Radiological weapons: how real is the threat?

After several months of US opposition to the recall of International Atomic Energy Agency (IAEA) - or other UN inspectors - into Iraq, the IAEA was readmitted at the end of May for a limited and heavily restricted mission: securing a small looted area (known as Location C) within the al-Tuwaitha facility 30 miles south of Baghdad.

More than 500 tonnes of natural uranium and 1.8 tonnes of low-enriched uranium were stored at al-Tuwaitha, plus smaller amounts of highly radioactive caesium-137, cobalt-60 and strontium-90. These materials were left over from Iraq's original nuclear weapons programme, conducted in the 1980s, and were sealed under IAEA safeguards after the 1991 Gulf War. The IAEA's new remit was limited to determining what was and is still missing and what it will take to recapture that material.

Although the IAEA reported on 16 July that it had accounted for most of the looted nuclear material, it could not account for at least 10kg of low-grade uranium, which may have been dispersed. US forces claimed to have recovered about 100 barrels and five radiological devices, possibly looted from the site.

As many as 400 looters a day have ransacked the al-Tuwaitha complex, regarded as the main site in Iraq's former nuclear weapons programme and covering an area of 48ha. Al-Tuwaitha housed several research reactors, plutonium processors and uranium enrichment facilities.

Seals placed at Iraqi nuclear sites by the IAEA during previous inspections had been broken. Metal containers of 300-400kg of natural and low-enriched uranium and uranium oxide (yellowcake - processed mined uranium) had been either stolen or tipped out, and the containers used for domestic purposes, such as for storing drinking water and food. Documents and laboratory equipment had also been taken. Some of the radioactive material was in powder form and could have been dispersed into the air through broken windows.

Another important looted site was the Baghdad Nuclear Research Facility, which houses the remains of the Osirak reactor bombed by Israel in 1981 and by the US in 1991, spent reactor fuel and radioactive isotopes including caesium-137 and cobalt-60: typical RDD materials.

The dirty bomb threat

Although the material looted in Iraq is unsuitable for making nuclear fission bombs, it will suit terrorists wanting to build RDDs. These devices comprise conventional high explosive (such as Semtex, which requires only small amounts for a massive explosion, is easy to handle and hard to detect) and either spent fuel from nuclear reactors (usually uranium or plutonium) or, more likely, medical radioisotopes used in industrial radiography, medical radiotherapy, industrial irradiators and thermo-electric generators. Such a radioisotope is caesium-137, a silvery metal isotope used commonly in medical radiotherapy. It emits powerful gamma radiation and has a half-life of three decades.

On detonation, a RDD would spew the radioactive material into the environment. The effects could range from deaths and injuries, including radiation sickness, in the immediate vicinity of the explosion to minimal immediate injuries and long-term risk of cancer in individuals in the contaminated area. In all cases extensive decontamination of the area would be necessary, which could take months. As with conventional bomb attacks, the emergency services may have to deal with secondary devices and multiple incidents.

Overall, it is the RDD's capacity to spread panic and chaos that makes it an effective terror weapon. Much depends on the amount and type of radioactive material used and the extent of, and conditions for, dispersal. In a computer simulation of a dirty bomb attack on New York, the detonation of 50g of caesium chloride in Lower Manhattan would spread radioactive fallout over 60 city blocks. An RDD explosion in Trafalgar Square, combining the same amount of caesium chloride with 4.5kg of conventional explosive, would produce a plume that, depending on wind direction, could reach Whitehall, Charing Cross and the City within minutes, and deposit radioactive particles onto suburbs 10 km away within half an hour.

Anyone 5km from the blast would face only a tiny increased risk of cancer (one in 1,000) as the background level would be largely unaffected. At 1km, radiation doses would rise to six times background level, increasing the risk of cancer by about one in 100. At 500m downwind from the blast, the risk of dying of cancer from this radiation exposure would be about one in 50, and at 200m radiation levels would be 80 times background level. Caesium-137 stays in the body for decades, concentrating in muscle where it irradiates muscle cells and nearby organs. A dirty bomb could make victims more susceptible to a subsequent biological or chemical weapon, because exposure to large amounts of ionising radiation can suppress the immune system.

The Chechen dirty bomb incident

The only known example of a RDD being laid (but not detonated) was by Chechen separatists in December 1995, when they planted a combined dynamite-caesium-137 package in Moscow's Ismailovsky Park. Neither the Chechens who planted it nor the original source of the caesium have been identified. However, the Chechen separatists could have acquired the caesium-137 from myriad sources, such as the chemical, agrochemical, gas, and oil industries, or from any hospital in Russia. The incident has been passed off as a stunt apparently designed to show how vulnerable Moscow was to a dirty bomb attack.

