Remote Optical Detection of Uranium and Plant Response to Uranium Exposure

Lauren Finney, University, My
Ultrafast laser-based spectroscopy is of interest for nuclear nonproliferation monitoring because it holds promise for in-field, rapid, and remote detection of nuclear materials. One of its features is the ability to elicit atomic and molecular signatures from solids, liquids, and gases. Because optical spectroscopy is not reliant on radioactive decay, both the radioactive and nonradioactive materials can be detected. The existence of atomic and molecular isotope shift can also offer isotopic
more » ... nsitivity. Lastly, at high peak powers, ultrafast lasers can undergo filamentation, which can enable optical excitation at long distances. One challenge with generation of filaments at high peak powers is the formation of multiple competing filaments that can be seeded by beam aberrations or, in general, its amplitude and phase structure. This work investigates the properties of filaments in the multi-filament regime via non-invasive optical emission spectroscopy (OES). The spatiotemporal molecular transitions and excitation/ionization mechanisms that occur are described. A genetic algorithm (GA) is used to manipulate the beam spatial phase and, therefore, the resulting multi-filament structure such that the filament-induced breakdown spectroscopy (FIBS) signal generation is optimized. FIBS is demonstrated for single-shot detection of uranium atomic and molecular spectral features that could also be suitable for measurements with isotopic discrimination. While direct detection of uranium is indispensable, there has been recent interest in using plants' response to their environment as an indirect sensor of nuclear activity. Current techniques used in-field to monitor plant health are either limited in their measurement distance or are significantly inhibited by large solar background. The use of pulsed laser-based methods provides a distinct time structure that accompanies optical signatures and also allows for powerful background rejection when used in conjunction with gated detectors. Filament-induced fluorescence (F-IF) [...]
doi:10.7302/4780 fatcat:iuunbjqnhvhdxnommwxpurhxga