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Nuclear forensic science seeks to identify the origin of nuclear materials found outside regulatory control. It is increasingly recognized as an integral part of a robust nuclear security program. This review highlights areas of active, evolving research in nuclear forensics, with a focus on analytical techniques commonly employed in Earth and planetary sciences. Applications of nuclear forensics to uranium ore concentrates (UOCs) are discussed first. UOCs have become an attractive target for nuclear forensic researchers because of the richness in impurities compared to materials produced later in the fuel cycle. The development of chronometric methods for age dating nuclear materials is then discussed, with an emphasis on improvements in accuracy that have been gained from measurements of multiple radioisotopic systems. Finally, papers that report on casework are reviewed, to provide a window into current scientific practice.

Several decades of research by Air Products and Ceramatec have recently culminated in the construction and operation of a test unit with the capacity to produce up to 100 tons per day of oxygen using planar, ceramic mixed conducting, ion transport membranes (ITM). In the first tonnage operation of this unit, over 16 tons/day of oxygen were produced. Smaller scale experiments demonstrated high purity oxygen production for over 15,000 hours. A parallel development effort has produced planar ceramic mixed conducting membranes to partially oxidize methane to produce syngas.

Resonance Ionization Mass Spectrometry (RIMS) has been developed as a method to measure uranium isotope abundances. In this approach, RIMS is used as an element-selective ionization process between uranium atoms and potential isobars without the aid of chemical purification and separation. The use of broad bandwidth lasers with automated feedback control of wavelength was applied to the measurement of the 235U/238U ratio to decrease laser-induced isotopic fractionation. In application, isotope standards are used to identify and correct bias in measured isotope ratios, but understanding laser-induced bias from first-principles can improve the precision and accuracy of experimental measurements. A rate equation model for predicting the relative ionization probability has been developed to study the effect of variations in laser parameters on the measured isotope ratio. The model uses atomic data and empirical descriptions of laser performance to estimate the laser-induced bias expected in experimental measurements of the 235U/238U ratio. Empirical corrections are also included to account for ionization processes that are difficult to calculate from first principles with the available atomic data. Development of this model has highlighted several important considerations for properly interpreting experimental results.

A National Nuclear Forensics Library (NNFL) assists a State to assess whether nuclear material encountered out of regulatory control is of domestic or international origin. By leveraging nuclear material registries, nuclear enterprise records, and safeguards accountancy information, as well as existing domestic technical capability and subject-matter domain expertise, states can better assess the effort required for setting up an NNFL. States who are largely recipients of nuclear and radiological materials and have no internal production capabilities may create an NNFL that relies on existing information rather than carry out advanced analyses on domestic materials.

We use imaging secondary ion mass spectrometry (SIMS) with a Cameca NanoSIMS 50 to determine the distribution and relative concentration of H in two uranium metal samples: sample1(LANL), as cast with less than 1 wppm H, sample2(Y12), outgassed 6 h in vacuum at 630 °C to remove hydrogen. H ion counts appear almost exclusively associated with ‘carbide’ inclusions, based on H − , C − and O − ion images for uranium surfaces sputter-cleaned in situ with a 16 keV Cs + ion beam. Two classes of inclusions are identified: small, micrometer to sub-micrometer inclusions and larger, clearly angular inclusion (⩾3 μm). In sample1(LANL) the large inclusions (⩾250/mm 2 ) show a low H − / C − ratio inside, and have H − / C − ratios at their perimeters comparable in magnitude to that seen in μm-size inclusions. Small inclusions (∼2500/mm 2 ) contain H more uniformly throughout and, averaged over the inclusion, the small inclusions have approximately 50 times higher relative H concentration than the large inclusions. Sample2(Y12) was found to have comparable H − / C − ratios in the large carbides, but no small inclusions were observed. Because of the matrix-sensitivity of SIMS, H / C ratios representing the actual composition of the inclusions cannot be derived from the H − / C − ratios without calibration UC samples with known H content, which are not currently available.

Five silicate fallout glass spherules produced in a uranium-fueled, near-surface nuclear test were characterized by secondary ion mass spectrometry, electron probe microanalysis, autoradiography, scanning electron microscopy, and energy-dispersive x-ray spectroscopy. Several samples display compositional heterogeneity suggestive of incomplete mixing between major elements and natural U ((238)U/(235)U = 0.00725) and enriched U. Samples exhibit extreme spatial heterogeneity in U isotopic composition with 0.02 < (235)U/(238)U < 11.84 among all five spherules and 0.02 < (235)U/(238)U < 7.41 within a single spherule. In two spherules, the (235)U/(238)U ratio is correlated with changes in major element composition, suggesting the agglomeration of chemically and isotopically distinct molten precursors. Two samples are nearly homogenous with respect to major element and uranium isotopic composition, suggesting extensive mixing possibly due to experiencing higher temperatures or residing longer in the fireball. Linear correlations between (234)U/(238)U, (235)U/(238)U, and (236)U/(238)U ratios are consistent with a two-component mixing model, which is used to illustrate the extent of mixing between natural and enriched U end members.

Resonance ionization mass spectrometry (RIMS) holds the promise of rapid, isobar-free quantification of actinide isotope ratios in as-received materials (i.e. not chemically purified). Recent progress in achieving this potential using two Pu test materials is presented. RIMS measurements were conducted multiple times over a period of two months on two different Pu solutions deposited on metal surfaces. Measurements were bracketed with a Pu isotopic standard, and yielded absolute accuracies of the measured 240Pu/239Pu ratios of 0.7 and 0.58 %, with precisions (95 % confidence intervals) of 1.49 and 0.91 %. The minor isotope 238Pu was also quantified despite the presence of a significant quantity of 238U in the samples.

The results of a joint effort by expert nuclear forensic laboratories in the area of age dating of uranium, i.e. the elapsed time since the last chemical purification of the material are presented and discussed. Completely separated uranium materials of known production date were distributed among the laboratories, and the samples were dated according to routine laboratory procedures by the measurement of the 230Th/234U ratio. The measurement results were in good agreement with the known production date showing that the concept for preparing uranium age dating reference material based on complete separation is valid. Detailed knowledge of the laboratory procedures used for uranium age dating allows the identification of possible improvements in the current protocols and the development of improved practice in the future. The availability of age dating reference materials as well as the evolvement of the age dating best-practice protocol will increase the relevance and applicability of age dating as part of the tool-kit available for nuclear forensic investigations.

