Use of an Infrared Spectroscopic Method for Isotopic Analysis of Gaseous Uranium Hexafluoride

A high performance infrared (HPIR) system was developed and demonstrated for the infrared absorption analysis of uranium-235 and uranium-238 isotopes in uranium hexafluoride gas samples. The method takes advantage of the recent commercial availability of quantum cascade lasers (QCL) and has required the use of advanced statistical data analysis, as well as materials selection due to the chemical reactivity of uranium hexafluoride gas. Sweeping the QCL over the spectral range and sampling via a high-rate analog-to-digital converter provided 0.0005 cm(-1) spectral resolution, allowing for high-precision measurements of the isotopic peak shift. A data analysis method was developed using principal component analysis to predict the isotope weight percent content of uranium-235. The HPIR precision, accuracy, and error were evaluated for a wide range of isotopic ratio samples (0.287-93.7 weight percent uranium-235), and the results were compared to the International Target Values (ITVs) set forth by the International Atomic Energy Agency (IAEA) for nondestructive and destructive analytical techniques used in safeguards verification under the Treaty on the Non-proliferation of Nuclear Weapons. The method meets or surpasses the IAEA ITVs for nondestructive analysis of samples with isotopic content of depleted to highly enriched. The results also demonstrated the capability of the HPIR system to correctly predict the uranium-235 weight percent content of a mislabeled sample whose isotopic distribution was validated by mass spectroscopic measurements. The HPIR measurement is nondestructive and, thus, allows for confirmatory analyses of the exact sample at a designated IAEA laboratory if higher resolution or a certified analysis is needed.