Standardisation and measurement of the decay scheme data of 243Am and 239Np

243Am is of great importance as a chemical yield tracer for the radiochemical determination of 241Am in environmental and other samples. 239Np can also be used in a similar fashion for 237Np, although there are significant limitations because of the short half-life. The use of both of these radionuclides has been inhibited by the absence of accurately standardised solutions and the poor quality of the associated decay data, particularly the γ-ray emission probabilities for 239Np. Standardised solutions of 239Np alone and of an equilibrium mixture of 243Am and 239Np have been prepared, and these solutions have been used in conjunction with an intrinsic Ge spectrometer to measure the relevant γ-ray emission probabilities.