Volatile radioisotopes represent a substantial health risk when released into the environment. To better understand the environmental fate of radioisotopes, the authors constructed a cylindrical steel-walled chamber to simulate the atmospheric processing of volatile radioactive gases. Optical modeling was performed for the properties of simulated sunlight in the chamber to better characterize atmospheric reaction studies. Optical simulations were performed using two wall materials (steel and thin-film silica) and validated against experimental measurements. This optical analysis methodology can be used to improve the fidelity of atmospheric models by accounting for optical inhomogeneities enabling a firmer grasp of radioisotopes’ environmental fate. Graphical abstract

Radioisotopes and hazardous gases can have undetermined environmental pathways. Researchers at Pacific Northwest National Laboratory constructed a chamber that complies with the requirements needed for an atmospheric reaction platform and the safety principles of interacting with hazardous dispersible sources to enable the environmental testing of these gases. Initial dynamic testing showed inter-chamber mixing completed from minutes to 1.5 h. The photooxidation of butyl iodine showed the presence of signals from reaction products and intermediaries for up to 50 h. Current detection limits of the chamber and analytical collection and testing approach were shown to be in the single-digit parts per billion levels. The comparisons between the measured oxidation trends and literature show the utility of performing laboratory experiments to validate the results of modeling for larger-scale scenarios. Researchers at Pacific Northwest National Laboratory constructed and tested an atmospheric chamber that begins to demonstrate the utility of such a chamber design for the study of the atmospheric fate of especially hazardous and radioactive gases.

Tracking mass through harsh environments requires surrogate particles that withstand the event and endure until sampling. Silica-covered quantum dots have been shown to withstand a range of environmental pHs from months to years; in this work they are shown to endure in anticipated local environments. Two methods of particle synthesis were employed to produce luminescent silica with particle diameters 0.1–4 μm. These tracer particles scale for mass production, tolerate harsh environments, and endure in debris. They could be deployed in places such as chemical explosions, industrial processes, geologic test beds, oil and gas fields, nuclear reactors, and geothermal plants to track mass under harsh conditions. Graphical abstract

In this study, five different metal coupons were evaluated for gaseous iodine [I2(g)] adsorption including two stainless steels (i.e., SS304 and SS316), two Inconel alloys (i.e., 625 and 718) and pure Ni (i.e., Ni-200) within a dynamic flow-through system where temperature, iodine concentration, flow rate, atmosphere, and relative humidity were controlled. Humidity was shown to be critical to iodine adsorption on SS304, SS316, and Ni-200 at ambient temperatures. The results presented herein provide evidence that a moisture-mediated reaction is occurring. However, higher humidity levels decrease the adsorption, suggesting an ideal range of humidity for the highest corrosion potential in these metals. A comparison of the five metal substrates showed the highest I2(g) adsorption in the following descending order: Ni-200 > SS304 > SS316 > 718 > 625. The Inconel 625 and 718 alloys were fairly inert to iodine adsorption under the conditions tested. Characterization of the coupons by scanning electron microscopy, energy dispersive X-ray spectroscopy, and X-ray diffraction of the Ni-200 coupon indicates that NiI2 formed and flaked off the surface as a black powder. The SS304 and SS316 coupons showed evidence of extensive reactions with I2(g) and formed a much more deliquescent corrosion product, which reacted with air when removed from the flow-through system for weighing on the analytical balance. A static system was also used to expose separate polished coupons to I2(g), which allowed for analysis of the corrosion layers via scanning electron microscopy. These findings assisted in predicting iodine adsorption behaviors on a variety of metal surfaces under near-ambient conditions.

The adsorption behavior of molecular iodine is important for understanding the spread of radioiodine in a nuclear accident. Prior experiments indicate that, in addition to the interaction with Fe, molecular iodine [i.e., I-2(g)] also interacts with the next most abundant components of austenitic stainless steel (i.e., Ni, and Cr) at room temperature. In this study, we investigate iodine adsorption on Fe, Ni, and Cr while focusing on understanding the variables affecting adsorption as well as the iodine compounds that are formed during adsorption. Scanning electron microscopy and energy-dispersive X-ray spectroscopy were used to characterize the surfaces of exposed metal particles and aid in the understanding of the morphology and chemistry of iodine interactions with the substrates. Inductively coupled plasma optical emission spectroscopy was used to detect low levels of metal iodides and X-ray photoelectron spectroscopy was used to confirm the formation of the metal iodides. The role of environmental factors (e.g., humidity and oxygen content) for iodine adsorption on metal substrates is addressed. The individual metals demonstrated formation of metal iodides for Fe and Ni particles from interaction with I-2(g). The formation of metal iodides may indicate the affinity of iodine for the respective metal. In this study, the iodine affinities ranked Fe > Ni > Cr as determined by the quantity of chemisorbed iodine. This trend is also supported by the distributions and proportions of metals in the corrosion product of the stainless steels. The exposures without oxygen and humidity indicate the potential of a multistep iodine adsorption process where iodine first attacks the oxide layer and then chemisorbs to the exposed metal.

