In nuclear physics, a fission reaction that is maintained because neutrons released by the splitting of some atomic nuclei themselves go on to split others, releasing even more neutrons. Such a reaction can be controlled (as in a nuclear reactor) by using moderators to absorb excess neutrons. Uncontrolled, a chain reaction produces a nuclear explosion (as in an atom bomb).
The white saltire comes from the flag of Scotland. The St Patrick's Cross was, in fact, taken from the arms of the powerful Geraldine family. The red cross of St George is taken from the flag of England. Effective date: 1 January 1801.