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

• Published in: arXiv.org 2017-07
• Main Authors: Abgrall, N, Arnquist, I J, Avignone, F T, Barabash, A S, Bertrand, F E, Bradley, A W, Brudanin, V, Busch, M, Buuck, M, Caja, J, Caja, M, Caldwell, T S, Christofferson, C D, P -H Chu, Cuesta, C, Detwiler, J A, Dunagan, C, Dunstan, D T, Efremenko, Yu, Ejiri, H, Elliott, S R, Gilliss, T, Giovanetti, G K, Goett, J, Green, M P, Gruszko, J, Guinn, I S, Guiseppe, V E, Haufe, C R S, Henning, R, Hoppe, E W, Jasinski, B R, Kidd, M F, Konovalov, S I, Kouzes, R T, Lopez, A M, MacMullin, J, Martin, R D, Massarczyk, R, Meijer, S J, Mertens, S, Meyer, J H, Myslik, J, O'Shaughnessy, C, Poon, A W P, Radford, D C, Rager, J, Reine, A L, Reising, J A, Rielage, K, Robertson, R G H, Shanks, B, Shirchenko, M, Suriano, A M, Tedeschi, D, Toth, L M, Trimble, J E, Varner, R L, Vasilyev, S, Vetter, K, Vorren, K, White, B R, Wilkerson, J F, Wiseman, C, W Xu, Yakushev, E, C -H Yu, Yumatov, V, Zhitnikov, I, Zhu, B X
• Format: Article
• Language: English
• Subjects: Background radiation; Beta decay; Beta rays; Cosmic rays; Crystal growth; Cutting fluids; Detectors; Enrichment; Etchants; Germanium; R&D; Radioisotopes; Recovery; Reprocessing; Research & development; Sensors; Shavings; Shielding
• ISSN: 2331-8422
• DOI: 10.48550/arxiv.1707.06255

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.