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Radioisotopes

here are millions of radioactive sources in use today across the United States and the world. Providing adequate security for all sources will take time, money, and national and international cooperation. However, some radioactive materials pose a greater threat, and demand immediate attention. The security threat depends on a number of factors, including the source's energy and type of radiation; the half-life of the isotope; and the amount of material. The shape, size, presence of protective layers (shielding) such as lead and other metals surrounding the material, and the portability of the material, also affect the source's threat level. Finally, the ease in scattering, or dispersing, the material is also taken into account. These guidelines help determine which materials are considered "high-risk" sources.

Low to Medium Risk Isotopes

The eight radioisotopes classified as high-risk (listed in the right-hand column) make up only a small fraction of the large number of radioisotopes in use around the world today. Those eight are considered high-risk because they tend to be prevalently used in radioactive sources emitting relatively large amounts of radioactivity. Most of the other radioisotopes currently in use may be considered only a medium to low risk.

Photo credit: U.S. Dept. of Energy
Isotopes are used in many industries to test the structural integrity of dams, aircraft, bridges, and pipelines—uses that are critical to ensuring public and worker safety

A number of factors must be considered when categorizing the security risk
posed by the various radioisotopes. For example, a radioisotope may emit strong gamma radiation, but have a very short half-life of 12 hours. This means that even if used by a terrorist, the radioactive contamination would probably not last long enough to cause real harm. The short half-life would thus decrease the radioisotope's terrorist appeal. Other factors include the weight, size, and mobility of the radioisotope and its container. Radioisotopes that are not easily dispersible will also not be as attractive to terrorists.

Photo credit: U.S. Dept. of Energy
Dozens of isotopes are used in medical diagnostics and scientific research.

Click on the radioactive sources in the right-hand column for detailed information on their individual properties, peaceful applications, and security/threat risk levels.

Radioisotopes:

• Overview/Low to Medium Risk Sources

Detailed information on High Security Risk Isotopes:

• Americium-241

• Californium-252

• Cesium-137

• Cobalt-60

• Iridium-192

• Plutonium-238-239

• Radium-226

• Strontium-90

This material is produced independently for NTI by the Center for Nonproliferation Studies at the Monterey Institute of International Studies and does not necessarily reflect the opinions of and has not been independently verified by NTI or its directors, officers, employees, agents.
Copyright © 2004 by MIIS.