X-ray fluorescence determination of uranium. I

The physical principle is presented of the origin of X-ray fluorescence radiation, and the fluorescence yield, the analytical application of X-ray fluorescence radiation and the types of detectors used for the detection of this radiation are described. Measuring equipment is described for isotope X-ray fluorescence analysis which makes possible the measurement and analytical use of the K lines of X-ray fluorescence radiation for the determination of heavy elements, mainly of uranium. The measuring equipment comprises an excitation equipment whose diagram is given. The isotope source selected is 139Ce with Esub(γ)=165.8 keV in a mixture with 141Ce with Esub(γ)=145.3 keV. The 139Ce+141Ce mixture was prepared by irradiation of cerium dioxide in a nuclear reactor. The X-ray fluorescence radiation of uranium was recorded with a planar Ge(Li) detector with a total volume of 0.08 cm3 and a 1000-channel analyzer. The resolution of the instrument was 2 keV for 152Eu (121.8 keV). The suitability of the developed equipment was proved by uranium determination. The experiments were oriented to ascertaining the direct proportion of the measured intensity of X-ray fluorescence radiation and the amount of uranium in the sample. The effect was investigated of the sample volume on the measured intensity of X-ray fluorescence and it was found that the intensity was practically the same for equal amounts of uranium. The over-all results of the experiment showed that the detection of X-ray fluorescence radiation should be improved, this by the use of detectors with higher resolution such as could measure the L line, the performance and configuration of the excitation equipment should also be improved, and that internal standards should be used in uranium determination. (J.P.)