This paper describes an approach to measuring extinct fission products that would allow for the characterization of a nuclear test at any time. The isotopic composition of molybdenum in five samples ...of glassy debris from the 1945 Trinity nuclear test has been measured. Nonnatural molybdenum isotopic compositions were observed, reflecting an input from the decay of the short-lived fission products 95Zr and 97Zr. By measuring both the perturbation of the 95Mo/96Mo and 97Mo/96Mo isotopic ratios and the total amount of molybdenum in the Trinity nuclear debris samples, it is possible to calculate the original concentrations of the 95Zr and 97Zr isotopes formed in the nuclear detonation. Together with a determination of the amount of plutonium in the debris, these measurements of extinct fission products allow for new estimates of the efficiency and yield of the historic Trinity test.
The accurate interpretation of uranium metal
230
Th/
234
U and
231
Pa/
235
U radiochronometry model ages requires an understanding of how uranium parent nuclides and decay progeny (
230
Th and
231
...Pa) behave during uranium metal casting. In order to directly measure the spatial distribution of
230
Th and
231
Pa in uranium metal before and after vacuum induction melting (VIM), Los Alamos National Laboratory identified uranium metal feedstock, characterized the metal feedstock, conducted a controlled casting experiment of an approximately 120 kg uranium metal rod, and characterized the cast metal. This study presents radiochronometry results and quantified
230
Th and
231
Pa VIM separation factors from bulk uranium.
230Th-excess is rare in most arc lavas, but common in the Cascades, yet the origin of such excesses remains unclear. At Mt. Shasta, age-corrected (230Th/232Th) and (238U/232Th) activity ratios range ...from 1.108 to 1.290 and from 0.987 to 1.309 (27.3% 230Th-excess to 6.1% 238U-excess), respectively. Although small degrees of zircon crystallization (<0.3%) may yield high (230Th/238U)0 in derivative magmas, high Zr contents, the lack of zircon as a liquidus phase, and low Th/U ratios in Mt. Shasta lavas argue against zircon fractionation. Instead, melting models suggest 230Th-excesses are imparted on lavas through mixing mantle-derived magmas with partial melts of a mafic amphibolite lower crust where garnet was produced in the residuum through amphibole and plagioclase destabilization. The hot nature of Cascade magmas suggests that high intrusion temperatures promoted dehydration melting in the deep crust.
At Mt. Shasta, the destruction of the ancestral cone (Sand Flat) was followed by four cone-building stages, three of which lie in the age range of U-series geochronology. Lavas within individual eruptive stages have relatively constant (230Th/232Th)0 ratios that are interpreted to reflect specific mixtures of mantle (m) and lower crustal (lc) melts that are characteristic of a specific stage (Mm:lc). High (230Th/232Th)0 ratios identify higher proportions of lower crust in the Misery Hill stage (Mm:lc=∼85:15), whereas low (230Th/232Th)0 ratios reflect the more mantle-like composition of the Shastina lavas (Mm:lc=∼95:5); in the case of Shastina lavas, very low 87Sr/86Sr ratios, down to 0.7029, support a substantial mantle contribution. Changes in (230Th/232Th)0 ratios correlate with eruptive volume, where the most voluminous stage (Misery Hill) is inferred to have the largest proportion of crustal melt and highest (230Th/232Th)0 ratios. Variable (230Th/238U)0 ratios within, and between, eruptive groups likely reflect a combination of residence time in the lower crust and differential assimilation of bulk, non-garnet-bearing crust that had (230Th/238U) = 1. The volume-(230Th/232Th)0 relations are accompanied by correlations with 87Sr/86Sr ratios, where the most radiogenic Sr is associated with the largest eruptive volumes, indicating that the largest magmatic episodes produced the largest amount of lower crustal interaction.
The new U–Th and Sr isotope measurements of this study, along with U-series data for other Cascade centers suggest that interaction with the lower crust exerts greater control on Cascade magma chemistry than previously recognized. Indeed, the relatively dry nature of the Cascades may offer a unique opportunity to better understand the influence of the deep crust in young continental arcs, as larger subduction components in other settings may overprint any lower crustal signature and produce lavas with large 238U-excesses.
