Abstract
The certification of a new standard reference material for small-angle scattering [NIST Standard Reference Material (SRM) 3600: Absolute Intensity Calibration Standard for Small-Angle X-ray Scattering (SAXS)], based on glassy carbon, is presented. Creation of this SRM relies on the intrinsic primary calibration capabilities of the ultra-small-angle X-ray scattering technique. This article describes how the intensity calibration has been achieved and validated in the certified Q range, Q = 0.008-0.25 Å-1, together with the purpose, use and availability of the SRM. The intensity calibration afforded by this robust and stable SRM should be applicable universally to all SAXS instruments that employ a transmission measurement geometry, working with a wide range of X-ray energies or wavelengths. The validation of the SRM SAXS intensity calibration using small-angle neutron scattering (SANS) is discussed, together with the prospects for including SANS in a future renewal certification.
Highlights
Introduction and backgroundSmall-angle X-ray and neutron scattering (SAXS and small-angle neutron scattering (SANS)) methods are widely used to achieve a quantitative microstructure characterization that is statistically representative of a given sample material
In the sections that follow, we describe how the glassy carbon calibration NIST Standard Reference Material (SRM) 3600 was selected and a calibration standard inventory established
We describe the development and certification of the absolute intensity calibration curve for Small-Angle X-ray Scattering (SAXS) dÆ/d versus Q using ultra-small-angle X-ray scattering (USAXS) measurements, together with evaluation of the associated uncertainties attributable to repeated measurement, sample variability and instrument setup
Summary
Small-angle X-ray and neutron scattering (SAXS and SANS) methods are widely used to achieve a quantitative microstructure characterization that is statistically representative of a given sample material. An ion chamber placed before the sample records any temporal variations in the incident beam flux and is used to normalize out any corresponding temporal fluctuations in the photodiode signal not associated with the sample These instrument attributes permit direct ‘primary’ calibration of the scattering intensity based on the fundamental definition of the differential scattering cross section per unit sample volume, dÆ/d, defined as the probability per unit incident X-ray flux and per unit sample volume of scattering into unit solid angle about a Figure 1 Schematic of APS USAXS measurement, Argonne National Laboratory. An inventory of SRM units is prepared, for which measurements of the desired property traceable to NIST primary standards have been made, complete with a full evaluation of the sources of uncertainty and their magnitudes (Taylor & Kuyatt, 1994)
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