A RADIOISOTOPE X-RAY FLUORESCENCE SPECTROMETER WITH A HIGH-RESOLUTION SEMICONDUCTOR DETECTOR - ANALYTICAL SENSITIVITY FOR ELEMENTS IN LOW ATOMIC NUMBER MATRICES

The analytical sensitivity of an X-ray fluorescence spectrometer utilizing a radioisotope exciter source and a high-resolution, lithium-drifted silicon detector was evaluated for elements in low atomic number matrices. The spectrometer system which was studied used 125l as the exciter source and contained a 30-mm2 detector with a resolution of 512 eV full-width at half-maximum (FWHM) at 6.40 keV. Known molybdenum samples ranging from 10 ng to 1 mg, and nickel samples ranging from 0.1 to 1 mg, were prepared and analyzed. It was found that the detection limit for molybdenum was 35 ng with a co. 5-mCi exciter source; precision in the submicrogram range was 10-20%. The detection limit for nickel was considerably poorer and was found to be 1 m9 for an exciter source strength of ca. 10 mCi. An examination of the various factors that affect the analytical sensitivity of the system showed that the sensitivity was limited primarily by poor detector geometry resulting from the small size of the high-resolution Si(Li) detector, and by background. A principal contributor to background was backscatter of the exciter source radiation by materials surrounding the source and detector. It was found that the radiation was being scattered mainly by air. © 1969, American Chemical Society. All rights reserved.