# Characterization of Ultra-High-Dose Rate Electron Beams with ElectronFlash [PERSON]
## 3 Results  
### Measurements of Dose Parameters  
The results of dose measurements performed with gafchromic films at the R100 point using the previously applicators described (A-d30 and A-d120) at 5 MeV and 7 MeV with a maximum pulse width of 4 us, are reported in Table 2. The uncertainty for the EBT-XD dose determination is \(\pm\)5%. In all cases, the dose per pulse is above the FLASH threshold (>1 Gy). It is worth noting that the dose per pulse of A-d30 is higher than A-d120 by a factor of approximately 6, due to the reduced surface of irradiation and the shorter length of the applicator. Table 3 reports the maximum instantaneous dose rate with a pulse duration of 4 us, and the average dose rate, calculated with the repetition frequency of 250 Hz. These dose rates, together with the dose per pulse, define the FLASH regime. We notice that the reference values of 10\({}^{6}\) Gy/s (instantaneous dose rate) and 100 Gy/s (average dose rate) are easily achieved with the A-d30 applicator normally used for in vivo experiments. In the case of the A-d120 applicator, the dose per pulse and the average dose rate fulfill  
Figure 4: EF at 5 MeV (**left**) and 7 MeV (**right**) normalized planar fluence out of the linac. The energy bin width is 50 keV. The two energy spectra were obtained using the TSTEP code, a derivative of Parmela, for beam dynamics simulation [29]. the reference values adopted for FLASH, while the instantaneous dose is a bit lower than \(10^{6}\) Gy/s (it is \(0.75\times 10^{6}\) Gy/s at \(7\) MeV and \(0.5\times 10^{6}\) G/s at \(5\) Mev), nevertheless, in ref. [7], it was shown that these values are sufficient to observe FLASH effects in radiobiological experiments. Furthermore, by making use of the values of the charge in the pulse of 4 us measured with the Faraday cup, we also calculated the dose per nC (Gy/nC). These data are reported in Table 4 for the same cases of Table 2.  
During the measurement campaign, we also investigated the dependence of the dose on the pulse width. Figure 5 reports the results for applicators A-d30 and A-d120 and at the energies of \(5\) MeV and \(7\) MeV. The dose was measured with the EBT-XD films positioned on the top of the Faraday cup. R-squared analysis shows a linear relationship between the dose and the pulse width. We also observe that in the case of the A-d30 applicator, the delivered dose per pulse is >1 Gy in the entire range of measurement. Conversely, in the case of the A-d120, the dose only reaches the FLASH threshold for irradiation pulses larger than \(2\) us. In the case of \(7\) MeV, the linear fit extrapolation does not cross the zero value, suggesting the uncertainty of pulse widths <1 us, and of the corresponding charge in the pulse. \begin{table}
\begin{tabular}{c c c} \hline
**Applicator Size o(mm)** & **7 MeV (Gy/nC)** & **5 MeV (Gy/nC)** \\ \hline
120 & 0.012 & 0.014 \\
30 & 0.08 & 0.11 \\ \hline \end{tabular}
\end{table} 
Table 4: Summary of film and Faraday cup measurements. Beam size: A-d30 (\(\phi=30\) mm) and A-d120 (\(\phi=120\) mm); the dose per pulse is calculated on film with an uncertainty of \(5\%\). The charge measurements were performed using a Faraday cup. The table shows the dose per pulse in Gy/nC, obtained with different applicators for a pulse duration of 4 μs. \begin{table}
\begin{tabular}{c c c} \hline
**Applicator Size o(mm)** & **7 MeV Dose per Pulse (Gy)** & **5 MeV Dose per Pulse (Gy)** \\ \hline
120 & 3 & 2 \\
30 & 19 & 12.3 \\ \hline \end{tabular}
\end{table} 
Table 2: Dose per pulse measurements with film (uncertainty of \(5\%\)), obtained with different applicators for a 4 pulse duration of μs at energies at \(5\) MeV and \(7\) MeV. \begin{table}
\begin{tabular}{c c c} \hline
**Applicator Size o(mm)** & **7 MeV Dose per Pulse (Gy)** & **5 MeV Dose per Pulse (Gy)** \\ \hline
120 & 3 & 2 \\
30 & 19 & 12.3 \\ \hline \end{tabular}
\end{table} 
Table 3: Dose rate measurements with the film (uncertainty of \(5\%\)), obtained with different applicators for a pulse duration of 4 μs at energies of \(5\) MeV and \(7\) MeV.