Question

Explain how an atomic bomb works.

Short answer

An atomic bomb operates on the principle of nuclear fission. Two subcritical masses of a fissile material are brought to a supercritical state by conventional explosives. A neutron source then triggers a nuclear reaction where the key element (uranium-235 or plutonium-239) breaks into two smaller nuclei and releases energy. The fission process causes a chain reaction and the energy created results in an explosion.

Step-by-step solution

Understanding the Structure

An atomic bomb generally comprises two parts of a sub-critical mass of fissile material (usually uranium-235 or plutonium-239) that, combined, will start a nuclear chain reaction. These pieces are placed in a casing and monitored by a neutron source.

Distribution and Initiation

To initiate the explosive chain reaction, conventional explosives placed around the bomb first detonate to bring the sub-critical masses to a supercritical state. The neutron source then emits neutrons to trigger the nuclear reaction.

Nuclear Fission and Chain Reaction

The key element in an atomic bomb, Uranium-235 or Plutonium-239, undergoes fission when it absorbs a neutron, breaking into two smaller nuclei and releasing several millions of electron volts of energy. This fission process also releases more neutrons which can then cause further fission in a chain reaction leading to an explosion.

The Explosion and Resulting Aftermath

When the chain reaction is allowed to proceed at an uncontrolled rate, it releases a massive amount of energy all at once, leading to an explosion. The aftermath of such an explosion includes not just the blast, but radioactive fallout that can cause contamination.