Improved Sample Loading for Plutonium Analysis by Thermal Ionization Mass Spectrometry and Alpha Spectroscopy

Thermal ionization mass spectrometry (TIMS) and alpha spectroscopy are powerful analytical techniques for the detection and characterization of Pu samples. These techniques are important for efforts in environmental monitoring, nuclear safeguards, and nuclear forensics. Measurement sensitivity and accuracy are imperative for these efforts. TIMS is internationally recognized as the “gold standard†for Pu isotopic analysis. Detection of ultra-trace quantities of Pu, on the order of femtograms, is possible with TIMS. Alpha spectroscopy has a long history of use in the detection and isotopic analysis of actinides and can be a simpler and less expensive alternative to mass spectrometer based techniques. The sensitivity and accuracy of both techniques is highly dependent upon the method of sample loading. High quality sample loading is often tedious, time consuming, and expensive. In this work, we sought to simplify and improve high quality sample loading for TIMS in an effort to expand the utility and improve the sensitivity of this technique. During these efforts a promising sample loading method for alpha spectroscopy was developed. Three improvements were developed for sample loading procedures for isotope ratio measurements of ultra-trace quantities of Pu using (TIMS). Firstly, a new filament geometry, the “dimpleâ€, was developed. The bead loading method was used for these analyses. Beads were loaded with New Brunswick Laboratory certified reference material (NBL CRM) Pu128 (239Pu and 242Pu) from an 8M HNO3 matrix. Overall ion counts and isotopic ratios measured using the dimpled filament geometry were compared to those measured when using the established V-shaped filament geometry. The average number of Pu counts detected when using dimpled filaments was approximately 34% greater than ion counts detected using V-shaped filaments. The accuracy and precision of isotopic ratio measurements were unaffected by the use of dimpled filaments. The well-like geometry of dimpled filaments aids in sample loading and alignment. Additionally, the use of dimpled filaments was found to reduce sample losses inside the ion source. Over the course of 25 measurements, no sample losses were experienced on dimpled filaments, in contrast to 15% total sample loss experienced with v-shaped filaments. Secondly, a polymer fiber architecture for TIMS sample loading was developed using similar sample loading procedures as those used in bead loading. Fibers with diameter of approximately 100 μm were prepared from triethylamine-quaternized-poly(vinylbenzyl chloride) cross-linked with diazabicyclo[2.2.2]octane. Total ion counts (239Pu + 242Pu) and isotope ratios obtained from fiber-loaded filaments were compared to those measured bead loading. Fiber loading was found to improve sensitivity, accuracy, and precision of isotope ratio measurements of Pu compared to the established resin bead loading method, while maintaining its simplicity. The average number of detected Pu+ counts was 180% greater and there was a 72% reduction in standard deviation of ratio measurements when using fiber loading. An average deviation of 0.0003 (0.033%) from the certified isotope ratio value of NBL CRM Pu128 was measured when fiber loading versus a deviation of 0.0013 (0.133%) when bead loading. The fiber formation method can be extended to other anion-exchange polymer chemistries, and therefore offers a convenient platform to investigate the efficacy of novel polymer chemistries in sample loading for TIMS. Thirdly, a sample loading procedure was developed that is based on a polymer thin film architecture. Rhenium filaments were degassed, dip-coated with a thin (~180 nm) hydrophobic base layer of poly(vinylbenzyl chloride) (PVBC), and spotted with an aqueous solution of triethylamine-quaternized-PVBC and a cross-liking agent (diazabicyclo[2.2.2]octane). Spotting resulted in the formation of a toroidal, hydrophilic extractive polymer disk surrounded by the hydrophobic base polymer. Thin film coated filaments were direct loaded with NBL CRM Pu128 from a 9 M HCl matrix. Aqueous sample droplets adhered to the extractive polymer spot, facilitating sample loading. The influence of spot thickness upon ion production was investigated. Overall ion counts and isotopic ratios obtained from thin film coated filaments were compared to those produced by the established resin bead loading method. Isotopic ratios were within error of those measured using the bead loading method with few background interferences. The average number of detected Pu+ counts was 175% greater when using thin film coated filaments with 20-30 μm thick