Correction factors for attenuation and scattering of the wall of a cylindrical ionization chamber in the 6-7 MeV high-energy photon reference field

Kowatari, Munehiko; Zutz, H.*; Hupe, O.*

In high energy photon reference fields the value of the air kerma rate is determined by using ionization chambers. From the charge collected inside the ionization chamber the dose can be calculated using a set of calibration and correction factors according to ISO 4037-2. A crucial parameter is the correction for the attenuation and scattering of the primary radiation due to the chamber wall. This parameter can be determined using Monte Carlo calculations. The evaluation of the factor was performed for a commercially available ionization chamber of the type Victoreen 550-3 under different build-up conditions. The results were verified by measurements in the R-F high energy photon fields according to ISO 4037-1 at the Physikalisch-Technische Bundesanstalt (PTB) and the Japan Atomic Energy Agency (JAEA).