From Sanford Underground Research Facility: “Physics, chemistry, biology and geophysics—but who’s counting?”

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From Sanford Underground Research Facility

9.5.18
Erin Broberg

Photos by Matt Kapust

BHSU Underground Campus
An underground campus used by experiments across the globe and managed by local university faculty and students.

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Sensitive physics experiments require radio-pure materials. That’s where the Black Hills State University Underground Campus (BHUC) comes in. The BHUC houses Sanford Lab’s low-background counting facility—a class-1,000 cleanroom containing several ultra-sensitive low background counters used to assay materials for ultra-sensitive experiments—and an adjoining workspace can be used for a variety of disciplines. Managed by BHSU, the facility partners with groups around the globe to create unique opportunities for collaborative research in physics, chemistry, biology and geophysics. The campus is also open to graduate and undergraduate students doing research in a variety of disciplines.

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Counting Minute Signatures
Sometimes going a mile underground isn’t enough. Rare event searches, such as Majorana’s search for neutrinoless double beta decay or LUX-ZEPELIN’s dark matter hunt, don’t just need to be shielded from cosmic rays—they also require some of the world’s cleanest materials.
“By clean, we mean radio-pure,” said Mount. “Researchers are looking for materials with lower and lower concentrations of radioactive elements.”
The tiniest amounts of radioactive elements in the very materials we use to construct our experiments can also overwhelm the rare-event signal. Radioactive elements can be found in rocks, titanium—even human sweat. As these elements decay, they emit signals that quickly light up ultra-sensitive detectors. To lessen these misleading signatures, researchers assay, or test, their materials for radio-purity using low-background counters (LBCs).
Located in the BHUC, the facility’s class-1,000 clean room houses five operational LBCs. The facility is open to all experimental users, not just those hosted by Sanford Lab.

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Low Background Counters
“The campus at Sanford Lab is an ideal location for these counters,” said Kevin Lesko, senior scientist at Lawrence Berkley National Lab (Berkeley Lab) who manages the measurement and control of backgrounds. “Not only does its depth create a shield for the detectors, but it’s in the thick of major physics experiments—it’s where the action is.”
These LBCs use germanium detectors housed in lead brick containers to screen materials, identifying ionizing radiation released by a material over time as its radioactive elements decay. This counting process helps researchers decide which types of materials are best-suited for their experiments. It also provides data to researchers, allowing them to calculate how much radioactivity they can expect to see coming from their materials over the life of the experiment.
“The dark matter and neutrino rare-event searches are reliant on these techniques for constructing their detectors,” said Mount. “These techniques are looking for the tiniest amounts of radioactive elements in the construction materials for some of the biggest physics experiments of our time.”

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Multidisciplinary University Research
The BHUC provides a space for students from across the state to preform interdisciplinary research underground. While physics students contribute to large-scale physics experiments by working with the low background counters, students from other disciplines can work on research in two areas adjoining the counting cleanroom.
“Biology students can study microbes in situ, and geology students can study the unique rock formations,” said Briana Mount, director of the BHUC.
Additionally, a National Science Foundation (NSF) program, Research Experience for Undergraduates (REU), gives students from around the country, opportunities to pursue research through the underground campus.

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K-12 Outreach
It’s not just college students who get to take advantage of the underground campus—even K-12 students can participate.
For example, the annual BHSU Robotics Competition pairs middle school students with BHSU students to create robots for an engaging competition on the 4850 Level. The college students take the programmed robots to an underground obstacle course where the robots must find their way through an obstacle course while middle school students watch and advise from the surface via videoconferencing.

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Counting Consortium
A consortium agreement between LBC owners allows the counters to be available to other universities and partners, creating new opportunities for collaborative research. While the counters are dedicated to supporting high-priority experiments, the consortium allows those counters to also be used for all collaborations and academic users when there is space to spare.

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Project Support
With global partnerships come remote users. Researchers assaying their materials from a distance can monitor results in real-time, while relying on daily support from BHSU faculty and students and Sanford Lab staff. Support includes changing samples in the detectors, monitoring the liquid nitrogen systems that purge radon from inside the detectors and assistance in the installation of detectors underground.

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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.
LUX/Dark matter experiment at SURFLUX/Dark matter experiment 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.

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.

Fermilab LBNE
LBNE