A Method for Measuring the Efficiency of Getters at Low Pressures

A method is described for measuring the rate at which gas is taken up by a getter at low pressures. The measurement is based on ascertaining the drop in pressure along a narrow tube through which the gas to be absorbed by the getter is passed. The pressures on either side of the tube are measured by means of ionization gauges. The values found for the rate of gettering (of air) vary between 10 cm 3 sec -1 for magnesium and 1 500 cm 3 sec -1 for a thorium getter. The values depend on the position of the getter in the valve and increase with increasing proximity between the getter and the region in the valve in which the gas molcules are exposed to the impact of electrons.