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How does an implosion-type atomic bomb create a critical mass?
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nuclear weapon
A test of a U.S. thermonuclear weapon (hydrogen bomb) at Enewetak atoll in the Marshall Islands, November 1, 1952.
In an implosion-type atomic bomb, a subcritical mass of fissionable material—typically plutonium—is compressed into a denser, supercritical state to initiate a chain reaction.12
The process functions through the following mechanism:
- Configuration: The fissile material is shaped into a sphere or a series of concentric shells, which is surrounded by a jacket of high explosives.12
- Compression: Upon simultaneous detonation, the explosives exert enormous pressure, imploding the material inward. This compression significantly increases the density of the core, packing the nuclei more tightly together.23
- Criticality: As the material becomes denser, the probability that an emitted neutron will strike another nucleus and cause fission increases. This transition from a subcritical to a supercritical state allows the chain reaction to proceed.21
- Reflectors: A tamper, or reflector, often surrounds the core to bounce escaping neutrons back into the fissile material, further aiding the achievement of critical mass.2