Samarium isotope compositions of uranium ore concentrates: A novel nuclear forensic signature.

Uranium ore is mined and milled to produce uranium ore concentrate (UOC), a regulated product of the nuclear fuel cycle. Diversion of UOC from the fuel cycle into possible weapons production is a key concern in global nonproliferation efforts. As such, the ability to trace the origin of seized nuclear materials is imperative to law enforcement efforts. Although isotopic signatures of UOCs have proven fruitful to pinpoint sample provenance, new isotopic signatures are needed because most existing isotopic signatures are not indicative of the original ore body from which the U is derived. In this work, we developed a new method to separate samarium (Sm) from a U-rich sample matrix and report the first Sm isotope compositions of 32 UOCs derived from a variety of worldwide uranium mines. Relative to terrestrial standards, approximately half the UOCs have resolved and anticorrelated 149Sm-150Sm isotope compositions, consistent with the capture of thermal neutrons by 149Sm in the ore body. The UOCs with anomalous Sm isotope compositions tend to derive from older (~>1.5Ga) and higher-grade ore bodies, although other factors, such as the presence of neutron moderators like water, also play a role. Nonetheless, the Sm isotope compositions of UOCs directly reflects the neutron fluence over the history of the original ore body and can be used to discern different geologic conditions associated with that ore body. As such, this work demonstrates the potential use of Sm isotopes as a novel nuclear forensics signature for origin assessment of UOCs.

Microscale Isotopic Variation in Uranium Fuel Pellets with Implications for Nuclear Forensics.

Until recently, the analysis and identification of nuclear fuel pellets in the context of a nuclear forensics investigation have been mainly focused on macroscopic characteristics, such as fuel pellet dimensions, uranium enrichment, and other reactor-specific features. Here, we report microscale isotopic heterogeneity observed in different fuel pellet fragments that were characterized in situ by nanoscale secondary ion mass spectrometry (NanoSIMS). The materials analyzed include fuel fragments obtained as part of the Collaborative Materials Exercise (CMX-4) organized by the Nuclear Forensics International Technical Working Group (ITWG), as well as a fuel pellet fragment from a commercial power reactor. Although the commercial fuel pellet showed a homogeneous 235U/238U ratio across the sample (within analytical error), NanoSIMS imaging of the CMX-4 fuel pellet fragments showed distinct microscale variations in the uranium isotopic composition. The average 235U enrichments were 2.2 and 2.9% for the two samples; however, the measured 235U/238U ratios varied between 0.0081 and 0.035 (0.79-3.3 atom % 235U) and between 0.0090 and 0.045 (0.89-4.3 atom % 235U). The measurement of 236U in one of the CMX-4 samples suggested the use of at least three uranium oxide powders of different isotopic compositions ("source terms") in the production of the pellets. These variations were not detected using the conventional bulk, macroscopic techniques applied to these materials. Our study highlights the importance of characterizing samples on the microscale for heterogeneities that would otherwise be overlooked and demonstrates the potential use of NanoSIMS in guiding further nuclear forensic analysis.

A composite position independent monitor of reactor fuel irradiation using Pu, Cs, and Ba isotope ratios.

When post-irradiation materials from the nuclear fuel cycle are released to the environment, certain isotopes of actinides and fission products carry signatures of irradiation history that can potentially aid a nuclear forensic investigation into the material's provenance. In this study, combinations of Pu, Cs, and Ba isotope ratios that produce position (in the reactor core) independent monitors of irradiation history in spent light water reactor fuel are identified and explored. These position independent monitors (PIMs) are modeled for various irradiation scenarios using automated depletion codes as well as ordinary differential equation solutions to approximate nuclear physics models. Experimental validation was performed using irradiated low enriched uranium oxide fuel from a light water reactor, which was sampled at 8 axial positions from a single rod. Plutonium, barium and cesium were chemically separated and isotope ratio measurements of the separated solutions were made by quadrupole and multi-collector inductively coupled mass spectrometry (Cs and Pu, respectively) and thermal ionization mass spectrometry (Ba). The effect of axial variations in neutron fluence and energy spectrum are evident in the measured isotope ratios. Two versions of a combined Pu and Cs based PIM are developed. A linear PIM model, which can be used to solve for irradiation time is found to work well for natural U fuel with <10% 240Pu and known or short cooling times. A non-linear PIM model, which cannot be solved explicitly for irradiation time without additional information, can nonetheless still group samples by irradiation history, including high burnup LEU fuel with unknown cooling time. 137Ba/138Ba is also observed to act as a position independent monitor; it is nearly single valued across the sampled fuel rod, indicating that samples sharing an irradiation history (same irradiation time and cooling time) in a reactor despite experiencing different neutron fluxes will have a common 137Ba/138Ba ratio. Modeling of this Ba PIM shows it increases monotonically with irradiation and cooling time, and a confirmatory first order analytical solution is also presented.