Nuclear forensic analysis was conducted on two uranium samples confiscated during a police investigation in Victoria, Australia. The first sample, designated NSR-F-270409-1, was a depleted uranium powder of moderate purity (∼ 1000 μg/g total elemental impurities). The chemical form of the uranium was a compound similar to K2(UO2)3O4 · 4H2O. While aliquoting NSR-F-270409-1 for analysis, the body and head of a Tineid moth was discovered in the sample. The second sample, designated NSR-F-270409-2, was also a depleted uranium powder. It was of reasonably high purity (∼ 380 μg/g total elemental impurities). The chemical form of the uranium was primarily UO3 · 2H2O, with minor phases of U3O8 and UO2. While aliquoting NSR-F-270409-2 for analysis, a metal staple of unknown origin was discovered in the sample. The presence of 236U and 232U in both samples indicates that the uranium feed stocks for these samples experienced a neutron flux at some point in their history. The reactor burn-up calculated from the isotopic composition of the uranium is consistent with that of spent fuel from natural uranium (NU) fueled Pu production. These nuclear forensic conclusions allow us to categorically exclude Australia as the origin of the material and greatly reduce the number of candidate sources.

Useful yields from resonance ionization mass spectrometry can be extremely high compared to other mass spectrometry techniques, but uranium analysis shows strong matrix effects arising from the tendency of uranium to form strongly bound oxide molecules that do not dissociate appreciably on energetic ion bombardment. We demonstrate a useful yield of 24% for metallic uranium. Modeling the laser ionization and ion transmission processes shows that the high useful yield is attributable to a high ion fraction achieved by resonance ionization. We quantify the reduction of uranium oxide surface layers by Ar+ and Ga+ sputtering. The useful yield for uranium atoms from a uranium dioxide matrix is 0.4% and rises to 2% when the surface is in sputter equilibrium with the ion beam. The lower useful yield from the oxide is almost entirely due to uranium oxide molecules reducing the neutral atom content of the sputtered flux. We demonstrate rapid isotopic analysis of solid uranium oxide at a precision of

This study combines electron microscopy equipped with energy dispersive spectroscopy to probe major element composition and autoradiography to map plutonium in order to examine the spatial relationships between plutonium and fallout composition in aerodynamic glassy fallout from a nuclear weapon test. A sample set of 48 individual fallout specimens were interrogated to reveal that the significant chemical heterogeneity of this sample set could be described compositionally with a relatively small number of compositional endmembers. Furthermore, high concentrations of plutonium were never associated with several endmember compositions and concentrated with the so-called mafic glass endmember. This result suggests that it is the physical characteristics of the compositional endmembers and not the chemical characteristics of the individual component elements that govern the un-burnt plutonium distribution with respect to major element composition in fallout.

Calcium–aluminum-rich inclusions (CAIs) are primitive objects that formed within the protoplanetary disk surrounding the young Sun. Recent Pb–Pb chronologic studies have demonstrated that CAIs are the oldest solar system solids, crystallizing 4567 Ma ago ( Amelin et al., 2002 , Connelly et al., 2012 ). The isotope systematics of CAIs therefore provide critical insight into the earliest history of the Solar System. Although Sm–Nd and Rb–Sr geochronometers are highly effective tools for investigating cosmochemical evolution in the early Solar System, previous studies of CAIs have revealed evidence for isotopically disturbed systems. Here we report new age data for Allende CAI Al3S4 derived from both the long-lived (147Sm–143Nd) and short-lived (146Sm–142Nd) isotopic systems. The 147Sm–143Nd chronometer yields an age of 4560 ± 34 Ma that is concordant with 207Pb–206Pb ages for CAIs and indicates that the Sm–Nd system was not significantly disturbed by secondary alteration or nucleosynthetic processes. The slope of the 146Sm–142Nd isochron defines the Solar System initial 146Sm/144Sm of 0.00828 ± 0.00044 . This value is significantly different from the value of 0.0094 determined by Kinoshita et al. (2012) . Ages recalculated from all published 146Sm–142Nd isochron data using the traditional 103 Ma half-life and the initial 146Sm/144Sm value determined here closely match Pb–Pb and 147Sm–143Nd ages determined on the same samples. In contrast, ages recalculated using the 68 Ma half-life determined by Kinoshita et al. (2012) and either of the initial 146Sm/144Sm values are often anomalously old. This is particularly true for the youngest samples with 146Sm–142Nd isochron ages that are most sensitive to the choice of 146Sm half-life used in the age calculation. In contrast to the Sm–Nd isotope system, the Rb–Sr system is affected by alteration but yields an apparent isochron with a slope corresponding to a much younger age of 4247 ± 110 Ma . Although the Rb–Sr system in CAIs appears to be disturbed, the initial 87Sr/86Sr value determined from the isochron is 0.698942 ± 0.000008 , and closely approximates estimates of the initial Solar System value. Although this isochron may be a mixing line, it might also record alteration on the Allende parent body in which Rb was added to the Al3S4 CAI that was initially largely devoid of Rb.

Nuclear weapons represent one of the most immediate threats of mass destruction. In the event that a procured or developed nuclear weapon is detonated in a populated metropolitan area, timely and accurate nuclear forensic analysis and fallout modeling would be needed to support attribution efforts and hazard assessments. Here we demonstrate that fissiogenic xenon isotopes retained in radioactive fallout generated by a nuclear explosion provide unique constraints on (1) the timescale of fallout formation, (2) chemical fractionation that occurs when fission products and nuclear fuel are incorporated into fallout, and (3) the speciation of fission products in the fireball. Our data suggest that, in near surface nuclear tests, the presence of a significant quantity of metal in a device assembly, combined with a short time allowed for mixing with the ambient atmosphere (seconds), may prevent complete oxidation of fission products prior to their incorporation into fallout. Xenon isotopes thus provide a window into the chemical composition of the fireball in the seconds that follow a nuclear explosion, thereby improving our understanding of the physical and thermo-chemical conditions under which fallout forms.

