The 32 nations with materials that can fuel atom bombs are typically mum on security, which looks to the public like a closed world of barbed wire and armed guards. Now, for the first time publicly, experts have surveyed the precautions each country has in place and ranked the nations from best to worst.

The United States has slightly reduced its numbers of strategic intercontinental missiles, bombers and nuclear warheads, but it continues to maintain a major advantage over Russia, according to figures released this week by the State Department.

Scientists have long sought easier ways to make the costly material known as enriched uranium — the fuel of nuclear reactors and bombs. However, activists are concerned that a potential breakthrough using laser enrichment could increase risks of proliferation and nuclear terrorism by making it both easier to accomplish and easier to conceal.

U.S. officials say the nation’s health system is ill-prepared to cope with a catastrophic release of radiation, despite years of focus on the possibility of a terrorist “dirty bomb” or an improvised nuclear device attack.

China's nuclear arsenal poses the most serious "mortal threat" to the United States among nation states, Director of National Intelligence James Clapper told the Senate on Thursday.

The Obama administration plans to soon begin to "educate" the U.S. Senate and the public on the strides made in scientific research and nuclear blast monitoring since the country last considered the Comprehensive Test Ban Treaty, a senior State Department official said yesterday

Pakistan has begun work on what independent experts say appears to be a fourth plutonium-producing reactor at the country's Khushab nuclear complex, a move that could signal a further escalation in Pakistan's arms race with arch-rival India.

The Obama administration's fiscal 2012 budget request calls for the United States to replace the land-, air-, and sea-based components of its nuclear deterrent, potentially setting the nation on a course that could cost hundreds of billions of dollars over five decade.

America's recent spate of nuclear mishaps may have roots in a broader geopolitical identity crisis for the nation's nuclear weapons program. And some observers say that the odds of a serious nuclear accident only increase as the crisis goes unresolved.

Russia said further cuts in nuclear weapons sought by the U.S. can be achieved only as part of a multinational accord limiting other types of armaments, a position that dims the Obama administration's chances for swift progress toward one of its biggest foreign policy goals. Future rounds of talks aimed at slashing Russia's large arsenal of short-range tactical nuclear weapons must involve other nuclear powers and focus as well on conventional warheads and weapons in space.