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GCSE Physics · key term
A nucleus with an arrangement of protons and neutrons that can change by emitting radiation.
Used by Edexcel and OCR
Specification 6.15, 6.23, 6.26 · Paper 1
Revise: Radiation ParticlesAlpha radiation is therefore matter travelling away from the unstable nucleus: each emitted alpha particle is a group of four nucleons.
A nucleus that can spontaneously emit radiation and change into a more stable nucleus.
Specification P6.1d · Paper 2 (Foundation), Paper 4 (Higher)
A nucleus that may undergo radioactive decay because it is not stable.
Revise: Unstable nuclei and radiationA particular unstable nucleus might decay soon or much later; we cannot predict exactly when it will happen.
A falling activity does not mean that individual nuclei gradually become less radioactive. Each undecayed unstable nucleus can still decay; there are simply fewer undecayed nuclei left.
If asked why radioactive decay is random, state that the decay time of a particular unstable nucleus cannot be predicted. Do not merely say that activity decreases randomly.
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