Low-level determinations of uranium and thorium in geologic samples by X-ray fluorescence

Trace levels of uranium and thorium in geologic samples are determined rapidly by a direct wavelength-dispersive X-ray fluorescence method. Relative intensity of scattered tube radiation was used as an internal standard to compensate for variations in instrumental operating characteristics. U and Th can be determined within a precision of ±10% and accuracy of ±15% or less with measuring times of 50 seconds for Th and 400 seconds for U, respectively. The results of XRF analysis were in good agreement with those of other methods such as neutron activation analysis and inductively coupled plasma atomic emission spectrometry. (author)