Saturation curves of parallel-plate ionization chambers

Area of Science:

• Medical Physics
• Radiation Detection and Measurement

Background:

• Current analytical expressions for ionization chambers are limited to the near-saturation region.
• Accurate description of the full saturation curve is crucial for precise radiation dosimetry.

Purpose of the Study:

• To present a novel analytical expression for the complete saturation curve of parallel-plate ionization chambers.
• To validate the expression against experimental data across a wide range of conditions.

Main Methods:

• Developed a new empirical analytical expression for ionization chamber saturation.
• Conducted measurements using x-ray sources (20-150 keV) and Cobalt-60 gamma rays.
• Analyzed the dependence of ion collection efficiency and extrapolated electric field on various parameters.

Main Results:

• The new expression shows excellent agreement with measurements from 0% to 100% collection efficiency.
• Demonstrated the impact of photoemission on saturation current for low-energy x-rays.
• Derived a universal ionization chamber constant experimentally.

Conclusions:

• The new analytical expression provides a comprehensive description of ionization chamber saturation.
• All saturation curve parameters can be determined from a single ionization current measurement.
• This simplifies and potentially improves the accuracy of radiation dosimetry procedures.