An assessment of antineutrino detection as a tool for monitoring nuclear explosions

The antineutrino is the only real-time inherently nuclear signature from a fission explosion that propagates great distances through air, water, and ground. The size and sensitivity of antineutrino detectors has increased dramatically in the last decade, and will continue to do so in the next, thanks in part to the renewed interest in neutrino physics brought on by the mounting evidence that neutrinos may have mass. The evolution of antineutrino detectors, and the evident interest of the signature as a means for monitoring nuclear tests motivates this review of the capabilities of existing and possible future detectors as test ban verification tools. Existing liquid scintillator ionization detectors, operating a few tens of meters below the Earth's surface and containing a few thousand tons of active material, could be used to monitor an area of a few square kilometers for nuclear explosions at the 1 kt level. Purified water Cerenkov detectors of sizes comparable to existing detectors (50,000 m3) could be used to detect 1 kt explosions at distances of a few tens of kilometers. The addition of neutron-absorbing dopants such as sodium chloride or gadolinium to purified water would allow range extension out to approximately 1000 km for sensitivity to a pulse of 10 antineutrino events from a 1 kt explosion. Beyond 1000 km, backgrounds from the world's nuclear reactors would become prohibitively large (at this assumed signal strength). The engineering hurdles for such detectors would be formidable. The size of a doped detector operating at the 100 km range, suitable for cooperative monitoring of existing nuclear test sites, is about 60 times that of the largest existing water detector, and would require a factor of several dozen more photomultiplier tubes than what is now used in large scale physics experiments. Capital costs (primarily phototubes, excavation and the cost of maintaining high radiopurity) would amount to several billion dollars, even for a detector at this modest range. Detectors sensitive to a 1 kt explosion at only a few kilometer distance would still cost tens of millions of dollars. Due to these limitations, practical applications of this method for nuclear test detection are almost certainly out of reach for the foreseeable future.

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