X/gamma-ray measurements of total activity in environmental samples without prior knowledge of isotopic abundance

The assay of transuranics in environmental samples by L X-ray spectrometry has al basic limitation. Since X-rays characterize the elements and not the isotopes, the total α-activity of the parent elements cannot be determined without prior knowledge of the isotopic composition. This limitation can usually be overcome by also measuring the weak intensity, low-energy (35-50 keV) γ-rays emitted in the parent decay. Although the statistical uncertainty in such measurements can be high, the uncertainty in the total activity as determined from L X-ray measurements, is much lower as a result of what we call the Peter-Paul effect. A soil sample from Rocky Flats containing 70 pCi/gsup(239,240)Pu with 240Pu/239Pu approx. equal to 0.1 was measured with our Si(Li)-NaI(Tl) prototype X/γ-ray spectrometer. The results are in good agreement with radiochemical analysis. (orig.)