The asymptotic behavior of the FP decay heat has been studied toward the very short cooling-time range down to 0.1s after a fission event. For this purpose we apply the second generation of the gross theory of β-decay and estimate the decay properties of short-lived FP nuclides. In order to reproduce the recent measurements adequately, we introduce a new parameter named the Q00-factor, and optimize it in terms of the calculation of the half-lives and the average β- and γ-ray energy releases per decay (Eβ− and Eγ-values). The favorable value of the Q00-factor is 1.0 for the half-lives and about 0.4 for the Eβ− and Eγ-values. The Eβ and Eγ-values thus calculated for the short-lived nuclides, whose β-decay Q-values are larger than 3–4 MeV, guarantee a good reproduction of asymptotic behavior of the measured decay heat toward the very short cooling-time range. Adoption of the present calculation to data files for the summation calculations is recommended from a practical point of view.
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