Ensuring the reliability of alpha counting

Measuring the alpha flux at the surface of materials from integrated circuits and their packages has been established as a method for more than 2 decades. Largearea low-background counting systems from two vendors were used; these systems operate as proportional counters.^1,2 The results gained from these measurements were used to categorize possible causes of counting errors into groups. Some of these causes are focused on in more detail by the use of examples. It is demonstrated how the cumulative density function (CDF) of a distribution of measured counting rates can be tested graphically for Poisson distribution using two methods. A systematic error is demonstrated and the influence of the duration of the measurements on the detection limit is explained. It is also shown how a suitable bias point can be found for counting tubes. Finally, a schematic of results from alpha counting is presented, and time-dependent changes of these counting rates are stated.