Comparing Environmental Dose Rate Meters: A Method to Determine Natural and Non-natural Variations in External Radiation Levels

A method is described to determine low excess dose rates from a radiation source in the environment, which are small compared to the natural fluctuations of the background radiation. First a 'virtual reference dose rate meter' is constructed from data of the national monitoring network, to know the natural variations of the background radiation. Results from this virtual monitor are then compared to data of dose rate meters at sites of interest, to determine non-natural or very local natural variations and excess dose rates. Daily averaged excess dose rates down to 2 to 3 nSv.h -1 can be identified. The method is applied successfully near nuclear installations in the Netherlands and can be used for all types of dose rate meters and sample frequencies. Finally, the calculations to derive the 'virtual reference dose rate meter' can also be used as a quality assessment (QA) tool for environmental radiation monitoring networks.