Abstract
Optical measurement techniques can address certain important challenges associated with nuclear safety and security. Detection of uranium over long distances presents one such challenge that is difficult to realize with traditional ionizing radiation detection, but may benefit from the use of techniques based on intense femtosecond laser pulses. When a high-power laser pulse propagates in air, it experiences collapse and confinement into filaments over an extended distance even without external focusing. In our experiments, we varied the initial pulse chirp to optimize the emission signal from the laser-produced uranium plasma at an extended distance. While the ablation efficiency of filaments formed by self-focusing is known to be significantly lower when compared to filaments produced by external focusing, we show that filaments formed by self-focusing can still generate luminous spectroscopic signatures of uranium detectable within seconds over a 10-m range. The intensity of uranium emission varies periodically with laser chirp, which is attributed to the interplay among self-focusing, defocusing, and multi-filament fragmentation along the beam propagation axis. Grouping of multi-filaments incident on target is found to be correlated with the uranium emission intensity. The results show promise towards long-range detection, advancing the diagnostics and analytical capabilities in ultrafast laser-based spectroscopy of high-Z elements.
Highlights
Mitigation of effects resulting from radioactive releases in nuclear systems such as nuclear power plants [1], enrichment, and reprocessing facilities would benefit from sophisticated methods for sensitive detection of actinides and rapid measurement of their spatial distribution
The results confirm the viability of filament-induced breakdown spectroscopy (FIBS) to detect uranium, which offers a promising path to remote measurements of uranium contamination
The challenges in performing emission spectroscopy of plasmas containing uranium have been associated with a congested spectrum containing more than 105 atomic and ionic lines originating from ∼1600 energy levels [38,39,40]
Summary
Mitigation of effects resulting from radioactive releases in nuclear systems such as nuclear power plants [1], enrichment, and reprocessing facilities would benefit from sophisticated methods for sensitive detection of actinides and rapid measurement of their spatial distribution. Laser-induced breakdown spectroscopy (LIBS) represents a robust method for in-situ, remote, and real-time analytical measurements of material composition [5,6,7]. This method has demonstrated its high versatility in extraterrestrial [8] and deep-sea exploration [9], detection and classification of explosives [10,11], analysis of soil contaminants [12], use in nuclear power plants and dry cask storage systems [13,14,15], and detection of nuclear materials in general [16,17,18]. The transient character of a particular emission type strongly depends on laser-sample coupling and thermodynamic parameters of the plasma
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