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Detecting gamma-ray bursts from space is really no different than finding and intercepting nuclear material illegally stowed inside shipping containers or even trains. At least that's the view of Scott Barthelmy, principal investigator of NASA's Goddard Space Flight Center in Greenbelt, Md. It was Barthelmy who created the Burst Alert Telescope (BAT) that has detected hundreds of gamma-ray bursts from all directions in the sky.

The BAT was originally designed to detect gamma-ray bursts from space in NASA's Swift mission. However, it has become quite apparent that the same technology can be applied to finding and intercepting nuclear material illegally stowed inside shipping containers or trains.

BAT carries out its job using a technique called a "coded aperture mask" that creates a gamma-ray shadow on its 32,768-pixel, cadmium-zinc-telluride (CZT) detector plane. The mask itself contains 52,000 randomly placed lead tiles that block some gamma rays from reaching the detectors. With each burst, some of the CZT detectors light up while others remain dark, shaded by the lead tiles. The angle of the shadow points to the direction of the gamma-ray burst. The instrument that is now flying on the Swift mission detects gamma-ray bursts, then targets itself toward the event in about one minute to make more detailed observations.

Now the Department of Energy has funded Barthelmy to build a prototype system using leftover components from the BAT project.
"We've already produced an instrument that has a 100-degree field of view and can pinpoint the location of a gamma-ray source. It's what you would need to find and intercept nuclear material stowed inside shipping containers," said Barthelmy.

The technology would distinguish isotopes and determine whether the detected nuclear material was medical in nature or posed a national security threat.

The next step, he said, is winning DHS funding and developing a second-generation prototype using the existing detectors. "We really want to move into the second stage."