We present a detailed characterization of the mineralogy, petrology, and oxygen isotopic compositions of twelve FUN CAIs, including C1 and EK1-4-1 from Allende (CV), that were previously shown to have large isotopic fractionation patterns for magnesium and oxygen, and large isotopic anomalies of several elements. The other samples show more modest patterns of isotopic fractionation and have smaller but significant isotopic anomalies. All FUN CAIs studied are coarse-grained igneous inclusions: Type B, forsterite-bearing Type B, compact Type A, and hibonite-rich. Some inclusions consist of two mineralogically distinct lithologies, forsterite-rich and forsterite-free/poor. All the CV FUN CAIs experienced postcrystallization open-system iron-alkali-halogen metasomatic alteration resulting in the formation of secondary minerals commonly observed in non-FUN CAIs from CV chondrites. The CR FUN CAI GG#3 shows no evidence for alteration. In all samples, clear evidence of oxygen isotopic fractionation was found. Most samples were initially ^(16)O-rich. On a three-oxygen isotope diagram, various minerals in each FUN CAI (spinel, forsterite, hibonite, dmisteinbergite, most fassaite grains, and melilite (only in GG#3)), define mass-dependent fractionation lines with a similar slope of ∼0.5. The different inclusions have different Δ^(17)O values ranging from ∼−25‰ to ∼−16‰. Melilite and plagioclase in the CV FUN CAIs have ^(16)O-poor compositions (Δ^(17)O ∼−3‰) and plot near the intercept of the Allende CAI line and the terrestrial fractionation line. We infer that mass-dependent fractionation effects of oxygen isotopes in FUN CAI minerals are due to evaporation during melt crystallization. Differences in Δ^(17)O values of mass-dependent fractionation lines defined by minerals in individual FUN CAIs are inferred to reflect differences in Δ^(17)O values of their precursors. Differences in δ^(18)O values of minerals defining the mass-dependent fractionation lines in several FUN CAIs are consistent with their inferred crystallization sequence, suggesting these minerals crystallized during melt evaporation. In other FUN CAIs, no clear correlation between δ^(18)O values of individual minerals and their inferred crystallization sequence is observed, possibly indicating gas-melt back reaction and oxygen-isotope exchange in a ^(16)O-rich gaseous reservoir. After oxygen-isotope fractionation, some FUN CAIs could have experienced partial melting and gas-melt oxygen-isotope exchange in a ^(16)O-poor gaseous reservoir that resulted in crystallization of ^(16)O-depleted fassaite, melilite and plagioclase. The final oxygen isotopic compositions of melilite and plagioclase in the CV FUN CAIs may have been established on the CV parent asteroid as a result of isotope exchange with a ^(16)O-poor fluid during hydrothermal alteration. We conclude that FUN CAIs are part of a general family of refractory inclusions showing various degrees of fractionation effects due to evaporative processes superimposed on sampling of isotopically heterogeneous material. These processes have been experienced both by FUN and non-FUN igneous CAIs. Generally, the inclusions identified as FUN show larger isotope fractionation effects than non-FUN CAIs. There is a wide spread in UN isotopic anomalies in a large number of CAIs not exhibiting large fractionation effects in oxygen, magnesium, and silicon. The question of why some FUN CAIs show more extreme UN isotopic effects is attributed by us to limited sampling and not a special source of isotopically anomalous material. We consider the majority of igneous CAIs to be the result of several stages of thermal processing (evaporation, condensation, and melting) of aggregates of solid precursors composed of incompletely isotopically homogenized materials. The unknown nuclear effects in CAIs are common to both FUN and non-FUN CAIs, and are not a special characteristic of FUN inclusions but represent the spectrum of results from sampling a very heterogeneous medium in the accreting Solar System.

We present major element and actinide composition data from a population of fallout glass samples produced from a single near-surface nuclear detonation. Glass major element compositions indicate that composition of local geology is a primary control on bulk fallout chemical composition. Uranium isotope compositions indicate that vaporized, residual fuel was incorporated into the melts prior to solidification, likely within seconds, and are consistent with two-component mixing between naturally-occurring uranium and residual uranium fuel. Model ages of the residual fuel in fallout are systematically inaccurate, biased towards older ages, and are consistent with two-component mixing between naturally-occurring daughter nuclides in local sediment and decay-derived daughter nuclides from residual nuclear fuel. Multiple processes such as mixing, agglomeration of melted sediment-derived droplets, and incorporation of condensates must all occur within the timescale between sediment melting and melt solidification.

Early in 2009, a state policing agency raided a clandestine drug laboratory in a suburb of a major city in Australia. During the search of the laboratory, a small glass jar labelled "Gamma Source" and containing a green powder was discovered. The powder was radioactive. This paper documents the detailed nuclear forensic analysis undertaken to characterise and identify the material and determine its provenance. Isotopic and impurity content, phase composition, microstructure and other characteristics were measured on the seized sample, and the results were compared with similar material obtained from the suspected source (ore and ore concentrate material). While an extensive range of parameters were measured, the key 'nuclear forensic signatures' used to identify the material were the U isotopic composition, Pb and Sr isotope ratios, and the rare earth element pattern. These measurements, in combination with statistical analysis of the elemental and isotopic content of the material against a database of uranium ore concentrates sourced from mines located worldwide, led to the conclusion that the seized material (a uranium ore concentrate of natural isotopic abundance) most likely originated from Mary Kathleen, a former Australian uranium mine.

Qingsongite (IMA 2013-30) is the natural analog of cubic boron nitride (c-BN), which is widely used as an abrasive under the name “Borazon.” The mineral is named for Qingsong Fang (1939–2010), who found the first diamond in the Luobusa chromitite. Qingsongite occurs in a rock fragment less than 1 mm across extracted from chromitite in deposit 31, Luobusa ophiolite, Yarlung Zangbu suture, southern Tibet at 29°13.86N and 92°11.41E. Five electron microprobe analyses gave B 48.54 ± 0.65 wt% (range 47.90–49.2 wt%); N 51.46 ± 0.65 wt% (range 52.10–50.8 wt%), corresponding to B 1.113 N 0.887 and B 1.087 N 0.913 , for maximum and minimum B contents, respectively (based on 2 atoms per formula unit); no other elements that could substitute for B or N were detected. Crystallographic data on qingsongite obtained using fast Fourier transforms gave cubic symmetry, a = 3.61 ± 0.045 A. The density calculated for the mean composition B 1.100 N 0.900 is 3.46 g/cm 3 , i.e., qingsongite is nearly identical to synthetic c-BN. The synthetic analog has the sphalerite structure, space group F 43 m. Mohs hardness of the synthetic analog is between 9 and 10; its cleavage is {011}. Qingsongite forms isolated anhedral single crystals up to 1 μm in size in the marginal zone of the fragment; this zone consists of ~45 modal% coesite, ~15% kyanite, and ~40% amorphous material. Qingsongite is enclosed in kyanite, coesite, or in osbornite; other associated phases include native Fe; TiO 2 II, a high-pressure polymorph of rutile with the αPbO 2 structure; boron carbide of unknown stoichiometry; and amorphous carbon. Coesite forms prisms several tens of micrometers long, but is polycrystalline, and thus interpreted to be pseudomorphic after stishovite. Associated minerals constrain the estimated pressure to 10–15 GPa assuming temperature was about 1300 °C. Our proposed scenario for formation of qingsongite begins with a pelitic rock fragment that was subducted to mid-mantle depths where crustal B originally present in mica or clay combined with mantle N (δ 15 N = −10.4 ± 3‰ in osbornite) and subsequently exhumed by entrainment in chromitite. The presence of qingsongite has implications for understanding the recycling of crustal material back to the Earth’s mantle since boron, an essential constituent of qingsongite, is potentially an ideal tracer of material from Earth’s surface.

