3.8.1.3
Radioactive decay is random and spontaneous
Radioactive Decay & Half-Life — AQA A-Level Physics
Key Definition
Radioactive decay — The spontaneous disintegration of a nucleus to form a more stable nucleus, resulting in the emission of an alpha, beta or gamma particle.
- Random means: each nucleus has an equal probability of decaying in any given time interval. You cannot predict which nucleus will decay next or when.
- Spontaneous means: the rate of decay is unaffected by external conditions (temperature, pressureForce per unit area. Measured in pascals (Pa), where 1 Pa = 1 N m⁻²., chemical state).
- It is only possible to estimate the proportion of nuclei that will decay in a given time periodThe time taken for one complete oscillation or wave cycle. Measured in seconds (s)..
- Evidence: a Geiger counter near a radioactive source gives irregular, unpredictable counts. The fluctuations in count rate demonstrate the random nature of decay.
Examiner Tips and Tricks
- Learn the precise definitions of 'random' and 'spontaneous' — they are different concepts.
- $Random = equal probability$ for each nucleus, unpredictable which one decays.
- $Spontaneous = not triggered$ by anything external.