engleski

Ionization coefficient in propane, propane-based tissue-equivalent and dimethyl-ether in strong non-uniform electric fields

Gas amplification in a proportional counter filled with propane, propane-based tissue-equivalent gas mixture (propane-TE) and DME (Dimethyl-ether) is measured. By using low pressures (2 – 50 kPa) relatively strong reduced electric fields are produced, which enabled a study of non-equilibrium effects. Gas gain data are analysed according to the field-gradient model and the reduced ionisation coefficient alpha/P is thus obtained. The assumption of electrons being in equilibrium with electric field fails to be valid in low-pressure gases, where the electric field strengths at the anode surface, Sa, above about 5x105 V m-1kPa-1 are obtained. Under non-equilibrium conditions alpha/P is not a unique function of the reduced electric field strength, but depends on the gas pressure as well. Good agreement with other experimental or theoretical alpha/P obtained mostly under equilibrium conditions is obtained at relatively weak electric field strengths. The presented alpha/P in strong fields may be used for a more accurate modelling of low-pressure counters.

ionization coefficient; proportional counter; gas amplification; low-pressure gas

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