On the weakness of passive radiation detectors

After seven years and billions of dollars, the US Domestic Nuclear Detection Office terminated an effort to use passive gamma-radiation monitors to screen cargo at ports of entry (see PHYSICS TODAY, September 2011, page 32 ). It’s a long-overdue cancellation.

Some of us with the relevant physics background and experience realized decades ago that the government was barking up the wrong tree when it was supporting passive means inherently inadequate for detecting fissionable materials.

Not likely to be any better are the new passive radiation detectors mentioned in the PHYSICS TODAY news item. The entire enterprise suffers from technical-policy strategic misdirection, having failed to promote definitive active-neutron interrogation—the only practical and proven means available to directly detect and distinguish fissionable materials, chemical explosives, and other smuggled items.

Because passive radiation-detection methods rely on natural radiation emitted from some substances of concern, they are thus limited and insufficient for screening cargo, with false alarms being no surprise. In contrast, active-neutron interrogation stimulates distinctive, identifiable radiation in essentially all dangerous materials.

As a citizen and retired physicist who had a substantive technical career in nuclear measurements, I can now freely protest the foreseeable and shameful waste of time and resources on inherently flawed passive-detection systems. The physics community long ago realized that fissile and fertile nuclear materials release radiation—or can be tweaked to emit radiation—that is characteristic, detectable, distinguishable, and penetrating, exactly what’s needed for identification.

Public funding would be much better spent on improving, qualifying, and deploying active-neutron interrogation systems that can definitively detect dangerous and smuggled nuclear and explosive materials and other contraband.