More than 10 years after the attacks of Sept. 11, the possibility that terrorist groups could obtain nuclear materials seems no less real to security experts, even as the threat posed by al-Qaeda recedes.

Former Sen. Sam Nunn is co-chairman of the Nuclear Threat Initiative. (Getty Images)

The least-secure nations with “weapons-usable” nuclear materials: North Korea, Pakistan and Iran. The most secure: Australia, Hungary and the Czech Republic. 

The United States comes in 13th place, tied with Belgium. It would have ranked second, the authors of the index noted, but for the sheer number of its nuclear sites. 

The survey was conducted by the Nuclear Threat Initiative, co-chaired by former Sen. Sam Nunn (D-Ga.), a vocal advocate on nonproliferation issues, as well as the Economist Intelligence Unit, and was based largely on publicly available data. The purpose, organizers said, was not to congratulate some countries and chastise others, but rather to provide governments with a tool to determine how better to secure their nuclear materials. 

Terrorists “will go where the material is most vulnerable,” Nunn said at an event to mark the index’s unveiling. “We have a global challenge, and we are in a race between cooperation and catastrophe.” 

In a foreword to the study, Nunn noted that, over the past 25 years, there has been some progress when it comes to nuclear security. Former Soviet states have returned nuclear weapons and joined the Nuclear Non-Proliferation Treaty, South Africa has dismantled its nuclear weapons program and the United States and Russia have moved to reduce the size of their arsenals.

But the overall picture painted by the report is bleak. In some countries – including Pakistan, where government instability is perennially worrisome – experts have found themselves unable to verify claims that arsenals are secure. Global stocks of nuclear materials are growing worldwide. And even countries that have minute amounts of fissile material, or none at all, can be used as safe havens or transit points for illicit nuclear activities. (The survey ranks those countries in a separate index, placing Somalia and Congo Republic last in line.)

“It’s not a piece of cake for terrorists, and we don’t want to pretend that it is,” Nunn said. “But it’s far from impossible.”

The full survey can be found here.