We report on the mineralogy, petrology, and in situ oxygen- and magnesium-isotope measurements using secondary ion mass spectrometry of 10 corundum-bearing calcium–aluminum-rich inclusions (CAIs) from the Adelaide (ungrouped), Murray and Murchison (CM) carbonaceous chondrites. We also measured in situ oxygen-isotope compositions of several isolated corundum grains in the matrices of Murray and Murchison. Most of the corundum-bearing objects studied are uniformly 16O-rich [Δ17O values range from −17‰ to −28‰ (2σ = ±2.5‰) (Δ17Oavr = −23 ± 5‰)], suggesting that they formed in a 16O-rich gas of approximately solar composition and largely avoided subsequent thermal processing in an 16O-poor gaseous reservoir. There is a large spread of the initial 26Al/27Al ratio [(26Al/27Al)0] in the corundum-bearing CAIs. Two Adelaide CAIs show no resolvable excess of radiogenic 26Mg (δ26Mg∗): the inferred (26Al/27Al)0 are (0.6 ± 2.0) × 10−6 and (−0.9 ± 1.2) × 10−6, respectively. Slopes of the model 26Al–26Mg isochrons in five CAIs from Murray and Murchison are (4.4 ± 0.2) × 10−5, (3.3 ± 0.3) × 10−5, (4.1 ± 0.3) × 10−5, (3.9 ± 0.4) × 10−5, and (4.0 ± 2.0) × 10−6, respectively. These values are lower than the canonical (26Al/27Al)0 ratio of (5.23 ± 0.13) × 10−5 inferred from the whole-rock magnesium-isotope measurements of the CV CAIs, but similar to the (26Al/27Al)0 ratio of (4.1 ± 0.2) × 10−5 in the corundum-bearing CAI F5 from Murray. Five other previously studied corundum-bearing CAIs from Acfer 094 (ungrouped) and CM carbonaceous chondrites showed no resolvable δ26Mg∗. We conclude that the corundum-bearing CAIs, as well as the solar corundum grains from matrices and acid-resistant residues of unequilibrated ordinary and carbonaceous chondrites, recorded heterogeneous distribution of 26Al in the Solar System during an epoch of CAI formation. The 26Al-rich and 26Al-poor corundum-bearing CAIs and solar corundum grains represent different generations of refractory objects formed during this epoch. As a result, its duration cannot be inferred from 26Al–26Mg systematics of CAIs. Oxygen-isotope composition of the protoplanetary disk was probably heterogeneous during this time reflecting either initial differences in oxygen isotopic compositions of the solid and gaseous reservoirs in the early Solar System or rapid isotopic evolution of these reservoirs in the protoplanetary disk with time. We suggest that 26Al was injected into the protosolar molecular cloud core, possibly by a wind from a neighboring massive star or by or a low-mass asymptotic giant branch star, prior to formation of CAIs and refractory grains, and was subsequently homogenized through the protoplanetary disk by radial mixing.

Background: Although cholesterol abundance affects cell function, its distribution within the plasma membrane is not established. Results: Cholesterol is uniformly distributed throughout the plasma membrane and is not enriched within sphingolipid domains. Conclusion: Sphingolipid organization in the plasma membrane is not dictated by direct cholesterol-sphingolipid interactions. Significance: Cholesterol abundance affects sphingolipid organization in the plasma membrane via an indirect mechanism., The plasma membranes of mammalian cells are widely expected to contain domains that are enriched with cholesterol and sphingolipids. In this work, we have used high-resolution secondary ion mass spectrometry to directly map the distributions of isotope-labeled cholesterol and sphingolipids in the plasma membranes of intact fibroblast cells. Although acute cholesterol depletion reduced sphingolipid domain abundance, cholesterol was evenly distributed throughout the plasma membrane and was not enriched within the sphingolipid domains. Thus, we rule out favorable cholesterol-sphingolipid interactions as dictating plasma membrane organization in fibroblast cells. Because the sphingolipid domains are disrupted by drugs that depolymerize the cells actin cytoskeleton, cholesterol must instead affect the sphingolipid organization via an indirect mechanism that involves the cytoskeleton.

– Metamorphosed clasts in the CV carbonaceous chondrite breccias Mokoia and Yamato-86009 (Y-86009) are coarse-grained, granular, polymineralic rocks composed of Ca-bearing (up to 0.6 wt% CaO) ferroan olivine (Fa34–39), ferroan Al-diopside (Fs9–13Wo47–50, approximately 2–7 wt% Al2O3), plagioclase (An37–84Ab63–17), Cr-spinel (Cr/(Cr + Al) = 0.19–0.45, Fe/(Fe + Mg) = 0.60–0.79), nepheline, pyrrhotite, pentlandite, Ca-phosphate, and rare grains of Ni-rich taenite; low-Ca pyroxene is absent. Most clasts have triple junctions between silicate grains, indicative of prolonged thermal annealing. Based on the olivine-spinel and pyroxene thermometry, the estimated metamorphic temperature recorded by the clasts is approximately 1100 K. Few clasts experienced thermal metamorphism to a lower degree and preserved chondrule-like textures. The Mokoia and Y-86009 clasts are mineralogically unique and different from metamorphosed chondrites of known groups (H, L, LL, R, EH, EL, CO, CK) and primitive achondrites (acapulcoites, brachinites, lodranites). On a three-isotope oxygen diagram, compositions of olivine in the clasts plot along carbonaceous chondrite anhydrous mineral line and the Allende mass-fractionation line, and overlap with those of the CV chondrule olivines; the Δ17O values of the clasts range from about −4.3‰ to −3.0‰. We suggest that the clasts represent fragments of the CV-like material that experienced metasomatic alteration, high-temperature metamorphism, and possibly melting in the interior of the CV parent asteroid. The lack of low-Ca pyroxene in the clasts could be due to its replacement by ferroan olivine during iron-alkali metasomatic alteration or by high-Ca ferroan pyroxene during melting under oxidizing conditions.

Two carbonatitic mineral assemblages, calcite + wollastonite and calcite + monticellite, which are encapsulated in two diamond grains from the Rio Soriso basin in the Juina area, Mato Grosso State, Brazil, were studied utilizing the NanoSIMS technique. The assemblages were formed as the result of the decomposition of the lower-mantle assemblage calcite + CaSi-perovskite + volatile during the course of the diamond ascent under pressure conditions from 15 to less than 0.8 GPa. The oxygen and carbon isotopic compositions of the studied minerals are inhomogeneous. They fractionated during the process of the decomposition of primary minerals to very varying values: δ18O from −3.3 to +15.4 ‰ SMOW and δ13C from −2.8 to +9.3 ‰ VPDB. These values significantly extend the mantle values for these elements in both isotopically-light and isotopically-heavy areas.

