Two metallic Pu-240 sources were certified as reference standards of s
pontaneous-fission activity and neutron flux. The certification result
s were used to determine the ratio T-alpha/T-sf of the alpha-decay and
spontaneous-fission half-lives of Pu-240. The ratio was found to be (
5.68 +/- 0.11) . 10(-8), which corresponds to T-sf = (1.16 +/- 0.02) .
1011 yr for an assumed value T-alpha = 6563 +/- 7 yr.