Saturation correction in pulsed fields of high dose-per-pulse

Current developments in accelerator technology and beam application have the potential to bring pulsed radiation sources with very high dose-per-pulse into clinical application. In particular, laser-based particle accelerators and pencil beam scanning using synchro-cyclotrons provide intensely pulsed beams. Current methods to determine the saturation correction factor (ks) in ionization chambers are not intended for use at such high dose-per-pulse, possibly leading to an inaccurate dosimetry. We present a method based on the numerical approximation of the ionization, charge reaction and transport processes in an ionization chamber, which is able to overcome the limitations of current procedures used to calculate ks . This numerical work is supported by experimental data of a plane-parallel advanced Markus ionization chamber irradiated with a pulsed electron beam of a dose-per-pulse up to 600 mGy. At a low collection voltage of 100 V a satisfactory description of the saturation correction dependency on dose-per-pulse can be achieved using existing models and tuning their parameter values. However, at the reference voltage of 300 V this is not possible and the newly presented method shows marked improvements. Chief among the additional effects considered in the presented numerical method is the shielding of the electric field by the liberated charges, which alters the dose-per-pulse dependency of ks in a way that can not be replicated by existing approaches.