International
Tables for
Crystallography
Volume C
Mathematical, physical and chemical tables
Edited by E. Prince

International Tables for Crystallography (2006). Vol. C, ch. 2.9, pp. 128-129

## Section 2.9.5. Experimental methodology

G. S. Smitha and C. F. Majkrzakb

aManuel Lujan Jr Neutron Scattering Center, Los Alamos National Laboratory, Los Alamos, NM 87545, USA, and bNIST Center for Neutron Research, National Institute of Standards and Technology, Gaithersburg, MD 20899, USA

### 2.9.5. Experimental methodology

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Neutron reflectivity measurements can be carried out in two principal ways: either (1) with a monochromatic incident beam of narrow angular divergence in the plane of reflection (defined by and where λ is constant, and Q is varied by changing the glancing angle of incidence, θ, relative to the sample surface; or (2) using a pulsed polychromatic incident beam, also of narrow angular divergence at fixed , and obtaining data over a range of Q values simultaneously by performing time-of-flight analysis on the reflected neutrons. For either method, the instrumental resolution is simply given as where Δ is the angular divergence of the reflected beam, and Δλ is the wavelength spread. In the case of a steady-state source, the wavelength resolution is determined by the monochromator, whereas the timing and moderator characteristics determine the wavelength resolution on a time-of-flight instrument. Although the second term in equation (2.9.5.1) is standard in scattering, it has a unique characteristic, in that the angular divergence of the reflected beam determines the resolution. This is the case because the sample is a δ-function scatterer, so that the angle of the incident beam can be determined precisely by knowing the reflected angle (Hamilton, Hayter & Smith, 1994). For a more complete description of both types of neutron reflectometry instrumentation, see Russell (1990).

### References

Hamilton, W. A., Hayter, J. B. & Smith, G. S. (1994). Neutron reflectometry as optical imaging. J. Neutron Res. 2, 1–19.
Russell, T. P. (1990). X-ray and neutron reflectivity for the investigation of polymers. Mater. Sci. Rep. 5, 171–271.