Advancements in accuracy of the alanine dosimetry system. Part 1. The effects of environmental humidity

A one-year study of the EPR signal of gamma-irradiated (Co-60) L-alpha-alanine with simultaneous monitoring of the cavity e-factor was undertaken. The widespread opinion that the EPR signal remains absolutely stable under normal laboratory storage conditions is inaccurate. At 0% humidity, the signal can be regarded as stable within +/-1% of its initial value for 6 months for 1 and 10 kGy doses, but for only 3 months for 100 kGy. When stood at the same relative humidity values up to 60%, the fading rates for dosimeters irradiated to 1 and 10 kGy are similar, whereas signals of dosimeters irradiated to 100 kGy fade considerably faster for all humidities. The rates of fading increase with the relative humidity, especially above 60% R. H. Environmental humidity also deteriorates the accuracy of alanine dosimetry by changing the resonant cavity e-factor. This is particularly important when irradiated alanine dosimeters are used as instrument calibration standards. Short-term changes in alanine EPR signal amplitudes were recorded upon removal of the irradiated dosimeters from their storage environments. The importance of an in situ standard to comet for measurement errors due to environmental effects is demonstrated. (C) 2000 Elsevier Science Ltd. All rights reserved.