Speaker
Description
Accurate simulations of the radionuclide inventories and measurable quantities such as activity, dose rates and decay heat are made possible by means of carefully evaluated decay data (DD). In an automated compilation of a DD library of more than 3800 nuclides, the DD files could notably suffer from: misreading of data from the sources, omitting of the emitted particle spectra during the process of conversion from the databases such as ENSDF into ENDF-6 format file, or associating a wrong spectra in the radiations section corresponding to each of the decay modes. Simple typographical mistakes (or glitches) could also be at fault. Review of the available updates in nuclear DD and correction of the files requires time, collaborative effort and feedback on validation exercises before each DD library release.
The decay_2020 library included 4035 files from the latest versions of the DD libraries/sub-libraries in ENDF-6 format (ENDF/B-VIII.0, JEFF-3.3, UKPADD-6.12, JENDL-2015 DDL, etc.), as well as several legacy JEF-2.2 and ENDF/B-VII(VII.1) files that included spectral data compared to their updated counterparts. A collaboration between the IAEA, UKAEA and LNHB-DDEP has been working on identifying discrepancies and improving of the decay files based on the decay_2020 library. To find the root cause of observed issues, the raw DD files were interrogated systematically. It was established that while some of noted issues were due to typos/glitches, other discrepancies were attributed to the adopted adjustments. For instance, in some JEFF-3.3 files the average beta and gamma energies remain as derived from the discrete data in their respective radiation sections, and therefore differ from the updated TAGS-based values adopted in the summary section (with spectral data omitted for several nuclides). All versions of these files are available for convenient side-by-side comparisons by the ENDF Radioactive decay data /MF8.MT457/ web-tool under ENDF retrieval system on the IAEA Web site: https://nds.iaea.org/endf, that provides translation into JSON format, data comparison and selective plotting of the spectral data included in ENDF libraries for nuclides of interest. Continuum spectra are currently available only for some of the fission-relevant nuclides in cases of beta-delayed neutron decays (a single continuum spectrum per decay mode). Current limitations of the ENDF-6 format and benefits of using the GNDS format for accommodation of complete datasets and spectral data for β-decay nuclides would also be discussed by G. Bailey in contribution to this conference.
Current decay_2020 library review results suggest that the discrepancies between the measured observables and predicted values could arise from the changes in the utilised DD library file versions, when even small differences could have vast repercussions in various applications, including fission and fusion energy industry and accelerators. Continuum nature of beta and neutrino spectra can affect light particle heating and bremsstrahlung corrections to photon spectra, therefore this data should be incorporated in the DD files or supplied additionally for simulations.
This work was supported, in part, by the IAEA Nuclear Data Section under contract 20210119-004.