The International Atomic Energy Agency attempts to keep track of all kinds of radioactive materials as they move around the globe. However as the world’s nuclear reactors continue to produce waste, and the nuclear five nations persist in having military nuclear programs, the IAEA’s task is a logistics nightmare. On the other hand, for budding terrorist organisations or countries with a nuclear deathwish, this is a black market dream.

Add the fall of the iron curtain, where it is generous to describe their nuclear stock taking as slapdash, and we are faced with tons nuclear materials that are unaccounted for. One potential use for this material is in dirty bombs.

A dirty bomb is not a nuclear weapon that creates a large blast. Rather, it is a combination of a traditional explosives attached to radioactive material designed to spread radioactive mater to create an area of contamination.

There is a considerable range of possible dirty bomb designs. Different explosive materials, applied in different quantities, would generate explosions of varying sizes, and different types and quantities of radioactive material would contaminate an area to different degrees.

The primary danger from the use of a dirty bomb is the explosive blast itself, even if the bomb uses a low-level radioactive source. Estimating exactly how much radiation might be at the site of the explosion would be difficult if the source of the radiation is unknown. The radioactive dust and smoke could spread and be dangerous to health if  inhaled.

In light of the Sept. 11, 2001, terrorist attacks, government and industry are trying to placate us by implementing additional measures to provide security against intentional misuse of radioactive sources. However there is so much of it around that it is practically imposible, as engineering industries and health services also routinely use radioactive materials.

In March 1998, the US town of Greensboro, North Carolina went on high alert after medical instruments used to treat cervical cancer disappeared from its General Hospital - each contained a small amount of radioactive caesium. Surveying the hospital with geiger counters showed they had not been misplaced. The State's radiological protection board took over. A citywide search on the ground and from the air failed to recover the equipment. Whoever took the caesium got away with it.

No amount of security can stop this threat, the only way is to create a nuclear free planet.