For three years, the Majorana collaboration has sought to demonstrate it can shield a sensitive, scalable, 44-kilogram germanium detector array from background radioactivity. In the Apennine Mountains of Italy at Gran Sasso National Laboratory (LNGS), researchers employed a slightly different design for GERDA (GERmanium Detector Array). Together, these two experiments achieved the lowest backgrounds of any neutrinoless double-beta decay experiment in the world. Now, the two are teaming up to scale up.
“The best things from GERDA and the best things from Majorana are now coming together for LEGEND-200,” said Cabot-Ann Christofferson, task leader of electroforming for LEGEND-200. LEGEND-200 (Large Enriched Germanium Experiment for Neutrinoless ββ Decay) will scale up the rare event search by using 200 kilograms of enriched germanium crystals and will be housed at LNGS.
The best of Majorana includes detector resolution and ultra-pure copper shielding that surrounds the detectors, while GERDA demonstrated the benefit of an active shield—a tank of liquid argon—surrounding the detector.
To prepare for the next phase in the search for this rare form of radioactive decay, Majorana brought back machinist Randy Hughes to prepare 110 pounds of ultra-pure electroformed copper. The copper, electroformed for the Majorana Demonstrator, is being cut in half and flattened to ½ inch-thick plates. Soon, it will be packed in a shielded container, trucked to Oak Ridge National Lab (ORNL) in Tennessee and shipped across the Atlantic Ocean. When it finally arrives in Europe, the copper will be machined into hundreds of parts for LEGEND-200.
Christofferson said the shipment of electroformed copper is just one of Majorana’s contributions to the next-generation design and construction. Although GERDA will be decommissioned to make space at LNGS for the installation of LEGEND-200, Majorana will be used to test detectors built for the next-generation.
“Majorana has proven itself fantastic for characterizing detectors,” said Christofferson. “When detectors are created for LEGEND-200, they will be placed in the Majorana experiment to be validated. This helps us figure out how they respond while LEGEND-200 is still being built, which is time well-spent before they go into the final experiment.”
In addition to copper shielding and testing detectors,Majorana will also be contributing enriched germanium to LEGEND-200.
“Of the forty-nine detectors inMajorana, some are enriched, and some are natural germanium,” said Christofferson. “The enriched detectors will leave Sanford Lab and eventually be placed in LEGEND-200.”
John Wilkerson of ORNL and the University of North Carolina, Chapel Hill, said, “The LEGEND-200 experiment is moving forward at a very quick pace. Modifications of the GERDA infrastructure at LNGS to accommodate the LEGEND-200 detector array are scheduled to start toward the end of 2019. U.S. and European groups are working collaboratively on the front-end electronics, the fiber system for reading out the liquid argon scintillation light and on the data acquisitions systems. Enriched germanium-76 detectors are being fabricated at two different vendors, and we will start characterization tests at Sanford Lab this summer.”
The collaboration expects the experiment to begin taking measurements in 2021.