## 7 Conclusions  
Within the framework of R2E activities at CERN, a 300 \(\upmu\)m thick silicon Timepix3 detector was characterized as a radiation monitor for the measurement of the mixed field of the LHC accelerator. The LHC radiation field includes different kinds of particles with broad energy spectra, all originating from the interaction of TeV-scale beam particles or secondary collision products, as simulated with the FLUKA Monte Carlo code. A detailed description of the Timepix3 Radiation Monitor was given, covering the hardware setup and of the Timepix detection principle based on the simultaneous measurement of the time-over-threshold (ToT) and time-of-arrival (ToA). The charge released in the interaction of ionizing particles within the pixel matrix is typically spread over multiple pixels, leading to the need for a cluster reconstruction algorithm to identify the individual particle hits, for which the DPE [48] package has been used. From the literature, it is known that the Timepix calibration procedure, which translates the measured ToT per pixel into deposited energy, presents several regions of distinct dependency, including complex \begin{table}
\begin{tabular}{c c c c c c c} \hline \hline \multirow{2}{*}{**Particle**} & \multicolumn{2}{c}{**Below Threshold**} & \multicolumn{2}{c}{**Linear Regime**} & \multicolumn{2}{c}{**Saturation Effects**} \\  & **Counts [\%]** & **TID [\%]** & **Counts [\%]** & **TID [\%]** & **Counts [\%]** & **TID [\%]** \\ \hline Protons & 12 \(\times\) 10\({}^{-6}\) & 1.14 \(\times\) 10\({}^{-8}\) & 97 & 76 & 3 & 24 \\ Muons & 0.7 \(\times\) 10\({}^{-3}\) & 7.51 \(\times\) 10\({}^{-4}\) & 99 & 93 & 0.8 & 7 \\ Pions & 15 \(\times\) 10\({}^{-3}\) & 8.16 \(\times\) 10\({}^{-4}\) & 99 & 95 & 0.3 & 5 \\ Electrons & 12 \(\times\) 10\({}^{-3}\) & 9.73 \(\times\) 10\({}^{-4}\) & 99 & 99 & 1.25 \(\times\) 10\({}^{-4}\) & 2.93 \(\times\) 10\({}^{-3}\) \\ \hline Photons & 22 & 2 & 78 & 98 & 0 & 0 \\ Neutrons & 92 & 1 & 7.4 & 28 & 0.4 & 71 \\ \hline \hline \end{tabular}
\end{table} 
Table 2: The expected fraction of particle counts and fraction of the total ionizing dose (TID) deposited in the Timepix3 Radiation Monitor, as simulated in FLUKA, below the detection threshold (8 keV), in the linear calibration regime, and above the saturation threshold of 2 MeV. saturation effects at high energy. To mitigate these effects, the Timepix3 Radiation Monitor is operated in hole collection mode at a partial bias voltage of 50 V, enhancing the charge sharing between pixels. The energy calibration of the Timepix3 Radiation Monitor was carried out at the Centro Nacional de Acceleradores (CNA) using quasi-mono energetic beams of protons (alphas) from 0.6 (1) to 5 (5.6) MeV stopping in the active volume of the sensor. The energy deposition in the passive front layers (a known 500 nm metalisation layer and a silicon dead layer of an unknown thickness but experimentally determined) is computed using dedicated Monte Carlo simulations performed with FLUKA. The clusters formed by the CNA beams are reconstructed and filtered using dedicated shape parameters, ensuring that single particle hits are fully reconstructed and isolated. The cluster-level calibration analysis indicates that the detector operates in a linear regime with \(\mathit{ToT}_{\mathit{reg}}(E_{dep})=E_{dep}\cdot 993\pm 93\) [25 ns/MeV] + \(N\cdot 23.10\cdot 2.14\) [25 ns/pixel], while evidence of saturation effects is visible for energy depositions above 2 MeV, especially for the case of proton beams. At the pixel level, the saturation is estimated to occur from around 600 keV. The larger levels of saturation observed with protons compared to alphas are found to be associated with a different degree of charge sharing in the respective clusters, thus confirming that operating the sensor with a reduced bias voltage to enhance charge sharing is a good strategy to mitigate the saturation. No evidence of high-energy non-linear saturation or volcano effect is observed in the data.