Signatures of muonic activation in the Majorana Demonstrator

Experiments searching for very rare processes such as neutrinoless double-beta decay require a detailed understanding of all sources of background. Signals from radioactive impurities present in construction and detector materials can be suppressed using a number of well-understood techniques. Background from in situ cosmogenic interactions can be reduced by siting an experiment deep underground. However, the next generation of such experiments have unprecedented sensitivity goals of 1028 years half-life with background rates of 10-5cts/(keV kg yr) in the region of interest. To achieve these goals, the remaining cosmogenic background must be well understood. In the work presented here, Majorana Demonstrator data are used to search for decay signatures of metastable germanium isotopes. Contributions to the region of interest in energy and time are estimated using simulations and compared to Demonstrator data. Correlated time-delayed signals are used to identify decay signatures of isotopes produced in the germanium detectors. A good agreement between expected and measured rate is found and different simulation frameworks are used to estimate the uncertainties of the predictions. The simulation campaign is then extended to characterize the background for the LEGEND experiment, a proposed tonne-scale effort searching for neutrinoless double-beta decay in Ge76

Experimental study of C 13 (α,n) O 16 reactions in the Majorana Demonstrator calibration data

Neutron captures and delayed decays of reaction products are common sources of backgrounds in ultrarare event searches. In this work, we studied C13(α,n)O16 reactions induced by α particles emitted within the calibration sources of the Majorana Demonstrator. These sources are thorium-based calibration standards enclosed in carbon-rich materials. The reaction rate was estimated by using the 6129-keV γ rays emitted from the excited O16 states that are populated when the incoming α particles exceed the reaction Q value. Thanks to the excellent energy performance of the Demonstrator's germanium detectors, these characteristic photons can be clearly observed in the calibration data. Facilitated by Geant4 simulations, a comparison between the observed 6129-keV photon rates and predictions by a talys-based software was performed. The measurements and predictions were found to be consistent, albeit with large statistical uncertainties. This agreement provides support for background projections from (α,n) reactions in future double-beta decay search efforts

Symmetry peculiarities of the intracrystalline fields layered semiconductor crystals (PbI₂)₍₁₋ₓ₎(BiI₃)ₓ

The results of our study deal with the NQR spectra of ¹²⁷| at 77 K in mixed layered semiconductor crystals (PbI₂)₍₁₋ₓ₎(BiI₃)ₓ in a wide range of content Pbl₂ and Bil ₃ 0 < x < 1. It is shown that in the range of content 0 < x < 0.02 the crystal (Bil₃)₍₁₋ₓ₎(Pbl₂)ₓ has the properties of the impure crystal Pbl₂, which contains intralayer Bil₃ clusters, and in the range 0.8 < x < 1 it contains intralayer clusters Pbl2. Under the concentration x = 0.10 and x = 0.80 the crystal (PbI₂)₍₁₋ₓ₎(BiI₃)ₓ undergoes a phase transition and in the concentration range 0.1 < x < 0.8 there is a new crystal (PbI₂)₍₁₋ₓ₎(BiI₃)ₓ, in which groups of atoms Pbl₂ and Pbl₃ are intercalants fully or partially ordered in the crystal system