Last week authorities in Kazakhstan announced that a container holding cesium-137, a radioactive material, disappeared, possibly after falling off a truck.

Details of the incident are sparse. The Kazakh government says it is searching for the container, which weighs over 100 pounds, but would not or could not say where it came from or where it might be headed.

It’s unclear how big of a threat the missing cesium poses, but experts say it highlights a growing global problem: As radioactive materials proliferate throughout the world, including in countries that don’t have the resources to secure, track or find them, there’s mounting fear that they could find their way into the hands of criminals and radical groups who could use them to build radioactive weapons, often referred to as dirty bombs.

“There’s concern that these sources are widely spread and easily accessible,” said Andrew Bieniawski, vice president of material security and minimization at the Nuclear Threat Initiative and a former top official in the U.S. National Nuclear Security Administration. “They’re used in everything from oil wells to the medical industry. You have thousands of these sources around the world, and people don’t realize they’re a threat.”

More...