Xraying Nanoparticles in Ball-Lightning and Fuel Injection jets

fireball.jpgObservations of ball-lightning – long-lived (2 to 50 seconds) bright fireballs size of baseball to beach ball – have been observed for centuries. Previous theoretical work ascribes the longevity of the ball lightnings to the slow oxidation process of silicon, forming nanoparticle networks. Now, Mitchell et al. Phys. Rev. Lett. 100, 065001 (2008) have created artificial ball-lightning using localized microwaves and have studied them in-situ with synchrotron radiation (using small-angle x-ray scattering), proving that the fireballs do indeed contain nanoparticles with sizes of the order 50 nm.

Small Angle X-ray Scattering, or SAXS, has been used to all kinds of samples – liquid, vapor or solid, but this may be the first time this technique was applied to plasma.

Meanwhile, Wang et al. (Nature Physics, advanced publication) performed an ultra-fast time resolved study of morphology of optically dense jets from fuel injector nozzle. The fuel_jet.jpgachieved microsecond temportal resolution is due to application of time-resolved full-field phase contrast imaging. Unlike typical radiography (such as used at the dentist’s office) that is sensitive to the mass density (adsorption) of material through intensity measurements, phase contrast measurements rely on phase changes.

For more details on phase contrast imaging see Wilkins et al., Nature 384, 335 – 338 (28 November 1996)

Techniques using visible light scattering are suffering from problems due to multiple scattering from various interfaces of jet droplets – ironically, these interfaces are precisely what serves as a contrast mechanism in the x-ray phase contrast imaging technique used by Wang et. al in this study.

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