|
International
Tables for Crystallography Volume F Crystallography of biological macromolecules Edited by M. G. Rossmann and E. Arnold © International Union of Crystallography 2006 |
International Tables for Crystallography (2006). Vol. F. ch. 6.2, p. 137
Section 6.2.1.5. Instrument resolution functions
a
Life Sciences Division M888, University of California, Los Alamos National Laboratory, Los Alamos, NM 8745, USA, and bSmall Angle Scattering Facility, Australian Nuclear Science & Technology Organisation, Physics Division, PMB 1 Menai NSW 2234, Australia |
For accurate data collection, the instrument smearing contribution to the data must be known with some certainty, particularly when data are collected over an extended range with multiple instrument settings. A balance must be struck between instrument smearing and neutron flux at the sample position; however, careful instrument design can produce: (i) a good signal-to-background ratio, thereby partially offsetting the flux limitation, and (ii) facilities and procedures for determining the instrument resolution function (Johnson, 1986![[link]](/graphics/greenarr.gif)
).
As an example, instrumental resolution effects in the small-angle neutron scattering (SANS) technique have been investigated in some detail. A `typical' SANS instrument is located on a cold neutron source with an extended (and often variable) collimation system. The sample is as large as possible and the detector is large with low spatial resolution. The instrument is best described by pin-hole geometry. Three major contributions to the smearing of an ideal curve are: (i) the finite λ, (ii) ![[\Delta \lambda/\lambda]](/teximages/fach6o2/fach6o2fi15.svg)
of the beam and (iii) the finite resolution of the detector. Indirect Fourier transform, Monte Carlo and analytical methods have been developed to analyse experimental data and predict the performance of a given combination of resolution-dependent elements (e.g. Wignall et al., 1988; Pedersen et al., 1990; Harris et al., 1995).
References
Harris, P., Lebech, B. & Pedersen, J. S. (1995). The three-dimensional resolution function for small-angle scattering and Laue geometries. J. Appl. Cryst. 28, 209–222.Google Scholar
Johnson, M. W. (1986). Editor. Workshop on neutron scattering data analysis. Rutherford Appleton Laboratory, Chilton, England. Bristol: Institute of Physics.Google Scholar
Pedersen, J. S., Posselt, D. & Mortensen, K. (1990). Analytical treatment of the resolution function for small-angle scattering. J. Appl. Cryst. 23, 321–333.Google Scholar
Wignall, G. D., Christen, D. K. & Ramakrishnan, V. (1988). Instrumental resolution effects in small-angle neutron scattering. J. Appl. Cryst. 21, 438–451.Google Scholar