Near-infrared (NIR) reflectance spectroscopy was examined as a potential tool for the determination of forensic signatures indicative of the chemical process history of uranium oxides. The ability to determine the process history of nuclear materials is a desired, but underdeveloped, area of technical nuclear forensics. Application of the NIR technique potentially offers a quick and non-destructive tool to serve this need; however, few data have been published on the compounds of interest. The viability of NIR was investigated through the analysis of a combination of laboratory-derived and real-world uranium precipitates and oxides. A set of reference uranium materials was synthesized in the laboratory using the commonly encountered aqueous precipitation reactions for uranium ore concentration and chemical separation processes (ammonia, hydrogen peroxide, sodium hydroxide, ammonium carbonate, and magnesia). NIR spectra were taken on a range of samples heat treated in air between 85 and 750 °C. X-ray diffraction patterns were also obtained to complement the NIR analysis with crystal phase information. Similar analyses were performed using a set of real-world samples, with process information obtained from the literature, to provide a comparison between materials synthesized in the laboratory and samples representative of industrial processes.

Resonance ionization mass spectrometry was used to measure the composition of the sputtered flux from 15 keV Ga+, Au+, Au2 + and Au3 + primary ions impacting a 235U enriched U3O8 standard. We demonstrate that molecular fragmentation decreases as the primary ion mass and nuclearity increases. Stopping and range of ions in matter calculations show that cluster ions (Au2 + and Au3 +) deposit more of their energy via direct knock-ons with near-surface target atoms, whereas monatomic ions (Ga+ and Au+) penetrate much deeper into the target sub-surface region. We correlate these results to the experimental observations by showing that increased cluster ion sputter yields partition the projectile energy over a larger number of sputtered molecules. Therefore, while cluster ions deposit more total energy into the near surface region of the target compared to monatomic ions, the energy per molecule decreases with projectile mass and nuclearity. Less energy per molecule decreases the number of U–O bond breaks and, consequently, leads to a decrease in molecular fragmentation. Additionally, the extent of molecular fragmentation as a function of ion dose was evaluated. We show that molecular fragmentation increases with increased ion dose; primarily as a result of sub-surface chemical damage accumulation. The relative intensity of this effect appears to be projectile independent.

Congruent evaporation of a crystalline material in vacuum is an extreme reaction in that backward reactions and transport processes in the reactant can be neglected. The evaporation is strongly governed by surface processes and intrinsic nature of the substance. A thorough knowledge of the atomistic evaporation mechanism is fundamental for better understanding reaction kinetics between gas and condensed materials in general. We have conducted a series of evaporation experiments of forsterite in vacuum for crystallographically oriented surfaces at 1500 to 1810 °C. The (100), (010), and (001) surfaces developed their own morphology characterized by evaporation pits and grooves originated from dislocation outcrops. Nominal overall evaporation rate (average retreat rate of a surface) shows significant anisotropy with the maximum difference by a factor of five below 1740 °C. The overall evaporation rates for individual surfaces are fitted with respective Arrhenius relationships, giving the highest activation energy for (100), intermediate for (001), and the lowest for (010). The anisotropy decreases to within 50% at ~1800 °C, which is caused by enhancement of evaporation from (010) owing to preferential evaporation around dislocation outcrops. “Intrinsic evaporation rates” estimated by subtracting contributions of initial roughness and the preferential evaporation around dislocations from the nominal overall evaporation rates show substantial anisotropy even at ~1800 °C. The “intrinsic evaporation rate” for (010) is adequately fitted by an Arrhenius relationship over the examined temperature range giving a single activation energy of 655 kJ/mol. The prevalence of steps with submicrometer to nanometer-scale height shows that forsterite evaporates mostly by layer-by-layer mechanism. The only exception is the (001) surface above ~1650 °C, on which such steps are absent except for surface-parallel minor facets which are rapidly diminishing with time. The (001) surface is inferred to evaporate by direct detachment mechanism at high temperatures. The change of evaporation mechanisms for (001) at around 1650 °C corresponds to a rough-smooth transition kinetically induced by an atomistic evaporation process.

A natural uranium silicate mineral, cuprosklodowskite, has been analyzed by Resonance Ionization Mass Spectrometry (RIMS) for uranium isotope composition under a variety of experimental conditions. While no significant isobaric interferences are observed in the mass regions of interest, molecular supression is incomplete, and varies with the method of neutral U atom production. Despite low measured useful yields under the present analytical arrangement, it is possible to measure uranium isotope composition directly from the sample surface with only a minimum of sample preparation. U-RIMS is a method deserving further development for analyses of environmental materials.

Gaseous uranium hexafluoride (UF6) is used for the enrichment of uranium and is known to be a very reactive and volatile gas. When a small amount of UF6 is released in the environment, it forms uranium oxyfluoride (UO2F2) particles and hydrogen fluoride from the reaction with atmospheric moisture. The UO2F2 particles settle on various surfaces within the enrichment facility where they are collected by safeguards organizations such as the International Atomic Energy Agency (IAEA) through a technique called environmental sampling. Despite their small size, the uranium isotopic composition of these particles is used to determine whether an enrichment facility is compliant with its declarations. Additional and complementary information on the particles' source, formation process and exposure history can be obtained from elemental, molecular and morphological analysis. As fluorine is not always detected in uranium particles originating from enrichment facilities, it is assumed that UO2F2 is unstable under certain environmental conditions. This study aims to determine how those environmental conditions affect the relative amount of fluorine in UO2F2 particles. Expressly for the purpose of this work, we prepared a set of UO2F2 particle samples from the hydrolysis of UF6 and stored these samples in environmental chambers at different temperature, humidity and lighting conditions. The NanoSIMS secondary ion mass spectrometer, with a nanometer-scale spatial resolution, was used to measure the F+/U+ secondary ion ratio of individual particles immediately after sample preparation, and at different time intervals. NanoSIMS analyses on single particles stored up to 7 months in dry air did not detect a significant decrease in the relative amount of fluorine. The exposure to high humidity however, resulted in a much lower F+/U+ ratio, up to 2 orders of magnitude below that of the particles stored in dry air. It should be noted that fluorine was still detected in these samples, even after 7 months of high humidity exposure.

The use of broad bandwidth lasers with automated feedback control of wavelength was applied to the measurement of {sup 235}U/{sup 238}U ratios by resonance ionization mass spectrometry (RIMS) to decrease laser-induced isotopic fractionation. By broadening the bandwidth of the first laser in a three-color, three-photon ionization process from a bandwidth of 1.8 GHz to about 10 GHz, the variation in sequential relative isotope abundance measurements decreased from 10% to less than 0.5%. This procedure was demonstrated for the direct interrogation of uranium oxide targets with essentially no sample preparation.

