Statistical fluctuations in the count rates

Principle

The observation of radioactive transformations is particularly suitable for familiarizing students with the peculiarities of randomly occurring events. The random character of decay processes is clearly recognizable simply from the acoustic detection of the counter tube pulses. The variations in the count rates registered under the same conditions lead to the question of the "correct" measured value. According to the depth of knowledge which is
aimed at, the evaluation of the results of the measurement can be limited to the consideration of the measured value variations, the calculation of the mean value and the determination of the maximum variation from the average value, or, with the grouping of count rates in subdivisions, an introduction can be made to the statistical way of looking at things.

In any case, for further experiments, the students should come to the realization that the relative random error of the individual measurements is smaller the greater the number of counts which are registered. The time of  measurement which is to be chosen therefore depends upon the desired measurement accuracy, the activity of the source of radiation and the distance of it from the counter tube, and must be so long that the number of counts is sufficiently large.

Task

To determine how large the variations are in the counts registered by the Geiger-Müller counter tube.

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