Neutron imaging has been demonstrated to be a powerful tool to measure the in situ water content of commercial proton exchange membrane fuel cells (PEMFCs) in two and three dimensions. The National Institute of Standards and Technology neutron imaging facility was designed to produce a high intensity, highly collimated neutron imaging beam to measure the water content of operating fuel cells. The details of the neutron optics and neutron detection are discussed in terms of the random uncertainty in measuring the liquid water thickness that is typical of operating PEMFCs.

We report on the development of a fast neutron detector using a liquid scintillator doped with enriched 6 Li. The lithium was introduced in the form of an aqueous LiCl micro-emulsion with a di-isopropylnaphthalene-based liquid scintillator. A 6 Li concentration of 0.15 % by weight was obtained. A 125 mL glass cell was filled with the scintillator and irradiated with fission-source neutrons. Fast neutrons may produce recoil protons in the scintillator, and those neutrons that thermalize within the detector volume can be captured on the 6 Li. The energy of the neutron may be determined by the light output from recoiling protons, and the capture of the delayed thermal neutron reduces background events. In this paper, we discuss the development of this 6 Li-loaded liquid scintillator, demonstrate the operation of it in a detector, and compare its efficiency and capture lifetime with Monte Carlo simulations. Data from a boron-loaded plastic scintillator were acquired for comparison. We also present a pulse-shape discrimination method for differentiating between electronic and nuclear recoil events based on the Matusita distance between a normalized observed waveform and nuclear and electronic recoil template waveforms. The details of the measurements are discussed along with specifics of the data analysis and its comparison with the Monte Carlo simulation.

Results of International Key Comparisons of National MeasurementStandards provide the technical basis for the Mutual Recognition Arrangement (MRA) formulated by Le Comité International des Poids et Mesures (CIPM). With many key comparisons already completed and a number of new key comparison experiments currently under way, we now have a better understanding of the statistical issues that need to be addressed for successfully analysing data from key comparisons and making proper interpretations of the results. There is clearly a need for a systematic approach to statistical analyses of key comparison data that can be implemented routinely by all participating laboratories.The determination of a key comparison reference value (KCRV) and its associated uncertainty and the degrees of equivalence are the central tasks in the evaluation of key comparison data. A satisfactory definition of a KCRV, however, is based on the assumption that all laboratories are estimating the same unknown quantity of the common circulating artefact, that is, the results from the different laboratories are mutually consistent. In this paper, we compare a number of statistical procedures for testing the consistency assumption.

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