## 4 Discussion  
Amplifications were implemented under varying tube voltage (kVp) and tube current-time product (mAs) conditions, owing to kVp and mAs being fundamental X-ray machine settings that are correlated to X-ray absorbed doses [20; 21]. In other words, radiation-induced signals as a result of tube voltage and tube current-time product alteration were amplified. All the amplified signals were linear to the tube current-time product (mAs) and tube voltage (kVp), similar to [PERSON] [22] and [PERSON]'s [5] work. Tube current-time product (mAs) is a tube setting that regulates the X-ray beam's population (number of photons in the X-ray beam) [14]. During mAs variation, Figure 5a shows a 3.49% decrease in the signal linearity coefficient (R-square) when the chip number was increased from 60 to 120. In this case, the R-square signifies the extent to which the signal data points conform to the linear fitting during mAs variation. When the chip number was doubled to 120 chips, it could be considered that there was no change in the linearity coefficient (the change was trivial). This is because only a 3.49% change was observed, and this change is below the 5% uncertainty (95% confidence interval) [23]. \begin{table}
\begin{tabular}{c c c c c} \hline \hline
**Signal Amplification Mode** & \multicolumn{3}{c}{**X-ray Beam Parameter**} \\ \hline  & Tube current-time & Tube Voltage & Dose & Source-to-Detector Distance, SDD \\  & product (mV/mAs) & (mV/kVp) & (mV/mGy) & 60 cm & 90 cm \\  & & & & Percentage increase in Signal \\  & & & & & Fading (\%) \\ Chip number increment & & & & \\ from 60 to 120 chips & 90.99 & 70.97 & 89.30 & 99.52 & 105.03 \\ Amplifier Board with a gain & & & & \\ of 10\({}^{9}\) V/A & 36.99 & 27.55 & 38.10 & 40.70 & 39.05 \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Percentage Signal Variation Per Unit X-ray Parameter. \begin{table}
\begin{tabular}{c c c c c} \hline \hline
**Amplification Mode** & \multicolumn{3}{c}{**CoV for Each X-ray Beam Parameter**} & \multicolumn{2}{c}{**Average CoV**} \\ \hline  & Tube current-time & Tube & Source-to-Detector & Based on each \\  & product—mAs (\%) & Voltage—kVp (\%) & Distance—SDD (\%) & amplification mode (\%) \\ Chip number increment & & & & \\ from 60 to 120 chips & 6.167 & 11.058 & 8.987 & 8.737 \\ Amplifier Board with a gain of 10\({}^{9}\) V/A & 9.028 & 10.067 & 9.177 & 9.424 \\ \hline \hline \end{tabular}
\end{table} 
Table 2: Signal coefficient of variation (CoV) associated with each amplification mode. Additionally, amplification of different radiation intensity-induced signals was realized with SDD variation. The detected signals during SDD variation highly conformed to the exponential decay fit, because radiation intensity reduces in the form of an exponential decay graph, as the distance from the radiation source (SDD) is increased. This exponential decay conforms to the Lambert-Beer Law [11; 24], I = I\({}_{0}\)E(\(-\)kx), where I\({}_{0}\) is the initial radiation intensity and I is the radiation intensity after the radiation travels a distance x through a medium with an absorption coefficient constant k.  
PIN photodiode active area is directly proportional to the collected signal, because the radiation-induced current (I\({}_{\rm D}\)) is equivalent to the product of the PIN photodiode constant (k), active area (A), depletion layer width (\(w\)), and the incident radiation's dose rate (D\({}_{\rm R}\)), i.e., I\({}_{\rm D}\) = k\(\Delta w\)D\({}_{\rm R}\)[25]. However, the magnitudes of k, A, and \(w\) are predetermined by the transducer manufacturer. Therefore, users cannot expand the transducer intrinsic active area size. Nonetheless, the effective active area could be increased by connecting multiple sole transducers in the form of an array. LED active area is directly proportional to the detected signal when applied as a radiation detector because LEDs could be assumed as photodiodes that do not detect, but rather emit light.