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Q & A: Ion Chambers

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Most recent answer: 10/22/2007
Q:
What is a cable free ion chamber?
- Matt Stayduhar
Pittsburgh, PA, United States
A:
Hello Matt,

An ion chamber is a device used to measure radioactivity. It does this with a volume of gas and has a high voltage applied from one end of the chamber to the other. If a high-energy particle, such as an electron, or more exotic particles from cosmic rays, passes through the chamber, it will knock a few electrons free from the molecules of gas within the chamber. The molecules missing some of their electrons are positively charged ions. The electrons will drift through the gas in the electric field (and the ions will drift in the opposite direction) towards the charged plates or wires on the ends. If the voltage is high enough, the electrons will pick up enough speed on their way to knock more electrons off of more gas molecules, amplifying the signal in a process known as an "avalanche." Sensitive electronic amplifiers read out the signals on the plates or wires and counters count how many of these signals are received in a particular amount of time. These count rates indicate the level of radioactivity. I imagine a cable-free one simply does not have an external connection for the required high voltage. Many of the portable ones have their own internal high-voltage generators.

These are used in radon surveys, maintaining airport search equipment, and anywhere the detection of energetic particles is needed.

Tom

(published on 10/22/2007)

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