Discussion
As radioactivity is a random phenomenon, the error in measuring activity in CPM can be reduced by :
Answer: A
The error is reduced by measuring the activity for a longer period of time.
Radioactive decay is random and follows Poisson statistics: if N counts are recorded, their standard deviation is √N. The relative error therefore falls as more counts are collected:
\[ \frac{\sigma}{N} = \frac{\sqrt{N}}{N} = \frac{1}{\sqrt{N}} \]
For example, 100 counts carry a 10% error, but 10,000 counts only 1%. Counting for longer collects more counts and so gives a more precise count rate in CPM.
A short counting time collects fewer counts and increases the relative error. Counting at intermittent intervals does not by itself increase the total counts, and a detector's 'current' does not change the randomness of decay.
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