RII Track-4: Research and Development of Ring-Contact Germanium Detectors

University Of South Dakota Main Campus, Vermillion SD

Investigators

Abstract

If neutrinos are proven to be their own anti-particles, it can offer an explanation of the prevalence of matter over anti-matter in the universe. The only experimentally feasible way to answer this question is to look for neutrinoless double-beta (0νββ) decay, a proposed form of nuclear decay. Large Ge crystals have a higher volume-to-surface ratio which is advantageous for the collection of signals and rejection of backgrounds in a search for 0νββ decay. GERDA and MAJORANA DEMONSTRATOR have proved that a Ge-based ton-scale experiment can be built with sufficient low-background that will achieve a sensitivity capable of the potential discovery of 0νββ decay. This RII Track-4 proposal will develop large-size Ge ring-contact (GeRC) detectors to further reduce backgrounds, complexity, and cost. The proposed research will advance Ge detector technology for cosmology, astronomy, homeland security, and industrial applications. Results from this project will be published in scholarly journals and disseminated through collaboration with industry. Research activities are closely integrated with education and outreach efforts: both graduate and undergraduate students will work on the project, thus gaining cutting-edge skills and expertise in Ge crystal purification and detector development. The main focus of undergraduate education and outreach activities is to encourage women to pursue STEM majors. The sensitivity goal for the Large Enriched Ge Experiment for Neutrinoless double beta (0νββ) Decay (LEGEND-1000) requires a background level of ≤1×10^(-5) events/keV/kg/year. LEGEND-1000 prefers large-size detectors (>3 kg per detector), which will further reduce backgrounds, complexity, and cost. This RII Track-4 proposal will explore large-size detectors through research and development (R&D) on GeRC detectors using high-purity Ge crystals grown by the University of South Dakota (USD). With the collaboration of Professor Rusty Harris (Host) of Texas A&M University (TAMU) and Professor John Wilkerson (collaborator) of University of North Carolina at Chapel Hill (UNC), the PI will fabricate GeRC detectors at TAMU and test them at UNC. Currently, LEGEND-200 has successfully tested inverted coaxial point-contact (ICPC) Ge detectors that have a typical mass of ~2 kg. To further increase the mass per detector, a new detector concept based on GeRC detectors is promising, as it can potentially be used to make a Ge detector as large as ~6 kg. Although they have been modeled, a GeRC detector has yet to be fabricated and tested for its energy resolution and pulse shape properties. The degradation of energy resolution seen with Ge detectors that is due to incomplete charge collection in large-size Ge crystals will also be an obstacle for LEGEND-1000. This project will help to resolve three key challenges: fabrication of a GeRC detector with a mass of ~2 – 3 kg, measurement of the energy resolution and pulse shape discrimination in a large-size GeRC detector, and analysis of the quality of USD-grown crystals. This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.