Elements of a Dirty Bomb,The nature of radioactivity is such that not all elements are suitable for use in an RDD

_{A "dirty bomb" is understood to be a weapon that uses a conventional chemical explosion to distribute radioactive materials. Unlike a nuclear weapon, which uses an atomic reaction to create an explosion of enormous force (and in which the force of the blast is the primary destructive element), a dirty bomb need only distribute radioactive elements into the atmosphere and disperse dangerous radioactivity in a given area, similar to the nuclear fallout dispersed after the detonation of a nuclear weapon. It is the relative simplicity of a dirty bomb that has long concerned anti-terrorism authorities. Such an explosive device is well within the technical capability of many terrorist groups; the trickier part is obtaining appropriate radioactive elements.}

The nature of radioactivity is such that not all elements are suitable for use in an RDD. The half-life of radioactive elements (the time it takes for half the atoms in a given mass of radioactive isotopes to decay into a stable element) ranges up to 700 million years in the case of uranium-235, which is not regarded as highly radioactive. Other isotopes have half-lives of a few hours, making them exceedingly dangerous for a short period—too short for terrorists to construct a bomb and explode it. The danger of radioactivity from such an isotope could be over within a short period. The half-life of cobalt-60, on the other hand, is 5.3 years, making it an ideal element for use in an RDD.

While acquiring a sufficient quantity of a suitable element is not simple, terrorists have many sources available. Radioactive isotopes are widely used, albeit in small quantities (home smoke detectors, for example, use minute quantities of radioactive materials).

Two isotopes are of particular concern to anti-terrorism officials: cesium-137, used in radiation devices to treat cancer and monitor oil wells, and cobalt-60, also used in cancer therapy and industrial radiography. These isotopes are used in devices that are usually operated under little security and are sometimes abandoned (or "orphaned"). These isotopes can be handled relatively easily, since they only do the most significant damage when inhaled. There are several sources of such elements in legitimate commerce, or they could be stolen during shipment. Gathered in sufficient quantity, such isotopes are regarded as "ideal" elements for use in an RDD.

Health Risks

Exposure to radioactive materials causes a variety of health problems, namely cancer and even death, depending on several factors:

• The amount of radioactive material.
• The method by which an individual is exposed.
• The length of time an individual is exposed.

In some cases, a layer of dead skin is enough to protect against harmful effects from some alpha emitters. Still, exposure to the same level of emitters inside the body (as a result of inhaling radioactive dust, for example) could almost certainly lead to lung cancer. The greater risk posed by exposure of internal organs to radioactivity is presented as a reason that makers of an RDD would try to distribute the radioactive material in the form of finely ground dust.

Some organs are particularly sensitive to different types of radioactive material. Bones, for example, tend to collect strontium and be significantly affected by strontium-90, as are breasts and blood. The thyroid tends to concentrate iodine, and iodine-131 can cause thyroid cancer.

Most treatments for exposure to radioactivity focus on cleansing the body of the radioactive substance as soon as possible. While some drugs are effective in combating the effects of radioactivity, they usually require that they be taken before exposure.

US authorities are divided over how much risk a dirty bomb might pose to individuals in the vicinity. Unresolved questions include how much danger the dispersed radioactive elements pose and for how long. Two basic schools of thought, the "linear" school and the "threshold" school, address this issue.

Advocates of a linear model, notably the Environmental Protection Agency (EPA), believe that if there are dangers of illness (e.g., contracting cancer) from a small amount of low-level radiation, those dangers increase proportionately to the amount of radioactive material spread over a given area.

Other experts believe there is a "threshold" effect, so even if the amount of low-level radiation is substantially increased due to an RDD, health risks are only increased once low-level radiation reaches a "threshold."

According to one estimate, three curies [a measure of the intensity of radioactivity] of an appropriate isotope, a fraction of a gram, dispersed over a square mile, "would make the area uninhabitable, according to the maximum dose currently recommended for the general population." This low level of radiation, according to current standards, might be expected to increase cancers by four per 100,000 people on top of 20,000 anticipated cancers from other causes.