Dead space time and so forth.
A Geiger counter can appear to return to zero or indicate a lower-than-expected reading at very high radiation levels due to the counter’s “dead time”. During the dead time, the Geiger-Müller tube is temporarily unable to register new radiation events, even if they occur. This is because the tube needs time to recover after each ionization event.
Here’s a more detailed explanation:
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Ionization and Dead Time:When radiation enters a Geiger-Müller tube, it causes ionization of the gas inside, creating a pulse of current that is registered as a count.
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Recovery Period:After each ionization event, the tube needs a brief period to recover and become sensitive to new radiation again. This period is called the dead time.
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High Radiation Rates:At very high radiation rates, so many particles are entering the tube that it spends a significant portion of its time in this “dead” state.
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Missed Counts:If a particle strikes the tube during its dead time, it won’t be counted, leading to an underestimation of the true radiation level.
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Apparent Return to Zero:In extreme cases, the counter may not be able to keep up with the rate of incoming radiation and will appear to indicate a much lower level, or even zero, as it effectively becomes saturated with radiation.
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Limitations:This is a limitation of Geiger counters, especially when measuring very high radiation levels. For accurate measurements at high radiation rates, ion chamber instruments are typically used.
