THE death of former Russian spy Alexander Litvinenko from polonium poisoning has left a trail of radioactivity stretching from London to Moscow.

Traces of the element have been found at 10 UK addresses, some aircraft that flew between the two cities have been grounded, while an Italian who dined with Litvinenko is being treated for radiation poisoning. Nearly 3000 people have called NHS direct, the UK's health service helpline, worried that they might have ingested polonium. The investigation now involves the security services in UK and Russia and even the US Federal Bureau of Investigation.

The panic and the disruption triggered by a dash of polonium, probably less than a microgram, has led to fears that polonium-210 may become the latest weapon of choice for assassins and terrorists.

However, a careful look at this highly radioactive element reveals it to be less a weapon of mass destruction than one of ...