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Abstract In order to model the fate and transport of particles following a nuclear explosion, there must first be an understanding of individual physical and chemical processes that affect particle formation. One interaction pertinent to fireball chemistry and resultant debris formation is that between uranium and oxygen. In this study, we use laser ablation of uranium metal in different concentrations of oxygen gas, either 16O2 or 18O2, to determine the influence of oxygen on rapidly cooling uranium. Analysis of recovered particulates using infrared absorption and Raman spectroscopies indicate that the micrometer-sized particulates are predominantly amorphous UOx (am-UOx, where 3 ≤ x ≤ 4) and UO2 after ablation in 1 atm of pure O2 and a 1% O2/Ar mixture, respectively. Energy dispersive X-ray spectroscopy (EDS) of particulates formed in pure O2 suggest an O/U ratio of ~ 3.7, consistent with the vibrational spectroscopy analysis. Both am-UOx and UO2 particulates convert to α-U3O8 when heated. Lastly, experiments performed in 18O2 environments show the formation of 18O-substituted uranium oxides; vibrational frequencies for am-U18Ox are reported for the first time. When compared to literature, this work shows that cooling timescales can affect the structural composition of uranium oxides (i.e., crystalline vs. amorphous). This indicator can be used in current models of nuclear explosions to improve our predicative capabilities of chemical speciation.

The optical filament-based radioxenon sensing can potentially overcome the constraints of conventional detection techniques that are relevant for nuclear security applications. This study investigates the spectral signatures of pure xenon (Xe) when excited by ultrafast laser filaments at near-atmosphericpressure and in short and loose-focusing conditions. The two focusing conditions lead to laser intensity differences of several orders of magnitude and different plasma transient behavior. The gaseous sample was excited at atmospheric pressure using ∼7 mJ pulses with a 35 fs pulse duration at 800 nm wavelength. The optical signatures were studied by time-resolved spectrometry and imaging in orthogonal light collection configurations in the ∼400 nm (VIS) and ∼800 nm (NIR) spectral regions. The most prominent spectral lines of atomic Xe are observable in both focusing conditions. An on-axis light collection from an atmospheric air–Xe plasma mixture demonstrates the potential of femtosecond filamentation for the remote sensing of noble gases.

ABSTRACT Objective: To evaluate the nature and rate of sports injuries in medical students, as well as the risk factors at these events. Methods: All student-athletes (218) from a Medical School, integrated in at least one of the six team sport modalities (soccer, rugby, indoor soccer, handball, basketball, and volleyball) in 2017, were included. Injuries affecting their performance, regardless of time loss, were included. Athlete-exposure (A-E) was defined as one student-athlete participating in one practice or game. Results: Injury rates were significantly higher in junior medical students (1st - 3rd year) (7.58 per 1000 A-E, 95%CI = 6.11-9.06) than in senior medical students (4th - 6th year) (4.49 per 1000 A-E, 95%CI = 3.26-5.73) (p < 0.001). Multi-sports athletes had higher injury rates (10.69 per 1000 A-E, 95%CI = 8.22-13.17) than single-sport athletes (4.49 per 1000 A-E, 95%CI = 3.51-5.47) (p = 0.002). More than 60% of reported injuries occurred in the lower limbs and the mechanism that accounted for most injuries in games was player contact (51%); whereas in practice, it was non-contact (53%). Conclusion: Junior medical students present a higher injury rate than seniors. Medical students practicing more than one modality had a higher injury rate than those involved in just one sport modality. Level of Evidence IV, Cross-Sectional Study.

Increased absorption of optical materials arising from exposure to ionizing radiation must be accounted for to accurately analyze laser-induced breakdown spectroscopy (LIBS) data retrieved from high-radiation environments. We evaluate this effect on two examples that mimic the diagnostics placed within novel nuclear reactor designs. The analysis is performed on LIBS data measured with 1% Xe gas in an ambient He environment and 1% Eu in a molten LiCl-KCl matrix, along with the measured optical absorption from the gamma- and neutron-irradiated low-OH fused silica and sapphire glasses. Significant changes in the number of laser shots required to reach a 3σ detection level are observed for the Eu data, increasing by two orders of magnitude after exposure to a 1.7 × 1017 n/cm2 neutron fluence. For all cases examined, the spectral dependence of absorption results in the introduction of systematic errors. Moreover, if lines from different spectral regions are used to create Boltzmann plots, this attenuation leads to statistically significant changes in the temperatures calculated from the Xe II lines and Eu II lines, lowering them from 8000 ± 610 K to 6900 ± 810 K and from 15,800 ± 400 K to 7200 ± 800 K, respectively, for exposure to the 1.7 × 1017 n/cm2 fluence. The temperature range required for a 95% confidence interval for the calculated temperature is also broadened. In the case of measuring the Xe spectrum, these effects may be mitigated using only the longer-wavelength spectral region, where radiation attenuation is relatively small, or through analysis using the iterative Saha–Boltzmann method.

