Gloomy experts believe it is only a question of time before someone uses a device that would spew radioactive debris over a city, making parts of it uninhabitable for years, New Scientist says.

International Atomic Energy Agency (IAEA) records point to "a dramatic rise" in the smuggling of radiological substances coined "dirty bombs", the raw material for this bomb, the British science weekly says in next Saturday's issue.

"In 1996, there were just eight of these incidents, but last year there were 51," the report says.

"Most cases are believed to have occurred in Russia and elsewhere in Europe. Smugglers target the radioactive materials used in factories, hospitals and research laboratories, which are not guarded as securely as those used by the nuclear industry."

A "dirty bomb" is not a nuclear bomb. It would use conventional explosive to disgorge radioactive material over a wide area, unleashing panic and making the area unusable.

Illicit trafficking

Since 1993, there have been 300 confirmed cases of illicit trafficking in radiological materials, 215 of them in the past five years.

But, according to the IAEA documents, the true figure may be far higher. There have been 344 further suspected cases of trafficking over the past 11 years that have not been confirmed by any of the 75 states that monitor this activity.

The agency adds that there are still 1000 radioactive sources that are unaccounted for in Iraq. And of 25 sources stolen from the Krakatau steel company in Indonesia in October 2000, only three have been recovered.

A terrorist attack of this kind is "a nightmare waiting to happen," Frank Barnaby, a nuclear consultant and former British nuclear military scientist, was quoted by New Scientist as saying.

"I'm amazed that it hasn't happened already."

And last year, Eliza Manningham-Buller, director-general of the British counter-intelligence agency MI5, said a crude radiological attack against a major western city was "only a matter of time," the report said.