Standoff Detection of Uranium and its Isotopes by Femtosecond Filament Laser Ablation Molecular Isotopic Spectrometry

Kyle C Hartig,Igor Jovanovic,Isaac Ghebregziabher

doi:10.1038/srep43852

Abstract

The ability to perform not only elementally but also isotopically sensitive detection and analysis at standoff distances is impor-tant for remote sensing applications in diverse ares, such as nuclear nonproliferation, environmental monitoring, geophysics, and planetary science. We demonstrate isotopically sensitive real-time standoff detection of uranium by the use of femtosecond filament-induced laser ablation molecular isotopic spectrometry. A uranium oxide molecular emission isotope shift of 0.05 ± 0.007 nm is reported at 593.6 nm. We implement both spectroscopic and acoustic diagnostics to characterize the properties of uranium plasma generated at different filament-uranium interaction points. The resulting uranium oxide emis-sion exhibits a nearly constant signal-to-background ratio over the length of the filament, unlike the uranium atomic and ionic emission, for which the signal-to-background ratio varies significantly along the filament propagation. This is explained by the different rates of increase of plasma density and uranium oxide density along the filament length resulting from spectral and temporal evolution of the filament along its propagation. The results provide a basis for the optimal use of filaments for standoff detection and analysis of uranium isotopes and indicate the potential of the technique for a wider range of remote sensing applications that require isotopic sensitivity.

Highlights

Laser-induced breakdown spectroscopy (LIBS) is presently widely used for its in-situ, remote, and real-time analysis capabilities[1,2,3,4]
The greater filament length determined by the acoustic measurement suggests that at filament-uranium interaction points outside of bounded region shown in Fig. 2, the filament intensity is below the breakdown threshold for uranium
We have demonstrated the use of F2-Laser Ablation Molecular Isotopic Spectrometry (LAMIS), a versatile all-optical detection technique, for standoff measurement of uranium with isotopic selectivity

Summary

Introduction

Laser-induced breakdown spectroscopy (LIBS) is presently widely used for its in-situ, remote, and real-time analysis capabilities[1,2,3,4]. In the LIBS technique, the output of a pulsed high-power laser is focused onto the surface of a sample of interest to generate a luminous micro-plasma. LIBS is an attractive method for remote measurements, but one of the challenges that arises is the ability to produce a small laser focal spot size on the sample surface at large distances[7]. Due to the small atomic isotope shift (typically < 0.02 nm), high resolution spectrometers, operation under rarefied atmospheric conditions, and thousands of laser shots are necessary to resolve the isotope shift. These limitations are not always compatible with remote measurements. The constant molecular emission SBR indicates that the filament propagation distance does not have a significant effect on the performance in F2-LAMIS measurements

Methods

Results

Conclusion