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Homeland Security

Radiological Attack: What It Is

"The ease of recovery from [a radiological] attack would depend to a great extent on how the attack was handled by first responders, political leaders, and the news media, all of which would help to shape public opinion and reactions."

- Making the Nation Safer
National Research Council (2002)

A radiological attack is the spreading of radioactive material with the intent to do harm. Radioactive materials are used every day in laboratories, medical centers, food irradiation plants, and for industrial uses. If stolen or otherwise acquired, many of these materials could be used in a "radiological dispersal device" (RDD).

Radiological Dispersal Devices, a.k.a. Dirty Bombs

A "dirty bomb" is one type of RDD that uses a conventional explosion to disperse radioactive material over a targeted area. The term dirty bomb and RDD are often used interchangeably in technical literature. However, RDDs could also include other means of dispersal such as placing a container of radioactive material in a public place, or using an airplane to disperse powdered or aerosolized forms of radioactive material.

A Dirty Bomb Is Not a Nuclear Bomb

A nuclear bomb creates an explosion that is thousands to millions of times more powerful than any conventional explosive that might be used in a dirty bomb. The resulting mushroom cloud from a nuclear detonation contains fine particles of radioactive dust and other debris that can blanket large areas (tens to hundreds of square miles) with "fallout". By contrast, most of the radioactive particles dispersed by a dirty bomb would likely fall to the ground within a few city blocks or miles of the explosion.

How an RDD Might be Used

It is very difficult to design an RDD that would deliver radiation doses high enough to cause immediate health effects or fatalities in a large number of people. Therefore, experts generally agree that an RDD would most likely be used to:

  • Contaminate facilities or places where people live and work, disrupting lives and livelihoods.
  • Cause anxiety in those who think they are being, or have been, exposed.

Detection and Measurement

Radiation can be readily detected with equipment carried by many emergency responders, such as Geiger counters, which provide a measure of radiation dose rate. Other types of instruments are used to identify the radioactive element(s) present.

What Do RDDs Do?

The Area Affected

Most dirty bombs and other RDDs would have very localized effects, ranging from less than a city block to several square miles. The area over which radioactive materials would be dispersed depends on factors such as:

  • Amount and type of radioactive material dispersed.
  • Means of dispersal (e.g. explosion, spraying, fire).
  • Physical and chemical form of the radioactive material. For example, if the material is dispersed as fine particles, it might be carried by the wind over a relatively large area.
  • Local topography, location of buildings, and other landscape characteristics.
  • Local weather conditions.

Spread of a Radioactive Plume

If the radioactive material is released as fine particles, the plume would spread roughly with the speed and direction of the wind. As a radioactive plume spreads over a larger area, the radioactivity becomes less concentrated. Atmospheric models might be used to estimate the location and movement of a radioactive plume.

Last Published Date: August 9, 2012
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