Study of the radiation field characteristics of a 137Cs irradiator by Monte Carlo simulation.

In this work a study of the energy fluence of the photon beam produced by a commercial irradiator that uses a single collimated 137Cs source is performed by employing the Monte Carlo code PENELOPE. A set of lead attenuators is placed at the exit window of the irradiator to vary the air kerma rate that is required to cover the instrument scales at a particular calibration distance. A possible variation in response due to this beam modification isalso investigated for LiF (TLD-100) dosimeters and for a secondary standard radiation protection level ionization chamber. The results show an important enhancement of beam mean energy from 633 to 642 keV as the lead attenuators increase in thicknesses. For this energy range, a maximum response change of 45% was found for LiF and 4.4% for the ionization chamber. These results reinforce the idea that a single source may very well be a practical solution for calibration laboratories without compromising the overall uncertainties acceptable for this application.