Year
2015
Abstract
Laser-Induced Breakdown Spectroscopy (LIBS) has the ability to perform rapid, real-time, elemental, and isotopic analysis of materials relevant to nuclear forensics, safeguards, and counterproliferation. LIBS involves the collection of light from a micro- plasma formed when a laser pulse ablates a material surface. The light emitted from the plasma can be spectrally analyzed to yield both elemental and isotopic composition. The non-destructive, expeditious, and in situ capabilities of LIBS have been identified by the IAEA as promising for the use in detection of nuclear materials and for the use in attribution process for interdicted materials. The intensity of the observed emission lines has been experimentally observed to depend not only on the analyte type and concentration, but also the sample matrix composition (including the presence of minor contaminants). This “matrix effect” is the consequence of the change of the excited state distribution of atoms and ions due to complex and diverse concurrent interactions among different species in the plasma. The matrix effect increases the difficulty of the interpretation of LIBS spectrum. We have been investigating the dynamics of the laser-produced plasma in simple and complex samples where the matrix effect is observed. Through the design of a unique LIBS measurement system that implements fast-gated shadowgraphy, interferometry, and spatially resolved spectral measurements we can study the temporal behavior of the LIBS plasma. The experimental effort is supplemented with ab initio theoretical atomic structure and plasma emission modeling to elucidate the fundamental atomic/electron interactions within the multi-element plasma. Detailed understanding of the matrix effect can not only help to elucidate the characteristics of the LIBS spectra, but also lead to their effective interpretation, thus increasing the value of the technique for material detection and quantification.