General collection efficiency for liquid isooctane and tetramethylsilane used as sensitive media in a parallel-plate...

The general collection efficiency has been measured in liquid isooctane (C8H18) and tetramethylsilane (Si(CH3)4) used as the sensitive media in a parallel-plate ionization chamber, with an electrode distance of 1 mm, intended for photon and electron dosimetry applications. The liquid ionization chamber was irradiated at different dose rates by 140 keV photons from the decay of radioactive 99mTc. The measurements were made at potential differences of 50, 100, 200 and 500 V. Measurements were performed for each liquid and electric field strength, with the decay rate of 99mTc used as the dose-rate reference. The maximum dose rate was about 150 mGy min-1 in each experiment. When the measured general collection efficiency values are compared with the theoretical predictions for collection efficiency in gases, it is found that the latter also describe the general collection efficiency in the two liquids within 1% of the saturation current for collection efficiencies down to 60% when using experimentally determined recombination rate constants and on mobilities characteristic of each of the liquids.