Doctoral Dissertations

Date of Award


Degree Type


Degree Name

Doctor of Philosophy


Nuclear Engineering

Major Professor

Robert Grzywacz

Committee Members

Steven Skutnik, Krzysztof Rykaczewski, Lawrence Heilbronn


Total absorption spectroscopy is a method of gamma-ray spectroscopy that has gained prominence in the past several decades, as nuclear data revisions are performed on older nuclear data, which is often incomplete. A strong understanding of underlying nuclear data, particularly fission and beta decay data, is essential for nuclear reactors and nuclear fuel decay heat. This PhD work involves the analysis of fission fragments 106Mo [Mo-106] and 106Tc [Tc-106]. These neutron rich isotopes contribute upwards of 6% of the cumulative fission yield of 241Pu [Pu-241] fission, and 4% of 239Pu [Pu-239] fission. Prior data for these two fission fragments only encompassed a fraction of the Q value energy, causing uncertainty as to the impact of these isotopes on nuclear decay heating within nuclear reactor fuel. Experiments were conducted at Argonne National Laboratory using the Modular Total Absorption Spectrometer in 2019-2020 yielding decay data for these isotopes. This data was analyzed, with key nuclear physics parameters determined. The analysis consists of spectral deconvolution using the Expectation-Maximization method deployed on GPU processors. The deconvolution process determined the beta feeding intensities which are used to construct updated decay schemes. The updated beta feeding intensities are used to determine the log-
ft values, nuclear matrix elements, and calculated beta energy spectra. Comparisons to literature sources were conducted. In the case of 106Mo [Mo-106], comparison to theory has good agreement with an oblate deformation shape. 106Tc [Tc-106] has been compared to previous work by Algora et al, and is in strong agreement for total gamma and beta energies well within uncertainty. Updated decay schemes were used to determine the impacts to nuclear fuel decay heat using the ORNL SCALE code.

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