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- ItemFate of plutonium at a former nuclear testing site in Australia(American Chemical Society, 2016-08-06) Ikeda-Ohno, A; Shahin, LM; Howard, DL; Collins, RN; Payne, TE; Johansen, MPA series of the British nuclear tests conducted on mainland Australia between 1953 and 1963 dispersed long-lived radioactivity and nuclear weapons debris including plutonium (Pu), the legacy of which is a long-lasting source of radioactive contamination to the surrounding biosphere. A reliable assessment of the environmental impact of Pu contaminants and their implications for human health requires an understanding of their physical/chemical characteristics at the molecular scale. In this study, we identify the chemical form of the Pu remaining in the local soils at the Taranaki site, one of the former nuclear testing sites at Maralinga, South Australia. We herein reveal direct spectroscopic evidence that the Pu legacy remaining at the site exists as particulates of Pu(IV) oxyhydroxide compounds, a very concentrated and low-soluble form of Pu, which will serve as ongoing radioactive sources far into the future. Gamma-ray spectrometry and X-ray fluorescence analysis on a collected Pu particle indicate that the Pu in the particle originated in the so-called "Minor trials" that involved the dispersal of weapon components by highly explosive chemicals, not in the nuclear explosion tests called "Major trials". A comprehensive analysis of the data acquired from X-ray fluorescence mapping (XFM), X-ray absorption near-edge structure (XANES), and extended X-ray absorption fine structure (EXAFS) suggests that the collected Pu particle forms a "core-shell" structure with the Pu(IV) oxyhydroxide core surrounded by an external layer containing Ca, Fe, and U, which further helps us to deduce a possible scenario of the physical/chemical transformation of the original Pu materials dispersed in the semiarid environment at Maralinga more than 50 years ago. These findings also highlight the importance of the comprehensive physical/chemical characterization of Pu contaminants for reliable environmental- and radiotoxicological assessment. © 2016 American Chemical SocietyCopyright © 2016 American Chemical Society.
- ItemInter-comparison of radon measurements from a commercial betaattenuation monitor and ANSTO dual flow loop monitor(MDPI, 2023-08-24) Riley, ML; Chambers, SD; Williams, AGRadon (Rn) is a radioactive, colourless, odourless, noble gas that decays rapidly. It’s most stable isotope, 222Rn, has a half-life of around 3.8 days. Atmospheric radon measurements play an important role in understanding our atmospheric environments. Naturally occurring radon can be used as an atmospheric tracer for airmass tracking, to assist in modelling boundary layer development, and is important for understanding background radiation levels and personal exposure to natural radiation. The daughter products from radon decay also play an important role when measuring fine particle pollution using beta-attenuation monitors (BAM). Beta radiation from the 222Rn decay chain interferes with BAM measurements of fine particles; thus, some BAMs incorporate radon measurements into their sampling systems. BAMs are ubiquitous in air quality monitoring networks globally and present a hitherto unexplored source of dense, continuous radon measurements. In this paper, we compare in situ real world 222Rn measurements from a high quality ANSTO dual flow loop, dual filter radon detector, and the radon measurements made by a commercial BAM instrument (Thermo 5014i). We find strong correlations between systems for hourly measurements (R2 = 0.91), daily means (R2 = 0.95), hour of day (R2 = 0.72–0.94), and by month (R2 = 0.83–0.94). The BAM underestimates radon by 22–39%; however, the linear response of the BAM measurements implies that they could be corrected to reflect the ANSTO standard measurements. Regardless, the radon measurements from BAMs could be used with correction to estimate local mixed layer development. Though only a 12-month study at a single location, our results suggest that radon measurements from BAMs can complement more robust measurements from standard monitors, augment radon measurements across broad regions of the world, and provide useful information for studies using radon as a tracer, particularly for boundary layer development and airmass identification. © 2023 by the authors. Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license.
