The Nuclear Regulatory Commission (NRC) was set to issue a final rule requiring physical protections for “byproduct materials”—highly radioactive elements that might be used to make a dirty bomb—as Physics Today went to press. Produced in nuclear reactors and accelerators, the materials are widely used in hospitals for radiotherapy and in irradiators for both research and treating blood for transfusions. High-activity isotopes for medical applications include cesium-137, cobalt-60, iridium-192, and strontium-90.
Cesium-137 in the form of cesium chloride is considered particularly attractive to terrorists because of its fine-powder consistency, penetrating gamma radiation, and widespread availability in lightly guarded settings such as hospitals, blood banks, and universities. Experts have warned that a radiological dispersion device—a dirty bomb—could render a large portion of a city uninhabitable for long periods and create widespread panic and economic havoc. Considerable contamination could be accomplished simply by dispersing CsCl from a tall building or airplane.
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