetic average areal (Sa) surface roughness measurements provide a rapid, non-destructive technique, producing efficient measurements with smaller standard uncertainties relative to 2D, arithmetic average profile (Ra) surface roughness measurements. Digital microscopy proved to be the superior technique over optical profilometry, in part due to its higher image quality, faster data acquisition capabilities, and multi-purpose potential in physical surface characterization. Using digital microscopy, fuel pellet Sa surface roughness varies in commercial reactor fuel pellets from 1.54±0.17μm to 2.11±0.12μm and does not appear to depend solely on the use of wet versus dry grinding techniques. Populations of pellets produced at three different commercial reactor fuel production facilities were distinguishable on the basis of Sa. Complementary to other key forensic characteristics, such as dimensions and enrichment, Sa measurements provide a promising nuclear forensic signature for sintered UO2 fuel pellets.
Three-quarters of the oceanic crust formed at fast-spreading ridges is composed of plutonic rocks whose mineral assemblages, textures and compositions record the history of melt transport and ...crystallization between the mantle and the sea floor. Despite the importance of these rocks, sampling them in situ is extremely challenging owing to the overlying dykes and lavas. This means that models for understanding the formation of the lower crust are based largely on geophysical studies and ancient analogues (ophiolites) that did not form at typical mid-ocean ridges. Here we describe cored intervals of primitive, modally layered gabbroic rocks from the lower plutonic crust formed at a fast-spreading ridge, sampled by the Integrated Ocean Drilling Program at the Hess Deep rift. Centimetre-scale, modally layered rocks, some of which have a strong layering-parallel foliation, confirm a long-held belief that such rocks are a key constituent of the lower oceanic crust formed at fast-spreading ridges. Geochemical analysis of these primitive lower plutonic rocks--in combination with previous geochemical data for shallow-level plutonic rocks, sheeted dykes and lavas--provides the most completely constrained estimate of the bulk composition of fast-spreading oceanic crust so far. Simple crystallization models using this bulk crustal composition as the parental melt accurately predict the bulk composition of both the lavas and the plutonic rocks. However, the recovered plutonic rocks show early crystallization of orthopyroxene, which is not predicted by current models of melt extraction from the mantle and mid-ocean-ridge basalt differentiation. The simplest explanation of this observation is that compositionally diverse melts are extracted from the mantle and partly crystallize before mixing to produce the more homogeneous magmas that erupt.
Image analysis techniques have been applied and shown to be a valuable tool in nuclear forensics analysis. The interlaboratory exercise reported here has tested quantitative and qualitative ...approaches for characterizing nuclear materials. Particle size, surface features and morphology descriptions were compared by four laboratories on a common image set generated by Scanning Electron Microscopy and Digital Light Microscopy. Quantitative analysis of the image sets through the Morphological Analysis for MAterials software highlighted the strength of image analysis, but also that the application of the software alone can introduce significant bias in the analysis. Qualitative morphology descriptions following the process outlined by Tamasi et al. (J Radioanal Nuclear Chem 307:1611–1619, 2015) were compared with a discussion on the robustness and reproducibility of the results. Future work should continue to focus on proficiency and standardization of image analysis through continued exercises within the extended nuclear forensics community.
Although there is limited direct evidence for supernova input into the nascent Solar System, many models suggest it formed by the gravitational collapse of a molecular cloud that was triggered by a ...nearby supernova. Existing lines of evidence, mostly in the form of short-lived radionuclides present in the early Solar System, are potentially consistent with this hypothesis, but still allow for alternative explanations. Since the natural production of 126Sn is thought to occur only in supernovae and this isotope has a short half-life (126Sn→126Te, t1/2=235ky), the discovery of extant 126Sn would provide unequivocal proof of supernova input to the early Solar System. Previous attempts to quantify the initial abundance of 126Sn by examining Sn-Te systematics in early solids have been hampered by difficulties in precisely measuring Te isotope ratios in these materials. Thus, here we describe a novel technique that uses hydride generation to dramatically increase the ionization efficiency of Te—an approximately 30-fold increase over previous work. This introduction system, when coupled to a MC-ICPMS, enables high-precision Te isotopic analyses on samples with <10ng of Te. We used this technique to analyze Te from a unique set of calcium-aluminum-rich inclusions (CAIs) that exhibit an exceptionally large range in Sn/Te ratios, facilitating the search for the short-lived isotope 126Sn. This sample set shows no evidence of live 126Sn, implying at most minor input of supernova material during the time at which the CAIs formed. However, based on the petrology of this sample set combined with the higher than expected concentrations of Sn and Te, as well as the lack of nucleosynthetic anomalies in other isotopes of Te suggest that the bulk of the Sn and Te recovered from these particular refractory inclusions is not of primary origin and thus does not represent a primary signature of Sn-Te systematics of the protosolar nebula during condensation of CAIs or their precursors. Although no evidence of supernova input was found based on Sn-Te systematics in this sample set, hydride generation represents a powerful tool that can now be used to further explore Te isotope systematics in less altered materials.
