BHSU Underground Campus

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.

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.

the crystals are wrapped in a copper cryostat.

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.”

Students assembling supports on a detector.

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.

A student mentor talks to the robot builder from underground.

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.

Students work on detector base beyond a detector

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.

A sciencist talks to a group in the BHUC.

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.

A counter which is being built and tested.

Future counting stations

“We’re going to need more space,” said Lesko. “LZ continues to dominate the queues, but it is hoped that DUNE, one tonne double beta decay, and generation three dark matter will continue to use the detectors, as well as expanding the users to environmental applications and health monitoring.”

There is room for up to ten low background counters in the BHUC, and researchers look forward to developing this multifaceted space.