Correction for volume recombination in liquid ionization chambers at high dose-per-pulse

Area of Science:

• Medical Physics
• Radiation Dosimetry
• Ionization Chamber Technology

Background:

• Accurate dose measurement is critical in radiation therapy and research.
• Liquid ionization chambers (LICs) offer potential advantages for high dose-per-pulse applications.
• Volume recombination is a significant factor affecting ionization chamber measurements at high dose rates.

Purpose of the Study:

• To quantify volume recombination in LICs at high dose-per-pulse.
• To evaluate the applicability of existing calculation models for high dose-per-pulse measurements in LICs.
• To determine if correction factors derived for air-filled chambers are suitable for LICs.

Main Methods:

• Two LICs (isooctane and tetramethylsilane) were irradiated with pulsed 20 MeV electrons.
• Saturation correction for volume recombination was determined using a Faraday cup reference.
• Measurements were conducted across a range of dose-per-pulse (5 mGy to 1 Gy) and pulse durations (5 ps to 10 ms).
• Experimental data were compared against Boag's models, the two-dose-rate method, and numerical calculations.

Main Results:

• In isooctane, experimental data aligned well with the two-dose-rate method, Boag's model (with free electron fraction), and numerical calculations.
• In tetramethylsilane, only Boag's model with a free electron fraction and numerical calculations showed good agreement.
• Numerical models accurately described pulse duration-dependent data for the isooctane chamber.

Conclusions:

• LICs with isooctane are suitable for high dose-per-pulse fields, utilizing the two-dose-rate method for volume recombination correction.
• Numerical calculations effectively model pulsed fields with variable durations in isooctane.
• Other liquid media, like tetramethylsilane, may necessitate additional considerations, such as free electron fractions, for accurate recombination correction.