ISSN:
1600-5724
Source:
Crystallography Journals Online : IUCR Backfile Archive 1948-2001
Topics:
Chemistry and Pharmacology
,
Geosciences
,
Physics
Notes:
For the case where the rotation axis of the monochromator crystal and that of the small specimen crystal are parallel, i.e. (+, −) or (−, +) configuration, the apparatus function in two-dimensional Δω, Δ2θ space is associated with the source, S, the monochromator crystal, M, and an idealized specimen crystal, c, which is vanishingly small and has zero mosaic spread. For any value of t (= tan θc/tan θM), the apparatus function is a product of the distributions (with their respective loci of translation) of: (i) the emissivity of S; (ii) the reflectivity over the length of M; (iii) the mosaic spread of M; and (iv) the wavelength band arising from the vector addition in Δω, Δ2θ space of the wavelength dispersion of M and of c. To combine the apparatus function with other components such as the mosaic spread of a real specimen crystal, its physical dimension, the size of the aperture in front of a quantum detector or the point-spread function of a position-sensitive detector, the appropriate mathematical operation in Δω, Δ2θ space is sequential convolution. Examples are given, for t = 0 (0.25) 1.0 (0.5) 2.0, of synthetic apparatus functions based on typical dimensions appropriate to neutron diffraction experimental arrangements. These are presented in Δω, Δ2θ(0) space, which corresponds to ω-scan data collection. The advantage of modifying these by affine transformation to Δω, Δ2θ(2) space or, equivalently, to correspond to ω–2θ-scan data collection, is demonstrated.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1107/S0108767393001060
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