Supercriticality

From Freepedia

Supercriticality refers to the condition of a nuclear mass after a certain number of neutrons has created a chain reaction in the mass. When a uranium mass is supercritical, it means that the escaping neutrons are colliding with more nuclei, which releases more neutrons to continue the process.

For example, one neutron would hit the nucleus, causing two neutrons to be released, which would then hit the next nucleus, causing four neutrons to be released, and so on.

A supercritical state is needed for a nuclear weapon to release its energy. Also, a nuclear reactor would need a minimal state of supercriticality in order to produce energy.

In contrast, subcritical is the state of a nuclear mass when more neutrons are escaping than colliding with nuclei.

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Also, the supercriticality of a nuclear mass refers to its ability to continue a nuclear reaction. This mass is the equivalent of 15kg of U-235 (eg 10kg maybe be compressed to form a supercritical mass in an implosion type fission bomb).

Without a supercritical mass, the explosion will not continue, as not enough neutrons will collide to form a chain reaction.