First measurement of antineutrinos from spent nuclear fuel confirms emissions persist after reactor shutdown

Even when the lights go out and nuclear reactors are turned off, the story inside the reactor core still has a great deal to tell. Radioactive, long-lived fission products continue to decay for months or even years, producing a faint flux of a specific type of particle known as antineutrinos. (Anti)neutrinos are the lightest and most elusive known particles in the universe, allowing them to escape unhindered from both the reactor and the surrounding shielding.