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The terms in bold link to topics in the AQA, Edexcel, OCR, WJEC and CCEA A-level specifications, as well as the IB, Pre-U and SQA exam specifications.
In nuclear power stations, thermal neutrons cause nuclear fission in controlled chain reactions. Excited atoms contain electrons in energy levels above the ground state. In lasers, photons stimulate the emission of further photons from excited atoms, producing photons of the same frequency, polarisation and phase that superpose to form a laser beam.
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