Background: The aim of this study was to identify risk factors contributing to the malignancy of colorectal polyps, as well as risk factors for recurrence after the successful endoscopic mucosal resection of large colorectal polyps in a referral center. Materials and Methods: This retrospective cohort study was performed in patients diagnosed with large (≥20 mm diameter) colorectal polyps and treated in the period from January 2014 to December 2019 at the University Hospital Medical Center Bezanijska Kosa, Belgrade, Serbia. Based on the endoscopic evaluation and classification of polyps, the following procedures were performed: en bloc resection, piecemeal resection or surgical treatment. Results: A total of 472 patients with large colorectal polyps were included in the study. The majority of the study population were male (62.9%), with a mean age of 65.7 ± 10.8 years. The majority of patients had one polyp (73.7%) less than 40 mm in size (74.6%) sessile morphology (46.4%), type IIA polyps (88.2%) or polyps localized in the descending colon (52.5%). The accessibility of the polyp was complicated in 17.4% of patients. En bloc resection was successfully performed in 61.0% of the patients, while the rate of piecemeal resection was 26.1%. Due to incomplete endoscopic resection, surgery was performed in 5.1% of the patients, while 7.8% of the patients were referred to surgery directly. Hematochezia (p = 0.001), type IIB polyps (p < 0.001) and complicated polyp accessibility (p = 0.002) were significant independent predictors of carcinoma presence in a multivariate logistic regression analysis. Out of the 472 patients enrolled in the study, 364 were followed after endoscopic resection for colorectal polyp recurrence, which was observed in 30 patients (8.2%) during follow-up. Piecemeal resection (p = 0.048) and incomplete resection success (p = 0.013) were significant independent predictors of polyp recurrence in the multivariate logistic regression analysis. Conclusions: Whenever an endoscopist encounters a complex colorectal lesion (i.e., a polyp with complicated accessibility), polyp size > 40 mm, the Laterally Spreading Tumor nongranular (LST-NG) morphological type, type IIB polyps or the presence of hematochezia, malignancy risk should be considered before making the decision to either resect, refer to an advanced endoscopist or perform surgery.

Abstract We demonstrate measurement of uranium isotopes in femtosecond laser ablation plumes using two-dimensional fluorescence spectroscopy (2DFS). The high-resolution, tunable CW-laser spectroscopy technique clearly distinguishes atomic absorption from 235U and 238U in natural and highly enriched uranium metal samples. We present analysis of spectral resolution and analytical performance of 2DFS as a function of ambient pressure. Simultaneous measurement using time-resolved absorption spectroscopy provides information on temporal dynamics of the laser ablation plume and saturation behavior of fluorescence signals. The rapid, non-contact measurement is promising for in-field, standoff measurements of uranium enrichment for nuclear safety and security.

Abstract The remarkable electronic properties of layered semiconducting transition metal dichalcogenides (TMDs) make them promising candidates for next-generation ultrathin, low-power, high-speed electronics. It has been suggested that electronics based upon ultra-thin TMDs may be appropriate for use in high radiation environments such as space. Here, we present the effects of irradiation by protons, iron, and silver ions at MeV-level energies on a WSe2/6H-SiC vertical heterostructure studied using XPS and UV-Vis-NIR spectroscopy. It was found that with 2 MeV protons, a fluence of 1016 protons/cm2 was necessary to induce a significant charge transfer from SiC to WSe2, where a reduction of valence band offset was observed. Simultaneously, a new absorption edge appeared at 1.1 eV below the conduction band of SiC. The irradiation with heavy ions at 1016 ions/cm2 converts WSe2 into a mixture of WOx and Se-deficient WSe2. The valence band is also heavily altered due to oxidation and amorphization. However, these doses are in excess of the doses needed to damage TMD-based electronics due to defects generated in common dielectric and substrate materials. As such, the radiation stability of WSe2-based electronics is not expected to be limited by the radiation hardness of WSe2, but rather by the dielectric and substrate.

Optical measurement techniques can address certain important challenges associated with nuclear safety and security. Detection of uranium over long distances presents one such challenge that is difficult to realize with traditional ionizing radiation detection, but may benefit from the use of techniques based on intense femtosecond laser pulses. When a high-power laser pulse propagates in air, it experiences collapse and confinement into filaments over an extended distance even without external focusing. In our experiments, we varied the initial pulse chirp to optimize the emission signal from the laser-produced uranium plasma at an extended distance. While the ablation efficiency of filaments formed by self-focusing is known to be significantly lower when compared to filaments produced by external focusing, we show that filaments formed by self-focusing can still generate luminous spectroscopic signatures of uranium detectable within seconds over a 10-m range. The intensity of uranium emission varies periodically with laser chirp, which is attributed to the interplay among self-focusing, defocusing, and multi-filament fragmentation along the beam propagation axis. Grouping of multi-filaments incident on target is found to be correlated with the uranium emission intensity. The results show promise towards long-range detection, advancing the diagnostics and analytical capabilities in ultrafast laser-based spectroscopy of high-Z elements.

In this paper the realization and optimization of two coreless open-loop bus bar current transducers based on a Hall effect sensor are presented. Two types of bus bar are evaluated: flat rectangular and rectangular with a restrictive region in the middle. Both realized transducers are capable of measuring AC and DC currents up to 300 A and 10 kHz frequency with nonlinearity less than 0.3% in the entire range. Several methods for resolving issues with the skin effect and stray magnetic fields are presented along with the experimental test results. Some of the presented methods are novel and have never been evaluated. [ABSTRACT FROM AUTHOR]