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

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Abstract
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 Xe125 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 Xe125 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 Xe125 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 Xe125 range measurements.

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