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Figure 1
Sketch of the neutron setup. The external magnetic field H0 ∥ ez is applied parallel to the wavevector k0 of the incident neutrons. In the small-angle approximation, the momentum-transfer or scattering vector, q = k1 − k0, varies in the plane perpendicular to k0, i.e. q ≅ {qx, qy, 0} = q {cos θ, sin θ, 0}. The magnitude of q for elastic scattering is given by q = (4π/λ) sin (ψ/2), where λ denotes the mean neutron wavelength (selected by the velocity selector) and ψ is the scattering angle. The angle θ specifies the orientation of q on the two-dimensional detector.

IUCrJ
Volume 7| Part 1| January 2020| Pages 136-142
ISSN: 2052-2525
https://doi.org/10.1107/S2052252519016439