Being able to place a detector aboveground also helps if you want to convince a reactor facility to get onboard. “Most operators of nuclear reactors don’t respond too kindly to building a 6-meter hole in the ground,” says Huber.

Proof that aboveground detectors could work came in 2018, when two projects—called Prospect and Chandler—on which Huber is a collaborator, did, in fact, catch the ghost particles at the surface. The combination of Watchman’s progress and this novel aboveground detection have helped kindle interest among officials who’d like to potentially put the technology to more than prototype, navel-gazing use. Recently, the Department of Energy commissioned a group, including Huber, to lay out where and how neutrino science could actually be useful for nuclear security. They looked at, for instance, whether the elusive particles could reveal nuclear tests, spent fuel, and reactor activity.

Although the official report isn’t ready yet, the team did, this spring, compile some of the findings into a publicly available paper titled “Neutrino Detectors as Tools for Nuclear Security.” The group found that, at least in the near term, neutrinos weren’t that useful for picking up explosions or spent fuel. But they could help, relatively soon, with reactor monitoring.

Bethany Goldblum, a nuclear engineer at the University of California, Berkeley, worked with Huber and others on the report. “We believe that using neutrinos for monitoring known reactors is the most immediate opportunity,” she says. Farther along, they could potentially hunt for hidden reactors. But the real opportunity, Goldblum thinks, is in checking up on the interiors of advanced reactors, like those that mix molten salt with the radioactive fuel, rather than using traditional solid fuel rods. “In existing reactors, we have adequate means,” she says, referring to the IAEA’s verification schemes. “States are comfortable, and we’re doing a good job with accounting. I don’t think neutrino monitoring really adds a whole lot there.”

That info in hand, the Department of Energy has also spun out a more practical study group, called NuTools, which aims to figure out where, in real life, their neutrino knowledge might be useful to nuclear-security practitioners who help enforce international safeguards. The discussions began this summer, with the webpage noting, pandemic-appropriately, “Where: All meetings virtual.”

“Research on this topic was driven by neutrino scientists interested in what, technologically, we have to do,” says Huber, who’s part of the group. “NuTools is saying, ‘Let’s talk to the people who are dealing with safeguards now to find out what would be useful to them.’ In a sense, it’s a market study.” The coalition’s officers hail from the Department of Energy’s national labs; the National Institute of Standards and Technology; and universities like MIT, Georgia Tech, and the Illinois Institute of Technology. Goldblum is also on that roster.

Goldblum, who trained as an applied nuclear physicist, became interested in security during a three-week public policy boot camp she took during graduate school. “I hadn’t really thought about the policy implications of my technical research,” she says. “After a few days at the boot camp, I was having nightmares of the nuclear holocaust.” She began to think about basic physics not as something neutral, but as something that has implications for the security of the whole world—something physicists have been struggling with at least since the Manhattan Project. Today, Goldblum shares her realizations with students and also as executive director of the Nuclear Science and Security Consortium, a research group sponsored by the National Nuclear Security Administration.

In fact, most people doing neutrino-nuclear work step over from “basic research”—or at least put a foot across the line—the way Goldblum did. It’s the kind of science-underlying-security work the consortium aims to enable.