Determination of the half-life of the spontaneous fission of240PU

Two metallic240Pu sources were certified as reference standards of spontaneous-fission activity and neutron flux. The certification results were used to determine the ratio TαTs&f of the alpha-decay and spontaneousfission half-lives of240Pu. The ratio was found to be (5.68+-0.11)·10−8, which corresponds to Ts&f=(1.16+0.02)·1011 yr for an assumed value Tα=6563+7yr.