## 6 Discussion  
Having thus calibrated and characterised the Timepix3 Radiation Monitor, it is at this stage relevant to assess its suitability to perform measurements in the CERN accelerator complex, e.g., in the LHC radiation field described in Section 2. Using the FLUKA model of the detector, additional simulations are employed to evaluate the energy deposited in the active volume of the sensor by particles with the characteristic energy distributions of the LHC mixed field, i.e., for the spectra shown in Figure 1. To a first approximation, the particles are assumed to be perpendicularly incident on the detector, even though in realistic cases, they may hit it at various angles depending on the radiation source location. The expected distribution of the deposited energies within the Timepix3 Radiation Monitor is shown in Figure 16 for the most prevalent particle species in the LHC mixed field. The detection efficiency for the charged particles in the silicon sensor is effectively 100%, and the majority of those that would reach the detector in the LHC tunnel have high energies and longer ranges, such that they pass through the entire active volume depositing similar amounts of energy (corresponding to the main peaks in Figure 16), implying that the detector can be used to measure charged particle fluxes, rather than being capable of restoring the full energy spectrum of Figure 16. Charged particles with shorter range can deposit more energy, up to a maximum given by the particle energy for which the range is equal to the active volume thickness (which is evaluated at \(W=250\,\mathrm{\SIUnitSymbolMicro m}\), for a bias voltage of \(V_{bias}=50\,\mathrm{V}\)), which is about \(5\,\mathrm{MeV}\) for protons and about \(2\,\mathrm{MeV}\) for muons and pions. At these energies, the distributions in the figure are exhibiting visible \"knees\". Concerning neutral particles, the energy deposition from photons does not exhibit peaks, and it is limited to a maximum of \(1\,\mathrm{MeV}\). Neutrons have a low detection efficiency, and when they interact elastically, their energy deposition is also expected to be low. Figure 16: Distribution of the energy deposited in the active volume of the Timepix3 Radiation Monitor by the particles composing the LHC mixed radiation field (from Figure 1), simulated with FLUKA with perpendicular incidence on the sensor. The vertical lines correspond to the detection threshold at \(8\,\mathrm{keV}\), below which pixel hits are missed, and the \(2\,\mathrm{MeV}\)/cluster level, above which one sees evidence of saturation effects. The neutron histogram is affected by the low detection efficiency, and it is scaled up by a factor of 10 for visualization purposes. The hadrons can also interact inelastically, in which case higher energy deposits are expected, often well beyond the saturation threshold, as clearly visible in Figure 16. Indeed, the simulations show that the largest energy depositions in the Timepix3 Radiation Monitor at the LHC are caused by inelastic nuclear reactions, which can be induced by neutrons and protons but also by pions. These could potentially be used to indirectly measure the HEH fluence (similarly to the RadMon detection mechanism [4]), either by operating with a high threshold, thereby filtering out the lower energy deposition events (i.e., the elastic interactions) or if the cluster properties would exhibit meaningful differences. Finally, Table 2 quantifies the fraction of particle hits from different particles in the LHC mixed field, leading to energy depositions below the detection threshold of 8 keV in the linear calibration region, and above the 2 MeV cluster-level saturation threshold. In addition, the table also quantifies the fraction of the total ionizing dose (equivalent to the fraction of deposited energy) falling into the same three categories.