The Model for Calculating the Type A Measurement Uncertainty of GM Counters from the Aspect of Device Miniaturization

In accordance with the general trend of the miniaturization of electronic components and devices, this paper shows the model for calculating the type A measurement uncertainty of the Geiger-Mueller (GM) counter. As a consequences of device miniaturization, reduction of the GM counting tube size results in a change in the reliability of the GM counter for radiation detection. Based on the enlargement law applied to distributions of extreme values (such as the Weibull distribution) the paper shows the derived theoretical expression which describes the trend of the type A measurement uncertainty followed by the GM counting tube reduction. In an experimental procedure, carried out under well controlled laboratory conditions, the area and volume effects caused by the change in the counting tube size were observed separately. Experiments were carried out on commercial counting tubes as well as on in-house counting tube models, both made in cylindrical geometry. The experimental results obtained, which are in compliance with the theoretically derived model, indicated that the random variable pulse rate, which belongs to the normal distribution due to its nature, with regard to modelling according to area and volume enlargement probability law, should be treated by the three-parameter Weibull distribution. All the obtained results in the paper have been explained based on elementary processes of electrical discharge in gases and are significant for engineering practice since they define the trend of GM counter measurement uncertainty of type A, and thus its functionality as a radiation instrument, during the course of device miniaturization.