The Washington Post reports: 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.

Western intelligence agencies were aware of the cobalt and watched anxiously for three years for signs that the militants might try to use it. Those concerns intensified in late 2014 when Islamic State officials boasted of obtaining radioactive material, and again early last year when the terrorists took over laboratories at the same Mosul college campus with the apparent aim of building new kinds of weapons.

In Washington, independent nuclear experts drafted papers and ran calculations about the potency of the cobalt and the extent of the damage it could do. The details were kept under wraps on the chance that Mosul’s occupiers might not be fully aware of what they had.

Iraqi military commanders were apprised of the potential threat as they battled Islamic State fighters block by block through the sprawling complex where the cobalt was last seen. Finally, earlier this year, government officials entered the bullet-pocked campus building and peered into the storage room where the cobalt machines were kept.

They were still there, exactly as they were when the Islamic State seized the campus in 2014. The cobalt apparently had never been touched.

“They are not that smart,” a relieved health ministry official said of the city’s former occupiers.

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. [Continue reading…]