On the Action of the Geiger Counter

Experiments performed with a Geiger point counter show that when the point is negative the sensitive surface is on the point, and not on the inner wall of the chamber, as suggested by Kutzner (Zeits f. Physik 23, 117, 1924). It is further shown that this sensitive surface can only be obtained when the point has been treated in a way which makes it catalytic. Such catalysts as iron oxide, copper oxide and platinum black work very well. Their activity is destroyed by catalytic "poisons" such as Hg, S${\mathrm{O}}_2$ and ${\mathrm{H}}_2$S. The experiments indicate that the gas layer usually adsorbed by such catalytic surfaces plays an important role in the action of the counter. The gas layer is demonstrated quite positively by observing the point during operation through a microscope in a darkened room. With a vacuum tube amplifier connected to the counter to actuate a relay at each count, a faint flash on the surface of the point is readily discernible for each click of the relay. When the point is positive no special treatment is needed to make it work. This is shown to be consistent with the explanation offered for the action of the chamber when the point is negative.