PHYSICISTS THOUGHT THEY had built the detector to rule them all. A mile underground in a former South Dakota gold mine, the Large Underground Xenon detector was the latest, greatest attempt to find dark matter, the elusive material that physicists think makes up a missing 25 percent of the universe’s mass. But last September, LUX retired after spending three years on its unsuccessful search. Its creators dismantled its computers and electronics and emptied 800 pounds of liquid xenon from its six-and-a-half-foot-tall tank. They pulled the equipment piece by piece up through a mine shaft.
No one has found evidence of dark matter, despite the fact that physicists’ measurements are more precise than ever. They’re already building LUX’s more-sensitive successor, LUX-ZEPLIN, which will search for weakly interacting massive particles, or WIMPs. But even if these ever-more-monstrous machines don’t find dark matter, physicists have found a client for their detector technology: the nuclear security industry.
Physicist Adam Bernstein of Lawrence Livermore National Laboratory studies dark matter with LUX. But he also adapts dark matter detectors into technology that’s a bit more practical. Watchdog agencies like the International Atomic Energy Agency, for example, can use dark matter detectors to look for missing nuclear material. “From a distance they seem like two totally different occupations,” says Bernstein. “But intellectually, making a dark matter detector is very similar to making a nuclear security detector.”
Now, LUX in its current form could never be used as a nuclear detector. For one thing, it’s not portable. And nuclear security agents run their tests on Earth’s surface, not a mile underground. The dirt and rock above LUX shields it from cosmic rays and other particles raining down on Earth, and it wouldn’t work above ground. “There would be so much noise,” says Ferenc Dalnoki-Veress, who works on nuclear nonproliferation at the Middlebury Institute for International Studies.
Physicists have to make these detectors affordable, too: LUX cost $10 million to develop and construct. “A dark matter detector is really the Cadillac of detectors,” says Dalnoki-Veress. “But sometimes what you really want is a Ford. Something that is cheap but still does the same thing.”