Evidence for Random Decay
A detector beside a radioactive source does not click at regular intervals. The apparatus can remain unchanged while the measured count still fluctuates.
Uneven counts are evidence of random decay
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Use equal counting intervals and keep the source–detector distance fixed. The detector then gives different readings because individual nuclear decays occur at unpredictable times.
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The bars fluctuate around a mean. A longer measurement or repeated trials reveal a stable average more clearly, but they still do not predict the next individual decay (9702/42/O/N/24 Q10(a)(iii)).
A fixed source and detector record 42, 35, 47 and 39 counts in four equal time intervals. What feature of radioactive decay do these fluctuations support?
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They support the random nature of radioactive decay. The time of an individual decay cannot be predicted, so equal intervals need not contain equal numbers of counts.