With increasing concerns about nuclear proliferation, a suggestion by Eric Christensen of Virginia Tech in Blacksburg and colleagues could be of great value. The idea echoes the discovery of the neutrino by Fred Reines and Clyde Cowan, by using a large volume of scintillator to look at antineutrino collisions with protons that produce a positron and a neutron, with most of the kinetic energy being carried by the positron. Direct energy measurements would allow the antineutrino spectrum from the reactor to be determined and – with a 20-tonne detector just outside a reactor building – could reveal the plutonium content, because plutonium emits a softer antineutrino spectrum.

Using North Korean reactors and the IR-40 reactor in Arak, Iran, as test cases, the researchers found that the removal of as little as 2 kg of plutonium could be detected within the 90 days required by the International Atomic Energy Authority. Some improvement on current technology for neutrino detectors would be needed, but this might be achievable within five years.