So you think quantum mechanics is hard? Try being a border patrol agent in today’s post-9/11 world. The US has some 360,000 vehicles, 5,100 trucks, 2,600 aircraft and 600 vessels entering at their legal checkpoints – every single day. The Department of Homeland Security wants to install some 2,400 radiation monitors at their border crossings to spot clandestine nuclear material, and they still have some way to go. But even now the system is overloaded with false alarms.

This biggest problem: innocuous kitty litter. Apparently the clay in cat litter gives off enough radiation to set off a gamma detector. And its emission signature is very close to that of highly-enriched uranium. The current high-purity germanium (HPG) detectors can’t tell the difference.

Barry Zink and colleagues at NIST in Boulder, Colorado, along with their Los Alamos collaborators, have developed a gamma-ray detector that has ten times better resolution than existing HPG detectors. It uses a transition-edge thermometer to record the temperature difference between a superconducting bilayer, and a tiny island of tin that absorbs incoming gamma rays. The sensitivity comes from cooling the sensor down to 100 millikelvin above absolute zero. Zink admits that 100 mK is a ‘somewhat challenging’ temperature to achieve, but says that cryogenic technology has vastly improved in the past decade.

How robust is it? In order to test their detector out on a range of nuclear materials Zink and co-workers drove their prototype 400 miles in a minivan to the National Nuclear Security Agency division at Los Alamos. The sensor survived the trip okay, and successfully detected one of the usual suspects for nuclear weapons: the plutonium-239 isotope.

Right now the biggest sensor array NIST has made has 16 sensors, but they plan to build a 100-sensor array. Although it will never be big enough for general screening of, say, entire vessels, the detector can help to analyse and verify nuclear stockpiles, and to screen suspicious material flagged by other techniques.

And it may help prevent some of those costly kitty-litter false alarms.

So you think quantum mechanics is hard? Try being a border patrol agent in today’s post-9/11 world. The US has some 360,000 vehicles, 5,100 trucks, 2,600 aircraft and 600 vessels entering at their legal checkpoints – every single day. The Department of Homeland Security wants to install some 2,400 radiation monitors at their border crossings to spot clandestine nuclear material, and they still have some way to go. But even now the system is overloaded with false alarms.

This biggest problem: innocuous kitty litter. Apparently the clay in cat litter gives off enough radiation to set off a gamma detector. And its emission signature is very close to that of highly-enriched uranium. The current high-purity germanium (HPG) detectors can’t tell the difference.

Barry Zink and colleagues at NIST in Boulder, Colorado, along with their Los Alamos collaborators, have developed a gamma-ray detector that has ten times better resolution than existing HPG detectors. It uses a transition-edge thermometer to record the temperature difference between a superconducting bilayer, and a tiny island of tin that absorbs incoming gamma rays. The sensitivity comes from cooling the sensor down to 100 millikelvin above absolute zero. Zink admits that 100 mK is a ‘somewhat challenging’ temperature to achieve, but says that cryogenic technology has vastly improved in the past decade.

How robust is it? In order to test their detector out on a range of nuclear materials Zink and co-workers drove their prototype 400 miles in a minivan to the National Nuclear Security Agency division at Los Alamos. The sensor survived the trip okay, and successfully detected one of the usual suspects for nuclear weapons: the plutonium-239 isotope.

Right now the biggest sensor array NIST has made has 16 sensors, but they plan to build a 100-sensor array. Although it will never be big enough for general screening of, say, entire vessels, the detector can help to analyse and verify nuclear stockpiles, and to screen suspicious material flagged by other techniques.

And it may help prevent some of those costly kitty-litter false alarms.