Background and study aim: Endoscopic therapy of brisk upper gastrointestinal bleeding remains challenging. A proprietary nanopowder (TC-325) has been proven to be effective in high pressure bleeding from external wounds. The efficacy and safety of TC-325 were assessed in a survival gastrointestinal bleeding animal model. Method: 10 animals were randomized to treatment or sham. All animals received intravenous antibiotics, H2-blockers and heparin (activated clotting time 2 × normal). In a sterile laparotomy the gastroepiploic vessels were dissected, inserted through a 1-cm gastrotomy, and freely exposed in the gastric lumen, and the exposed vessel lacerated by needle knife. The treatment group received TC-325 by a modified delivery catheter while the sham group received no endoscopic treatment. Time to hemostasis, and mortality at 60 minutes, 24 hours, 48 hours, and 7 days were noted. Necropsy was performed in all animals. Results: Spurting arterial bleeding was achieved in all animals. No control animal showed hemostasis within the first hour compared with 100 % (5 / 5) in the treatment arm (mean 13.8 minutes, P < 0.0079). Durable hemostasis was achieved with no evidence of rebleeding after 1 and 24 hours in 80 % (4 / 5) of the treated animals compared with none in the control group ( P < 0.0098). None of the control animals survived more than 6 hours. Necropsy at 1 week in treated animals revealed healed gastrotomy without foreign body granuloma or embolization to the lung or brain. Conclusion: TC-325 is safe and highly effective in achieving hemostasis in an anticoagulated severe arterial gastrointestinal bleeding animal model.

Micrometer-scale analyses of a calcium-, aluminum-rich inclusion (CAI) and the characteristic mineral bands mantling the CAI reveal that the outer parts of this primitive object have a large range of oxygen isotope compositions. The variations are systematic; the relative abundance of (16)O first decreases toward the CAI margin, approaching a planetary-like isotopic composition, then shifts to extremely (16)O-rich compositions through the surrounding rim. The variability implies that CAIs probably formed from several oxygen reservoirs. The observations support early and short-lived fluctuations of the environment in which CAIs formed, either because of transport of the CAIs themselves to distinct regions of the solar nebula or because of varying gas composition near the proto-Sun.

Cholesterol is believed to be an important component in compositionally distinct lipid domains in the cellular plasma membrane, which are referred to as lipid rafts. Insight into how cholesterol influences the interactions that contribute to plasma membrane organization can be acquired from model lipid membranes. Here we characterize the lipid mixing and phase behavior exhibited by 15N-dilaurolyphosphatidycholine (15N-DLPC)/deuterated distearoylphosphatiylcholine (D70-DSPC) membranes with various amounts of cholesterol (0, 3, 7, 15 or 19 mol%) at room temperature. The microstructures and compositions of individual membrane domains were determined by imaging the same membrane locations with both atomic force microscopy (AFM) and high-resolution secondary ion mass spectrometry (SIMS) performed with a Cameca NanoSIMS 50. As the cholesterol composition increased from 0 to 19 mol%, the circular ordered domains became more elongated, and the amount of 15N-DLPC in the gel-phase domains remained constant at 6–7 mol%. Individual and micron-sized clusters of nanoscopic domains enriched in D70-DSPC were abundant in the 19 mol% cholesterol membrane. AFM imaging showed that these lipid domains had irregular borders, indicating that they were gel-phase domains, and not non-ideally mixed lipid clusters or nanoscopic liquid-ordered domains.

We report 53 Mn– 53 Cr and 26 Al– 26 Mg isotopic data, obtained by in-situ SIMS analysis, for feldspathic clasts in polymict ureilites DaG 319 and DaG 165. The analyzed clasts belong to the “albitic lithology,” the most abundant population of indigenous feldspathic materials in polymict ureilites, and are highly fractionated igneous assemblages of albitic plagioclase, Fe-rich pyroxenes, phosphates, ilmenite, silica, and Fe(Mn, K, P, Ti)-enriched glass. Glass in DaG 165 clast 19 has extremely high and variable 55 Mn/ 52 Cr ratios (500–58,000) and shows correlated 53 Cr excesses up to ∼ 1500‰, clearly indicating the presence of live 53 Mn at the time of formation. The slope of the well-correlated isochron defined by glass and pyroxenes from this clast corresponds to ( 53 Mn/ 55 Mn) = (2.84 ± 0.10) × 10 − 6 (2 σ ). Data for less 55 Mn/ 52 Cr-enriched glasses from DaG 319 clast B1, as well as phosphates from several other clasts, are consistent with this isochron. The 53 Mn/ 55 Mn ratio obtained from the isochron implies that these clasts are 0.70 ± 0.18 Ma younger than the D'Orbigny angrite, corresponding to the absolute age of 4563.72 ± 0.22 Ma. Plagioclase in DaG 319 clast B1 has a fairly constant 27 Al/ 24 Mg ratio of ∼ 900 and shows resolvable 26 Mg excesses of ∼ 2‰. The slope of the isochron defined by pyroxene and plagioclase in this clast is (3.0 ± 1.1) × 10 − 7 (2 σ ), corresponding to a time difference of 5.4 (− 0.3/+0.5) Ma after CAI (assuming the canonical initial 26 Al/ 27 Al ratio of 5 × 10 − 5 ) and an age 0.5 (− 0.3/+0.5) Ma younger than D'Orbigny. Its absolute age (relative to D'Orbigny) is 4563.9 (+ 0.4/−0.5) Ma, in agreement with the 53 Mn– 53 Cr age from clast 19. These data provide the first high-precision age date, ∼ 5.4 Ma after CAI, for ureilites, giving a minimum estimate for the age of differentiation of their parent asteroid. Interpretation of this age for the thermal and physical history of that asteroid depends on a number of currently unknown or model-dependent parameters, including its size, bulk composition, and oxidation state, and the petrologic relationship between the feldspathic clasts and main group ureilites.

We present the first direct visualization and quantification of water and ion uptake into the core of individual dormant Bacillus thuringiensis subsp. israelensis ( B. thuringiensis subsp. israelensis ) endospores. Isotopic and elemental gradients in the B. thuringiensis subsp. israelensis spores show the permeation and incorporation of deuterium in deuterated water (D 2 O) and solvated ions throughout individual spores, including the spore core. Under hydrated conditions, incorporation into a spore occurs on a time scale of minutes, with subsequent uptake of the permeating species continuing over a period of days. The distribution of available adsorption sites is shown to vary with the permeating species. Adsorption sites for Li + , Cs + , and Cl − are more abundant within the spore outer structures (exosporium, coat, and cortex) relative to the core, while F − adsorption sites are more abundant in the core. The results presented here demonstrate that elemental abundance and distribution in dormant spores are influenced by the ambient environment. As such, this study highlights the importance of understanding how microbial elemental and isotopic signatures can be altered postproduction, including during sample preparation for analysis, and therefore, this study is immediately relevant to the use of elemental and isotopic markers in environmental microbiology and microbial forensics.

