The saturation loss for plane parallel ionization chambers at high dose per pulse values

The use of plane parallel ionization chambers with electron beams with high dose per pulse entails dose uncertainties due to the overestimation of the ion recombination factor, k, up to 20% if conventional dosimetric protocol s are used. In this work MD-55-2 radiochromic films have been used as refer ence dosimeters to obtain dose to water per pulse D-w(GAF) values for three Novac7 (Hitesys) electron beams of E-0 = 5.8 MeV. However, the beam calibr ation by MD-55-2 alms is time consuming and the use of plane parallel chamb ers is fundamental for a periodic quality control procedure. Three plane pa rallel chambers have been used and the general formula for the k determinat ion has been tested using the calibration doses, D-w(GAF). In particular, c onsistent ion recombination factors k(sat)(V-0) (with the ion chamber polar ized at V-0), that follow the Boag theory, have been estimated at different dose per pulse values for the three plane parallel ionization chambers. Th is means that at present any ion chamber needs a specific k(sat)(V-0) deter mination by using a reference dosimeter for which the response is independe nt of the dose rate. An accurate determination of k(sat)(V-0), using a refe rence quality beam, can be used to determine the dose to water per pulse fo r electron beams of different quality and geometrical configuration.