Nuclear physicists may have just invented a 'zero-knowledge' warhead inspection system

A team of researchers revealed something that might make nuclear disarmament process easier: a new technique that nuclear inspectors can use to verify whether a warhead is active, inactive, or a fake—all without learning anything about its design.
The new method—still theoretical—is a kind of physical encryption that allows warhead scanning without revealing too much. Inspectors would send a high-energy x-ray beam through a warhead in which some of the x-ray photons would be absorbed by nuclear materials. As in medical imaging, the pattern of x-rays that emerges can reveal the geometry of what’s inside the warhead. To scramble that information, the emerging beam is directed onto an "encryption foil"—a set of materials picked by the warhead's owner and not revealed to the inspector. The x-ray photons hitting the foil cause it to emit gamma rays, via a process known as nuclear resonance fluorescence, which can then be picked up by a nearby detector.
The amount and frequencies of the gamma rays would provide a signature of the layout and composition of the warhead. But, because of encryption foil, that layout and composition would not be discernible to the inspectors. If the inspectors can first test a known active warhead and use it as a model, they would then be able to identify the status of any subsequently tested warheads with 99.9% accuracy. Because the identity of the foil's material will remain unknown to the inspectors, it would be impossible for them to use the detected radiation to infer the design of the warhead.

http://www.sciencemag.org/news/2016...nted-zero-knowledge-warhead-inspection-system

 

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Using the EM physics criteria of saying gamma rays are more energetic than x-rays, nuclear resonance fluorescence should not allow allow x-rays to trigger emission of gamma rays unless the foil was radioactive.

Reading the supplemental material makes this clearer. "x-rays" are man-made in machines, "gamma rays" are from isotopes.

The "x-rays" is a beam of synchrotron radiation which photon energy up to 3-4 MeV.
The "foil" is a patchwork of isotopes of interest, including fissionable isotopes.

The "x-rays" light up and selectively absorbed by the warhead, the transmitted beam hits the foil, the fluorescence from the foil is detected and we lay odds on if the warhead conforms to others of its type. We check it from multiple angles to make sure.

http://www.pnas.org/content/early/2016/07/13/1603916113.abstract

 

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Is there a glitch there, allowing gaming of the system by proffering a cleverly set up inactive warhead as the model?

 

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