Insecure radioactive sources

Radioactive material for such a bomb can be found in many countries, including the US, where radioactive waste material is located at more than 70 commercial nuclear power sites in 31 states and where business and research facilities are estimated to have misplaced almost 1,500 pieces of equipment containing radioactive materials in the past eight years. However, nuclear security is most lax in hundreds of installations and industrial sites in the former Soviet Union (FSU).

The Soviets were known to have produced tens of thousands of pieces of radioactive equipment for uses ranging from medical diagnostics to military communications. Many such devices were simply abandoned after the Soviet break-up in 1991. Some regions are so littered with radioactive detritus that published tourist guides caution travellers to watch out for them. About 40kg of weapons-grade material have been stolen over the last 10 years. To date, 280 confirmed cases of criminal trafficking of radioactive material have been confirmed. According to US nuclear officials, Chechen rebels have stolen radioactive metals over a period of 12 months, possibly including plutonium, caesium, strontium and low-enriched uranium, from the Volgodonskaya nuclear power station in the southern region of Rostov.

In the 1970s, Soviet scientists developed Project Gamma Kolos, in which scores of radioactive items were dispatched to the countryside, the aim being to expose plants to radiation and measure the growth effects. All the experiments used a lead-shielded canister containing enough caesium-137 to contaminate a small city. Any one container could give off in a small space more than 10,000 curies (a unit of radioacivity) - 10 times the output of a radiation therapy machine.

Between 100 and 1,000 items are missing, not counting stocks of caesium in loose storage in Russia. They would be ideal for terrorists as they are small, portable and possess a potent core of caesium chloride in the form of pellets or, more frequently, a fine powder. In a 10-month sweep of Georgia, the IAEA discovered five radiological items; four more have been found in Moldova.

Recent commitments from the Russian government to co-operate with the US in the retrieval of missing caesium items reflect a growing awareness that dirty bombs are a growing problem for Russia. At the first global conference hosted by the IAEA in Vienna, in March 2003, increased international funding to secure radioactive materials in the FSU was recommended.

Readiness for an RDD attack

The US (and British) governments have repeatedly highlighted the threat from dirty bombs after the attacks of 11 September 2001. Only since then has the US effort expanded to include non-fissile radioactive material such as caesium-137. Rather than as a response to the Chechen attempt, the interest first arose from intelligence reports that Al-Qaeda terrorists were exploring the use of radiological weapons. It grew with the discovery by US troops of detailed bomb-building instructions in Afghan caves used by Al-Qaeda forces; the arrest of a US citizen, Jose Padilla, in June 2002, suspected of planning a RDD attack; and, most recently, in June 2003, the arrest of a Thai national in Bangkok with a reportedly large quantity - 30kg - of caesium-137.

Following a series of unspecific warnings about a possible chemical, biological, radiological or nuclear attack, the UK government in June 2003 proposed to increase its powers in civil emergency situations. The Civil Contingencies Bill aims to create a single framework for civil emergencies. The legislation would grant extra emergency powers to enable the executive to make decisions without parliament's immediate approval and declare local states of emergency.

In the event of an RDD attack, first responders, aided by troops, would rescue casualties from the 'hot zone', the area closest to the incident. Decontamination would take place in a surrounding area, the 'warm zone', while a survivor rest centre and command-and-control vehicles would be in the 'cold zone'. The mass decontamination methods could include low-pressure water spray from fire hoses, portable showers and the use of large, purpose-built mobile units as well as fixed facilities away from the scene.

The US government is introducing the use of new, 'smart' radiation detectors at border checkpoints, ports, and airports. But because there are other ways for nuclear materials to get in, an extensive radiation detection system distributed throughout major cities may be the only sure way of detecting the movement of radioactive material or a radiological device.

Traditional radiation detectors - Geiger counters - do not identify specific radiation emitters. Every radioactive element gives off a certain unique pattern or 'signature' of energy, so the new gamma ray detectors have been developed that use germanium and cadmium zinc telluride, providing the ability to discern isotopes in weapons - like uranium or plutonium - from a wide range of naturally occurring isotopes. The new detectors will therefore give security and law enforcement personnel a better way to screen out potentially false alarms, such as a shipping container that contains only minute amounts of caesium for medical experiments. Much depends, however, on whether the detectors will be distributed to first responders.

Some believe that the cost of decontamination could exceed the value of the contaminated property and that it cannot be assumed that people will be willing to return to previously contaminated areas. Even after an extensive cleanup, workers in Florida are still refusing to return to buildings that received anthrax-laden letters in October 2001. Also, some radiological materials bind chemically to surfaces, making a large-scale decontamination very difficult.

As radiological devices explode in the same way as conventional bombs, all explosions would have to be monitored immediately for radiation. The US National Nuclear Security Administration, which would respond to a radiological incident, plans to recruit more scientists to handle decontamination and evacuation, and to expand the ad-hoc Nuclear Emergency Search Teams to seek and destroy suspect devices.

Andy Oppenheimer is an expert in nuclear, biological and chemical weapons for Jane's Information Group