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Effect of radiation rate on electret ionization chambers
1Department of Radiation Oncology, McGill University, Montreal, Canada.
Physics in Medicine and Biology
|October 1, 1995
Summary
Radiation-induced conductivity in Teflon FEP film affects electret ionization chamber dosimetry. Surface charge loss depends on radiation rate, but can be optimized for flat response.
Area of Science:
- Materials Science
- Radiation Physics
- Dosimetry
Background:
- Electret ionization chambers (EICs) are used for radiation dosimetry.
- Teflon polyfluoroethylene propylene (FEP) film is a common material in EICs.
- Radiation-induced conductivity (RIC) can affect EIC performance.
Purpose of the Study:
- To investigate the dependence of RIC on radiation rate in Teflon FEP film.
- To understand the impact of RIC on EIC charging efficiency and air-kerma measurements.
- To determine conditions for stable EIC response across varying radiation rates.
Main Methods:
- Measuring RIC in 254-micron Teflon FEP film under varying radiation rates.
- Analyzing surface-charge density changes before and after irradiation.
- Correlating EIC response with air-kerma rate.
Main Results:
- RIC was found to be dependent on the radiation rate.
- Surface charge loss in the FEP film increases with higher air-kerma rates.
- EIC charging efficiency is reduced due to RIC, leading to overestimated air-kerma values.
Conclusions:
- RIC in Teflon FEP film is a significant factor in EIC dosimetry.
- Surface charge migration and recombination are rate-dependent phenomena.
- Optimizing physical parameters can achieve a stable EIC response over a broad range of air-kerma rates.