Imagine delving into the depths of the Earth, not for treasure or adventure, but to safeguard a precious metal that could unlock the universe's greatest mysteries. That's the thrilling reality of transporting ultrapure copper from the Sanford Underground Research Facility (SURF) to fuel the global quest for dark matter. But here's where it gets controversial: is this repurposing of materials from defunct experiments a brilliant act of scientific resourcefulness, or does it highlight how underfunded research forces labs to stretch resources thin? Stick around, because this journey reveals secrets most people never consider about the unseen forces shaping our world.
For Cabot-Ann Christofferson and Alissa Love, their morning started like so many others: descending 4,850 feet into the Earth's core in a sturdy metal cage, arriving at the deepest underground lab in the U.S. Yet, this particular day pulsed with extra intensity. The duo had invested countless hours meticulously crafting, scrubbing, and packaging ultra-pure copper—originally created for the Majorana Demonstrator project—to send it abroad for a cutting-edge dark matter sensor in France.
"It's fascinating how surplus copper produced for Majorana in 2013 or 2014, and later dismantled in 2021, is getting a fresh purpose," remarked Christofferson, a research scientist at South Dakota Mines who oversees SURF's copper electroforming lab. "Portions of the Majorana Demonstrator are enduring through this new venture in France's dark matter research."
But why endure the hassle of shuttling this copper between subterranean labs? The answer lies in its unparalleled purity, produced at SURF and vital for the success of some of physics' most delicate experiments. To help beginners grasp this, think of dark matter as an invisible, mysterious substance that makes up about 27% of the universe—it's like the 'missing puzzle piece' that gravitationally influences galaxies, yet we've never directly observed it.
And this is the part most people miss: managing background radiation is key to spotting such elusive phenomena. Radiation surrounds us constantly, from natural sources like the sun to man-made ones, but in everyday life, it's harmless—like that kitchen butter knife that poses no threat. However, for physicists chasing rare events, such as a dark matter particle brushing against an atom, even minor radiation 'noise' would drown out the signal. To illustrate, imagine trying to hear a whisper in a noisy stadium; that's the challenge here.
To cut down on this interference, researchers construct their tools from materials that radiate minimally. That's why manufacturing often shifts underground, where sites like SURF—buried nearly a mile below—block cosmic rays that would contaminate surface-made items with radioactive marks.
The ascent from 4,850 feet takes roughly 12 minutes, and once above, the team sprang into action, stowing boxes into a vehicle. Still clad in their lab gear, Christofferson and Love embarked on a 50-mile trek from Lead to rendezvous with a semi-truck hauling a specialized steel-lined crate. "We had only about an hour of exposure to cosmogenic radiation on the surface before sealing it in the shielded container," Christofferson explained. "Escaping the high altitude of SURF is crucial, as elevated sites amplify cosmic ray exposure."
This robust container, designed to deflect radiation, opens and closes via a manual gear mechanism. Sealed inside, the cargo commenced its extensive voyage across North America and the vast Atlantic.
Christofferson has spearheaded SURF's copper electroforming team for over 15 years at the Davis Campus, deep underground. The technique entails gradually layering copper onto a submerged template in an electrified copper bath—a process that sounds simple but demands precision to achieve such extreme purity.
A significant portion of SURF's efforts powered the Majorana Demonstrator, now being phased out, but its copper has become a hot commodity for DAMIC-M (DArk Matter In CCDs at Modane), a dark matter probe. Paolo Privitera, a professor at the University of Chicago and spokesperson for the DAMIC-M team, shared, "SURF boasts a one-of-a-kind subterranean setup for cultivating ultrapure copper in custom baths, then shaping it for experiments. No other location offers this capability."
At SURF, the group refurbished and prepped the copper for dispatch. Alissa Love, a master's student in chemistry at South Dakota Mines, managed the operation. "It was exhilarating to see the team produce and shape copper for various projects, then handle the detailed cleaning and prep for shipment," she said. "Watching the culmination of this effort, with the copper heading out the door to France, felt rewarding."
For Jaret Heise, SURF's science director, the copper's versatility stands out. "These resources, once dedicated to neutrino decay hunts, now bolster the worldwide push to uncover dark matter's essence," he noted.
Boosting the worldwide dark matter pursuit, the Modane Underground Laboratory—nestled beneath the Alps in a tunnel linking France and Italy—hosts the full DAMIC-M setup. As detailed in a University of Chicago article, detectors like DAMIC-M capture fleeting instances where a dark matter particle strikes an atom, generating a detectable signal that might unveil its properties.
DAMIC-M operates similarly to a digital camera, but instead of capturing light particles (photons), it targets dark matter. The silicon chips within will be encased by SURF's purest copper, which is essential to filter out misleading signals from impure materials' radiation. "From prior tests, we knew Majorana copper's exceptional purity," Privitera added. "The SURF team, under Cabot-Ann's guidance, adapted the existing copper to DAMIC-M specs. The Majorana team's input and SURF's expertise were pivotal to our achievements."
While indirect clues abound for dark matter—from galaxy rotations to cosmic microwave background—direct detection remains elusive. Hundreds of experiments worldwide vie for the breakthrough, and DAMIC-M has already explored uncharted realms with a prototype, as published in a summer Physics Review Letters paper and discussed in a June SURF "Deeper Talk" seminar. SURF's copper will propel DAMIC-M further into novel territories.
"Lacking SURF's electroformed copper, we couldn't attain our planned sensitivity," Privitera stated. "Our partnership with SURF has excelled, and I anticipate it continuing with future enhancements. Full accolades go to Cabot-Ann for the copper parts' superior quality and seamless execution—she's been an outstanding ally, and SURF is fortunate to have her."
Christofferson highlighted science's teamwork and SURF's role in global advancement. "Even if you don't host the experiment, every lab contributes to broader knowledge. Collaboration is essential; no single underground site can make these discoveries alone."
Set to commence data gathering in 2026, DAMIC-M will operate for years, yielding fresh perspectives on dark matter and perpetuating SURF's trailblazing in electroformed copper.
What do you think—should we invest more in underground labs to accelerate discoveries like this, or does the secrecy of such deep-earth research spark concerns about transparency? And here's a controversial twist: some argue that chasing dark matter distracts from pressing Earth-bound issues like climate change; is science prioritizing cosmic mysteries over human survival? Share your views in the comments—do you agree, disagree, or have a counterpoint? Let's discuss!
