Enriched 76Ge detectors for the MAJORANA DEMONSTRATOR

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This is an exciting time in our quest to understand neutrinos -- fundamental particles that play key roles in the early universe, in cosmology and astrophysics, and in nuclear and particle physics. Results from neutrino oscillation experiments have provided compelling evidence that neutrinos have mass and give the first indication that the Standard Model of nuclear and particle physics is incomplete. With the realization that neutrinos are massive, there is an increased interest in investigating their intrinsic properties. Understanding the neutrino mass generation mechanism, the neutrino character (Majorana or Dirac), the absolute neutrino mass scale, and the neutrino mass spectrum are some of the main focuses of the immediate future's neutrino experiments. The intellectual merit of this award is based on the fact that a sensitive search for the neutrino-less nuclear double-beta decay is the only practical way to determine if neutrinos are Majorana particles (their own antiparticles). This exotic decay is the most sensitive test of lepton-number conservation, which is an important symmetry in elementary particle physics. With the goal of ultimately realizing a 1-tonne scale neutrino-less nuclear double-beta decay experiment using Germanium (Ge) detectors, the Majorana collaboration is assembling a prototype referred to as the Demonstrator that is intended to confirm that background levels low enough to justify such a large experiment can be reached. The baseline plan for the Demonstrator is for 15 kg of Ge detectors fabricated from Ge enriched in the double-beta isotope 76-Ge. Because most of the cost of such an experiment is the apparatus associated with it and not enriched Ge, and because one can increase the mass of instrumented 76-Ge significantly without increasing that base cost, there is the opportunity to "increase" the physics reach of the project for a reasonable, incremental additional cost. This award provides support for extra Ge detectors fabricated from enriched material to improve the physics reach.Broader Impacts: The technology of larger, lower-background HPGe arrays developed from a tonne-scale experiment can be expected to enable a new generation of highly efficient, ultra-low-background gamma spectroscopy measurements. Among the fields that stand to benefit from this new generation of technology are: direct dark matter searches; measurements for environmental monitoring; atmospheric, ocean, and groundwater environmental transport; methods of radioactive dating; reactor monitoring; bioassay for determining very low occupational exposures to radiation; and biological studies involving radiotracers at very low activities. An E&O program with the Morehead Planetarium on the campus of U. of North Carolina will bring underground science to the public.