Slit smearing effects in the Bonse–Hart small-angle X-ray diffractometer

Abstract

Slit smearing effects have been experimentally investigated for a typical Bonse-Hart small-angle diffractometer. This instrument was found to satisfy the cl iteria for infinite slit-height configuration for a wide range of angular divergence-limiting schemes. Standard mathematical desmearing methods applied to the data show excellent agreement with scattering data obtained from an essentially slit-correctionless instrument.* Note added in proof :-Fedorov et al. (1969) have employed such a method to check slit-correction procedures in the Kratky camera.

Everything SAXS: small-angle scattering pattern collection and correction

“…Desmearing of the data is therefore required, unless effort and intensity is expended to collimate the beam in the perpendicular direction as well [105,65]. An additional drawback to these instruments is the requirement for a step-scanning evaluation of the scattering curve 5 , which increases measurement times considerably.…”

“…instruments discussed in sections 2.2.2 and 2.2.3), though model smearing rather than data desmearing is still recommended [65,151]. As slit-smeared instruments have existed as long as small-angle scattering itself, desmearing procedures are available of many types and vintages.…”

“…While a large variety of crystalline materials can be used in the instrument, the channel-cut crystals are usually made from either silicon or germanium due to their high degree of crystalline perfection over large sizes [5]. These crystals have Darwin widths (FWHM) for the common (111) and (220) x-ray reflections of about 0.0002 • , thus defining the q-resolution for most such instruments to be about 0.001 nm −1 (where the multiple reflections do not change the Darwin width, but improve the off-reflection rejection) [26,178,40,65,106]. When a higher resolution is required, for example to measure larger structures, the combination of high-energy and higher-order crystalline reflections can lead to a ten-fold increase in resolution [82].…”

“…Through rotation of the analyser crystal, the scattered intensity at various angles can be evaluated with an extremely high angular precision or resolution. A few standalone instruments have been constructed on synchrotrons [26,40,84,81], and several more have been built as complementary instruments around laboratory x-ray sources (tube-as well as rotating anode sources) [17,65,106,26].…”

Comparison of small angle X-ray scattering data obtained under different collimation conditions

“…Other tests (Schmidt, 1970;Kent & Brumberger, 1970) have compared the curves obtained by applying different correction methods to the same scattering curve, which was usually a theoretical test function but which in one case (Schmidt, 1970) was an experimental curve. Gravatt & Brady (1969) have succeeded in obtaining a scattering curve for essentially perfect collimation. Although the intensity was very low, the curve agreed well with the corrected curve obtained for the same sample with an apparatus for which the slit length could be considered infinite.…”