Choice of scans in neutron diffraction

Neutron-diffraction experiments on single-crystal samples are generally carried out using either an ω-scan (crystal rotating, detector fixed) or a θ–2θ scan (detector coupled 2:1 to the crystal). In order for the center of the diffracted beam to enter the detector on its centerline at all angular settings of the crystal during the scan of a Bragg reflection, neither of these conventional scanning techniques is optimum. A formula is derived which gives the optimum coupling between the detector and the crystal motions, and it is suggested this mode of scanning should be implemented in performing neutron-diffraction experiments on single crystals.