# Simultaneous SAXS/SANS Method at D22 of ILL: Instrument Upgrade
## 3 Results and Discussion
### Reduction of the Gamma Background by Lead Shielding  
10 cm thick lead metal sheets were attached to the concrete walls towards the neighboring IN15 and WASP instruments to reduce the gamma radiation at the SAXS detector position in the D22 experimental zone. Additionally, several lead shielding walls were constructed and installed on the class of the SAXS instrument (Figure 1). The shielding walls include (i) a cone-shaped wall (nose) of lead-based material in front of the detector vacuum chamber, (ii) a lead wall along the final neutron collimation line, and (iii) a lead wall on the side of SAXS vacuum chamber. The current design has been pre-tested so that the X-ray detector inside the vacuum chamber is appropriately shielded from radiation for all possible positions of the X-ray detector in the detector tube. In the photograph of Figure 1, the installed lead-based shielding walls attached to the SAXS chassis are visible. A double-energy threshold EIGER 2 X 1M detector replacing a single-energy threshold EIGER R 1M detector is currently in operation and has been placed inside the vacuum chamber of the SAXS system. It allows the use of an upper and a lower adjustable energy discriminator (for instance, at 4 keV and 10 keV) to select a sensitive energy range close to the characteristic energy of the employed X-ray source (Cu K\({}_{\alpha}\) 8 keV). Here, background measurements were recorded for two extreme configurations of neutron collimation lengths, referred to in the following as'short' (2.8 m) and 'long' (17.6 m). The SAXS background measurements were performed inside the D22 zone using the single-energy (4 keV) and the double-energy threshold (4 and 10 keV) modes for both the lead shielded and the unshielded SAXS instrument. The unshielded system represents a configuration where the lead shielding walls i, ii, and iii (cf. Figure 1) are not installed. From the data visualized in Figure 2, it can be concluded that the detected background signal can be substantially reduced by the lead shielding for both neutron collimation lengths (2.8 and 17.6 m). Further reduction of the background can be achieved by switching the X-ray detector from the single-energy threshold mode (th1 mode: 4 keV, dashed area) to the difference mode (diff mode: 4-10 keV, solid area) (cf. Figure 2). Measurements were performed for both the short (SD1 = 0.55 m red bars) and the long (SD2 = 1.64 m blue bars) SSD\({}_{\text{X-ray}}\) of the SAXS system. The achieved total background SFs are summarized in Table 1.  
Figure 1: **(a)** Three lead shielding walls: (i) a cone of lead-based material, (ii) lead wall along the final part of the neutron collimation line, and (iii) a lead wall (2 tons) along the vacuum chamber of the X-ray detector. The shielding walls can be easily craned and then firmly attached to the metal chassis of the SAXS setup. Red and yellow arrows indicate the directions of the X-ray and neutron beams, respectively. The unshielded SAXS instrument (detector) represents a configuration where the lead shielding walls i, ii, and iii are not implemented during SAXS operation. A double-energy threshold X-ray detector was placed inside the vacuum tube, replacing the previously employed single-energy threshold detector. (b) A zoomed-in detail of the sample environment of the SAXS/SANS instrument, displaying a sample at an angle of 45\({}^{\circ}\) relative to both of the orthogonal neutron and X-ray beams. Figure 2: Background intensity collected using EIGER2 X 1M detector while neutron shutter is opened for two different neutron collimation lengths (2.8 m and 17.6 m). Two measurements for the single-energy threshold mode (dashed area, th1 mode = 4 keV) and two for the double-energy mode (solid area, diff = 4–10 keV) were performed for both the shielded and unshielded SAXS instrument. All background measurements were repeated for short (red, SD1 = 0.55 m) and long (blue, SD2 = 1.63 m) SDD\({}_{\text{X-ray}}\). Lab environment data are based on background intensity measurements while the reactor power was off.