toroidal spots. The use of dimpled filaments further aided sample loading by providing a well-shaped substrate to deposit the sample droplet. No sample loss was experienced with the thin film loading method over the course of 65 sample analyses. Finally, thin films used in this design were found to slow filament aging under atmospheric conditions, facilitating the bulk production of filaments for future analyses. During this work, an unreported form of rhenium surface oxidation was discovered. Rhenium is the most common ionization filament material for Pu analysis by TIMS. Degassing is a common preparation technique for rhenium filaments and is performed to clean filaments before analysis. Degassing involves resistively heating the filaments under high vacuum to volatilize and degrade contaminants. Collaborators at Savannah River National Laboratory reported anecdotally that the use of excessively aged filaments (on the order of 2 months of aging in atmosphere after degassing) decreased the sensitivity and precision of TIMS analyses. Although optimization studies regarding degassing conditions have been reported, little work has been done to characterize filament aging after degassing. In this study, the effects of filament aging after degassing were explored to determine a “shelf-life†for degassed rhenium filaments, and methods to limit filament aging were investigated. Zone-refined rhenium filaments were degassed by resistance heating under high vacuum before exposure to ambient atmosphere for up to 2 months. After degassing, the nucleation and preferential growth of oxo-rhenium crystallites on the surface of polycrystalline rhenium filaments was observed by atomic force microscopy and scanning electron microscopy (SEM). Compositional analysis of the crystallites was conducted using SEM-Raman spectroscopy and SEM energy dispersive X-ray spectroscopy, and grain orientation at the metal surface was investigated by electron back-scatter diffraction mapping. Spectra collected by SEM-Raman suggest crystallites are composed primarily of perrhenic acid. The relative extent of growth and crystallite morphology were found to be grain dependent and affected by the dissolution of carbon into filaments during annealing (often referred to as carbonization or carburization). Crystallites were observed to nucleate in region specific modes and grow over time through transfer of material from the surface. The roles of atmospheric humidity and carburization on the oxidation characteristics (i.e. aging) of rhenium filaments were studied. Degassed and carburized filaments were aged for up to 79 days under dry and humid conditions, and the growth of oxo-rhenium crystallites was investigated intermittently by SEM to construct growth profiles. SEM images were analyzed to determine average crystallite size, number density, and percent surface coverage. Crystallite growth was found to be suppressed by both filament carburization and dry storage conditions (~13% relative humidity). Under humid conditions (75% relative humidity), crystallite growth progressed steadily over the investigatory period, reaching \u3e2.3% surface coverage within 79 days of aging. Atomic ion production of Pu+ was suppressed by approximately 20% and the standard deviation of isotope ratio measurements was increased by 170% when filaments with 1% oxide surface coverage were used in sample loading. Measurement sensitivity and reproducibility are imperative for applications involving ultra-trace analysis of Pu by TIMS. These findings offer validation for observations regarding the detrimental effect of excessive filament aging post-degassing, improve the understanding of conditions that impel the oxidation of rhenium filaments, and provide practical means to suppress the growth of oxides. PVBC nanolayers were found to slow the growth of oxo-rhenium crystallites on the filament surfaces and may serve as an alternative carbon source for filament carburization. A novel substrate for the simultaneous concentration of actinides and sample preparation for alpha spectroscopy was developed using thin films originally intended for TIMS sample loading. Substrate preparation involved forming ultrathin films (10-180 nm) of quaternary amine anion-exchange polymers on glass and silicon by dip-coating. Samples were loaded by submerging the polymer-coated substrates into acidified solutions of Pu or natural water with elevated uranium concentrations. High resolution (25-30 keV) alpha spectra were acquired from these substrates under certain loading conditions indicating that through further development they may be a useful, inexpensive, and potentially field deployable platform serving national security and environmental sampling applications

