Parallel-plate ionization chamber response in cobalt-60 irradiated transition zones

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Abstract
The authors study the acceptance of a Capintec parallel-plate ionization chamber. The Capintec chamber is used for dose measurements in a lead and polystyrene slab phantom irradiated with cobalt-60 .gamma. rays. The authors define an enhancement ratio to quantify the dose measurements. The enhancement ratio equals the ratio of dose measured with the lead slab present to dose measured under equilibrium conditions in polystyrene atequal primary beam attenuation. The measured enhancement ratio at the exit side of the lead/styrene interface is 25% lower than the Monte Carlo predicted enhancement ratio. The authors propose that geometric acceptance limitations of the Capintec chamber to large-angle, low-energy electrons are the cause for this difference. A Monte Carlo simulation of the Capintec chamber acceptance confirms the hypothesis.
Funding Information
  • National Institutes of Health (CA 11051)