TES microcalorimeter SEM-EDS system for rare-earth elements analyses

Objective: A field-emission scanning electron microscope (FE-SEM) with energy-dispersive X-ray spectrometer (EDS)detector of a superconducting transition-edge sensor (TES) microcalorimeter is a new system for electron-microprobe chemical analyses. FE-SEM with TES was used for qualitative and semi-quantitative analyses of rareearth elements (REE) at a low accelerating voltage of 5 kV. Four characteristic M-lines were detected in the LaB ₆ spectrum: LaMζ at 640, LaMαβ at 841, LaMγ at 1021, and a weak line (M ₂N ₄ transition) at 1100 eV. The spectra of other rare-earth borides, rare-earth phosphates, and monazite were assigned in the same way as the La M-lines were. For quantitative analyses, we used a calibration curve method, using standard specimens of known chemical compositions. Linear calibration curves for plots of P, Ca, La, Ce, Pr, andNd intensities versus each weight percentage were obtained. Semi-quantitative analyses of rare-earth minerals should be c rried out at low accelerating voltages using a calibration curve method. In a TES-EDS system, a low accelerating voltage can be used to improve the spatial resolution, without the sensitivity disadvantages of low-energy X-ray emissions. Moreover, a strong increase in the Mαβ intensity with increasing atomic number Z was seen, so the detection limits of heavy REE as much lower than those of light REEs. These results suggest that the TES-EDS system could be a useful analytical tool in rare-earth mineralogy.