Uncertainty on the wave vector transfer

In ideal conditions, the (elastic) wave vector transfer q is related to the incident wave vector k0 and to the scattering angle 0 by the equality [see (6.3.18)] 

For a given experiment 5k0/k0 is determined by the quality of the incident beam and 50 by a compromise between luminosity and resolution of the diffractometer. The result (6.5.4) indicates that Sq increases when the diffraction angle 0 decreases there exists a qmin for which Sq — qmin. For values of q smaller than qmiB, the resolution becomes rather poor. Thus, the reciprocal space interval which can be used by the experimentalist is limited by instrumental widths and in particular by 50. For a neutron diffractometer, we have, typically, 

The reciprocal space domain also has an upper bound. Actually, for 0 = it, we have [see (6.5.3)] 

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