NASA's Compton Gamma Ray Observatory plunged into the Pacific Ocean, in a planned de-orbit, in 2000. But its spare parts are now being used to help detect dirty bombs.

James Ryan, an astrophysicist at the University of New Hampshire in Durham, has recycled parts from one of the telescope's old instruments. He aims to detect γ-rays emitted by radioactive substances, such as plutonium, uranium and caesium. These elements could be used in bombs that combine conventional explosives with radioactive material.

“If we can detect aluminium-26 on the other side of the Galaxy, we can detect this stuff on the other side of the street,” says Ryan, who presented results from a prototype detector on 12 May in Boston, at a conference sponsored by the Institute of Electrical and Electronics Engineers and the US Department of Homeland Security.