This paper deals with the problem of establishing degrees of equivalence for national measurement standards participating in regional key comparisons (RMO KC), with respect to a key comparison reference value (KCRV), using measurement results obtained by linking national metrology institutes (NMIs). Two types of key comparisons are considered, which differ in applying either a material measure or a measuring instrument as a travelling measurement standard.The results obtained by linking NMIs are used to determine transformation procedures for measurement results of the RMO KC so that the transformed results can be compared directly with CIPM KC results.Formulae are given for evaluating the degrees of equivalence of the national measurement standards of laboratories participating in the RMO KC, with respect to the KCRV, taking into account possible correlations between measurement results.

To ensure the validity of their national standards, National Metrology Institutes, NMIs, participate regularly in international comparisons. In the area of neutron metrology, Section III of the Consultative Committee for Ionizing Radiation is in charge of the organization of these comparisons. From September 2011 to October 2012, the eleventh key comparison, named CCRI(III)-K11, took place at the AMANDE facility of the LNE-IRSN, in France. Participants from nine NMIs came with their own primary reference instruments, or instruments traceable to primary standards, with the aim of determining the neutron fluence, at 1 m distance from the target in vacuum, per monitor count at four monoenergetic neutron fields: 27 keV, 565 keV, 2.5 MeV and 17 MeV. The key comparison reference values (KCRV) were evaluated as the weighted mean values of the results provided by seven participants. The uncertainties of each KCRV are between 0.9 % and 1.7 %. The degree of equivalence (DoE), defined as the deviation of the result reported by the laboratories for each energy from the corresponding KCRV, and the associated expanded uncertainty are also reported and discussed.

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