page_title: Ionization chamber
section_title: Hand-held
hierarchical_section_title: Ionization chamber / Instrument types / Hand-held
caption_attribution_description: Environmental Health Specialist Jamie A. Keeley, of EG&amp;G Florida Inc., uses an ion chamber dose rate meter to measure radiation levels in one of three radioisotope thermoelectric generators (RTGs) that will provide electrical power to the Cassini spacecraft on its mission to explore the Saturnian system. The three RTGs and one spare are being tested and monitored in the Radioisotope Thermoelectric Generator Storage Building in the KSC's Industrial Area. The RTGs use heat from the natural decay of plutonium to generate electric power. RTGs enable spacecraft to operate far from the Sun where solar power systems are not feasible. The RTGs on Cassini are of the same design as those flying on the already deployed Galileo and Ulysses spacecraft. The Cassini mission is targeted for an Oct. 6 launch aboard a Titan IVB/Centaur expendable launch vehicle. External radiation inspection of the Cassini-Huygens spacecraft's Radioisotope Thermoelectric Generators.
context_page_description: The ionization chamber is the simplest of all gas-filled radiation detectors, and is widely used for the detection and measurement of certain types of ionizing radiation; X-rays, gamma rays, and beta particles. Conventionally, the term "ionization chamber" is used exclusively to describe those detectors which collect all the charges created by direct ionization within the gas through the application of an electric field. It only uses the discrete charges created by each interaction between the incident radiation and the gas, and does not involve the gas multiplication mechanisms used by other radiation instruments, such as the Geiger counter or the proportional counter.
  Ion chambers have a good uniform response to radiation over a wide range of energies and are the preferred means of measuring high levels of gamma radiation. They are widely used in the nuclear power industry, research labs, radiography, radiobiology, and environmental monitoring.
context_section_description: Ion chambers are widely used in hand held radiation survey meters to measure beta and gamma radiation. They are particularly preferred for high dose rate measurements and for gamma radiation they give good accuracy for energies above 50-100 keV.
  There are two basic configurations; the "integral" unit with the chamber and electronics in the same case, and the "two-piece" instrument which has a separate ion chamber probe attached to the electronics module by a flexible cable.
  The chamber of the integral instrument is generally at the front of the case facing downwards, and for beta/gamma instruments there is a window in the bottom of the casing. This usually has a sliding shield which enables discrimination between gamma and beta radiation. The operator closes the shield to exclude beta, and can thereby calculate the rate of each radiation type.
  Some hand held instruments generate audible clicks similar to that produced by a G-M counter to assist operators, who use the audio feedback in radiation survey and contamination checks. As the ion chamber works in current mode, not pulse mode, this is synthesised from the radiation rate.
caption: Hand-held integral ion chamber survey meter in use
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