Abstract
Laser induced breakdown spectroscopy (LIBS) is a rapid atomic emission spectroscopy technique that can be configured for a variety of applications including space, forensics, and industry. LIBS can also be configured for stand-off distances or in-situ, under vacuum, high pressure, atmospheric or different gas environments, and with different resolving-power spectrometers. The detection of uranium in a complex geological matrix under different measurement schemes is explored in this paper. Although many investigations have been completed in an attempt to detect and quantify uranium in different matrices at in-situ and standoff distances, this work detects and quantifies uranium in a complex matrix under Martian and ambient air conditions. Investigation of uranium detection using a low resolving-power LIBS system at stand-off distances (1.6m) is also reported. The results are compared to an in-situ LIBS system with medium resolving power and under ambient air conditions. Uranium has many thousands of emission lines in the 200–800nm spectral region. In the presence of other matrix elements and at lower concentrations, the limit of detection of uranium is significantly reduced. The two measurement methods (low and high resolving-power spectrometers) are compared for limit of detection (LOD). Of the twenty-one potential diagnostic uranium emission lines, seven (409, 424, 434, 435, 436, 591, and 682nm) have been used to determine the LOD for pitchblende in a dunite matrix using the ChemCam test bed LIBS system. The LOD values determined for uranium transitions in air are 409.013nm (24,700ppm), 424.167nm (23,780ppm), 434.169nm (24,390ppm), 435.574nm (35,880ppm), 436.205nm (19,340ppm), 591.539nm (47,310ppm), and 682.692nm (18,580ppm). The corresponding LOD values determined for uranium transitions in 7Torr CO2 are 424.167nm (25,760ppm), 434.169nm (40,800ppm), 436.205nm (32,050ppm), 591.539nm (15,340ppm), and 682.692nm (29,080ppm). The LOD values determine for uranium emission lines using the medium resolving power (10,000λ/Δλ) LIBS system for the dunite matrix in air are 409.013nm (6120ppm), 424.167nm (5356ppm), 434.169nm (5693ppm), 435.574nm (6329ppm), 436.205nm (2142ppm), and 682.692nm (10,741ppm). The corresponding LOD values determined for uranium transitions in a SiO2 matrix are 409.013nm (272ppm), 424.167nm (268ppm), 434.169nm (402ppm), 435.574nm (1067ppm), 436.205nm (482ppm), and 682.692nm (720ppm). The impact of spectral resolution, atmospheric conditions, matrix elements, and measurement distances on LOD is discussed. The measurements will assist one in selecting the proper system components based upon the application and the required analytical performance.
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