The Path to a Nuclear Weapon
Terrorists would have to overcome enormous technical and logistical obstacles before they could set off a nuclear bomb in a U.S. city. Counterterrorism and nuclear experts say the danger is more distant than immediate.
Simple Bomb Designs
A gun-type fission device, such as the "Little Boy" bomb dropped on Hiroshima, would be the most likely design used by a nuclear terrorist. An implosion bomb, such as the "Fat Man" bomb dropped on Nagasaki, would be more difficult to make.
SOURCES: Nuclear Threat Initiative, Project on Managing the Atom, General Accounting Office, How Stuff Works | By Cristina Rivero and Laura Stanton — The Washington Post