Measurements of Resolution vs. Wavelength

The spectrometer response is measured using a purely elastic coherent scatter (e.g., Grafoil, Carbopack, carbon black). If there were no magnetic field integral inhomogeneities, the response would remain at unity out to the highest possible fields. The effect of these inhomogeneities (to decrease the polarization at the echo point) increases with the number of precessions the neutrons undergo, that is, with increasing field and increasing wavelength.

The upper plot shows on a log-log scale the wavelength dependence of the resolution function. The color-coded lines show the time limit imposed by the maximum field integral of the spectrometer.

The lower plot shows the resolution as a function of the Fourier time scaled by the inverse cube of the wavelength. The effect of instrumental inhomogeneities will be greater at the longer wavelengths as the number of precessions for a particular field setting will be greater.