From Sanford Underground Research Facility: “MAJORANA preps copper for use in LEGEND-200”

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Sanford Underground levels

From Sanford Underground Research Facility

May 6, 2019
Erin Broberg

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A cut is made across a cylinder of copper by machinist Randy Hughes. Matthew Kapust

For three years, the Majorana collaboration has sought to demonstrate it can shield a sensitive, scalable, 44-kilogram germanium detector array from background radioactivity.

U Washington Majorana Demonstrator Experiment at SURF

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.

Gran Sasso LABORATORI NAZIONALI del GRAN SASSO, located in the Abruzzo region of central Italy

MPG GERmanium Detector Array (GERDA) at Gran Sasso, Italy

“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 at Gran Sasso.

LEGEND Collaboration

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 in Majorana, 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.

LNGS- Schematic showing the timing system used to measure neutrino arrival times at the OPERA detector

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About us.
The Sanford Underground Research Facility in Lead, South Dakota, advances our understanding of the universe by providing laboratory space deep underground, where sensitive physics experiments can be shielded from cosmic radiation. Researchers at the Sanford Lab explore some of the most challenging questions facing 21st century physics, such as the origin of matter, the nature of dark matter and the properties of neutrinos. The facility also hosts experiments in other disciplines—including geology, biology and engineering.

The Sanford Lab is located at the former Homestake gold mine, which was a physics landmark long before being converted into a dedicated science facility. Nuclear chemist Ray Davis earned a share of the Nobel Prize for Physics in 2002 for a solar neutrino experiment he installed 4,850 feet underground in the mine.

Homestake closed in 2003, but the company donated the property to South Dakota in 2006 for use as an underground laboratory. That same year, philanthropist T. Denny Sanford donated $70 million to the project. The South Dakota Legislature also created the South Dakota Science and Technology Authority to operate the lab. The state Legislature has committed more than $40 million in state funds to the project, and South Dakota also obtained a $10 million Community Development Block Grant to help rehabilitate the facility.

In 2007, after the National Science Foundation named Homestake as the preferred site for a proposed national Deep Underground Science and Engineering Laboratory (DUSEL), the South Dakota Science and Technology Authority (SDSTA) began reopening the former gold mine.

In December 2010, the National Science Board decided not to fund further design of DUSEL. However, in 2011 the Department of Energy, through the Lawrence Berkeley National Laboratory, agreed to support ongoing science operations at Sanford Lab, while investigating how to use the underground research facility for other longer-term experiments. The SDSTA, which owns Sanford Lab, continues to operate the facility under that agreement with Berkeley Lab.

The first two major physics experiments at the Sanford Lab are 4,850 feet underground in an area called the Davis Campus, named for the late Ray Davis. The Large Underground Xenon (LUX) experiment is housed in the same cavern excavated for Ray Davis’s experiment in the 1960s.

LBNL LZ project at SURF, Lead, SD, USA, will replace LUX at SURF

In October 2013, after an initial run of 80 days, LUX was determined to be the most sensitive detector yet to search for dark matter—a mysterious, yet-to-be-detected substance thought to be the most prevalent matter in the universe. The Majorana Demonstrator experiment, also on the 4850 Level, is searching for a rare phenomenon called “neutrinoless double-beta decay” that could reveal whether subatomic particles called neutrinos can be their own antiparticle. Detection of neutrinoless double-beta decay could help determine why matter prevailed over antimatter. The Majorana Demonstrator experiment is adjacent to the original Davis cavern.

LUX’s mission was to scour the universe for WIMPs, vetoing all other signatures. It would continue to do just that for another three years before it was decommissioned in 2016.

In the midst of the excitement over first results, the LUX collaboration was already casting its gaze forward. Planning for a next-generation dark matter experiment at Sanford Lab was already under way. Named LUX-ZEPLIN (LZ), the next-generation experiment would increase the sensitivity of LUX 100 times.

SLAC physicist Tom Shutt, a previous co-spokesperson for LUX, said one goal of the experiment was to figure out how to build an even larger detector.
“LZ will be a thousand times more sensitive than the LUX detector,” Shutt said. “It will just begin to see an irreducible background of neutrinos that may ultimately set the limit to our ability to measure dark matter.”
We celebrate five years of LUX, and look into the steps being taken toward the much larger and far more sensitive experiment.

Another major experiment, the Long Baseline Neutrino Experiment (LBNE)—a collaboration with Fermi National Accelerator Laboratory (Fermilab) and Sanford Lab, is in the preliminary design stages. The project got a major boost last year when Congress approved and the president signed an Omnibus Appropriations bill that will fund LBNE operations through FY 2014. Called the “next frontier of particle physics,” LBNE will follow neutrinos as they travel 800 miles through the earth, from FermiLab in Batavia, Ill., to Sanford Lab.

FNAL LBNE/DUNE from FNAL to SURF, Lead, South Dakota, USA


LBNE

U Washington Majorana Demonstrator Experiment at SURF

The MAJORANA DEMONSTRATOR will contain 40 kg of germanium; up to 30 kg will be enriched to 86% in 76Ge. The DEMONSTRATOR will be deployed deep underground in an ultra-low-background shielded environment in the Sanford Underground Research Facility (SURF) in Lead, SD. The goal of the DEMONSTRATOR is to determine whether a future 1-tonne experiment can achieve a background goal of one count per tonne-year in a 4-keV region of interest around the 76Ge 0νββ Q-value at 2039 keV. MAJORANA plans to collaborate with GERDA for a future tonne-scale 76Ge 0νββ search.

LBNL LZ project at SURF, Lead, SD, USA

CASPAR at SURF


CASPAR is a low-energy particle accelerator that allows researchers to study processes that take place inside collapsing stars.

The scientists are using space in the Sanford Underground Research Facility (SURF) in Lead, South Dakota, to work on a project called the Compact Accelerator System for Performing Astrophysical Research (CASPAR). CASPAR uses a low-energy particle accelerator that will allow researchers to mimic nuclear fusion reactions in stars. If successful, their findings could help complete our picture of how the elements in our universe are built. “Nuclear astrophysics is about what goes on inside the star, not outside of it,” said Dan Robertson, a Notre Dame assistant research professor of astrophysics working on CASPAR. “It is not observational, but experimental. The idea is to reproduce the stellar environment, to reproduce the reactions within a star.”