A flux- and background-optimized version of the NanoSTAR small-angle X-ray scattering camera for solution scattering

Abstract

A commercially available small-angle X-ray scattering camera, NanoSTAR from Bruker AXS, has been modified to optimize its use for weakly scattering solution samples. The original NanoSTAR is a pinhole camera with two Göbel mirrors for monochromating and making the beam parallel, and with a two-dimensional position-sensitive gas detector (HiSTAR) for data collection. The instrument has one integrated vacuum. It was constructed for position-resolved studies and thus has a small beam size at the sample position. In the present work, the instrumental configuration has been optimized by numerical calculations based on phase-space analysis and Monte Carlo simulations in order to obtain a higher flux. This has led to a setup in which the beam at the sample is larger and the collimation part of the instrument is longer, so that divergence of the beam is similar to that of the original camera. An extra pinhole is included after the Göbel mirrors to make the beam size well defined after the mirrors. The camera thus has genuine three-pinhole collimation. The use of electron-microscope pinholes minimizes parasitic scattering. At the University of Aarhus, the modified camera is installed on a powerful rotating-anode X-ray source (MacScience 6 kW Cu with a 0.3 × 0.3 mm effective source size). Measurements have been performed on a wide variety of weakly scattering samples, such as surfactant micelles, homopolymer solutions, block copolymer micelles, proteinsetc. The data are routinely converted to absolute scale using the scattering from water as a primary standard. The standard configuration covers the range of scattering vectors from 0.01 to 0.35 Å−1with a flux of 1.7 × 107photons s−1for CuKα radiation at a generator power of 4.05 kW. The camera is easily converted to a high-resolution version covering 0.0037 to 0.22 Å−1with a loss of flux of about a factor of 10, as well as to a position-resolved version.