General collection efficiency in liquid iso-octane and tetramethylsilane used as sensitive media in a thimble ionization chamber

The general collection efficiency in the dielectric liquids iso-octane (C8H 18; 2-2-4 trimethylpentane) and tetramethylsilane (Si(CH3)(4)), used as sen sitive media in a thimble liquid ionization chamber (LIC) with a liquid lay er thickness of 1 mm, has been studied. Measurements were made for continuo us radiation at varying dose rates using 140 keV photons from the decay of Tc-99m for chamber polarizing voltages of 50, 100 and 500 V. The maximum do se rate in each measurement session was about 150 mGy min(-1). The experime ntal results were compared with theoretical general collection efficiencies calculated by the equation for the general collection efficiency in gases. The results show that the general collection efficiency in a thimble LIC f or continuous radiation can be calculated with the equation for the general collection efficiency in gas ionization chambers, using the same chamber g eometry correction factors and analogous characteristic ion recombination p arameters for the dielectric liquids.