Abomb" is the type of weapon you would build if you could not construct a conventional nuclear device

By Dr David Whitehouse
BBC News Online science editor
It would be messy but effective for many reasons

It would consist of a bomb made of conventional explosives such as TNT, salted with radioactive material

Abomb could wreak havoc in a big city and cause national panic
Such a bomb would be straightforward to construct ifhad access to radioactive material and were able to transport it without detection

The obvious place to obtain radioactive material would be from a nuclear weapon. It is not unknown for criminals to offer such material

But to most experts' knowledge, no suchbomb has actually been built

**Difficult to counter**
Experts say that such a weapon could be locally devastating as well as causing fear and panic nationally

The dispersal of radioactive material in an urban area could have severe consequences for anyone who was contaminated with radioactive material, though depending upon how much nuclear material was present the conventional explosive could cause the most damage

Effective decontamination would present health authorities with severe problems, not least because the extent of the nuclear fall-out would at first be unknown

The US seized Jose Padilla onrelated suspicions in 2002
The 1995 Sarin gas attack on the Tokyo subway demonstrated just how difficult it can be to deal with such events. Abomb would be far more difficult to counter

A contaminated region could be rendered uninhabitable for years and people exposed to radiation would have to be monitored for the rest of their lives. Those contaminated could be subjected to an increased risk ofand other diseases

**Unmarked vans**
In the past decade, there have been over 175 cases of terrorist and criminal incidents involving the smuggling and attempted procurement of radioactive material. It has been speculated that some nuclear material was lost after the chaotic fragmentation of the Soviet Union

In the wake of the Cold War, for example, large numbers of small, portable nuclear generators were simply abandoned in former Soviet territory

Late in 2001, three woodcutters in northwest Georgia suffered massive injuries after stumbling on one of these radio thermal generators in the forest

Special teams would be needed to deal with contamination

Alternatively, nuclear material could be stolen from a hospital, a food irradiation plant or some other research site. A recent official study said that US business and research facilities had simply lost track of nearly 1,500 pieces of equipment with radioactive parts since 1996

In January 2002 it was reported that in the wake of last September's terrorist attacks, President Bush put the US Nuclear Energy Support Team
(Nest) on standby withto covertly search for any evidence that abomb attack could be being planned

It has been reported that Nest surveillance teams have been patrolling some cities with unmarked vans containing gamma-ray and neutron detectors (both signatures of radioactive materials) to determine if such a terrorist cell planning such an attack could be detected

Between its establishment in 1975 and the summer of 2002, Nest responded to over 100 cases of nuclear threats from criminals and. They were all hoaxes.