> 100 m fiber-coupled microchip laser-induced breakdown spectroscopy for remote elemental analysis applications

This study aims to develop ultralong fiber-optic cable (FOC) coupled microchip laser - induced breakdown spectroscopy (mLIBS) to reveal the elemental distribution and local composition of nuclear fuel debris in an accident-damaged reactors at Fukushima Daiichi Nuclear Power Station (FDNPS). Currently at FDNPS, the distance between the area where humans can safely work in a sufficient space and the nuclear fuel debris is expected to be > 100 m. Therefore, it becomes crucial to analyze the light transmittance performance of FOC-coupled mLIBS systems over such long distances in a high-radiation environment. Therefore, this study focuses on the influence of gamma radiation dose and FOC length on the transmittance of the visible and near-infrared (NIR) wavelengths through FOCs. Compared with an FOC with low-OH groups, that with high-OH groups exhibits better light transmittance performance in both wavelength regions in a high-radiation environment. Furthermore, the light transmittance performance of the high-OH FOC extended up to 500 m in length is tested in a radiation-free environment. From the measurement results, the maximum FOC length for microchip crystal oscillation is estimated to be > 800 m, although attenuation is observed with the increase in FOC length. Finally, we analyze the ultralong FOC-coupled mLIBS system through the detection of gadolinium (Gd) in mixed oxide samples. The strong emission lines of Gd were only available in the visible wavelength region. Therefore, quantitative analysis of Gd is successfully performed in the visible region using the mLIBS system coupled with up to 300-m-long FOCs, with the limits of detection being between 0.1% and 0.2%. (c) 2024 Optica Publishing Group under the terms of the Optica Open Access Publishing Agreement