How ISIS nearly stumbled on the ingredients for a ‘dirty bomb’

On the day the Islamic State overran the Iraqi city of Mosul in 2014, it laid claim to one of the greatest weapons bonanzas ever to fall to a terrorist group: a large metropolis dotted with military bases and garrisons stocked with guns, bombs, rockets and even battle tanks.

But the most fearsome weapon in Mosul on that day was never used by the terrorists. Only now is it becoming clear what happened to it.

Locked away in a storage room on a Mosul college campus were two caches of cobalt-60, a metallic substance with lethally high levels of radiation. When contained within the heavy shielding of a radiotherapy machine, cobalt-60 is used to kill cancer cells. In terrorists’ hands, it is the core ingredient of a “dirty bomb,” a weapon that could be used to spread radiation and panic…

Why the Islamic State failed to take advantage of its windfall is not clear. U.S. officials and nuclear experts speculate that the terrorists may have been stymied by a practical concern: how to dismantle the machines’ thick cladding without exposing themselves to a burst of deadly radiation.

More certain is the fact that the danger has not entirely passed. With dozens of Islamic State stragglers still loose in the city, U.S. officials requested that details about the cobalt’s current whereabouts not be revealed.

They also acknowledged that their worries extend far beyond Mosul. Similar equipment exists in hundreds of cities around the world, some of them in conflict zones.

“Nearly every country in the world either has them, or is a transit country” through which high-level radiological equipment passes, said Andrew Bieniawski, a vice president for the Washington-based Nuclear Threat Initiative who once led U.S. government efforts to safeguard such materials.

“This,” he said, “is a global problem.”