Radiological attack: 'Manhattan would be uninhabitable for years'

If a "dirty bomb" were to be set off in New York, every building in Manhattan and for miles around might have to be demolished, concludes one of the United States' most distinguished scientific bodies.

If a "dirty bomb" were to be set off in New York, every building in Manhattan and for miles around might have to be demolished, concludes one of the United States' most distinguished scientific bodies.

The Federation of American Scientists, which cites 52 Nobel prizewinners among its sponsors, says a bomb made using just one piece of radioactive cobalt could make the city uninhabitable for decades, and seriously contaminate one thousand square kilometres of the states of New Jersey, Connecticut and New York.

Three months ago – long before last week's debacle was even a glimmer in Attorney General John Ashcroft's eye – the federation's president, Dr Henry Kelly, warned the Senate Committee on Foreign Relations that the "threat of a malicious radiological attack in the US" was "credible".

He presented the results of a study – carried out by the federation and Princeton University – into what might happen if a bomb containing just a single "pencil" of intensely radioactive cobalt-60 was exploded at the southern tip of Manhattan on a calm day with a slight south-westerly breeze. Plants used to disinfect food by irradiation often contain hundreds of these "pencils", each just a foot long and an inch in diameter.

The danger, as the report makes clear, is not that the bomb would immediately kill people, although deaths would probably result from the force of the explosion. The real threat would come from long-term radioactive contamination, causing hundreds of thousands of fatalities from cancer over decades.

The investigation concluded that Wall Street, Greenwich Village, Times Square, and the swathe of New York stretching up to Central Park that contains most of its skyscrapers would become as contaminated as the no-go area permanently established around Chernobyl. One in 10 people who continued to live in a 300-block area downwind from the bomb would develop cancer. And a huge area stretching 70 miles downwind would be so badly affected that, under US government rules, it would have to be evacuated and the buildings decontaminated or destroyed. In practice, the study says, "demolition may be the only practical solution".

Could it happen? There would probably, as the federation points out, be little difficulty in finding radioactive material. Food-irradiation facilities are poorly guarded – and the world is awash with similar, or even more dangerous, radioactive sources used in industry, medicine and university laboratories. Some two million sites in the US alone are licensed to use radioactive materials, and the government admits that 1,500 sources have gone missing over the past five years. And last year President Bush cut the budget for protecting nuclear waste – and weapons – by 93 per cent.

It would be much harder, says the nuclear consultant John Large, to explode the bomb so that radiation was widely dispersed. The radioactive material would have to be heavily shielded if any terrorist trying to make or use the bomb were not to die within minutes; an X-ray machine typically contains a radioactive source the size of a cod liver oil pill inside shielding as big as a coffee jar.

A successful bomb would have to be designed with great sophistication, first to break open the "coffee jar", then to gradually heat the radioactive source so that it vaporised, and finally to scatter it to the winds.