Optimization of geometry for x‐ray analysis of rare earth materials

A method of sample excitation is proposed for obtaining good sensitivity and detection limits for rare earth elements (57 ≤ Z ≤ 69) by energy‐dispersive X‐ray fluorescence analysis using a 241 Am radioisotope source. Detection limits of about 100—300 ng for most of the elements using a thin multi‐element sample on a Mylar backing are obtained for a counting time of 1 h with a 100 mCi source. The configuration employed is a close‐coupled collimated side source geometry in which the sample is mounted at 45° to the plane of the detector. This geometry was found to be superior to the commonly used wide annular geometry in terms of the detection limits obtained for the analysis of rare earth elements. A comparative study of the performance of different source geometries using both Mylar‐ and cellulose‐based samples is described.