Ion Chambers

Posted on Feb 5, 2014

These `ion chambers` are nothing more than a bare wire stuck through a hole into a metal can! No special gas or sealing is required. For best performance it is probably a good idea to add a desiccant to the inside of the can to keep the humidity low. (I didn`t!) Build one; its really simple! When ionizing radiation (ultra-violet light, x-rays, etc

Ion Chambers
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. ) pass through a gas, collisions with the gas molecules produces ion pairs, typically charged molecules and free electrons. If an electric field is present, the ions will move apart, each moving in opposite directions along the electric field lines until they encounter the conductors that are producing the electric field. An ion chamber is an extremely simple device that uses this principle to detect ionizing radiation. The basic chamber is simply a conducting can, usually metal, with a wire electrode at the center, well insulated from the chamber walls. The chamber is most commonly filled with ordinary dry air but other gasses like carbon dioxide or pressurized air can give greater sensitivity. A DC voltage is applied between the outer can and the center electrode to create an electric field that sweeps the ions to the oppositely charged electrodes. Typically, the outer can has most of the potential with respect to ground so that the circuitry is near ground potential. The center wire is held near zero volts and the resulting current in the center wire is measured. The voltage required to sweep the ions to the conductors before a significant number of them recombine or stick to a neutral molecule is usually under 100 volts and is often just a few volts. The resulting current is extremely low in most situations and detecting individual x-rays is difficult, especially with ordinary air at atmospheric pressure. These...

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