Calibration of dosimeters at 80-120 keV electron irradiation

We describe calorimeters for dose measurement at low-energy electron accelerator energies (80–120 keV). Three calorimeters with different characteristics were designed and their dose response and measurement uncertainties were characterized. The heatedair between the electron beam exit window of the accelerator and the calorimeter absorber influences significantly the response of the calorimeter and a thermal model was applied to quantify this effect. All three calorimeters are capable of measuringabsolute dose, and can thus be used for calibration of other dosimeters. The calorimeter was used to calibrate thin-film dosimeters (Risø B3 and alanine films) by irradiation at the 80–120 keV electron accelerators. This calibration was compared to a 10MeV calibration, and we show that the radiation response of the dosimeter materials (the radiation chemical yield) is constant at these irradiation energies. However, dose gradients within the dosimeters, when it is irradiated at low electron energies,mean that calibration function here will depend on both irradiation energy and the required effective point of measurement of the dosimeter. These are general effects that apply to any dosimeter that has a non-linear response function and where dosegradients are present within the dosimeter.