- #1
DragonPetter
- 830
- 1
An ionization chamber is like a capacitor in many ways. The gas inside is the dielectric, and if ionization occurs, the ionized dielectric atom or molecule will no longer be able to store the same energy at a voltage potential. The chamber will have dielectric breakdown during ionization, where the mainstream DC method for measuring this is to collect the charge and essentially measure the leakage current of the "capacitor". Because the dielectric is breaking down and the electric field is altered from the displaced ionization charges, the capacitance value should also be altered, at least while radiation is present.
Many capacitive measurement techniques are not accurate and rely on charging the capacitor over a time period to measure the time constant; leakage would change the accuracy of this technique, and the technique might not even measure a change in capacitance. A more accurate capacitive measurement is to use a tuned wien-bridge with an AC signal applied.
I am curious if the idea to place an ionization chamber as the measured capacitor in a wien bridge would be a feasible alternative to the DC+electrometer method. If the proper frequency and amplitude of an AC signal is applied to the bridge, the ionized particles will oscillate to this frequency to some degree, where both a lower voltage or a higher frequency will cause less displacement (these factors I think would play a part in recombination). The bridge should measure a change in capacitance from this ionization, where it falls out of balance and produces a voltage.
If a high enough frequency were selected for the wien bridge to be very sensitive, I wonder if this would be a feasible way to detect ionization in the chamber.
I attached a block diagram of the idea I'm considering. The frequency difference measurement would be in the case of closed loop, while the voltage measurement would be used if the loop were open. Is this a round about way of measuring the same thing that the DC method will give, and would there be no benefit from this alternative? I'm expecting it to be easily shot down, but I can't really stop thinking about it until I know why it won't work.
Many capacitive measurement techniques are not accurate and rely on charging the capacitor over a time period to measure the time constant; leakage would change the accuracy of this technique, and the technique might not even measure a change in capacitance. A more accurate capacitive measurement is to use a tuned wien-bridge with an AC signal applied.
I am curious if the idea to place an ionization chamber as the measured capacitor in a wien bridge would be a feasible alternative to the DC+electrometer method. If the proper frequency and amplitude of an AC signal is applied to the bridge, the ionized particles will oscillate to this frequency to some degree, where both a lower voltage or a higher frequency will cause less displacement (these factors I think would play a part in recombination). The bridge should measure a change in capacitance from this ionization, where it falls out of balance and produces a voltage.
If a high enough frequency were selected for the wien bridge to be very sensitive, I wonder if this would be a feasible way to detect ionization in the chamber.
I attached a block diagram of the idea I'm considering. The frequency difference measurement would be in the case of closed loop, while the voltage measurement would be used if the loop were open. Is this a round about way of measuring the same thing that the DC method will give, and would there be no benefit from this alternative? I'm expecting it to be easily shot down, but I can't really stop thinking about it until I know why it won't work.
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