Plasma flow reactor for steady state monitoring of physical and chemical processes at high temperatures.

We present the development of a steady state plasma flow reactor to investigate gas phase physical and chemical processes that occur at high temperature (1000 < T < 5000 K) and atmospheric pressure. The reactor consists of a glass tube that is attached to an inductively coupled argon plasma generator via an adaptor (ring flow injector). We have modeled the system using computational fluid dynamics simulations that are bounded by measured temperatures. In situ line-of-sight optical emission and absorption spectroscopy have been used to determine the structures and concentrations of molecules formed during rapid cooling of reactants after they pass through the plasma. Emission spectroscopy also enables us to determine the temperatures at which these dynamic processes occur. A sample collection probe inserted from the open end of the reactor is used to collect condensed materials and analyze them ex situ using electron microscopy. The preliminary results of two separate investigations involving the condensation of metal oxides and chemical kinetics of high-temperature gas reactions are discussed.

Análisis molecular del gen de la VP4 de la cepa de rotavirus bovino tipo P[5] aislada de becerros en el Estado Yaracuy / Molecular analysis of the VP4 genes of bovine rotavirus strain type P[5] isolated from calves in Yaracuy State

La diarrea neonatal bovina indiferenciada es una enfermedad multifactorial que afecta a una alta proporción de becerros (50% o más) causando hasta un 40% de mortalidad en los primeros 30 d de vida. Entre los agentes causales se incluyen muchos enteropatógenos (bacterias, virus, protozoarios), con predominio de infecciones combinadas. Entre los virus, los rotavirus constituyen los principales agentes causales de gastroenteritis aguda en diferentes especies animales. Su genoma, de 11 segmentos de ARN de doble cadena, puede rearreglarse genéticamente en coinfecciones de diferentes cepas, produciendo una progenie viral con un nuevo fenotipo. En la ganadería bovina venezolana, se han descrito los rotavirus con una prevalencia de 20-30% en animales con cuadros de diarrea entre 2-6 sem de edad. Los serotipos G6 y el genotipo P1 se han reportado con mayor frecuencia en becerros de la región central de Venezuela. Cepas de rotavirus bovino del grupo A fueron detectados por inmunoensayo enzimático (ELISA) y electroforesis en gel de poliacrilamida (PAGE), en 32 de 280 (11,43%) muestras de heces de becerros de 15 fincas del estado Yaracuy, Venezuela. La secuencia nucleotídica se logró para una de las variantes detectadas (A610). En el análisis comparativo de las secuencias de la VP8* (fragmento de la VP4) mostró corresponder al genotipo P[5]. Estos datos constituyen el primer reporte de una cepa de rotavirus bovino genotipo P[5], que circula en las fincas del estado Yaracuy, Venezuela, pudiendo servir de apoyo para la incorporación de este grupo viral en las vacunas que se utilizan en el país.

The undifferentiated neonatal bovine diarrhea is a multifactorial disease that affects a high proportion of calves (50% or more) causing up to 40% of mortality in the first 30 d of life. Among the infectious agents known to cause diarrhea in calves are the rotavirus and coronavirus. Rotaviruses are the major causative agents of acute gastroenteritis in different animal species. Their 11-segment genome of double ARN chain can genetically re-arrange different strains, producing a viral progeny with new or atypical phenotype. Rotaviruses have been described in the bovine Venezuelan cattle, with a prevalence of 20-30% in animals between 2-6 weeks of age, with episodes of diarrhea. The serotypes G6 and the genotype P1 have been reported with higher frequency in calves from the central region of Venezuela. In this investigation, rotavirus strains of cattle from Group A were detected by the enzyme-linked immunosorbent assay (ELISA) and the polyacrylamide gel electrophoresis (PAGE) in 32 of 280 (11.43%) stool samples of calves in 15 farms in the State of Yaracuy, Venezuela. The nucleotide sequence was obtained for one of the variants detected (A610) and the comparative analysis of the sequences of the VP8* (the VP4 fragment) corresponded to the P [5] genotype. These data constitute the first report of a strain of bovine rotavirus genotype P[5], which circulates in the States of Yaracuy, Venezuela, and can serve as a support for the inclusion of this viral group to the vaccines that are being used in the country.

Oxygen isotope variations at the margin of a CAI records circulation within the solar nebula.

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.