Alpha Backgrounds and Their Implications for Neutrinoless Double-Beta Decay Experiments Using HPGe Detectors

The observation of neutrinoless double-beta decay (0nubetabeta) would prove the Majorana nature of the neutrino and show the non-conservation of lepton number. The nature of the neutrino (Majorana or Dirac) has implications for theories of the matter / anti-matter asymmetry of the universe, the generational structure of fundamental massive particles, and the mass of the neutrino.;The MAJORANA DEMONSTRATOR is a 0nubetabeta experiment using germanium as both detector (HPGe detectors) and source to look for the decay 76Ge → 76Se + 2 e--. The experimental signature for this search is a peak in the energy spectrum at 2039 keV, corresponding to the sum of the kinetic energies of the two emitted electrons where no neutrinos are emitted. Searches for 0nubetabeta are hindered by obscuring backgrounds, and so experiments require that such backgrounds be understood and mitigated as much as possible.;A potentially important background contribution to MAJORANA and other double-beta decay experiments could come from decays of alpha-emitting isotopes in the 232Th and 238U decay chains on and near the surfaces of the detectors. An alpha particle, emitted external to an HPGe crystal, can lose energy before entering the active region of the detector, either in some external-bulk material or within the dead region of the crystal. The measured energy of the alpha will then only be a partial amount of its total kinetic energy and might coincide with the energy expected from neutrinoless double-beta decay. Measurements were performed to quantitatively assess this background. This dissertation presents results from these measurements and compare them to simulations using Geant4 and to an analytic model. Surface-contamination requirements are calculated for double-beta decay experiments using high-purity germanium detectors.