Multi-frame x-ray radiography and image tracking for quantification of expansion in laser-driven tin ejecta microjets.

One regime of experimental particle-laden flow study involves ejecta microjets-often defined as a stream of micrometer-scale particles generated through shock interaction with a non-uniform surface and generally travel above 1 km/s. In order to capture the change in characteristics as a function of propagation time, we apply a multi-frame x-ray radiography platform to observe and track the jet transport dynamics. A synchrotron x-ray source allows us to perform quantitative analyses and comparisons between the eight images captured by the imaging system.

Single-pulse (100 ps) extended x-ray absorption fine structure capability at the Dynamic Compression Sector.

Determining real-time changes in the local atomistic order is important for a mechanistic understanding of shock wave induced structural and chemical changes. However, the single event and short duration (nanosecond times) nature of shock experiments pose challenges in obtaining Extended X-ray Absorption Fine Structure (EXAFS) measurements-typically used for monitoring local order changes. Here, we report on a new single pulse (∼100 ps duration) transmission geometry EXAFS capability for use in laser shock-compression experiments at the Dynamic Compression Sector (DCS), Advanced Photon Source.

Structural Transformation and Melting in Gold Shock Compressed to 355 GPa.

Gold is believed to retain its ambient crystal structure at very high pressures under static and shock compression, enabling its wide use as a pressure marker. Our in situ x-ray diffraction measurements on shock-compressed gold show that it transforms to the body-centered-cubic (bcc) phase, with an onset pressure between 150 and 176 GPa. A liquid-bcc coexistence was observed between 220 and 302 GPa and complete melting occurs by 355 GPa.

Direct Observations of a Dynamically Driven Phase Transition with in situ X-Ray Diffraction in a Simple Ionic Crystal.

We report real-time observations of a phase transition in the ionic solid CaF_{2}, a model AB_{2} structure in high-pressure physics. Synchrotron x-ray diffraction coupled with dynamic loading to 27.7 GPa, and separately with static compression, follows, in situ, the fluorite to cotunnite structural phase transition, both on nanosecond and on minute time scales.

Observation of a rare earth ion-extractant complex arrested at the oil-water interface during solvent extraction.

Selective extraction of metal ions from a complex aqueous mixture into an organic phase is used to separate toxic or radioactive metals from polluted environments and nuclear waste, as well as to produce industrially relevant metals, such as rare earth ions. Selectivity arises from the choice of an extractant amphiphile, dissolved in the organic phase, which interacts preferentially with the target metal ion. The extractant-mediated process of ion transport from an aqueous to an organic phase takes place at the aqueous-organic interface; nevertheless, little is known about the molecular mechanism of this process despite its importance.

Microphase formation at a 2D solid-gas phase transition.

Density modulated micro-separated phases (microphases) occur at 2D liquid interfaces in the form of alternating regions of high and low density domains. Brewster angle microscopy (BAM) images demonstrate the existence of microphases in cluster, stripe, and mosaic morphologies at the buried interface between hexane and water with fluoro-alkanol surfactant dissolved in the bulk hexane. At high temperature, the surfactant assembles at the interface in a 2D gaseous state.