Abstract: An x-ray fluorescence instrument for measuring the presence of lead in a sample. The lead is bombarded with gamma rays from a source thereof and in turn, emit x-rays. The x-rays are detected by a scintillation detector which emits photons that are directed to a photomultiplier tube which provides signals to an electronic processor including multichannel analyzers to provide output signals representative of the lead present in the sample. The instrument includes a cone plug disposed between the gamma ray source and the detector to prevent gamma rays from directly striking the detector.