An Apparatus for the Measurement of the Scattering of Low Velocity Ions in Gases at Low Pressure

An apparatus is described for the measurement of the scattering of low velocity ions in gases. This consists essentially of an ion source, focusing devices, a magnet for velocity and species selection, and a measuring chamber. Technique of construction and operation is described which enables scattering curves to be obtained where the effective cross-sectional area is plotted against ion velocity down to a velocity of two volts. This apparatus has been found useful for condensable gases such as water, as well as for non-condensable gases. It has been constructed in such a way that ion neutralization as well as elastic scattering can be quantitatively determined as a function of velocity.