# X-ray-Induced Heating in the Vicinity of the X-ray Interaction Point
## 1 Introduction  
Intense X-ray sources can cause radiation damage to samples, creating undesirable artifacts [1; 2; 3; 4]. In macromolecular crystallography, radiation can cause specific chemical and structural damage and errors in the interpretation of the resulting structure [2]. In addition, the energy absorbed by the X-rays increases the temperature of the sample [5]. In particular, dose-rate-dependent damage can have the effect of heating a crystal sample [6]. The X-ray-induced temperature increase of a sample can have a significant effect on the structural data collection at room temperature [7]. Serial crystallography (SX) using X-ray free electron lasers (XFEL) or synchrotron X-rays enables the determination of the room-temperature structure of macromolecules [8; 9; 10]. In serial femtosecond crystallography (SFX) using XFEL, crystal samples are exposed to X-ray pulses for several tens of femtoseconds [9; 11; 12]. In serial synchrotron crystallography (SSX) using synchrotron X-rays, crystals are exposed to X-rays for several picoseconds to hundreds of milliseconds [13; 14; 15]. SX techniques have reduced X-ray radiation damage compared to conventional macromolecular crystallography (MX) because the exposure time to the crystal is shorter [16; 15]. In addition, SX techniques with pump-probe experiments using optical lasers or mix-and-inject experiments can visualize time-resolved molecular reactions, providing a more detailed structure-based molecular mechanism [17; 18]. Therefore, SX provides structural information with higher biological accuracy than conventional MX [19]. In SX experiments, a large number of crystals are continuously delivered to the X-ray point using a sample delivery method, such as a liquid injector [20; 21; 22], injector/syringewith a viscous medium [23; 24; 25; 26; 27], fixed-target scanning method [28; 29; 30; 31; 32], and hybrid methods [33; 34; 35; 36; 37]. For liquid jet injection methods, such as a gas dynamic virtual nozzle (GDVN) or liquid jet injectors, the crystal suspension is delivered at a high flow rate (0.1-10 \(\upmu\)L/min) to generate a stable injection stream [38]. For injector/syringes with a viscous medium, crystals embedded in the viscous medium provide a stable injection stream at a low flow rate, which is useful for applications in synchrotron or XFEL facilities with low repetition rates [23; 24; 25; 26; 27]. When SX sample delivery method uses an injector or syringe, one location in the injection stream is continuously exposed to X-rays. In a fixed-target scanning method, diffraction data are collected when the sample holder containing the crystal sample is raster-scanned [28; 29; 30; 31; 32]. Sample holders made of silicon [39], silicon nitride [28; 40], Mylar [41], nylon mesh [31], and polyimide [31; 42] or polymers [43; 44] have been used previously. In a fixed-target SFX experiment, the sample holder is exposed to X-rays according to the XFEL repetition rate [31; 41; 43]. In a fixed-target SSX, the sample holder is continuously exposed to X-rays if the shutter is not used [45]. During an SX experiment, crystal samples are exposed only once as they continuously pass through the X-ray interaction point; however, because one point is continuously exposed to the X-rays, it is expected that energy absorption by the sample or its container would affect the temperature around the sample when the speed of the sample delivery is low. Several investigations have been conducted on radiation damage and the effect of heating at sample locations exposed to X-rays [5; 7], but little is known about the heating effect in the vicinity of the X-ray interaction point. Here, we investigated the temperature change near the X-ray interaction point. An increase in temperature was observed in the solutions in the capillary or on metal plates when in the vicinity of the X-ray-exposed area. Additionally, the effect of distance to the X-ray exposure point on heat transfer and the reduction in the rise of the temperature using the shutter were investigated.