Analysis of Beta-Ray Data Important to Decay Heat Predictions

Recently obtained experimental total beta-ray spectra for 77 radionuclides created during fission of ²³⁵U are compared with predicted total beta-ray spectra based on beta-ray transition energies and intensities of individual components currently available in the Evaluated Nuclear Structure Data File (ENSDF). In addition, experimental average beta-ray energies <E_β> for 100 radionuclides are compared with evaluated/theoretical <E_β> from four compilations, namely, (a) a 1982 compilation, (b) the 1989 and current ENSDF, (c) a 1988 compilation by the Japanese Nuclear Data Committee, and (d) predictions using the microscopic theory of Klapdor and Metzinger. None of these evaluations/ predictions is superior in reproducing the experimental data. A comparison of the experimental <E_β> with the total available beta decay energies Q_β indicates that the approximation <E_β> ≈ Q_β/3 somewhat overestimates <E_β> on the average; however, the ratio R = <E_β>/Q_β varies between 0.11 and 0.46, and there is no discernible trend in R compared with Q_β or <E_β> nor a discernible difference for radionuclides having T_1/2 ≤ 2 s compared with those having T_1/2 > 2 s. Lastly, the intensities of possible ground-state decay transitions were estimated for 47 radionuclides and compared with similar data in ENSDF. In 14 cases, a nonzero ENSDF value is supported by the experimental data, and in 8 cases a zero value in ENSDF is supported by the lack of experimental data suggesting a high-energy ground state beta-ray transition. Of the remaining 25 radionuclides, the experimental data for 9 cases suggest that increases are needed in the ENSDF, and for 16 radionuclides the data indicate the need for smaller values of the ground-state transition intensities from those given in the ENSDF, being zero for 4 nuclides (^80,81Ga, ⁸⁴As, and ¹⁴⁵Cs).