Kalliopi Kaperoni

Proton therapy offers superior dose localization, yet the biological effects of low-energy protons relevant to superficial tissues remain underexplored. We report the design and validation of a proton irradiation setup developed at the Tandem Accelerator of NCSR “Demokritos” for controlled radiobiological experiments. Monte Carlo simulations using Geant4 and Monte Carlo Damage Simulation (MCDS—Monte Carlo Damage Simulation) were used to determine proton energy spectra, linear energy transfer (LET), and predicted DNA damage yields. A single layer (15–20 μm in thickness) of human keratinocytes (HaCaT) was irradiated at doses from 0.65 to 3.65 Gy, and γ-H2AX foci were quantified as markers of tracks including one or more DNA double-strand breaks. The system achieved a uniform dose rate of 0.37 Gy/min, as calculated with Geant4, with a mean proton energy of 4.1 MeV (LET ≈ 8 keV/μm). A strong correlation (R² = 0.93) was observed between proton dose and γH2AX foci per nucleus (~10 foci/Gy), reflecting damage-inducing proton tracks rather than individual DNA double-strand breaks. At higher doses, an increased fraction of cells exhibited pan-nuclear γH2AX staining, characterized by a diffuse γH2AX signal throughout the nucleus and commonly associated with extensive or clustered DNA damage and global chromatin phosphorylation. These responses are consistent with the well-established dense ionization patterns produced by low-energy protons, as indicated by the LET spectrum and supported by MCDS-predicted clustered damage yields. While the γH2AX assay does not directly resolve simple versus complex DNA lesions, the agreement between Monte Carlo modeling and the observed cellular stress responses indicates that the irradiation platform reliably reproduces the expected biological signatures of low-energy proton exposure. Consequently, the developed system provides a robust experimental tool for systematic investigations of cellular radiosensitivity and radiotoxicity, with potential applications in skin dosimetry and radioprotection.

Accurate neutron flux measurements in fusion reactors are essential, in order to determine the feasibility and progress of the reaction as well as for safety issues. Semiconductor neutron detectors exhibit promising characteristics for operation in the extreme environmental conditions of fusion reactors. Silicon, Diamond and Silicon Carbide are the most studied and anticipated materials for constructing detectors with high efficiency and irradiation resistance. The ITER fusion reactor is expected to run D-D plasma measurements in the near future, so the detection of 2.45 MeV neutrons with appropriate detectors is of great and immediate importance. In the present work the study of 2.45 MeV neutrons interactions with a silicon, diamond and silicon carbide detector was made, using GEANT4 [1] simulations, in order to compare their response. An experimental study will follow at the neutron production facility of the TANDEM accelerator of the I.N.P.P. of the NCSR “Demokritos”, with detectors provided by CIVIDEC Instrumentation GmbH, so the geometry of the simulations was built accordingly. A quasi-monoenergetic neutron beam of 2.45 MeV was produced through ³H(p,n) reactions in a TiT target. Due to the low cross section of the reaction, biasing techniques were implemented in the simulation to increase the counting rate and thus producing realistic results. These biasing techniques were studied, with various tests and the parameters affecting the choice of the biasing factor are shown and discussed.