he damage caused by a dirty bomb depends on the amount of radioactive and conventional explosive material in the bomb, as well as such factors as wind, the size of the buildings in the area attacked, and the ballistic at detonation. People in the immediate vicinity would likely die from the force of the conventional explosion itself. Some survivors of the blast might die of radiation poisoning in the weeks afterwards. Those farther away from the explosion might suffer radiation sickness in the weeks afterward but recover. Over time, risks of cancer in the affected area would rise. The attack area could be not usable again, or it may require months of intense cleanup efforts, somewhat like the fumigation of the Hart Senate Office Building after the anthrax letters attacks.

Background

    Materials are radioactive if their atomic nuclei, or centers, spontaneously disintegrate, or decay, with high-energy fragments of this disintegration flying off into the environment. Several kinds of particles can so be emitted, and are collectively referred to as radiation. The radiation produced by radioactive materials provides a low-cost way to disinfect food, sterilize medical equipment, treat certain kinds of cancer, find oil, build sensitive smoke detectors, generate electricity, etc. As a result, significant amounts of radioactive materials are stored in laboratories, food irradiation plants, oil drilling facilities, nuclear plants, medical centers, experimental reactors, and many other sites.


Sample cases

    We will briefly refer to three cases to illustrate the range of impacts that could be created by malicious use of comparatively small radioactive sources: the amount of cesium that was discovered recently abandoned in North Carolina, the amount of cobalt commonly found in a single rod in a food irradiation facility, and the amount of americium typically found in oil well logging systems. In all cases we will assume that the material is released on a calm day. We assume that the material is distributed by an explosion that causes a mist of fine particles to spread downwind in a cloud. People will be exposed to radiation in several ways.

    First, they will be exposed to material in the dust inhaled during the initial passage of radiation cloud. We assume that at least 25% of the material is in particles small enough to be inhaled. The material will stay in the body and lead to a long term exposure.

    Second, anyone living in the affected area will be exposed to material deposited from the dust that settles from the cloud. They will be continuously exposed to radiation from this dust, since the gamma rays penetrate clothing and skin.

*    People would also be exposed to radiation from contaminated food and water sources.


Makings of a dirty bomb

     Hundreds of small radioactive power generators are scattered across the former Soviet Union, and several other countries. These lethal devices can be used as possible components in a weapon to be used in a terrorist asymmetric strike. Radio-thermal generators, RTGs, used by the Soviets to power navigational beacons and communications equipment in remote areas, each containing up to 40,000 curies of highly radioactive strontium or cesium.

    Even a tiny fraction of a single curie of strontium has a high probability of causing a fatal cancer. These two materials, which cannot be used to make nuclear weapons, can be combined with conventional explosives to build a dirty bomb or radiological bomb.

    There are literally hundred of places, and countries, where terrorists use and have access to materials for such a bomb, including dumping grounds for medical waste. In some RTGs, the device's core typically is a flash light-size capsule of strontium 90, surrounded by thick lead to absorb the radiation. If broken, it radiates fatal doses of radiation.

    The most accessible nuclear device for any terrorist would be a radiological dispersion bomb. This so-called 'dirty bomb' would consist of waste by-products from nuclear reactors wrapped in conventional explosives, which upon detonation would spew deadly radioactive particles into the environment. This is an expedient weapon, in that radioactive waste material is relatively easy to obtain. Radioactive waste is widely found throughout the world, and in general is not as well guarded as actual nuclear weapons. In the United States, radioactive waste is located at more than 70 commercial nuclear power sites in 31 states. Enormous quantities also exist overseas — in Europe and Japan in particular. Tons of wastes are transported long distances, including between continents (Japan to Europe and back).

    Cuba, since 1988 has two experimental nuclear reactors in La Habana. Very low power. One is a 10 Watts. The other is referred to as zero Watts. They are used for nuclear medicine and research on nuclear biotechnology. But they do generate nuclear waste.  In Russia, security for nuclear waste is especially poor, and the potential for diversion and actual use by Islamic radicals has been shown to be very real indeed. In 1996, Islamic rebels from the break-away province of Chechnya planted, but did not detonate, such a device in Moscow's Izmailovo park to demonstrate Russia's vulnerability.

    This dirty bomb consisted of a deadly brew of dynamite and one of the highly radioactive by-products of nuclear fission — Cesium 137. Extreme versions of such gamma-ray emitting bombs, such as a dynamite-laden casket of spent fuel from a nuclear power plant, would not kill quite as many people as died on Sept. 11. worst-case calculation for an explosion in downtown Manhattan during noontime: more than 2,000 deaths and many thousands more suffering from radiation poisoning.

    Treatment of those exposed would be greatly hampered by inadequate medical facilities and training. The United States has only a single hospital emergency room dedicated to treating patients exposed to radiation hazards, at Oak Ridge, Tenn. A credible threat to explode such a bomb in a U.S. city could have a powerful impact on the conduct of U.S. foreign and military policy, and could possibly have a paralyzing effect. Not only would the potential loss of life be considerable, but also the prospect of mass evacuation of dense urban centers would loom large in the minds of policy-makers.

    The threat from radiological dispersion dims in comparison to the possibility that terrorists could build or obtain an actual atomic bomb. An explosion of even low yield could kill hundreds of thousands of people. A relatively small bomb, say 15-kilotons, detonated in Manhattan could immediately kill upwards of 100,000 inhabitants, followed by a comparable number of deaths in the lingering aftermath. Fortunately, bomb-grade nuclear fissile material (highly enriched uranium or plutonium) is relatively heavily guarded in most, if not all, nuclear weapon states.

    Nonetheless, the possibility of diversion remains. Massive quantities of fissile material exist around the world. Sophisticated terrorists could fairly readily design and fabricate a workable atomic bomb once they manage to acquire the precious deadly ingredients (the Hiroshima bomb which used a simple gun-barrel design is the prime example).   

    Obviously, intelligence that helps localize the bomb is the main key to success. Just as obviously, intelligence of such quality is seldom available — as proven on Sept. 11. Such a search could be truly looking for a needle in a haystack, as detection normally would succeed only if the detectors come within a few feet or so of the hidden bomb. Disabling a bomb is easy by comparison. A radiological bomb might be surrounded by a tent enclosure several tens of feet in height and width, then filled with a special foam to contain the deadly radioactive material (such as Cesium 137) if the bomb explodes during further defusing attempts.

    For a nuclear device, a set of options for disabling the weapon are available, including using explosives to wreck the bomb's wiring to prevent the triggering of the nuclear detonators. Because of the difficulty inherent in finding a nuclear weapon once it entered the country, near-term U.S. response efforts would be best focused on prevention and intervention to secure possible sources of nuclear terrorism.

Conclusion

    The events of September 11 have created a need to very carefully assess our defense needs and ensure that the resources we spend for security are aligned with the most pressing security threats. The threat of malicious radiological attacks in the US is quite real, quite serious, and deserves a vigorous response.

    There is no immediate way for the public to distinguish a dirty bomb explosion from a regular explosion. All nations classified as terrorist nations, have access to these materials, and certainly most of them, including Cuba, have the technology and capacity to build dirty bombs. Cuba has had nuclear medicine for years, two experimental nuclear reactors given by the Soviet Union, and access to materials such as cobalt, cesium, strontium, iridium, and americium.