...There have been dozens of cases of trafficking in radiological materials over the past three years, along with what some weapons experts describe as a disturbing new trend. While most sellers of such materials have traditionally been amateurs -- opportunists and lone actors in search of easy profits -- authorities are now seeing a surge of interest among criminal groups. In a string of incidents from the Caucasus and Eastern Europe to West Africa and South America, gangs have stalked and stolen radiological devices to sell for profit or to use in crimes ranging from extortion to murder.

The new interest in radiological material by smugglers and criminal networks complicates an already difficult task confronting governments: how to stop terrorists from obtaining any of the tens of thousands of powerful radiological sources around the world that are currently in private hands or have simply been discarded. In Georgia and other unstable corners of the world, radioactive materials are turning up on black markets alongside more traditional contraband, such as drugs or Kalashnikov rifles.

They are a currency of the global gray zone, a dangerous mixture of failed states, porous borders and weak law enforcement, where the tools of terrorism are bought and sold...