for
three Novac7 (Hitesys) electron beams of E0 =5.8
MeV. However, the beam calibration by MD-55-2 films is time consuming and the
use of plane parallel chambers is fundamental for periodic quality control procedure.The saturation loss for plane parallel ionization chambers at high dose per pulse values
A.Piermattei*, S. delle Canne*, L. Azario*, A. Russo*, A. Fidanzio*, R. Miceli*, A. Soriani **, A. Orvieto** , M. Fantini **.
* Istituto di Fisica, Università Cattolica del S.Cuore, Roma, Italy
**Hitesys S.p.A., Aprilia (LT), Italy
Short title: Saturation loss for ion -chambers
PACS : 87.53 Hv
Abstract
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 protocols are used.
In this work MD-55-2 radiochromic films have been
used as reference dosimeters to obtain absolute dose to water per pulse for
three Novac7 (Hitesys) electron beams of E0 =5.8
MeV. However, the beam calibration by MD-55-2 films is time consuming and the
use of plane parallel chambers is fundamental for periodic quality control procedure.
Three plane parallel chambers have been used and
the general formula for the k determination has been tested using the calibration
doses,
. In particular coherent ion recombination factors ksat(V0)
(with the ion chamber polarized at V0), that
follow the Boag theory, have been estimated at different dose per pulse values
for the three plane parallel ionization chambers. This means that at present
any ion chamber needs a specific ksat(V0)
determination by using a reference dosimeter that present an independent response
to the dose rate. An accurate determination of ksat(V0)
using a reference quality beam, can be used to determine the dose to water per
pulse for electron beams of different quality and geometrical configuration.