•We investigate mechanisms of 230Th-enrichment in the Mt. Shasta stratocone lavas.•U–Th and Sr isotopes constrain the role of crustal interaction in magma evolution.•Partial melting of mafic amphibolite lower crust imparts 230Th-excesses on lavas.•A range of Th-excess reflects variable residence time and bulk crust assimilation.•Mantle and crustal melts mix to create eruptive units with distinct (230Th/232Th)0.
The isolation and purification of protactinium from uranium materials is essential for
231
Pa–
235
U radiochronometry, but separating Pa from uranium-niobium alloys, a common material in the nuclear ...fuel cycle, is challenging due to the chemical similarity of Pa and Nb. Here we present three resin chromatography separation techniques for isolating Pa from U and Nb which were independently developed by three different laboratories through ad hoc adaptations of standard operating procedures. Our results underscore the need for and value of purification methods suitable for a diversity of uranium-based materials to ensure the operational readiness of nuclear forensics laboratories.
The plutonium rapid response in vitro bioassay method described here was designed to determine
238
Pu,
239
Pu, and
240
Pu concentration in urine samples from workers with potential internal ...contamination. Results provide quick and actionable information about the level of contamination necessary to assist making further medical decisions, including chelation therapy. The radiochemical procedure can be performed within approximately 48 h, including sample preparation, measurement(s) by alpha spectrometry and/or inductively coupled plasma mass spectrometry (ICP-MS), and data evaluation.
The radiochronometric model age is an important signature in nuclear forensic analysis. Recent studies have illustrated the need for controlled experiments on the behavior of decay products during ...uranium metal casting to provide a foundation for interpretation of discordant model ages. A variety of uranium metal and alloy samples cast under known conditions were analysed by three laboratories. This work is the first multi-laboratory study of its kind to explore how these progeny isotopes are chemically fractionated from uranium metal during casting. The intercomparison allowed for capability demonstration and method development on samples and provided data to increase our understanding of the behavior of decay progeny in these complex systems.
Bioassay monitoring is an important capability for any facility that works with significant amounts of radioactive material. The speed at which these analyses can be made is critical in the event of ...a potential exposure. In this study, we present a new method that facilitates the rapid separation of uranium from a urine matrix for assay and isotopic determination by inductively coupled plasma mass spectrometry. This method is validated with archived urine samples that were previously analyzed using established, more time consuming methods. The sources of uncertainty for uranium assay and isotopic measurements are modelled using the Monte Carlo method to better understand the precision and accuracy of this method at the limit of quantification.
Improved methods employed at Los Alamos National Laboratory for
231
Pa/
235
U radiochronometry are outlined. We present elution curves obtained during
233
Pa tracer preparation from
237
Np. ...Additionally, we report model ages for uranium certified reference materials (CRMs) exhibiting a range of
235
U enrichments including the first
231
Pa/
235
U model ages for CRMs U200 and U900. Our results enable these CRMs to be used, with increased confidence, as quality control materials during nuclear forensics investigations.
New measurement and assessment techniques have been applied to the radiochemical reevaluation of the Trinity Event. Thirteen trinitite samples were dissolved and analyzed using a combination of ...traditional decay counting methods and the mass spectrometry techniques. The resulting data were assessed using advanced simulation tools to afford a final yield determination of 24.8 ± 2 kt TNT equivalent, substantially higher than the previous U.S. Department of Energy released value of 21 kt.
Application of the
231
Pa/
235
U radiochronometer for nuclear forensic investigations is challenged by a lack of certified reference materials with
231
Pa/
235
U model purification dates. The Japan ...Atomic Energy Agency, Los Alamos National Laboratory, and Lawrence Livermore National Laboratory completed an interlaboratory study measuring
231
Pa/
235
U model ages of New Brunswick Laboratory CRM U100. Results from independent laboratories were combined to calculate a consensus
231
Pa/
235
U model purification date for CRM U100 of March 26, 1959 ± 237 days. This
231
Pa/
235
U consensus date for CRM U100 may be used by the nuclear forensic community for quality control of
231
Pa/
235
U radiochronometry measurements of unknown materials.
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