# Simultaneous SAXS/SANS Method at D22 of ILL: Instrument Upgrade
## 2 Materials and Methods  
An advanced SAXS system based on a Copper/Molybdenum (K\({}_{\alpha}\); 8.0/17.4 keV) switchable microfocus rotating anode X-ray generator (Rigaku MM007 HF DW) and a Dectris EIGER2 X 1M detector with a continuously variable sample-to-detector distance (SDD\({}_{\rm X-ray}\)) from 0.55 m up to 1.63 m in a vacuum tube is dimensionally suitable for installation on the D22 SANS instrument at ILL (Figure 1). For Cu K\({}_{\alpha}\) radiation of 8 keV (\(\lambda\approx\) 0.1540 nm wavelength), the absolute value of the scattering vector \(q\) can be selected to range between 0.005 and 0.5 A\({}^{-1}\) by the SDD\({}_{\rm X-ray}\). Due to the unsuitability of copper radiation for iron containing samples (such as magnetite, maghemite, and hematite) and for reaching higher penetration depths, the X-ray source can easily be switched to Mo K\(\alpha\) radiation of 17.4 keV. The short wavelength (0.071 nm) of the Mo radiation also allows the \(q\) range of the SAXS instrument to be extended [23]. With a Rigaku VariMaxTM beam divergence control (BDC) system mounted on the X-ray source, the dual wavelength (Cu and Mo) optics can be operated. A control software can be used to automate the VariMax DWTM optics when changing from one X-ray source to the other, so that the operation of the whole system can proceed easily. A collimation length of approximately 56 cm is composed of three different types of slits. The first tungsten carbide slit suitable for both Cu and Mo radiation is placed directly after the mirror on the source, however, two scatterless slits (JJ X-ray) are positioned at the end of the collimation. The last two scatterless slits, either silicon (used for Cu radiation) or GaAs (used for Mo radiation), define the divergence of the primary beam. The whole assembly (X-ray source, optics and collimation system) can be moved along three axes (x, y, z), enabling a fine tune of the X-ray beam position, so that both the X-ray and neutron beam can be superimposed at the same sample position. The beam size (FWHM) of 0.5 \(\times\) 0.5 mm at the sample position provides a flux of approximately 1.5 \(\times\) 10\({}^{7}\) photons/s (Cu source). The components of the system are mounted on a standalone metal rack that makes it easily movable for use on the D22 instrument. The floor of the experimental zone is equipped with an adjustable metal support, allowing fast and precise positioning of SAXS system. Via a plug-and-play operation, the instrument can be used within half an hour following the installation process (1 h). NICOS control software (MLZ), combined with a TANGO environment, is used to control the whole instrument, including the motors and the SAXS data detection system. A goniometer (Huber) with six degrees of freedom is employed to achieve movements of the sample. The sample is typically positioned at 45\({}^{\circ}\) relative to both of the orthogonal X-ray and neutron beams. Following the sample position, an evacuated detector tube hosts a double energy threshold EIGER2 X 1M detector (pixel size = 75 \(\times\) 75 \(\upmu\)m\({}^{2}\)). No beam stop is required to attenuate the direct beam, thus enabling investigations with direct beam intensity at the detector (no beam-stop shadow). We refer readers to our previous work [23] for more details on the instrument specifications. Background intensity measurements at the X-ray detector were measured at different experimental conditions, including neutron collimation lengths and SDD\({}_{\rm X-ray}\). Upon installing an optimized lead shielding arrangement on the metal chassis of SAXS setup, as well as employing a double energy threshold detector, the overall background reduction factor was evaluated compared with both the unshielded SAXS instrument and a single energy threshold detector. An extensive preliminary test prior to the latest instrumental upgrade was performed. The current results on background suppression demonstrate the achievements of increasing the signal-to-noise ratio on the X-ray detector.