Abstract
The JRC applied six measurement techniques to standardise the activity of an 241Am solution in the frame of the 2003 key comparison CCRI(II)-K2.Am-241. The methods used were alpha-particle counting at a defined small solid angle, high-efficiency particle and photon counting with a windowless 4π CsI(Tl) sandwich spectrometer, 4π alpha counting with a pressurised proportional counter, alpha-gamma coincidence counting and sum counting with a small pressurised proportional counter and a NaI(Tl) well detector, and 4π counting with a liquid scintillation counter. All results were consistent and an unusually low measurement uncertainty of 0.054% was achieved. An overview is presented of the outcome of the key comparison exercise, which demonstrates international equivalence.
Highlights
Through Key Comparisons, National Metrology Institutes (NMIs) with advanced measurement capabilities for accurate radioactivity measurements demonstrate international equivalence of their activity standards and contribute to a common definition of the SI-derived unit becquerel [1]
In the period 2002–2003, an unusually large amount of CCRI(II) key comparisons were held in which samples from a radioactive solution were distributed to NMIs and the results of their activity measurements were collected by the BIPM and directly compared [5]
Since there is no objective arbiter in interlaboratory comparisons at the highest level of metrological accuracy, the Key Comparison Reference Value (KRCV) is a consensus value derived from the activity concentration values provided by the participating laboratories
Summary
Through Key Comparisons, National Metrology Institutes (NMIs) with advanced measurement capabilities for accurate radioactivity measurements demonstrate international equivalence of their activity standards and contribute to a common definition of the SI-derived unit becquerel [1]. The major correction was due to self-absorption of the alpha particles inside the source material and substrate (VYNS + gold) This contribution was examined by performing additional measurements after covering the sources with an extra foil of the same composition and thickness. An uncertainty of 0.2% was assigned to the self-absorption correction, and in the same order of magnitude, 0.21% was attributed to the extrapolation of the energy spectrum to compensate for the non-recorded fraction of events below the discrimination level (Fig. 6) This resulted in a combined uncertainty of 0.3%. The busy-period signals from the MCA are processed by the second live-time clock gate of the same LGN unit This redundant count rate is used as a check value only. A reconstruction is made on the basis of three pieces of information: (1) an anonymised preliminary graphics file containing most of the measurement results by different methods obtained from BIPM through a private communication, (2) a more official version of the graph in pdf format
Sign-in/Register to view highlights & summary 
Published Version (
Free)
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call