The threat comes from the chaois that ensues from any change of government and the insecurity of nuclear materials that could be used to fashion a bomb.
Olli Heinonen, head of U.N. nuclear safeguards inspections worldwide until last year, pointed to substantial looting that took place at Iraq's Tuwaitha atomic research facility near Baghdad after Saddam Hussein was toppled in 2003.
In Iraq, "most likely due to pure luck, the story did not end in a radiological disaster," Heinonen said.
In Libya, "nuclear security concerns still linger," the former deputy director general of the International Atomic Energy Agency (IAEA) said in an online commentary.
Libya's uranium enrichment program was dismantled after Gaddafi renounced weapons of mass destruction eight years ago. Sensitive material and documentation including nuclear weapons design information were confiscated.
But the country's Tajoura research center continues to stock large quantities of radioisotopes, radioactive waste and low-enriched uranium fuel after three decades of nuclear research and radioisotope production, Heinonen said.
Refined uranium can have civilian as well as military purposes, if enriched much further.
For a terrorist with access to such materials, the challenge would be to build a device that would spread the radioactive contamination over the widest possible area. That takes an expertise lacking in all except trained terrorists from al-Qaeda labs.
Unless that stash of low level radioactive material is secured, I don't see us being quite as lucky as we were with the Iraqi stockpile.