After more than thirty years a new key comparison of thermal neutron fluence measurements was organized by section III of CCRI. The comparison was carried out by rotating four transfer instruments among the four participants (CIAE, PTB, NMIJ and NPL).The stability of the detectors was repeatedly verified by the pilot laboratory between the measurements. Each of the four transfer devices had a different dependence of the fluence response on the neutron energy. Hence the comparison was also sensitive to the knowledge of the spectral distributions of the facilities used by the participants for their measurements. The results of the comparison showed signs of inconsistencies which could not be resolved during the analysis. Therefore the arithmetic mean of the results was used to calculate the key comparison reference value. Main text. To reach the main text of this paper, click on Final Report. Note that this text is that which appears in Appendix B of the BIPM key comparison database kcdb.bipm.org/.The final report has been peer-reviewed and approved for publication by the CCRI, according to the provisions of the CIPM Mutual Recognition Arrangement (CIPM MRA).
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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