Gas gain measurement in helium-isobutane mixtures filled-proportional counters

The gas amplification properties have been investigated in four types of helium-isobutane gas mixtures consisting of 0.95, 2, 4 and 10% admixture of isobutane. Diethorn, Zastawny and Charles gas gain formulae were examined in a wide gain range and the relevant gas constants have been experimentally determined. A slight preference is accorded to the Zastawny formula which is found more flexible in describing the experimental gas gain data. Finally, a simple interpretation of the effect of isobutane percentage in the mixtures on the values of Diethorn gas constants is also presented.