Phonons are important carriers of energy and information in many cryogenic devices used for quantum information science and in fundamental physics experiments such as dark matter detectors. In these systems phonon behaviors can be dominated by interfaces and their atomic structures; hence, there is increasing demand for a more detailed understanding of interfacial phonon transport in relevant material systems. Previous studies have focused on understanding thermal transport over the entire phonon spectrum at and above room temperature. At ultralow temperatures, however, knowledge is missing regarding athermal phonon behavior due to the challenge in modeling the extreme conditions in microscale, heterogeneous cryogenic systems, as well as extracting single-phonon information from a large ensemble. In this paper, we delineate the effects of interfacial atomic structures on phonon transport using a combination of classical molecular dynamics (MD) and phonon wave-packet simulations, to illustrate the consistency and differences between the ensemble- and single-phonon dynamics. We consider three single-crystal Si surface reconstructions---$(1\ifmmode\times\else\texttimes\fi{}1), (\sqrt{3}\ifmmode\times\else\texttimes\fi{}\sqrt{3})$ and $(7\ifmmode\times\else\texttimes\fi{}7)$---and model both experimentally observed $\mathrm{Si}(1\ifmmode\times\else\texttimes\fi{}1)/\mathrm{Al}$ interfaces and hypothesized $\mathrm{Si}(\sqrt{3}\ifmmode\times\else\texttimes\fi{}\sqrt{3})$/Al and $\mathrm{Si}(7\ifmmode\times\else\texttimes\fi{}7)/\mathrm{Al}$ interfaces. The overall interfacial thermal conductance calculated from non-equilibrium MD shows that for the $\mathrm{Si}(1\ifmmode\times\else\texttimes\fi{}1)/\mathrm{Al}$ system, the presence of Al twin boundaries can hinder phonon transport and reduce thermal conductance by 2--12% relative to single-crystal Al; whereas the Si $(\sqrt{3}\ifmmode\times\else\texttimes\fi{}\sqrt{3})$ and $(7\ifmmode\times\else\texttimes\fi{}7)$ reconstructions can enhance it by 6--19%. Normal mode decomposition reveals that both the increase and decrease in conductance are related to inelastic phonon scattering. Single-phonon wave-packet simulations predict phonon transport properties consistent with non-equilibrium MD, while further suggesting that phonon polarization conversion is significant even when elastic transmission dominates, and that the interfacial structures have anisotropic impacts on atomic vibrations along different lattice directions. Our findings suggest avenues for achieving selective phonon transport via controlling interfacial structures of materials using atomically precise fabrication techniques, and that the phonon wave-packet formalism is a potentially powerful method for developing a detailed understanding of non-equilibrium phenomena in the low-temperature limit.

Tracing the flow of solid matter during an explosion requires a rugged tag that can be measured by a unique identifiable signature. Silica-covered semiconductor quantum dots (QDs) provide a unique and tunable photoluminescent signature that emits from within a sacrificial outer layer. Five types of silica-covered zinc sulfide QDs were synthesized and covalently bound to commercial luminescent powders. The combination of five dots and five powders enables a matrix of 25 unique tags. The tracers are shown to be tolerant of environments associated with chemical explosives and provides a unique tag to evaluate debris fields.