Sun Stuff Comets are thought to be remnants of the Sun's protoplanetary disk; hence, they hold important clues to the processes that originated the solar system. Matzel et al. (p. 483 , published online 25 February) present Al-Mg isotope data on a refractory particle recovered from comet Wild 2 by the NASA Stardust mission. The lack of evidence for the extinct radiogenic isotope 26 Al implies that this particle crystallized 1.7 million years after the formation of the oldest solar system solids. This observation, in turn, requires that material formed near the Sun was transported to the outer reaches of the solar system and incorporated into comets over a period of at least two million years.

Preliminary analysis of the oxygen isotopic composition of the solar wind recorded by the Genesis spacecraft suggests that the Sun is 16O-rich compared to most chondrules, fine-grained chondrite matrices, and bulk compositions of chondrites, achondrites, and terrestrial planets (Δ17O = –26.5‰ ± 5.6‰ and –33‰ ± 8‰ (2σ) versus Δ17O ~ ±5‰). The inferred 16O-rich composition of the Sun is similar or slightly lighter than the 16O-rich compositions of amoeboid olivine aggregates and typical calcium-aluminum-rich inclusions (CAIs) from primitive (unmetamorphosed) chondrites (Δ17O = –24‰ ± 2‰), which are believed to have condensed from and been melted in a gas of approximately solar composition (dust/gas ratio ~ 0.01 by weight) within the first 0.1 Myr of the solar system formation. Based on solar system abundances, 26% of the solar system oxygen must be initially contained in dust and 74% in gas. Because solar oxygen is dominated by the gas component, these observations suggest that oxygen isotopic composition of the solar nebula gas was initially 16O-rich. Due to significant thermal processing of the protosolar molecular cloud silicate dust (primordial dust) in the solar nebula and its possible isotope exchange with the isotopically evolved solar nebula gas, the mean oxygen isotopic composition of the primordial dust is not known. In CO self-shielding models, it is assumed that primordial dust and solar nebula gas had initially identical, 16O-rich compositions, similar to that of the Sun (Δ17O ~ –25‰ or –35‰), and solids subsequently evolved toward the terrestrial value (Δ17O = 0). However, there is no clear evidence that the oxygen isotopic compositions of the solar system solids evolved in the direction of increasing Δ17O with time and no 16O-rich primordial dust have yet been discovered. Here we argue that the assumption of the CO self-shielding models that primordial dust and solar nebula gas had initially identical 16O-rich compositions is incorrect. We show that igneous CAIs with highly fractionated oxygen isotopic compositions, fractionation and unidentified nuclear effects (FUN), and fractionation (F) CAIs, have Δ17O ranging from –0.5‰ to –24.8‰. Within an individual FUN or F CAI, oxygen isotopic compositions of spinel, forsterite, and pyroxene define a mass-dependent fractionation trend with a constant Δ17O value. The degree of mass-dependent fractionation of these minerals correlates with the sequence of their crystallization from the host CAI melt. These observations and evaporation experiments on CAI-like melts indicate that FUN and F CAIs formed by melting of solid precursors with diverse Δ17O values in vacuum (total pressure 50☉) ejecta. The 16O-depleted compositions of chondrules, fine-grained matrices, chondrites, and achondrites compared to the Sun's value reflect their formation in the protoplanetary disk regions with enhanced dust/gas ratio (up to 105× solar).

Precise measurement of the 238 U/ 235 U ratio in geologic samples is now possible with modern techniques and mass spectrometers. Natural variations in this ratio have been shown in previous studies. In this study, data obtained from uranium ore concentrates of mining facilities around the world show clear evidence that the depositional redox environment in which uranium is precipitated is the primary factor affecting 238 U/ 235 U fractionation. Low-temperature uranium deposits are, on average, isotopically ∼ 0.4‰ heavier than uranium deposited at high temperatures or by non-redox processes. 238 U/ 235 U ratios coupled with 235 U/ 234 U ratios in the same sample provide evidence that the redox transition (U VI → U IV ) at low temperatures is the primary mechanism of 238 U/ 235 U fractionation and that aqueous alteration plays a very limited, if any, role in fractionation of the 238 U/ 235 U ratio. The isotopic variation of U is therefore a potential signature that can be used to trace the origin of uranium ore concentrate.

Researchers have been suggesting that there is a need to examine the wider social context and its role in influencing flood risk management strategies; this has also been joined by a call for further research into the risks of increased rainfall as part of overall climate change. In response to these calls this research study examines the case studies of two pluvial, meaning of or caused by rainfall, flood events; the Calgary, Canada floods of 2013 and the Montrose, Scotland floods of 2016. These events were considered to be 1 in 100 year low probability scenarios and caused significant disruption to the affected areas. The study focuses on the examination into the social context of such events; by examining the risk perceptions before the event, the flood management strategies used and the social impact of the events it was possible to gain insight into the wider picture of pluvial flooding. The analysis of the cases demonstrated that the perceptions of the events were low, due to the unusual nature of the events, but the forecasting of a flood and the issuing of warnings helped to reduce the impact and predict the areas that were most likely to be affected. It has also highlighted the importance of setting common goals, and engaging with, all the necessary stakeholders to improve the effectiveness of strategies and responses. The study concludes by indicating issues that may be of interest to decision makers and researchers in the field of risk management.

The deepest rocks known from within Earth are fragments of normal mantle (≈400 km) and metamorphosed sediments (≈350 km), both found exhumed in continental collision terranes. Here, we report fragments of a highly reduced deep mantle environment from at least 300 km, perhaps very much more, extracted from chromite of a Tibetan ophiolite. The sample consists, in part, of diamond, coesite-after-stishovite, the high-pressure form of TiO 2 , native iron, high-pressure nitrides with a deep mantle isotopic signature, and associated SiC. This appears to be a natural example of the recently discovered disproportionation of Fe 2+ at very high pressure and consequent low oxygen fugacity (fO 2 ) in deep Earth. Encapsulation within chromitite enclosed within upwelling solid mantle rock appears to be the only vehicle capable of transporting these phases and preserving their low-fO 2 environment at the very high temperatures of oceanic spreading centers.

By making modifications to our previously established measurement setup, we increased our abundance sensitivity for 233U by three orders of magnitude and can now measure 233U/238U ratios as low as 10−13. Because 233U has separate production pathways than 236U, it can provide valuable information on the particular source of anthropogenic uranium in a sample. We demonstrated the utility of our improved capability by using 233U to distinguish separate sources of anthropogenic uranium in a set of samples collected from a contaminated site. In the future, we plan to apply our new capability to characterizing 233U in a wide range of uranium materials.

