Evaluated experimental data for radioactive decays and reactions for known nuclides (U, Np, Pu, Am, Cm, Bk, Cf) of A = 240 are presented together with adopted values for level energies, γ-ray energies, relative branching ratios and other nuclear properties.
This revision was primarily motivated by the need for re-evaluation of absolute gamma-ray intensities from the ɛ decay of 240Am to 240Pu. These quantities are essential for determining precise and accurate cross-sections for the 241Am(n,2n)240Am reaction using fast neutrons (see e.g. Americium Workshop, Santa Fe, New Mexico, September 2007, 2008To06, 2007Ta01, 2006Pe14) and 241Am(γ,n) reaction (see e.g. 2006Ri08). For 240U, the γ-ray data have now become available.
The data sets for 244Pu α decay to 240U; 244Cm α decay to 240Pu and 244Cf α decay to 240Cm have been adapted from evaluations by 1998Ak04 and 2003Ak04. For 244Cm decay, evaluation by 2006BeZL under the Decay Data Evaluation Project (DDEP) is also used. The γ-ray data (energies and intensities) for 240Cm decay are not considered (by the evaluators) as well established.
Most detailed data are available only for 240Pu. Extensive data in the second potential well are available for this nuclide together with fission isomers and several superdeformed (SD) structures. For other nuclides spectroscopic data are rather sparse in the literature; especially for the following radioactive decays: The ɛ decays of 240Cf, 240Bk and 240Cm; multipolarities of γ-ray transitions in 240Np from 240U decay; γ-ray transitions from 244Cf α decay and %ɛ branch of 244Cf decay; spins and parities of excited states in 240U and multipolarities of associated γ-ray transitions in 240U.
This work supersedes earlier full evaluations of A = 240 published by 2004Ch64, 1984Sh34, 1977Sc13, 1970Sc39; and an evaluation published in update mode by 1990Sh04.