239U and 243Am decay data

Precise alpha-particle emission probabilities of 243Am are available in the literature. Beta-particle emission probabilities of 239U cannot be accurately determined by beta spectrometry. However, since both 243Am alpha decay and 239U beta decay lead to excited states of 239Np, it is possible to determine the 239U beta-particle emission probabilities as functions of the 243Am alpha-particle emission probabilities by comparing the gamma-ray spectra of 243Am and 239U. The precision of the alpha-particle emission probabilities is thus transferred to the beta-particle emission probabilities as determined in this manner. High resolution spectrometric measurements of 239U and 243Am gamma rays are reported, along with precise beta-particle emission probabilities of 239U. Use is made of recently measured alpha-particle emission probability data and account is taken of the recommended data for gamma-ray reference standards.