研究目的
Investigating the gas-phase oxidation of uranium (U), plume chemistry, and the corresponding impact on optical emission features of the U plasma produced via nanosecond laser ablation.
研究成果
The study provides insight into the spatial characteristics of molecular formation in a laser-produced U plasma. It reveals that U atoms and UO molecules are segregated in space, with UO existing at cooler regions of the plasma where conditions favor molecular recombination. The segregation between the distribution of U atoms and UO species is more apparent at later times of plasma evolution with lower oxygen partial pressures. At higher oxygen partial pressures, significant variation in plume morphology is seen for UO species, which can be related to higher oxide (UxOy) formation further from the target.
研究不足
The study is limited by the shot-to-shot variations due to presence of instabilities in the image data, which cannot be avoided. Fluctuations were estimated at less than 8%. The interaction between a high-Z (U) plume and a low-Z ambient gas is complex, and the assumption of the plume to be spherically symmetric may be an over simplification.
1：Experimental Design and Method Selection:
Plasmas were produced via nanosecond laser ablation of a natural U target in a chamber where U oxidation was controlled by varying the oxygen partial pressure in an argon cover gas. Monochromatic imaging of U atoms and monoxide (UO) molecules was performed using narrow bandpass optical filters.
2：Sample Selection and Data Sources:
A natural U target was used. The light emitted from the U plasma was collected with a lens and focused to a 400 mm multimode fiber.
3：List of Experimental Equipment and Materials:
Nd:YAG laser (1064 nm, 6 ns full-width half-maximum (FWHM)), anti-reflection coated plano-convex lens with a focal length of 15 cm, vacuum chamber, gas manifold, intensifed CCD (ICCD) camera (PI-MAX4, 1024 × 1024 pixels), telephoto lens, narrow bandpass filters centered at 404 nm and 593.5 nm, 0.5 m Czerny-Turner spectrograph (Spectrapro 2500), Andor iStar ICCD camera.
4：5 nm, 5 m Czerny-Turner spectrograph (Spectrapro 2500), Andor iStar ICCD camera.
Experimental Procedures and Operational Workflow:
4. Experimental Procedures and Operational Workflow: The laser was focused normal to a U metal target. The target was mounted in a vacuum chamber. Emission images were collected by placing an ICCD camera orthogonal to the plasma expansion direction. Monochromatic imaging of U atomic and UO molecular species was performed by inserting narrow bandpass filters in front of the camera. Spatially-integrated OES was performed, where the light emitted from the U plasma was collected with a lens and focused to a 400 mm multimode fiber.
5：Data Analysis Methods:
The emission images were processed by stretching contrast, sharpening, and smoothing using MATLAB R2018a. A false color-map was applied after image processing to emphasize intensity variations.
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