Abstract: Ionization detector capable of operation at elevated temperatures and utilizing iron-55 as a radioactive source within the ionization chamber.

Abstract: A method and apparatus for selectively detecting the presence and concentration of a constituent in a gas sample, such as for example the presence of the vapors emitted by explosives and drugs in the atmosphere. A sample flow is drawn through a switching device into a detector and the output of the detector is correlated with the operation of the switching device. The switching device is actuated at periodic intervals between first and second conditions. In the first condition the switching device interrupts the flow of the constituent of interest to the detector while allowing the remainder of the sample to pass into the detector. In the second condition all the gas sample passes into the detector. The changes in detector output result from the presence of the constituent and the magnitude of the changes indicate the concentration of the constituent in the gas sample.