Analysis of gadolinium oxide using microwave-enhanced fiber-coupled micro-laser-induced breakdown spectroscopy

We report on the analysis of pure gadolinium oxide (Gd₂O₃) and its detection when mixed in surrogate nuclear debris using microwave-enhanced fiber-coupled micro-laser-induced breakdown spectroscopy (MWE-FC-MLIBS). The target application is remote analysis of nuclear debris containing uranium (U) inside the Fukushima Daiichi Nuclear Power Station. The surrogate nuclear debris used in this study contained gadolinium (Gd), cerium (Ce), zirconium (Zr), and iron (Fe). Ce is a surrogate for U, and Gd₂O₃ is an excellent hazard index because it is incorporated into some fuel rods. Gd detection is essential for assessing debris prior to the retrieval process. Surrogate debris was ablated by an 849 ps 1064 nm micro-laser under atmospheric pressure conditions while a helical antenna propagated 2.45 GHz 1.0 kW microwaves for 1.0 ms into the laser ablation, which was then characterized by a high-speed camera and high-resolution spectrometers. The results showed that microwave-induced plasma expansion led to enhanced emission signals of Gd I, Zr I, Fe I, Ce I, and Ce II. No self-absorption of Gd emissions was evident from the detection limit calibration graphs. Moreover, microwave irradiation decreased the standard deviations of the Gd and Ce emissions and lowered the Gd detection limit by 60%.