Science correspondent Miles O'Brien examines the threat that radioactive "dirty bombs"could pose to cities in the U.S., and what's being done to prevent a radiological attack from happening.

In a sting operation orchestrated by the federal government, congressional investigators who set up a bogus company were able to purchase materials for a dirty bomb, despite Nuclear Regulatory Commission oversight.

By PBS News Hour

Two teams of government investigators testing the effectiveness of radiation monitors at U.S. borders were able to smuggle in enough radioactive material to make two "dirty bombs," a federal report released Monday said.

By PBS News Hour

In an atomic bomb, the energy or force of the weapon is derived only from nuclear fission - the splitting of the nucleus of heavy elements such as plutonium or highly enriched uranium into lighter nuclei.

By PBS News Hour