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Nuclear Weapons

» Subsections: Fission Page — Fusion Page — Effects of Nuclear Weapons — Video Clips

On August 6, 1945, a gigantic mushroom cloud billowed up in the air at the city of Hiroshima, Japan. The US fighter jet Enola Gay zoomed away as 5 square miles were instantly leveled by a bomb with the force of twenty-thousand tons of TNT. A massive shock wave created winds more powerful than a tornado. An intense fireball of hot gas vaporized everything it came in contact with. Intense thermal radiation ignited enormous fires.

At 8:15AM the city had a population of about 400,000 residents. By 8:17AM the population had dropped to approximately 320,000 people. Modern studies analyzing the number of deaths place the immediate death toll at 80,000 that day, plus an additional 60,000 people who perished by the end of the year from radiation sickness.

Three days later, the Fat Man was dropped on Nagasaki with similar devastation. Emporer Hirohito surrendered with the following words:

The enemy has begun to employ a new and most cruel bomb, the power of which to do damage is indeed, incalculable, taking the toll of many innocent lives. Should we continue to fight, it would not only result in an ultimate collapse and obliteration of the Japanese nation, but also it would lead to the total extinction of human civilization... It is [in accordance] to the dictates of time and fate that we have resolved to pave the way for a grand peace for all the generations to come by enduring the [unavoidable] and suffering what is insufferable.
Emperor Hirohito, August 15, 1945
Click here to listen to an American radiobroadcast of Hirohito's surrender speech delivered in 1945. (7 mins 58 secs)

This was the start of the nuclear era.

The first nuclear bombs to be used during war were "Fat Man" and "Little Boy," both of which caused destruction in two Japanese cities. Because of such massive destruction, nuclear weapons have not been used since 1945. There are three things necessary to build an atomic bomb:

Fuel that can undergo fusion or fission
Triggering device
A way to allow most of the fuel to fission or fuse prior to the explosion, which prevents the bomb from fizzling out

The designs and types of nuclear bombs specifically address these three components.

Interesting Fact
The yield of a nuclear weapon is its TNT equivalent. Thus, a nuclear weapon with yield of 150 kilotons is equivalent to 150,000 tons of TNT.

Designs and Types

Nuclear Fission

» View: Main Page — Physics of Nuclear Fission — Gun-Type Design — Implosion-Type Design — Neutron Initiator

The first nuclear devices invented and deployed were powered by nuclear fission. Fission is the process of splitting the nucleus of an atom into two smaller fragments. Uranium-235 and Plutonium-239 are the most commonly used fuels in nuclear fission reactions. Elements such as these can undergo induced fission, which means if a neutron collides with the nucleus, the atom will absorb the neutron, become unstable, and split apart immediately.

Nuclear Fusion

» View: Main Page — Physics of Nuclear Fusion —Teller-Ulam Design Page

Fusion nuclear devices, also known as thermonuclear weapons or hydrogen bombs, were developed as more powerful and more efficient nuclear weapons after the invention of fission bombs. The Tsar Bomba ("king of the bombs"), detonated by the Soviet Union on August 30, 1961, was the largest hydrogen bomb ever exploded on Earth. It was estimated to have a destructive yield equivalent to 60 million tons of TNT. In comparison, the fission weapons deployed over Japan in WW II had a yield of 15 thousand tons of TNT.

Effects of Nuclear Weapons

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In addition to the deadly blast and heat effects of the primary detonation, nuclear bombs result in deadly gamma rays and other radiation. Exposure to intense radiation causes sickness and death in humans, especially in the form of cancer.

Nuclear Explosion Video Clips

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See multimedia video clips of nuclear explosions and related broadcasts. Witness the awesome destructive power of actual detonations of nuclear bombs in testing situations.