Some Experiments with Adjustable Geiger-M ller Counters

Abstract

Special counters are described in which it is possible to alter the effective length as well as the material and diameter of the anode without opening them. This is a distinct advantage in that the effects of these factors on the counter characteristics can be studied without complication due to changes in the gas filling and the nature of the cathode surface brought about by opening the counters or by making separate counters with anodes of different diameters. It was observed that, while in a given counter the anode material and the nature of its surface have little or nothing to do with the characteristics, there is an optimum anode diameter for which the best plateaux are obtained, a factor of obvious practical importance in counter design. The photosensitivity to visible light and longer wavelengths caused by high counting rates or by continuous discharges was shown to be due to some surface phenomenon on the cathode. It has been shown in a simple manner that the discharge is not localized, but spread along the length of the counter. It was observed that the plateau length and slope improve at first, but then deteriorate when the effective length of the counter is reduced by shielding the anode wire at both ends with glass capillary tubes. With metal capillaries, however, the plateau characteristics are best when the full length of the cathode is used.