Nonetheless, Figure clearly reveals that any considered thresholds are undercut frequently. This is why in some cases, gold nanostructure formation is regarded as a benchmark experiment for successfully sealed liquid cells. To investigate the existence of an experimentally relevant threshold for gold precipitation in HAuCl4-solution under exposure with ionizing irradiation, a 20 mM HAuCl4-solution was exposed to a Cu Kα X-ray beam. With roughly 1 Gy s -1 , this experiment was performed at a dose rate of about nine orders of magnitude below the lowest dose rate depicted in peaks match well to lattice planes of gold. Another ultra-low dose rate-mediated reductive gold synthesis was conducted for 42 h while repeatedly performing in situ XRD scans in 2 h intervals with a temporal resolution of 20 min (Figure ). An apparent increase in diffraction peak intensity with continuous irradiation is obtained. The visible peak splitting is due to incomplete monochromatization, which led to two diffraction peaks for Kα1 and Kα2, respectively. Additionally, due to the geometry of the liquid cell, the sample thickness could only be approximated roughly, leading to a slight shift in the peak baseline. Nevertheless, the obtained Bragg peaks match literature values for fcc gold. Notably, the first indication of peaks related to gold is visible even after the first measurement, indicating that irradiation-induced gold reduction is not negligible during liquid-phase X-ray studies. This agrees with reports on X-ray-mediated gold reduction within minutes. electron irradiation are available, more general g-values acquired for low-linear energy transfer (LET) radiation such as photons are used here. In contrast to kinetic simulations describing LP-TEM conditions, a steady-state condition is neither obtained within milliseconds nor for the duration of the experiment. Instead, a constant increase of Au 0 over hours is expected until the system saturates in a steady state where almost all gold is reduced to pristine Au. As Au 0 is insoluble in water, it is expected to precipitate immediately. Furthermore, surfaces providing nucleation sites or seed crystals are known to support this process (heterogeneous nucleation). Thus, this simulation agrees with the constant increase in diffraction peak intensities presented in Figure .