We report both oxygen- and magnesium-isotope compositions measured in situ using a Cameca ims-1280 ion microprobe in 20 of 166 CAIs identified in 47 polished sections of 15 CR2 (Renazzo-type) carbonaceous chondrites. Two additional CAIs were measured for oxygen isotopes only. Most CR2 CAIs are mineralogically pristine; only few contain secondary phyllosilicates, sodalite, and carbonates – most likely products of aqueous alteration on the CR2 chondrite parent asteroid. Spinel, hibonite, grossite, anorthite, and melilite in 18 CAIs have 16O-rich (Δ17O = −23.3 ± 1.9‰, 2σ error) compositions and show no evidence for postcrystallization isotopic exchange commonly observed in CAIs from metamorphosed CV carbonaceous chondrites. The inferred initial 26Al/27Al ratios, (26Al/27Al)0, in 15 of 16 16O-rich CAIs measured are consistent with the canonical value of (4.5–5) × 10−5 and a short duration ( 0.9 + 2.2 - 0.7 My. Eight of the 166 CR2 CAIs identified are associated with chondrule materials, indicating that they experienced late-stage, incomplete melting during chondrule formation. Three of these CAIs show large variations in oxygen-isotope compositions (Δ17O ranges from −23.5‰ to −1.7‰), suggesting dilution by 16O-depleted chondrule material and possibly exchange with an 16O-poor (Δ17O > −5‰) nebular gas. The low inferred (26Al/27Al)0 ratios of these CAIs ( 2 My after crystallization of CAIs with the canonical (26Al/27Al)0 and suggest evolution of the oxygen-isotope composition of the inner solar nebula on a similar or a shorter timescale. Because CAIs in CR2 and CV chondrites appear to have originated in a similarly 16O-rich reservoir and only a small number of CR2 and CV CAIs were affected by chondrule melting events in an 16O-poor gaseous reservoir, the commonly observed oxygen-isotope heterogeneity in CAIs from metamorphosed CV chondrites is most likely due to fluid–solid isotope exchange on the CV asteroidal body rather than gas–melt exchange. This conclusion does not preclude that some CV CAIs experienced oxygen-isotope exchange during remelting, instead it implies that such remelting is unlikely to be the dominant process responsible for oxygen-isotope heterogeneity in CV CAIs. The mineralogy, oxygen and magnesium-isotope compositions of CAIs in CR2 chondrites are different from those in the metal-rich, CH and CB carbonaceous chondrites, providing no justification for grouping CR, CH and CB chondrites into the CR clan.

Mineralogical observations, chemical and oxygen–isotope compositions, absolute 207Pb–206Pb ages and short-lived isotope systematics (7Be–7Li, 10Be–10B, 26Al–26Mg, 36Cl–36S, 41Ca–41K, 53Mn–53Cr, 60Fe–60Ni, 182Hf–182W) of refractory inclusions [Ca,Al-rich inclusions (CAIs) and amoeboid olivine aggregates (AOAs)], chondrules and matrices from primitive (unmetamorphosed) chondrites are reviewed in an attempt to test (i) the x-wind model vs. the shock-wave model of the origin of chondritic components and (ii) irradiation vs. stellar origin of short-lived radionuclides. The data reviewed are consistent with an external, stellar origin for most short-lived radionuclides (7Be, 10Be, and 36Cl are important exceptions) and a shock-wave model for chondrule formation, and provide a sound basis for early Solar System chronology. They are inconsistent with the x-wind model for the origin of chondritic components and a local, irradiation origin of 26Al, 41Ca, and 53Mn. 10Be is heterogeneously distributed among CAIs, indicating its formation by local irradiation and precluding its use for the early solar system chronology. 41Ca–41K, and 60Fe–60Ni systematics are important for understanding the astrophysical setting of Solar System formation and origin of short-lived radionuclides, but so far have limited implications for the chronology of chondritic components. The chronological significance of oxygen–isotope compositions of chondritic components is limited. The following general picture of formation of chondritic components is inferred. CAIs and AOAs were the first solids formed in the solar nebula ∼4567–4568 Myr ago, possibly within a period of −10‰) and have (26Al/27Al)0 similar to those in chondrules ( −5‰) nebular gas. The majority of chondrules within a chondrite group may have formed over a much shorter period of time (

The 26Al–26Mg isotope systematics in 33 petrographically and mineralogically characterized plagioclase-rich chondrules (PRCs) from 13 carbonaceous chondrites (CCs) – one ungrouped (Acfer 094), six CR, five CV, and one CO – reveal large variations in the initial 26Al/27Al ratio, (26Al/27Al)0. Well-resolved 26Mg excesses (δ26Mg) from the in situ decay of the short-lived nuclide 26Al (t1/2 ∼ 0.72 Ma) were found in nine chondrules, two from Acfer 094, five from the CV chondrites, Allende and Efremovka, and one each from the paired CR chondrites, EET 92147 and EET 92042, with (26Al/27Al)0 values ranging from ∼3 × 10−6 to ∼1.5 × 10−5. Data for seven additional chondrules from three CV and two CR chondrites show evidence suggestive of the presence of 26Al but do not yield well defined values for (26Al/27Al)0, while the remaining chondrules do not contain excess radiogenic 26Mg and yield corresponding upper limits of (11–2) × 10−6 for (26Al/27Al)0. The observed range of (26Al/27Al)0 in PRCs from CCs is similar to the range seen in chondrules from unequilibrated ordinary chondrites (UOCs) of low metamorphic grade (3.0–3.4). However, unlike the UOC chondrules, there is no clear trend between the (26Al/27Al)0 values in PRCs from CCs and the degree of thermal metamorphism experienced by the host meteorites. High and low values of (26Al/27Al)0 are found equally in PRCs from both CCs lacking evidence for thermal metamorphism (e.g., CRs) and CCs where such evidence is abundant (e.g., CVs). The lower (26Al/27Al)0 values in PRCs from CCs, relative to most CAIs, are consistent with a model in which 26Al was distributed uniformly in the nebula when chondrule formation began, approximately a million years after the formation of the majority of CAIs. The observed range of (26Al/27Al)0 values in PRCs from CCs is most plausibly explained in terms of an extended duration of ∼2–3 Ma for the formation of CC chondrules. This interval is in sharp contrast to most CAIs from CCs, whose formation appears to be restricted to a narrow time interval of less than 105 years. The active solar nebula appears to have persisted for a period approaching 4 Ma, encompassing the formation of both CAIs and chondrules present in CCs, and raising important issues related to the storage, assimilation and mixing of chondrules and CAIs in the early solar system.