Hybrid interferometric/dispersive atomic spectroscopy of laser-induced uranium plasma

Abstract

An established optical emission spectroscopy technique, laser-induced breakdown spectroscopy (LIBS), holds promise for detection and rapid analysis of elements relevant for nuclear safeguards, nonproliferation, and nuclear power, including the measurement of isotope ratios. One such important application of LIBS is the measurement of uranium enrichment (235 U/ 238 U), which requires high spectral resolution (e.g., 25 pm for the 424.4 nm U II line). High-resolution dispersive spectrometers necessary for such measurements are typically bulky and expensive. We demonstrate the use of an alternative measurement approach, which is based on an inexpensive and compact Fabry-Perot etalon integrated with a low to moderate resolution Czerny-Turner spectrometer, to achieve the resolution needed for isotope selectivity of LIBS of uranium in ambient air. Spectral line widths of ~10 pm have been measured at a center wavelength 424.437 nm, clearly discriminating the natural from the highly enriched uranium.

Significance of ambient conditions in uranium absorption and emission features of laser ablation plasmas

“…Limited studies exist on the practicality of LA-OES for U identification [3,13,16,19]. Notably, LA-OES proves practical in detecting isotopic shifts of elements including U [21][22][23][24][25][26][27]. Reported U detection limits employing LA-OES are on the order of parts per million (ppm) [20,28,29].…”

Dual-comb spectroscopy of laser-induced plasmas

“…For example, in LIBS, obtaining sufficient spectral resolution to resolve intrinsic spectral linewidths in a laser ablation plume presents significant challenges and requires very large spectrographs, further reducing spectral bandwidth. Intrinsic LIBS emission linewidths of atomic transitions are often <10 pm, especially for heavy elements such as U 32 , 33 . Approaches have been used to increase spectral resolution in LIBS measurements, such as combining a Fabry−Perot etalon with a spectrograph 32 , 34 .…”

“…Intrinsic LIBS emission linewidths of atomic transitions are often <10 pm, especially for heavy elements such as U 32 , 33 . Approaches have been used to increase spectral resolution in LIBS measurements, such as combining a Fabry−Perot etalon with a spectrograph 32 , 34 . Echelle spectrographs 33 are capable of measuring broad spectral bandwidths at high spectral resolution.…”

Combination of atomic lines and molecular bands for uranium optical isotopic analysis in laser induced plasma spectrometry

“…Cremers et al [13] also performed isotopic analysis on 6 Li and 7 Li with LIBS under atmospheric pressure. For heavy elements, uranium has been mostly studied [13,14,17,18]. Doucet et al [14] reported the first study of uranium isotopic analysis with atmospheric pressure LIBS.…”

“…[13] utilized a spectrometer with a resolution of 75,000, and reported baseline separated isotopic components for the U II 424.437 nm line in atmospheric pressure LIBS. Recently, Morgan et al [17] developed and applied a hybrid interferometric/dispersive spectrometer to measure laser-induced plasma from a metallic uranium foil, and reported that the 235 U-238 U isotope shift at U II 424.437 nm was resolved in ambient air. We previously performed uranium isotopic analysis in soil matrix with atmospheric-pressure LIBS, and compared the effectiveness of several fitting algorithms to extract isotopic information from the LIBS atomic spectra [18].…”