This special issue of Metrologia on radionuclide metrology is the first of a trilogy on the subject of ionizing radiation measurement, a field that is overseen by Sections I, II and III of the CIPM's Consultative Committee for Ionizing Radiation (CCRI). The idea was first proposed at the 2003 series of CCRI Section meetings, with the general aim of showcasing the relevance and importance of metrology in ionizing radiation to a broader metrological audience. After the 2005 meeting of Section II (measurement of radionuclides), the radioactivity aspect of the project began to move forward in earnest. A working group was set up with the brief that the special issue should be of use by experienced metrologists as an overview of the 'state of the art' to compare progress and scientific content with those in other fields of metrology, as a resource for new metrologists joining the field and as a guide for users of radioactivity to explain how traceability to the international measurement system may be achieved.
Since mankind first became aware of the existence of radioactivity just over a century ago (due to its discovery by Becquerel and further work by the Curies), much has been learnt and understood in the interim period. The field of radionuclide metrology that developed subsequently is broad-based and encompasses, amongst others, nuclear physics (experimental and theory), chemistry, mathematics, mathematical statistics, uncertainty analysis and advanced computing for data analysis, simulation and modelling. To determine the activity of radionuclides accurately requires elements of all of these subjects. In more recent decades the focus has been on the practical applications of radioactivity in industry and the health field in particular. In addition, low-level environmental radioactivity monitoring has taken on ever greater importance in the nuclear power era. These developments have required new detection instrumentation and techniques on an ongoing basis to ensure the improvement in accuracy and precision of measurement as demanded by the stringent requirements of the user community, such as the correct calibration of nuclear instrumentation. This leads into the need for traceability to national measurement standards maintained by the national metrology institutes. As part of the radioactivity traceability chain, as for all areas of metrology, it is vital that systems are in place to ensure that national standards can be checked for worldwide uniformity and measurement equivalence.
Many of the resulting areas are covered by the topics in this special issue, although specifically excluded from the scope of the publication are topics that are widely covered in other publications due to their application in applied metrology—for example, radiochemistry, environmental gamma spectrometry and alpha spectrometry. There are three sections to this issue, starting with papers on how the CIPM Mutual Recognition Arrangement has been implemented for radionuclide metrology, following into the bulk of the publication with articles on the `state of the art' in radionuclide metrology and ending with traceability to national/international standards in nuclear medicine, environmental monitoring, radiation protection and decommissioning. This special issue in essence follows on from earlier BIPM Monographies that were published in order to provide the base information for radionuclide metrology. In many respects they complement the special issue since much of their content is still valid today, particularly those published more recently as an aid to ensuring consistency of method and data. The BIPM Monographies are freely available to download from the BIPM website at http://www.bipm.org/en/publications/monographies-ri.html.
The papers in the special issue draw on the experience of radionuclide metrologists who have been involved in their area of expertise for many years. The authors give readers an insightful account of the selected topics through in-depth review articles. We are indeed indebted to them for accepting this difficult and time-consuming task and also thank the many researchers recognized in the articles who have contributed to expanding the field over many years. The considerable effort put into this issue would not have been possible without input from the appointed referees, as well as the project team also comprising Yoshio Hino, Jose-Marie Los Arcos, Mike Unterweger and Brian Zimmerman. Thanks are also due to the Metrologia Editor, Jeffrey Williams, and the editorial staff for their sterling efforts in keeping the issue on track and the publication on schedule. Last, but not least, we thank Prof. Georgio Moscati, President of the CCRI, and Dr Penny Allisy-Roberts, Executive Secretary of the CCRI, for their continuous interest and support for the project.
