Real-Time Zero-Knowledge-Protocol Radiography
for Warhead Verification

Future arms control agreements may require verification of individual warheads, rather than counting of delivery vehicles. This presents the daunting challenge of verifying that an object presented as a warhead, or “Treaty Accountable Item,” TAI, is truly as claimed – while at the same time learning nothing about its design or composition. To address this challenge, we propose to expose an object presented as a TAI to a beam from a 14 MeV neutron source, producing a real-time radiographic image on a 2D scintillator. In parallel with this, a second beam from the same neutron source would be imaged on a second identical scintillator, with no intervening object. This second scintillator would, however, be backed by a transparency carrying a printed complement of the image produced on the first. Adding these two images with a halfsilvered mirror and presenting the summed image to a sensitive camera would provide a high-precision, real-time image corresponding to the signal to be seen from an open beam – for the case in which the printed complement is matched to the nominal TAI. Using the same complement for multiple nominal TAIs constitutes a form of real-time Zero-Knowledge-Protocol differential radiography, allowing the Inspector to be assured that all items, potentially including verified, so-called “golden,” warhead(s), are indistinguishable. We denote this additive approach ZKP+. A subtractive, or ZKP–, version would be simpler, using a single scintillator with a printed complement of the TAI affixed to its back. A third variant would be to direct the two neutron beams through, for example, a nominal TAI and a golden warhead. These would be viewed by a photodiode through opposite sides of a rotating coded mask with anti-symmetry, such that identical images on opposite sides provide a steady signal, as in the CONFIDANTE concept for imaging neutron sources.