Radioisotope-Excited X-Ray Fluorescence Analysis and its Applications to Geochemical Exploration in Greenland
The principles of X-ray fluorescence ar e briefly described. In particular, two methods of radioisotope X-ray fluorescence analysis ar e discussed: (a) radioisotope X-ray fluorescence analysis by means of portable apparatus incorporating scintillation or proportional counters and balanced differenti...
Risø National Laboratory
|Summary:||The principles of X-ray fluorescence ar e briefly described. In particular, two methods of radioisotope X-ray fluorescence analysis ar e discussed: (a) radioisotope X-ray fluorescence analysis by means of portable apparatus incorporating scintillation or proportional counters and balanced differential X-ray filters, and (b) radioisotope X-ray fluorescence spectrometry by means of Si(Li) or Ge(Li) semiconductor detectors. For a portable radioisotope X-ray fluorescence analyser calibration curves were established for Cr, Ni.Cu.Zn, Zr, Nb, Mo, La+Ce, and Pb in rock powders, Ti.Zr, and Nb in plane cut rock surfaces, and Zr, Nb, and La+Ce in rock outcrops. Detection limits found from calibration data were 0.3% Cr, 0.06% Ni, 0.14%Cu, 0.14%Zn, 0.04% Zr 0.07% Nb, 0.03% Mo, 0.02% La+Ce and 0.1 % Pb in rock powders, 0.07% Ti, 0.4% Zr and 0.1% Nb in cut rock surfaces, and 0.14% Zr, 0,15% Nb and 0.16% La+Ce in rock outcrops. Values for the accuracy and the precision of these analyses ar e given. Special investigations include the dependence of the analytical result on the grain size of the sample material and experiments regarding the critical sample weight. Si(Li) and Ge(Li) X-ray spectrometers for the analysis of rock samples are described. Two methods of X-ray spectrum reduction carried out by means of a 32K computer were investigated: simple channel-by-channel integration and least-squares fitting. Calibration data on rock powders yielded for the Si(Li) X-ray spectrometer (lmCi Cd for excitation of characteristic X-rays) 23 ppm Rb, 110 ppm Sr, 69 ppm Zr, 206 ppm Nb, and 172 ppm Mo as detection limits for the analysis of rock powders. For plane cut rock surfaces and the Ge(Li) X-ray pectrometer (10 mCi Am for excitation purpose) detection limits of 400 ppm Ce and 180 ppm Nd were obtained. The influence of interferences on the analytical result such as overlapping of X-ray peaks, absorption of X-rays in the sample and grain-size effects are dealt with. Special emphasis is given to the correction of X-ray intensities by ...|