The Processing of Enriched Germanium for the MAJORANA DEMONSTRATOR and R&D for a Possible Future Ton-Scale Ge-76 Double-Beta Decay Experiment

Abstract

The MAJORANA DEMONSTRATOR is an array of point-contact Ge detectors fabricated from Ge isotopically enriched to 88% in Ge-76 to search for neutrinoless double beta decay. The processing of Ge for germanium detectors is a well-known technology. However, because of the high cost of Ge enriched in Ge-76, special procedures were required to maximize the yield of detector mass and to minimize exposure to cosmic rays. These procedures include careful accounting for the material; shielding it to reduce cosmogenic generation of radioactive isotopes; and development of special reprocessing techniques for contaminated solid germanium, shavings, grindings, acid etchant and cutting fluids from detector fabrication. Processing procedures were developed that resulted in a total yield in detector mass of 70%. However, none of the acid-etch solution and only 50% of the cutting fluids from detector fabrication were reprocessed. Had they been processed, the projections for the recovery yield would be between 80 -- 85%. Maximizing yield is critical to justify a possible future ton-scale experiment. A process for recovery of germanium from the acid-etch solution was developed with yield of about 90%. All material was shielded or stored underground whenever possible to minimize the formation of Ge-68 by cosmic rays, which contributes background in the double-beta decay region of interest and cannot be removed by zone refinement and crystal growth. Formation of Ge-68 was reduced by a significant factor over that in natural abundance detectors not protected from cosmic rays.

Submitted to NIM-A

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• Measurement of Neutrino Oscillation by the K2K Experiment
• Results from a search for the $0\nu \beta \beta$-decay of ${}^{130}Te$
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• Exotic dark matter search with the Majorana Demonstrator
• Energy Calibration of Germanium Detectors for the MAJORANA DEMONSTRATOR
• Combining Hybrid and Opaque Scintillator Techniques in the Search for Double Beta Plus Decays
• Double Beta Decay Experiments at Canfranc Underground Laboratory
• Signatures of muonic activation in the Majorana Demonstrator
• Interpretable Boosted Decision Tree Analysis for the Majorana Demonstrator
• An assay-based background projection for the MAJORANA DEMONSTRATOR using Monte Carlo Uncertainty Propagation