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Calibration of reference materials

One of PTB’s central tasks is the realization and dissemination of the legal units. For radioactivity measurements in medicine, technology, radiation protection or environmental protection, the legal unit for the radioactive decay, the unit Becquerel (Bq), is disseminated via ceding of activity standards or the calibration of reference materials. With their aid, the legally prescribed quality assurance for measurements of the environmental radioactivity is, for example, performed for the Opens external link in new windowIntegrated Measurement and Information System IMIS. In most cases, the activity standards are used to calibrate the detection efficiency (="sensitivity") of measuring devices (="detectors") for the detection of specific radionuclides. This procedure is sufficient as long as type and properties of the calibration sample - the activity standard - agree as far as possible with those of the test samples. If suitable activity standards are not available, reference materials may be used. It is possible to have the activity determined by PTB in various sample matrices with small measurement uncertainties. Such "certified reference materials" are, for example, used for the validation of sample- and/or nuclide-specific analysing or measurement procedures.

One of the tasks of the federal coordinating laboratorys within the scope of the IMIS is the performance of intercomparisons with realistic reference materials. For this purpose, PTB cedes a suitable activity standard solution to the coordinating laboratory which organizes an intercomparison. The federal coordinating laboratory then prepares an environmental sample homogeneously spiked with this activity standard solution (e.g. soil, milk, water, sediment) and distributes subsets of the reference material (="intercomparison sample") for radionuclide determination to the measuring laboratories. In addition to spiked reference materials, the coordinating laboratories also make non-spiked environmental samples (e. g. radioactive waste water, tailings from uranium mining, industry, sediments, filter sludges from water treatment) as reference material available. After the specific activities of the radioactive nuclides are determined with small uncertainty by the measurements of PTB performed on a randomly selected sample subset, the reference values are traceable to a primary national standard. This traceability is required by the most recent international quality management standards.

Apart from the "IMIS laboratories", other laboratories (university and research centres at home and abroad) also make regular use of the IMIS intercomparisons for external quality assurance so that in the last years the number of participants has increased to up to 130.

Further information about the IMIS intercomparisons and other intercomparisons can be found on the web page of the Opens external link in new windowCoordinating Offices(in German) or in the Opens external link in new windowIRIS data base on the webpage of the Bundesanstalt für Materialforschung und -prüfung (Opens external link in new windowBAM).

In addition to its collaboration in IMIS intercomparisons, PTB analyzes in cooperation with the Opens external link in new windowInternational Atomic Energy Agnecy IAEO or the national metrology institute of the USA, the National Opens external link in new windowInstitute of Standards and Technology (NIST), regular environmental materials which are to be made available as future reference materials for quality assurance analyses in the whole world. The measurement values of PTB and other renowned laboratories serve to determine the reference values (="theoretical values") for the nuclide-specific activities in these materials. Furthermore, PTB is one of the official ALMERA laboratories of IAEO (ALMERA stands for Analytical Laboratories for the Measurement of Environmental Radioactivity).

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