Lifetime of the long-lived isomer of 236Np from α-, β- and electron-capture decay measurements

Abstract

Abstract The half-life of long-lived 236Np, due to α, β and electron-capture decay, was found to be 1.55 × 105 yr. Of all decays, 88% populate excited states in 236U and 12% populate levels in 236Pu. Lifetimes measured by growth of the ground states of 236U and 236Pu agree with values from corresponding γ de-excitations in these daughter nuclei. Therefore, nearly all the electron-capture decays populate the 6+ level of the ground-state band in 236U. Similarily, essentially all the β− decay populates an analogous 6+ level in 236Pu, which de-excites through a previously unreported transition of 158.3 keV. If a very weak γ-ray at 894 keV can be ascribed to a level in 232U populated by β decay of 232Pa, its existence establishes a 0.2% α-branching decay in 236Np.