Quantitative analysis of thorium in graphite using femtosecondlaser-induced breakdown spectroscopy br

In order to promote the application of Laser-Induced Breakdown Spectroscopy (LIBS) in the nuclear industry, in this paper, a femtosecond LIBS(fs-LIBS) system was used to quantitatively analyze Thori-um (Th) in a highly pure graphite matrix. According to the Th concentrations in the Thorium-based fuel, atotal of 9 homemade Th2O3-graphite mixture samples with Th concentrations that varied from 0.35% to35.15% were prepared by the standard addition method. The favorable experimental parameters such as thetreatment methods for LIBS detection, laser pulse energy and delay times were studied before the quantitat-ive analysis. The results show that the signal intensity of the fs-LIBS spectrum acquired by the scanning withmoving method is significantly higher than that without the moving method. For the Th I 396.21 nm line, theRelative Standard Deviation (RSD) value of multiple measurements for the scanning method was just 5.7%,which was much lower than that of without the moving method (20.4%). The Th spectral lines show obvioussaturation due to the self-absorption effect in the higher concentration region, and thus the basic calibrationmethod was no longer applicable. Therefore, an exponential function was used to fit the spectral line intens-ity and concentration in the whole concentration region, and the concentration saturation threshold valuescorresponding to the analytical lines Th I 394.42, 396.21, and 766.53 nm were obtained. The basic calibra-tion method has good detection performance when the calibration curves were constructed by using a lowerconcentration below the saturation threshold. For the peak area and peak intensity of each analytical line, us-ing the internal standard method with the internal standard line (C I 247.85 nm), a good linear relationshipcan be found between them and the Th concentrations in the whole concentration region, especially for ana-lytical line Th I 766.53 nm with a higher saturation threshold. The internal standard method had good predic-tion performance for unknown samples with higher concentrations. The above results show that fs-LIBS hasthe potential to monitor and analyze the thorium concentration in the thorium-based fuel cycle