Wrapped around our world like a giant invisible donut is one of Earth's strangest features.The Van Allen radiation belts are swarms of high-energy charged particles trapped in the web of Earth's magnetic field, many accelerated to near-light speeds.Normally, the high-speed particles are considered a space hazard that satellite engineers and human exploration missions need to plan for.But nuclear physicist Areg Danagoulian of MIT thinks they could become an unlikely ally, helping detect nuclear weapons hidden in Earth orbit."I started studying the literature on the radiation environment in outer space and found out about the large populations of trapped protons, as reported in many previous studies," Danagoulian told ScienceAlert."This is where it clicked: protons and spallation on uranium."Danagoulian describes the concept in a paper published in Nature.
The mid-century boom of nuclear testing was a strange time – deeply destructive in many ways, but also deeply informative.High-altitude nuclear tests revealed just how devastating a nuclear explosion in space could be, damaging satellites and flooding near-Earth space with radiation.In 1967, global powers signed the Outer Space Treaty, in which all agreed not to station nuclear weapons in outer space.So far, so reassuring – except for one small problem.We currently have no practical way to verify that everyone is abiding by it… and without a way to verify compliance, even an international treaty begins to resemble a gentleman's agreement.In 2024, a few pieces fell into place for Danagoulian. One of his students was studying a process called neutron spallation, in which high-energy particles knock neutrons out of atomic nuclei.At the same time, colleagues were talking about the threat of a Russian satellite carrying a nuclear device.The Starfish Prime nuclear test, detonated 400 kilometers (248 miles) above the Pacific Ocean in 1962, roughly the same altitude at which the ISS orbits today. The explosion created an artificial radiation belt that damaged several satellites. (US Air Force)The two concepts came together in Danagoulian's mind to produce one simple idea.The Van Allen belts are already bombarding satellites with high-energy protons. Why not use that natural particle beam to search for hidden uranium?"When the satellite carrying a thermonuclear weapon passes through the inner Van Allen Radiation belts surrounding Earth, protons in that belt knock out many neutrons from uranium nuclei," he explained."By devising a very particular type of neutron detector, one can detect these neutrons – which would be a tell-tale sign of unusual quantities of uranium on a satellite."Danagoulian's work is a feasibility study, which means it doesn't demonstrate a working system. Instead, it argues that the physics is sound and that the necessary technologies already exist.
