A review of intercomparison exercises run by NPL from 1989–1997

Abstract

The National Physical Laboratory is the national standards laboratory of the UK and is charged with maintaining primary measurement standards in the UK. These include standards in the field of ionising radiation and, in common with other National Standards Laboratories, NPL develops and maintains absolute standards of radioactivity. These are used to calibrate secondary standard instruments and also to prepare traceable standards of radioactivity at levels appropriate to the user community. Over the past eight years NPL has run a series of six environmental radioactivity measurement intercomparisons, aimed at evaluating the capabilities of laboratories measuring environmental radioactivity in the UK. This paper reviews the general progress made over the years by the participating laboratories with reference to those laboratories who are accredited by the United Kingdom Accreditation Service (UKAS). The first exercises made clear that (1) there was no account taken of cascade summing effects in γ-ray spectrometry measurements by many laboratories, (2) the calibration standards used, in some cases, were completely inappropriate for the work being undertaken, and (3) the nuclear decay data utilised by many laboratories (and in some cases, supplied by reputable manufactures) were either of an old vintage or incorrect. Over the years, the situation has changed somewhat in that participants are more aware of the pitfalls of measuring radioactivity. Finally, the effect that this has had on NPL's activities in the area of radionuclide metrology will also be described.