Comparison of two radiometric methods for the determination of americium-241 in plutonium containing materials

Abstract

Two methods for the determination of ²⁴¹Am based on gamma-ray measurements are presented and compared: (i) isotope dilution gamma-ray spectrometry (IDGS) with ²⁴³Am and (ii) direct high-resolution gamma-ray spectrometry (HRGS). In the IDGS method, a spike was added and the Am was separated by partition chromatography. The intensity ratio of the gamma-ray energies was measured at 59.537 and 74.67 keV for ²⁴¹Am and ²⁴³Am, respectively. The ²⁴¹Am content was calculated from calibration graphs obtained for six standard solutions prepared by the addition of known amounts of ²⁴¹Am reference solutions to weighed aliquots of ²⁴³Am spike solutions. The ²⁴¹Am content in several Pu containing materials was calculated with respect to Pu, which was determined independently by titration. Eight samples were analysed, six measurements being carried out for each sample. The ²⁴¹Am content ranged from 0.9 to 3.5% with a relative standard deviation from ±0.12 to ±0.35%. In the HRGS method, the gamma-ray spectra of all the chemically untreated solid samples and of all solutions containing about 4 mg of Pu in 100 ml of solution were measured in the energy range 0–307 keV. The spectra were evaluated with a multi-group analysis program and the ²⁴¹Am content was calculated with respect to Pu from the gamma-ray energy intensities in the 94–104 keV series of peaks. The relative standard deviation was within ±1% and there was no systematic difference in comparison to the isotope dilution method.