New aspects of environmental monitoring using flat phosphate glass and thermoluminescence dosemeters

At the Karlsruhe Monitoring Service photoluminescence dosimetry (PLD) systems have been used in environmental monitoring since the middle of the 1960s. Nowadays flat glass dosemeters with a pattern approval by the Physikalisch Technische Bundesanstalt (PTB) and full automatic readout using pulsed UV laser excitation and pre-dose suppression have replaced the old PLD system. The special advantages of glass dosemeters for this application are above all the long-term stability of field and calibration dosemeters and the insensitivity to ambient temperature and humidity. Based on twenty years experience and the recent progress in routine monitoring by introducing new dosimetry systems, the paper discusses actual results of flat glass PLD systems and LiF thermoluminescence dosimetry (TLD) systems, which have been simultaneously used for environmental monitoring. The PLD system with a fading of about 1% is stable without any temperature treatment. Due to the instability of electron traps in TLD-700 and the temperature dependent fading, TLD-700 underestimates the natural radiation background by 5 to 10% depending on seasonal effects, which is demonstrated in a ten years experiment in the environment. The response to cosmic rays found to be 0.91 for PLD and 0.82 for TLD-700, indicates a more pronounced under-response of TLD. Without applying individual calibration factors for each PL dosemeter, the coefficient of variation for the readout at 0.1 mSv is about 10%. Calibration procedures and correction factors are discussed which may improve the consistency of environmental dose results.