Novel analytical approaches to determining the trapped 38Ar/36Ar ratio of gases contained within Martian meteorites are presented and applied to the Martian regolith breccia Northwest Africa (NWA) ...7034 and paired stone NWA 11220. The resulting data indicate that extensive mass-dependent fractionation of atmospheric Ar may have occurred within 150 million years of planetary formation, ostensibly as a result of diffusion-limited hydrodynamic escape. The inferred fractional loss of Ar and lighter atmospheric constituents exceeds 50%. These data suggest that volatiles derived from planetary outgassing and/or impactors may dominate the present abundance of atmospheric Ar.
Novel analytical approaches to determining the trapped 38Ar/36Ar ratio of gases contained within Martian meteorites are presented and applied to the Martian regolith breccia Northwest Africa (NWA) ...7034 and paired stone NWA 11220. The resulting data indicate that extensive mass-dependent fractionation of atmospheric Ar may have occurred within 150 million years of planetary formation, ostensibly as a result of diffusion-limited hydrodynamic escape. The inferred fractional loss of Ar and lighter atmospheric constituents exceeds 50%. In conclusion, these data suggest that volatiles derived from planetary outgassing and/or impactors may dominate the present abundance of atmospheric Ar.
•Isotopic taggants could provide a unique identifier for nuclear material.•Mo and W isotope compositions of base nuclear fuels are variable and non-natural.•Base nuclear materials need to be analyzed ...before any isotopic taggant is added.•Mo and W are not ideal candidates for isotopic tagging.•Elements less affected by fuel cycle processing are better isotopic taggant candidates.
The addition of isotopically enriched taggants to material at the front end of the nuclear fuel cycle could be a powerful tool used to assist law enforcement authorities should material outside of regulatory control be found. Two potential candidates for this purpose are molybdenum (Mo) and tungsten (W) as both elements have five or more stable isotopes and are trace elements contained within nuclear fuel. However, there is a concern that Mo and W could undergo isotope fractionation during processes like uranium enrichment and to date, it is unknown if nuclear fuels have natural Mo and W isotope compositions. If Mo and W isotopic variability is present in nuclear fuels, this would hinder the use of these elements as isotopic taggants because it would be difficult to discern the original taggant isotope composition with high confidence. Therefore, a set of 16 low enriched uranium (LEU) fuel pellets from US commercial producers was analyzed using multi collector-inductively coupled plasma mass spectrometry (MC-ICPMS) to determine Mo and W isotope compositions (i.e., 94Mo/92Mo, 95Mo/92Mo, 96Mo/92Mo, 97Mo/92Mo, 98Mo/92Mo, 183W/182W, 184W/182W, and 186W/182W). Relative to terrestrial standards, LEU fuel pellets have variable Mo and W isotope compositions, thereby complicating the use of these elements as isotopically enriched taggants. As such, this work demonstrates that the isotope composition of any potential taggant must be well characterized in the base nuclear fuel prior to any taggant addition. Furthermore, these results suggest that Mo and W are not ideal candidates for isotopically enriched taggants.
A multiproxy record from a fast‐growing stalagmite reveals variable hydroclimate on the California coast across the 8.2 kyr event and a precursor event likely caused by initial drainage of proglacial ...Lake Agassiz. Using speleothem δ44Ca, we develop the first semiquantitative estimates of paleorainfall variability for California through calibration with measurements of the modern climate and cave environment. We find that the magnitude of rainfall variability during the 8.2 kyr event approached the multiyear variability observable in the recent past (1950–2019) and the magnitude of variability during the precursor event likely exceeded this range. Additionally, we observe other instances of multidecadal variability comparable in magnitude to the precursor event during the record. Our work suggests that speleothem calcium isotope ratios are a powerful semiquantitative means to reconstruct paleorainfall, although numerous factors must be assessed in each cave system before applying this approach.
Plain Language Summary
Modeling of future climate suggests that California may experience increased frequency of both extremely wet and extremely dry periods in the 21st century, leading to the emergence of “climate whiplash” phenomena which would significantly stress the state's water‐sensitive infrastructure. Understanding hydroclimate changes in California's past can help planners prepare for extremes that may be more severe than those of the historical record. However, existing paleoclimate records are often limited to qualitative interpretations of hydroclimate change, restricting their usefulness. We present new calcium isotope measurements from a California stalagmite that grew from 6,900 to 8,600 years ago, revealing variability in rainfall amounts on the California coast during and surrounding the 8.2 kyr event, an abrupt cold snap noted in other global paleoclimate records 8,200 years ago. We generate semiquantitative estimates of annual rainfall rates during the 8.2 kyr event period and compare them with modern annual rainfall amounts, finding that the magnitude of rainfall variability during and surrounding the 8.2 kyr event approaches and in some cases exceeds that of California today. This work indicates that California may have experienced even more intense “climate whiplash” phenomena in the past than during recent decades, suggesting that future planning may need to consider greater wet and dry extremes.
Key Points
The first semiquantitative estimates of paleorainfall rates from Ca isotope ratios measured in a California stalagmite
The magnitude of rainfall variability in coastal California during the 8.2 kyr and precursor event approaches/exceeds that of recent decades
Stalagmite Ca isotope ratios facilitate more direct comparison of paleorainfall with modern climate data, but important questions remain
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