Information in spectra from sources containing “aged” 241Am as from TRU waste

The Ge γ-ray spectra of 241Am were studied using sources of 241Am that had not been purified from their daughter activities for many years. In spite of the fact that the first member of the 241Am decay chain, 237Np, has a half-life of 2.14×106 years, the grow-in of the second member of the 241Am decay chain, 27-day 233Pa could be clearly observed. This unexpected observation is possible when the parent emits low-intensity γ-rays while the progeny emits high-intensity γ-rays. A calculation of the ratio of the parent to daughter γ-ray emission rates for the 241Am 322-keV γ-ray and the 233Pa 312-keV γ-ray as a function of time from purification verifies that this is the case for the 322-keV 241Am γ-ray and the 312-keV 233Pa γ-ray. These γ-rays may be used in the assay of transuranic waste to determine its age, when 241Am is present in the waste, and also to assay for 237Np in excess of that expected from grow-in of its 241Am parent.