- ItemIntercalated water drives anomalous thermal expansion in the tetragonal zircon structured bismuth vanadate BiVO4 photocatalyst(Wiley, 2024-07-15) Mullens, BG; Marlton, FP; Nicholas, MK; Permana, AJ; Brand, HEA; Maynard‐Casely, HE; Chater, PA; Kennedy, BJThe thermal transformation of the tetragonal‐zircon (tz‐) to tetragonal‐scheelite (ts‐)BiVO4was studied byin situsynchrotron X‐ray diffraction, thermogravimetric analysis, and Fourier‐transformed infrared spectroscopy. Upon heating, the tetragonal zircon polymorph of BiVO4(tz‐BiVO4) transitioned to thets‐polymorph between 693–773 K. Above 773 K, single phasets‐BiVO4was observed before transitioning to the monoclinic fergusonite (mf‐) polymorph upon cooling. An anomaly in thermal expansion was observed between 400–500 K, associated with the loss of intercalated H2O/NH4+from the coprecipitation procedure. Heatingtz‐BiVO4resulted in contraction of the V−O bond distance and VO4polyhedra volume, ascribed to rotation of the tetrahedra groups. Attempts to study this by neutron diffraction failed due to the large incoherent scatter from the hydrogenous species. Efforts to remove these species while maintaining thetz‐BiVO4structure were unsuccessful, suggesting they play a role in stabilizing thetz‐polymorph. The local structure of bothmf‐BiVO4 andtz‐BiVO4 were investigated by X‐ray pair distribution function analysis, revealing local distortions. © 2024 The Authors. Chemistry - An Asian Journal published by Wiley-VCH GmbH.
- ItemX-ray absorption spectroscopy of phosphine-capped Au clusters(MDPI, 2023-04-28) Sharma, SK; Johannessen, B; Golovko, VB; Marshall, ATThe structural determination of ultrasmall clusters remains a challenge due to difficulties in crystallisation. Often the atomically precise clusters undergo structural change under the influence of the environment. X-ray absorption spectroscopy (XAS) can be an attractive tool to study the electronic and geometric properties of such clusters deposited onto various supports under in situ conditions. Herein, [Au6(dppp)4](NO3)2, [Au9(PPh3)8](NO3)3, [Au13(dppe)5Cl2]Cl3, and Au101(PPPh3)21Cl5 clusters were studied using XAS. The clusters exhibited distinct features compared to bulk gold. XANES results show a systematic increase in the absorption edge energy and white line intensity, with a decrease in cluster nuclearity. The EXAFS of clusters are sensitive to nuclearity and ligands and were fitted with their known crystal structures. This study advances the understanding of the phosphine-ligated metal clusters relevant to practical applications in catalysis and sensing. © 2023 by the authors. Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license.
- ItemEnhancing P2/O3 biphasic cathode performance for sodium‐ion batteries: a metaheuristic approach to multi‐element doping design(Wiley, 2024-06-11) Paidi, AK; Park, WB; Paidi, VK; Lee, JH; Lee, KS; Ahn, H; Avdeev, M; Chae, KH; Pyo, M; Wu, JX; Sohn, KS; Ahn, D; Lu, JSodium‐ion batteries (SIBs) have emerged as a compelling alternative to lithium‐ion batteries (LIBs), exhibiting comparable electrochemical performance while capitalizing on the abundant availability of sodium resources. In SIBs, P2/O3 biphasic cathodes, despite their high energy, require furthur improvements in stability to meet current energy demands. This study introduces a systematic methodology that leverages the meta‐heuristically assisted NSGA‐II algorithm to optimize multi‐element doping in electrode materials, aiming to transcend conventional trial‐and‐error methods and enhance cathode capacity by the synergistic integration of P2 and O3 phases. A comprehensive phase analysis of the meta‐heuristically designed cathode material Na0.76Ni0.20Mn0.42Fe0.30Mg0.04Ti0.015Zr0.025O2 (D‐NFMO) is presented, showcasing its remarkable initial reversible capacity of 175.5 mAh g−1 and exceptional long‐term cyclic stability in sodium cells. The investigation of structural composition and the stabilizing mechanisms is performed through the integration of multiple characterization techniques. Remarkably, the irreversible phase transition of P2→OP4 in D‐NFMO is observed to be dramatically suppressed, leading to a substantial enhancement in cycling stability. The comparison with the pristine cathode (P‐NFMO) offers profound insights into the long‐term electrochemical stability of D‐NFMO, highlighting its potential as a high‐voltage cathode material utilizing abundant earth elements in SIBs. This study opens up new possibilities for future advancements in sodium‐ion battery technology. © 1999-2025 John Wiley & Sons, Inc or related companies.