Scientists from the Max-Planck-Institut für Kernphysik (MPIK) in Heidelberg, Germany, have announced the first successful detection of antineutrinos from an inactive nuclear reactor. The research team behind the historic achievement said that detecting antineutrinos, which they described as “the most elusive particle in the Universe,” could improve monitoring, maintenance, safety, and security of nuclear reactors. For example, the long-lived fission products inside nuclear reactors continue to decay for months, or in some cases, years after a reactor is no longer in use. This ongoing radioactive decay can produce what the team termed a “faint flux” of the most elusive particle in the universe: antineutrinos. Because antineutrinos interact only extremely weakly with matter, they pass almost unhindered through the reactor vessel and surrounding shielding.