The assessment of external photon dose rate in the vicinity of nuclear power stations. An intercomparison of different monitoring systems

Four environmental dose rate instruments having different detectors, a high pressure ionisation chamber, a Geiger-Muller counter, a proportional counter and a scintillation counter, were used to make continuous measurements over a four month period of the air kerma rate at a location close to a nuclear power station. The responses of each of these detectors to the natural radiation and to the radiation from the power station are given. Estimations by three of the dose rate instruments of the air kerma from all the radiation components are intercompared with the results from three different types of thermoluminescence dosemeter. The results clearly demonstrate that accurate estimations of doses in the environment arising from a nuclear facility can only be obtained if the responses of the detectors used to the different radiation components at that location are accurately evaluated. By correcting the measured air kerma values by the accurately determined detector responses the standard deviation, expressed as a percentage of the mean value of the total air kerma for the instruments and the TLDs, was reduced from 20% to 5%.