Uncertainties and characteristic limits of counting and spectrometric dosimetry systems

Highlights: • Uncertainty determination for ambient dose rate assessment in the environment. • Metrological supported determination of decision threshold and detection limit according ISO 11929. • Comparison of counting and spectrometric dosimetry systems for the ambient dose rate determination. • Proposed new secondary standard for environmental dosimetry based on spectrometry. - Abstract: In the event of a radiological emergency, early and reliable knowledge of radioactivity concentrations is important information for organising countermeasures to protect the general public and emergency workers. This is ensured by all European countries in operating airborne radioactivity and dose rate early warning networks. To increase the provided information, the development of new secondary standards based on scintillation detectors for the measurement of ambient dose rate equivalent was initiated in 2014. This paper shows the state-of-the-art of uncertainties and characteristic limits of low dose rate measurement that can be achieved by scintillation-based detector (CeBr₃) and gas-based detectors (a high-pressure ionization chamber, HPIC). The comparison of the devices shows the performance and the metrological potential of the CeBr₃ detector: Its uncertainty is already very close to the uncertainty of reference values. Looking at the question how to select a reference instrument, the CeBr₃ detector with a special data evaluation is even superior to the HPIC and qualifies therefore as a modern secondary standard: Providing both, dose rate and nuclide information.