Recycled NASA telescope to be used for bomb detection

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London, May 10 : An astrophysicist has recycled parts from one of NASA's Compton Gamma Ray Observatory's old instruments for bomb detection.

According to a report in Nature News, the 9-year mission of NASA's Compton Gamma Ray Observatory ended in 2000 with a plunge into the Pacific Ocean.

But instead of the space telescope's parts being wasted away, James Ryan, an astrophysicist at the University of New Hampshire in Durham, recycled one of them to detect gamma rays emitted by radioactive substances, such as plutonium, uranium and caesium, which could be used in dirty bombs combining conventional explosives with radioactive material.

There are many techniques for spotting radioactive materials. Some sensors pick up neutrons spat out by radioactive atoms. This technique is very sensitive - neutrons cannot be shielded by lead or concrete walls - but somewhat non-discriminatory.

Gamma rays, although they can be shielded, are emitted with specific energies depending on their parent nuclei, thus providing a potential fingerprint of the radioactive material.

Many commercial gamma-ray detectors, however, can't detect the direction of a source.

Directionality is particularly useful, for example, if scanning rows of shipping containers rather than single trucks at border crossings, or when tracking a dirty bomb.

Keeping these facts in mind, Ryan decided to use the gamma ray detector of the Compton Gamma Ray Observatory for use in bomb detection.

The Compton device detects light emitted by electron scattering, caused by gamma rays hitting two layers in the instrument. These two detections allow a user to track the direction of the incoming rays.

According to Ryan, using the device from a distance of 10 metres, he can pinpoint a source like caesium to within a third of a metre from side-to-side.

"It'll work, but it's not optimal, given the fact it's so dated," said Nick Mascarenhas, a physicist at Sandia National Laboratory in Livermore, California, who is building his own directional radiation detector. "It's probably going to have limitations," he added.

Even if the nearly 20-year-old Compton telescope technology isn't the best available kit to turn into a commercial bomb-sniffing tool, homeland security is certainly benefiting by learning from, or borrowing, astrophysical tools that can 'image' the location of radioactive sources, rather than just detecting their presence.

"We're showing that imaging has very powerful advantages," said Mascarenhas.

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