The Predictive Utility of Competitive Trait Anxiety, Social Support, and Daily Hassles for Athletic Injury

The purpose of this study was to examine the predictive utility of competitive trait anxiety, using a multidimensional measure (Sport Anxiety Scale, Smith, Smoll, & Schutz, 1990) with an added directional component (Jones & Swain, 1992), social support (Social Provisions Scale, Russell & Cutrona, 1984), daily hassles (Daily Hassles Scale, Kanner, Coyne, Schaefer, & Lazarus, 1981), and gender for athletic injury frequency and severity. Questionnaires were administered to 10 male and female high school basketball teams (N= 103) at the beginning of the 2000 - 2001 season, and injury data was collected from that point throughout the regular season. No significant results emerged in the predictive analyses, possibly because participants were not particularly stressed. Explanations for these results and considerations for improving the quality of this research within the high school population are discussed.

Artificial Dendritic Computation: The case for dendrites in neuromorphic circuits

Bio-inspired computing has focused on neuron and synapses with great success. However, the connections between these, the dendrites, also play an important role. In this paper, we investigate the motivation for replicating dendritic computation and present a framework to guide future attempts in their construction. The framework identifies key properties of the dendrites and presents and example of dendritic computation in the task of sound localisation. We evaluate the impact of dendrites on an BiLSTM neural network's performance, finding that dendrite pre-processing reduce the size of network required for a threshold performance.Comment: 11 pages, 3 figures. Replacement to correct an author's nam

Alternative Sample Loading Preparation for Thermal Ionization Mass Spectrometry

This contribution describes a new sample loading method for Thermal Ionization Mass Spectrometry (TIMS), which is used in nuclear safeguards and non-proliferation efforts worldwide and is known as the “gold standard” in isotopic ratio measurements of plutonium. TIMS analysis is used to determine grades of nuclear material and the extent of enrichment at production sites. The current sample loading method for TIMS analysis is known as “bead-loading”. While it provides the lowest detection limit of any known method for plutonium analysis, bead-loading is a difficult, time consuming, and expensive method that results in up to 20% sample loss. The major encumbrance of the method is the need to manually place a small polymer bead (~40 μm diameter) containing the plutonium sample onto a narrow and fragile ionization filament. We have developed an alternative sample loading method that eliminates the difficult and time-consuming steps by pre-coating the ionization filaments with a thin polymer film. Sample loading times have been reduced from hours to minutes. The films remain stably anchored to the filament, thus preventing sample loss. Ongoing TIMS measurements are testing our hypothesis that the method will increase overall measurement efficiency/sensitivity by isolating the sample in close proximity to the filament

A nearly complete skull of the sauropod dinosaur Diamantinasaurus matildae from the Upper Cretaceous Winton Formation of Australia and implications for the early evolution of titanosaurs

Titanosaurian sauropod dinosaurs were diverse and abundant throughout the Cretaceous, with a global distribution. However, few titanosaurian taxa are represented by multiple skeletons, let alone skulls. Diamantinasaurus matildae, from the lower Upper Cretaceous Winton Formation of Queensland, Australia, was heretofore represented by three specimens, including one that preserves a braincase and several other cranial elements. Herein, we describe a fourth specimen of Diamantinasaurus matildae that preserves a more complete skull—including numerous cranial elements not previously known for this taxon—as well as a partial postcranial skeleton. The skull of Diamantinasaurus matildae shows many similarities to that of the coeval Sarmientosaurus musacchioi from Argentina (e.g. quadratojugal with posterior tongue-like process; braincase with more than one ossified exit for cranial nerve V; compressed-cone–chisel-like teeth), providing further support for the inclusion of both taxa within the clade Diamantinasauria. The replacement teeth within the premaxilla of the new specimen are morphologically congruent with teeth previously attributed to Diamantinasaurus matildae, and Diamantinasauria more broadly, corroborating those referrals. Plesiomorphic characters of the new specimen include a sacrum comprising five vertebrae (also newly demonstrated in the holotype of Diamantinasaurus matildae), rather than the six or more that typify other titanosaurs. However, we demonstrate that there have been a number of independent acquisitions of a six-vertebrae sacrum among Somphospondyli and/or that there have been numerous reversals to a five-vertebrae sacrum, suggesting that sacral count is relatively plastic. Other newly identified plesiomorphic features include: the overall skull shape, which is more similar to brachiosaurids than ‘derived' titanosaurs; anterior caudal centra that are amphicoelous, rather than procoelous; and a pedal phalangeal formula estimated as 2-2-3-2-0. These features are consistent with either an early-branching position within Titanosauria, or a position just outside the titanosaurian radiation, for Diamantinasauria, as indicated by alternative character weighting approaches applied in our phylogenetic analyses, and help to shed light on the early assembly of titanosaurian anatomy that has until now been obscured by a poor fossil record

