## 5 Results
### Determination of X-ray Dose Rate  
The bremsstrahlung yield is actually proportional to the atomic number of the irradiated medium. Considering the generation of electromagnetic radiation in electron beam water treatment installation, two media were considered: water and steel, as this type of media can be found under beam exit, depending on the facility of the design. In the case of water, the atomic number is low, and the yield of conversion is very low. The yield of electron of energy 930 keV conversions into electromagnetic radiation, according to simulated data is 0.16 % for 5 mm thick water layer and 0.54 % for 0.5 mm thick steel converter. Figure 4: Simulated energy spectrum of electromagnetic radiation generated by the beam of electrons of energy 930 keV. Figure 3: Simulated and experimentally determined depth dose curve of electron beam for irradiation conditions with ILU 6 accelerator. The increasing energy of electrons and the larger atomic number of target material the electrons interact with results in increasing conversion yield, as shown in Table 1.  
The conversion yield in water, which is composed of low atomic number elements hydrogen and oxygen, even in the case of irradiation with electron of energy 10 MeV, is less than 5%. In comparison, irradiation of gold, which has an atomic number of 79, can result in almost 30% conversion yield. Considering irradiation of steel, which is mainly composed of iron, with an atomic number of 26, with the addition of chromium, carbon and other alloying elements, it can be expected that the conversion yield can be similar to that of copper. The energy distribution of generated electromagnetic radiation for experimental conditions was simulated and presented in Figure 4. The overall penetration of X-rays corresponds to the penetration of photon energy between the minimum and maximum energies of the spectrum and determines penetration ability of X-rays in water and air, which contributes to the irradiating area design. According to simulated data, X-rays generated by electrons characterized with energy 930 keV in 5 mm thick water layer, which is a converter causing the generation of electromagnetic radiation, would deposit their energy in the distance less than 60 cm of water, whereas the dose rate decreases about 80% in a distance 1 m from the target in the air (Figure 5). The simulated X-ray field intensity indicated location of the highest dose and the decrease observed in the parallel and perpendicular direction to the scanned beam for the 50 cm scanning width (Figure 6). The simulated data are presented at a distance of 1 m from the converter. To determine the decrease in dose rate depending on the distance from the accelerator window, measurements were performed. The target, which was 5 mm thick water or a 0.5 mm steel sheet was placed 25 cm under the beam and the dose rate was controlled in 5 reference positions, as shown in Table 2.  
A significant amount of energy of generated electromagnetic radiation remained unabsorbed in a distance of about 1 m from the accelerator window, however in case of water irradiation the measured radiation field was almost ten-times lower than in the case of steel irradiation. \begin{table}
\begin{tabular}{c c c c c} \hline \hline \multirow{2}{*}{**Energy of** **Electrons [MeV]**} & \multicolumn{4}{c}{**Material of the Target**} \\ \cline{2-5}  & **Water** & **Aluminum** & **Copper** & **Gold** \\ \cline{2-5}  & \multicolumn{4}{c}{**Conversion Yield [\%]**} \\ \hline
2 & 1.1 & 1.1 & 2.6 & 7.3 \\
4 & 2.0 & 2.2 & 5.1 & 13.5 \\
6 & 3.0 & 3.3 & 7.6 & 18.8 \\
8 & 3.9 & 4.5 & 10.0 & 24.0 \\
10 & 4.6 & 5.7 & 11.8 & 28.1 \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Dependence of the electron conversion yield into electromagnetic radiation yield depending on the energy of electrons and material of the target [37].