external exposure facility NMG website The Nuclear Metrology Group (NMG) at NPL (National Physical Laboratory, UK) maintains primary radiation measurement standards and provides mixed field plus neutron and gamma reference irradiation facilities for calibration and dosimetry research. The facility dose rates range from 1 μGy/h to mGy/h and supports metrology research and dissemination of dosimetry standards across the UK and internationally. It underpins the traceability chain for radiation protection measurements. Located at NPL. Paul Schofield