Scientists call for defensive action over radiological attacks

· Litvinenko murder could inspire new terror method
· More restricted access to some substances urged

A group of scientists warned yesterday that terrorists could learn from last year's murder of Alexander Litvinenko to carry out radiological attacks on cities far more devastating than a dirty bomb.

While a dirty bomb - using explosives to disperse radioactive material - would be unlikely to kill more than a hundred people, the scientists argue, several hundred could be killed if they swallowed or inhaled the material, like Mr Litvinenko, who drank tea laced with a lethal isotope, polonium-210, in London last November.

In an article in the journal Survival, the three authors from King's College London call on the government to take precautionary measures, for example restricting access to radioactive materials which are now commonly available and easy to dissolve in water, allowing them to be sprayed over a large number of people.

"Terrorists have already shown considerable interest in acquiring 'dirty bombs'. They may now try to replicate the murder of Litvinenko on a larger scale, or contrive other means to place radioactive sources inside, or in direct contact with, their victims," warns the article in Survival, a quarterly published by the International Institute for Strategic Studies.

The authors call such methods I3, for inhalation, ingestion and immersion. One of the writers, Peter Zimmerman, a nuclear physicist, said yesterday that a well-planned radiological attack "would be capable of killing several hundred, maybe upwards of a thousand, and paralysing a city without any question at all."

The article does not provide details of the most devastating method of attack the authors have conceived, for security reasons, but Professor Zimmerman described one scenario using a water-soluble radioactive isotope widely used in hospitals and industry: "I can then tap into the anti-fire spray in a theatre, and if I can trigger the spray, I can soak everyone in the room."

Polonium-210, which was used in Mr Litvinenko's murder, is even more deadly because it emits alpha radiation, which is not picked up by radiation sensors.

The King's College scientists also believe that an I3 attack would inspire more terror than a chemical or biological or even a dirty bomb attack, because of public horror that the radioactive material could be widely dispersed before it became clear the attack had taken place.

Another of the authors, Brooke Rogers, a social psychologist who is working with the Home Office to help prepare the government response to such an attack, said: "People are less afraid of a biological attack, like the plague, because they believe it can be treated."

She said an intensive information campaign was necessary to keep the public informed and prevent panic. Prof Zimmerman argued other steps could be taken, making industrial and medical radiation sources much harder to come by. For example, the production of the water-soluble radioactive isotope in powdered form should be stopped, and replaced in hospitals and factories with a glassy non-soluble variant.