Determining the ratio of 239Pu to 241Am in wounds by measuring the L gamma x-rays with a Si(Li) detector.

A Si(Li) planar detector provides sufficient photopeak resolution to resolve the 20.16-keV U L gamma x rays resulting from 239Pu decay and the 20.78-keV Np L gamma x rays resulting from 241Am decay. The energies and, therefore, the absorption coefficients of the two x rays are very similar; thus, the ratio of the peaks for a source embedded in tissue remains approximately the same for the two x rays up to at least 6 mm. Measurements of 239Pu-to-241Am ratios by this method in deep wounds agree with results obtained by radiochemical analysis of excised tissue.