A NEW METHOD FOR MEASURING THE DEPTHS OF EMBEDDED RADIOTRACER ATOMS USING A PRECISION β-RAY SPECTROMETER

A quantitative method has been developed for measuring the mean depth within a solid of those radioactive atoms which decay with the emission of monoenergetic conversion electrons. By acceleration to kev energies in a mass separator 16.8-hour Xe 125 atoms were injected into metal foils, and the intense K 54.96 and K 188.4 conversion lines were then scanned in the Chalk River π√2 β-ray spectrometer. The manner in which these conversion line shapes varied with Xe 125 depth was calibrated by covering the foil surfaces with known thicknesses of Al or Au; it was found that the peak heights decreased in an approximately exponential manner with increasing Xe 125 depths. With this calibration, mean depths can be determined under unknown conditions; the maximum sensitivity is about 6 atom layers (15 Å) under the most favorable conditions. Examples are given of the application of the method to metal oxidation studies and to Xe 125 range measurements.