Doctoral Dissertations
Date of Award
12-2025
Degree Type
Dissertation
Degree Name
Doctor of Philosophy
Major
Physics
Major Professor
Yuri Efremenko
Committee Members
Kate Jones, Eric Lukosi, Robert Grzywacz
Abstract
Neutrinoless double-beta (0νββ) decay, if discovered, provides clear evidence of the existence of Majorana neutrinos and constrain or measure effective Majorana neutrino mass. Total lepton number conservation is violated in this decay, leading to the interpretation of matter-antimatter asymmetry in the Universe. Due to the very low probability of such a process, extremely low background conditions are required to observe the 0νββ decay signal (monoenergetic peak at 2039 keV for 76Ge). The next-generation LEGEND-1000 experiment aims to observe 0νββ decay with 1000 kg of high-purity enriched germanium 76Ge detectors submerged in liquid argon located deep underground. 42K is one of the radioactive isotopes produced in natural liquid argon; its β-decay overlaps the 0νββ decay signal region and causes a significant background. Monte Carlo simulations are performed to study the impact of 42K background on the germanium detector. The encapsulation of germanium detectors with low-background (radiopure) material would be an efficient and effective way to suppress the 42K background. In collaboration with the LEGEND group at ORNL, my work focuses on the R&D of the 3D-printing of low-background materials that can be used to encapsulate germanium detectors and also build radiopure detector components. We developed procedures and equipment to build ultra-clean 3D- printable materials. We also developed a vacuum system to measure outgassing rates of the 3D-printed materials. We performed the Monte Carlo simulation for the gamma-ray spectrometer and performed radioassay. Radiopurity results of 3D-printed samples are presented.
Recommended Citation
Mirza, Mohammad Ibrahim, "Mitigation Strategies of 42K Background and Development of Radiopure Materials for the LEGEND-1000 0νββ Decay Experiment. " PhD diss., University of Tennessee, 2025.
https://trace.tennessee.edu/utk_graddiss/13569