Metal intercalation into layered topological insulator materials such as the binary chalcogenide Bi2X3 (X=Te or Se) has yielded novel two-dimensional electron-gas physics, phase transitions to superconductivity, as well as interesting magnetic ground states. Of recent interest is the intercalation-driven interplay between lattice distortions, density wave ordering, and the emergence of new phenomena in the vicinity of instabilities induced by intercalation. Here, we examine the effects of Cu-intercalation on the ternary chalcogenide Bi2Te2Se. We report the discovery, in Cu0.3Bi2Te2Se, of a periodic lattice distortion at room temperature, together with a charge density wave transition around Td = 220K. We also report, for the first time, a complete study of the CuxBi2Te2Se system, and the effect of Cu-intercalation on crystal structure, phonon structure, and electronic properties for 0.0 $\le$ x $\le$ 0.5. Our electron diffraction studies reveal strong Bragg spots at reciprocal lattice positions forbidden by ABC stacking, possibly resulting from stacking faults, or a superlattice. The c-axis lattice parameter varies monotonically with x for 0 $\lt$ x $\lt$ 0.2, but drops precipitously for higher x. Similarly, Raman phonon modes $A^2_{1g}$ and $E_g$ soften monotonically for 0 $\lt$ x $\lt$ 0.2 but harden sharply for x $\gt$ 0.2. This indicates that Cu likely intercalates up to x $\sim$0.2, followed by partial site-substitutions at higher values. The resulting strain makes the 0.2 $\lt$ x $\lt$ 0.3 region susceptible to instabilities and distortions. Our results point toward the presence of an incommensurate CDW above Td = 220 K. This work strengthens prevalent thought that intercalation contributes significantly to instabilities in the lattice and charge degrees of freedom in layered chalcogenides.

Among several Fe-based systems recently found to be superconducting are phases within the Fe1+dSe (FS) and Fe1+dSe1-xTex (FST) families, along with their intercalant-variants. A few groups have recently reported that isostructural Fe1+dTe (FT), although generally reported to be non-superconducting, exhibits trace superconductivity near 10 K upon exposure to oxygen. On the other hand, exposure to oxygen degrades superconductivity in FS, yet improves it in FST for high Te content as well as for high Fe content. We performed a comprehensive study to investigate the effects of oxygen exposure in bulk single crystals of Fe-1 (+/-) Te-d using photoelectron spectroscopy, x-ray diffraction, electron diffraction, and Magnetic Field Modulated Microwave Spectroscopy. We report a change in the oxidation state from Te-0 to Te4+ and Fe-0 to Fe2+/3+ in agreement with others. However, this does not lead to superconductivity. In addition, oxygenation leads to the evolution of trace quantities of an iron-deficient minority phase consistent with an oriented crystalline intergrowth of FeTe2 within the Fe1+dTe crystal lattice.

Sodium-ion batteries are potential alternatives to lithium-ion batteries due to the natural abundance, and relatively low cost, of sodium. When used as a Na-ion battery cathode material, P2-type Na0.67Mn0.625Fe0.25Ni0.125O2(NMFO) displays high reversible capacity (185 mAhg(-1)) and undergoes structural transitions between P6(3)/rnmc, P6(3) (OP4) and orthorhombic Cmcm during charge-discharge cycling between 1.5 and 4.3 V. Using Rietveld crystal structure refinement, we report that these structural transitions are completely suppressed in Na0.67Mn0.625Fe0.25Ni0.125O2 (NMFNO) during cycling. Interestingly, during discharge to 1.5 V, a mixture of two separate P6(3)/mmc phases appears. Reversible capacity and specific energy of NMFNO are superior up to 100 cycles in the 1.5-4.0 V range, and to at least 200 cycles for 2.0-4.0 V. NMFNO displays first-cycle specific energy of 335 Whg(-1), compared with 275 Whg(-1) for NMFO. Scanning Electron Microscopy of the cathode surfaces after 200 cycles reveals performance-eroding cracks, and a solid electrolyte interface (SEI). Electrochemical Impedance Spectroscopy (EIS) shows that the total impedance of NMFNO between 1000 kHz and 0.1 Hz is significantly lower than NMFO after 200 cycles. We conclude that Ni substitution stabilizes the crystal structure by suppressing structural transitions in NMFO during cycling.

We used neutron reflectivity to complement X-ray reflectivity characterization of PCBM-based layers formed on poly(3-hexylthiophene) (P3HT). Single-layer analyses were used to provide reliable scattering length density values for bilayer fitting. Atomic force microscopy analyses showed trends similar to the reflectivity experiments when observing upper surfaces. Styrene polymers added to PCBM in small concentrations (ca. 10%) led to processing advantages while retaining substantial electron mobility, about 0.001 cm(2)/V s. The further introduction of a relatively heavy bromo substituent on the styrene rings greatly increased the film smoothness, as revealed by increases of the oscillation amplitudes in the reflectivity. In addition, the bromine heavy atom increased the X-ray reflectivity scattering length density of the upper layer. Finally, we present data consistent with PCBM becoming partially mixed with the P3HT as the PCBM is spin coated from a solution with poly(bromostyrene) to form an overlying film, consistent with predictions based on published phase diagrams of the P3HT-PCBM system.