On the use of in‐pile collimators in inelastic neutron scattering

The influence of an in-pile collimator is shown for two cases: A. Divergence α0 of the incoming beam large compared to the mosaic width η of the monochromating crystal and the divergence α1 after the crystal (α0 > η, α1). B. 2η > α0, α1. If the same energy resolution for a three-axis spectrometer is required, an optimized comparison of the counting rates in these two cases reveals a factor of two in favour of case B. This is an important reduction in measuring time for investigations of horizontal dispersion branches, for quasielastic and incoherent scattering, where only the energy (no momentum) resolution is concerned.