Nuclear fission chain reaction
A self-sustaining process where neutrons released in one fission event trigger further fissions. If the average number of secondary neutrons per fission (k, the multiplication factor) exceeds 1, the chain reaction accelerates exponentially.
Formula
k = neutrons in generation n+1 / neutrons in generation n
Real World
The Chernobyl reactor disaster in 1986 occurred partly because operators disabled safety systems, allowing k to exceed 1 unchecked — triggering a runaway chain reaction and explosion.
Exam Focus
State clearly whether k > 1, k = 1, or k < 1 and link each case to its outcome (supercritical, critical, subcritical) — examiners expect all three compared.
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