The impact of pasture and non-pasture diets on the sensory and volatile properties of whole milk powder

peer-reviewedThis study evaluated the impact of three distinct diets; perennial ryegrass (GRS), perennial ryegrass/white clover (CLV) and total mixed ration (TMR), on the sensory properties and volatile profile of whole milk powder (WMP). The samples were evaluated using a hedonic sensory acceptance test (n = 99 consumers) and by optimised descriptive profiling (ODP) using trained assessors (n = 33). Volatile profiling was achieved by gas chromatography mass spectrometry using three different extraction techniques; headspace solid phase micro-extraction, thermal desorption and high capacity sorptive extraction. Significant differences were evident in both sensory perception and the volatile profiles of the WMP based on the diet, with WMP from GRS and CLV more similar than WMP from TMR. Consumers scored WMP from CLV diets highest for overall acceptability, flavour and quality, and WMP from TMR diets highest for cooked flavour and aftertaste. ODP analysis found that WMP from TMR diets had greater caramelised flavour, sweet aroma and sweet taste, and that WMP from GRS diets had greater cooked aroma and cooked flavour, with WMP derived from CLV diets having greater scores for liking of colour and creamy aroma. Sixty four VOCs were identified, twenty six were found to vary significantly based on diet and seventeen of these were derived from fatty acids; lactones, alcohols, aldehydes, ketones and esters. The abundance of δ-decalactone and δ-dodecalactone was very high in WMP derived from CLV and GRS diets as was γ-dodecalactone derived from a TMR diet. These lactones appeared to influence sweet, creamy, and caramelised attributes in the resultant WMP samples. The differences in these VOC derived from lipids due to diet are probably further exacerbated by the thermal treatments used in WMP manufacture

Citizen Science, Education, and Learning: Challenges and Opportunities

Citizen science is a growing field of research and practice, generating new knowledge and understanding through the collaboration of citizens in scientific research. As the field expands, it is becoming increasingly important to consider its potential to foster education and learning opportunities. Although progress has been made to support learning in citizen science projects, as well as to facilitate citizen science in formal and informal learning environments, challenges still arise. This paper identifies a number of dilemmas facing the field—from competing scientific goals and learning outcomes, differing underlying ontologies and epistemologies, diverging communication strategies, to clashing values around advocacy and activism. Although such challenges can become barriers to the successful integration of citizen science into mainstream education systems, they also serve as signposts for possible synergies and opportunities. One of the key emerging recommendations is to align educational learning outcomes with citizen science project goals at the planning stage of the project using co-creation approaches to ensure issues of accessibility and inclusivity are paramount throughout the design and implementation of every project. Only then can citizen science realise its true potential to empower citizens to take ownership of their own science education and learning

Discordant Responses Between Primary Head and Neck Tumors and Nodal Metastases Treated With Neoadjuvant Nivolumab: Correlation of Radiographic and Pathologic Treatment Effect.

PD-1 blockade represents a promising treatment in patients with head and neck squamous cell carcinoma (HNSCC). We analyzed results of a neoadjuvant randomized window-of-opportunity trial of nivolumab plus/minus tadalafil to investigate whether immunotherapy-mediated treatment effects vary by site of involvement (primary tumor, lymph nodes) and determine how radiographic tumor shrinkage correlates with pathologic treatment effect. Patients and Methods: Forty-four patients enrolled in trial NCT03238365 were treated with nivolumab 240 mg intravenously on days 1 and 15 with or without oral tadalafil, as determined by random assignment, followed by surgery on day 31. Radiographic volumetric response (RVR) was defined as percent change in tumor volume from pretreatment to posttreatment CT scan. Responders were defined as those with a 10% reduction in the volume of the primary tumor or lymph nodes (LN). Pathologic treatment effect (PTE) was defined as the area showing fibrosis or lymphohistiocytic inflammation divided by total tumor area. Results: Sixteen of 32 patients (50%) with pathologic evidence of LN involvement exhibited discordant PTE between primary sites and LN. In four patients with widely discordant adjacent LN, increased PTE was associated with increased infiltration of tumor CD8+ T cells and CD163+ macrophages, whereas stromal regulatory T cells were associated with low nodal PTE. RVR correlated with PTE at both primary tumor (slope = 0.55, p \u3c 0.001) and in LN (slope = 0.62, p \u3c 0.05). 89% (16/18) of radiographic non-responders with T1-T3 primary sites had no (n = 7) or minimal PTE (n = 9), whereas 15/17 (88%) of radiographic responders had moderate (n = 12) or complete (n = 3) PTE. Conclusion: Nivolumab often induces discordant treatment effects between primary tumor sites and metastatic lymph nodes within subjects. This treatment discordance was also demonstrated in adjacent lymph nodes, which may correlate with local immune cell makeup. Finally, although these data were generated by a relatively small population size, our data support the use of early radiographic response to assess immunotherapy treatment effect in HNSCC