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A high-resolution neutron diffraction investigation of a nickel powder sample at room temperature was performed at three different experimental geometries using the ASTACUS diffractometer at Otaniemi. In spite of the correlation between adjacent channels, the diffraction patterns were analysed by the ordinary profilerefinement procedure adapted especially to the present conditions. The correctness of the results was supported by an analysis of the integrated intensities. The weighted mean value for the Debye-Waller parameter, BNi, of 0.425 (+0.065) A 2 was in reasonable agreement with literature values.

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One of the problems arising in profile analyses of white-beam powder diffraction experiments is that in order to assess the reliability of the refined structure parameters allowance must be made not only for errors in the actual powder data but also for uncertainties in the various wavelength-dependent corrections involved. As a means for such assessments the present work provides a general method in which the incident white neutron flux spectrum is assumed to be measured and combined with the other wavelength-dependent factors to form a set of effective incident intensities with known statistical properties for the diffraction peaks. Given that appropriate models are used for both the powder spectrum and the effective fluxes, the unknown model parameters and their accuracies can be estimated optimally through a single least-squares fit of the available experimental data. By applying the formalism to a real nickel powder measurement, it was shown that the precision of the parameter estimates may depend considerably on the errors of the wavelength-dependent corrections, unless these are known with much higher accuracies than the diffraction pattern. In the example this proved true especially for the scale factor and the temperature factor.