## 3 Results and Discussion  
### Test of Photon Counting Imaging in Space  
Our Wide-angle Aurora Imager has been in orbit for over six years. The detector utilizes the photon counting detector described in this paper, although it adopts more conventional Al shielding measures. Instead of a local protective box, the electronics box uses an overall Al thickening measure. So far, no changes to the function or performance of electronic devices due to TID have been noticed. To observe the transient disturbance of charged particles on the detector, a dark background test was performed within the SAA region. Figure 6 presents six dark background images taken by two sets of photon-counting imaging detectors before and after the FY-3D satellite passed through the SAA. Further information regarding the scientific instrument can be found in our previously published articles [20; 21]. The dark background images were taken in the absence of incident photons, which determines the detection system's lower limit of dynamic range. The images were captured at a latitude and longitude of (14.26\({}^{\circ}\) N, 53.95\({}^{\circ}\) W) prior to the satellite entering the SAA region, as seen in Figure 6b,c. The exposures were 50, and the dark count rates ranged from 0 to 10 kcps. However, the dark count rates increased drastically when the satellite was in the SAA region, reaching a range of 10 kcps to 20 kcps, as displayed in Figure 6h, due to the radiation effect of the high-energy charged particles. Figure 6d,e depicts a single-exposure image taken at (20.42\({}^{\circ}\) S, 61.79\({}^{\circ}\) W). The number of bright spots in the image increased significantly, with even the presence of irregular \begin{table}
\begin{tabular}{c c c c c} \hline \hline
**Materials** & **Density** & **Atomic Number (Z)** & **Atomic Weight (A)** & **Z/A** \\ \hline Aluminum (Al) & 2.7 g/cm\({}^{3}\) & 13 & 26.98 g/mol & 0.48 \\ High-Density & 0.95 g/cm\({}^{3}\) & 2.25 & \(\star\) & \(\star\) \\ Tantalum (Ta) & 16.6 g/cm\({}^{3}\) & 73 & 180.95 g/mol & 0.40 \\ \hline \hline \end{tabular} \({}^{\star}\)The atomic weight of polyethylene cannot be defined as it is a polymer composed of repeating units of ethylene monomer (C2H4).  
\end{table} 
Table 1: Parameters of three materials. bright lines. Correspondingly, Figure 6f,g shows images obtained from the satellite at (54.06\({}^{\circ}\) S, 72.94\({}^{\circ}\) W) after it passed through the SAA region. There were also 50 exposures, and the dark count rates decreased back to their original levels before entering the SAA region, as shown in Figure 6h. Figure 6: _Cont._  
In order to improve the quantum efficiency and the electron gain of detectors, materials with lower work functions are usually implemented for the photocathode of the incident window of the detector and the aperture of the microchannel plate. When the satellite enters the SAA region, high-energy charged particles are able to penetrate the protective structure of the detection system. These particles interact with the photocathode or the aperture wall of the microchannel plate and produce secondary electrons. After the secondary electrons have been multiplied, they are output to the detector anode under the influence of an electric field. This, in turn, is followed by an electronic circuit that converts the electrons into voltage pulses. The discriminator can recognize and count such pulses, leading to an increase in the dark count. When the instrument is removed from the SAA region, high-energy charged particles in space will return to a normal distribution, and the dark count of the system will fall back to its typical level. We should remain vigilant to large increases in particle flux in the SAA region caused by high solar activity years or other space events.