Doctor of Philosophy (PhD)


Physics and Astronomy

Document Type



Nuclear reactors produce an extremely diverse population of beta-decaying isotopes. Accurate and precise knowledge of the beta-decay properties of these isotopes is vital to safe reactor operations as well as informing next-generation reactor design. These beta-decay properties not only impact the design and operation of nuclear reactors, but they influence the expected antineutrino flux and spectrum measured from nuclear reactors. Historical measurements of many of these isotopes are subject to a systematic bias referred to as the Pandemonium Effect, because the low-efficiency, high-precision detectors used to perform the measurements results in misinterpreting weak gamma cascades from high- energy levels as direct beta feeding to low-energy levels that the cascades decay through, rather than the high-energy levels the cascade originated from. The Pandemonium Effect can be corrected by measuring the beta decay of these isotopes with high-efficiency, low- precision detectors such as the Modular Total Absorption Spectrometer (MTAS). MTAS was used to measure the beta-feeding intensities of 105Rh, 105Ru, 105Tc, and 105Mo at Argonne National Laboratory. From the updated beta-feeding intensities of 105Tc and 105Mo determined in this work, corrections to the expected antineutrino energy spectrum from these isotopes have been calculated. An important aspect of beta decay that is often neglected is the shape of the beta-energy spectrum from these decaying isotopes. The shape of the beta-energy spectrum is often neglected because isolating individual beta-energy spectra is challenging, and thus many individual beta-energy spectra are assumed to be that of an allowed beta decay. This work also presents the Beta Spectrum Module (βSM), a novel detector system that when coupled to MTAS is capable of isolating individual beta-energy spectra. Initial measurements of the spectral shape for the ground-state beta decays of both 137Cs and 90Y using the βSM and a portion of MTAS are presented.



Committee Chair

Blackmon, Jeffrey C.



Available for download on Sunday, May 17, 2026

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Nuclear Commons