Abstract: Method and apparatus for detecting the presence of very small concentrations of certain vapors and gases in air or other gaseous backgrounds. A gas sample is ionized by a source of ionizing radiation. The sample of ionized gas is then directed through a recombination region where ions are selectively recombined. The ionized gas is further directed through a drift region where the ions are subjected to a drift potential and separated into different groups, depending upon their mobilities. In an alternate embodiment, the ionized gas is first directed through a drift region, followed by a recombination region.

Abstract: An improved gas ionization cell with compensation for variations in flow rate of the gas and variations in radioactive source intensity. A gas sample is directed past a source of ionizing radiation and through a recombination region to an ion collection screen, where output current is monitored to give an indication of trace gases or vapors present in the gas under surveillance. Compensation for changes in gas flow rate and source intensity is provided by taking a portion of the gas subjected to the ionizing radiation and directing that portion of the gas through a channel by-passing the recombination region of the cell and past a pair of conductive probes. The first probe of the pair is biased at a predetermined voltage, while electric current is monitored at the second probe spaced downstream from the first probe.