INDUCED BREAKDOWN SPECTROSCOPY; EMISSION-SPECTROSCOPY; PLASMA; PULSES; RATIO; AIR; PROPAGATION; GENERATION

The ability to perform not only elementally but also isotopically sensitive detection and analysis at standoff distances is important 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 filamenturanium 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.

Laser ablation (LA); Laser induced fluorescence (LIF); Laser-induced breakdown spectroscopy (UBS); Plasma chemistry; Combustion;INDUCED BREAKDOWN SPECTROSCOPY; EXCITED ATOMIC FLUORESCENCE; INDUCED ALUMINUM PLASMA; SELECTIVE EXCITATION; URANIUM; ALO; SOLIDS; SPECTROMETRY; EVOLUTION; DYNAMICS

Oxygen present in the ambient gas medium may affect both laser-induced breakdown spectroscopy (LIBS) and laser-induced fluorescence (LIF) emission through a reduction of emission intensity and persistence. In this study, an evaluation is made on the role of oxygen in the ambient environment under atmospheric pressure conditions in LIBS and laser ablation (LA)-LIF emission. To generate plasmas, 1064 nm, 10 ns pulses were focused on an aluminum alloy sample. LIF was performed by frequency scanning a CW laser over the 396.15 nm (3s(2)4s S-2(1/2) -> 3s(2)3p P-2 degrees(3/2)) Al I transition. Time-resolved emission and fluorescence signals were recorded to evaluate the variation in emission intensity caused by the presence of oxygen. The oxygen partial pressure (p(o)) in the atmospheric pressure environment using N-2 as the makeup gas was varied from 0 to 400 Torr O-2. 2D-fluorescence spectroscopy images were obtained for various oxygen concentrations for simultaneous evaluation of the emission and excitation spectral features. Results showed that the presence of oxygen in the ambient environment reduces the persistence of the LIBS and LIF emission through an oxidation process that depletes the density of atomic species within the resulting laser-produced plasma (LPP) plume. (C) 2017 Elsevier B.V. All rights reserved.

INDUCED BREAKDOWN SPECTROSCOPY; BORON ISOTOPIC RATIO; ABLATION PLASMAS; EMISSION FEATURES; INFRARED-SPECTRA; ENERGY-LEVELS; LIBS; NANOSECOND; SPECTROMETRY; PERFORMANCE

We report on the observation of uranium monoxide (UO) emission following fs laser ablation (LA) of a uranium metal sample. The formation and evolution of the molecular emission is studied under various ambient air pressures. Observation of UO emission spectra at a rarefied residual air pressure of similar to 1 Torr indicates that the UO molecule is readily formed in the expanding plasma with trace concentrations of oxygen present within the vacuum chamber. The persistence of the UO emission exceeded that of the atomic emission; however, the molecular emission was delayed in time compared to the atomic emission due to the necessary cooling and expansion of the plasma before the UO molecules can form. (C) 2017 Optical Society of America

Laser-induced breakdown spectroscopy; Stress corrosion cracking; Chlorine; Alkali elements;ATMOSPHERE

Chlorine can play an important role in the process of stress corrosion cracking of dry cask storage canisters for used nuclear fuel, which are frequently located in marine environments. It is of significant interest to determine the surface concentration of chlorine on the stainless steel canister surface, but measurements are often limited by difficult access and challenging conditions, such as high temperature and high radiation fields. Laser-induced breakdown spectroscopy(LIBS) could enable chlorine concentration measurements while meeting the other constraints of this application, but suffers from high excitation energy of chlorine and the interference of the atomic emission lines of iron, thus limiting the sensitivity of detection, especially when LIBS has to be delivered over an optical fiber. We demonstrate that chlorine surface concentrations in the range of 0.5-100 mg/m(2) can be inferred by the detection and quantification of sodium contained in chlorine salts if the speciation and neutralization of salts are not of major concern, whereas minor components of sea salt such as magnesium and potassium are less attractive as surrogates for chlorine due to the lower sensitivity of LIBS for their detection and quantification. The limit of detection, measurement accuracy, and other features and limitations of this surrogate measurement approach are discussed. (C) 2017 Elsevier B.V. All rights reserved.