Knowns and unknowns in radioactivity measurements
A JRC scientist presented a "state-of-the-problem" report in radioactivity measurements on uncertainty estimation and overconfidence in analytical models to represent physical reality.
As science-based decision making also depends on reliable measurement results, it is even more important to be aware of the uncertainty of the results. Recently, JRC scientist Stefaan Pommé contributed to a special issue of the journal, Metrologia dealing with uncertainty in standardisation measurements of radioactivity. In a new review of published in-depth case studies, he draws conclusions about the current state of the art in radionuclide metrology. A lot has been achieved over the last century since the discovery of radioactivity. We have built up a rich database of decay characteristics for thousands of radionuclides; we know the different types of radiation emitted and have a good understanding of how to measure them in various detectors. Computer simulations can reproduce particle and photon transport in the most complicated experimental configurations.
However, persisting discrepancies in outcomes of inter-comparison studies and among published data are reminders that complete statistical control of our methods has not been achieved. It is argued that the problem lies mainly in incomplete uncertainty assessment. Evidence shows that uncertainty estimations differ greatly from one laboratory to another. Reliability in metrology can only be achieved through a deep understanding of the measurand and the method applied to measure it. Redundancy of measurement methods and regular participation in intercomparisons are indispensable tools to protect against overconfidence in a particular technique.
Surprisingly, many decay characteristics of even the most relevant nuclides are still in need of improvement for optimal use in applications for nuclear energy, medicine, safety and security, environmental monitoring, nuclear dating, astrophysics, etc. Errors in reference measurements of radioactivity have an impact on every nuclear application in the world that relies on SI-traceable calibration standards and fundamental decay data.
The JRC strives for harmonisation of the measurement system through the performance of top quality reference measurements of activity and decay parameters, the organisation of inter-comparison studies and proficiency tests, education and training, method development and standardisation of procedures and nomenclature.