arXiv subjects

F. Matias

Publications and source records attributed to F. Matias.

4 recordsLinked to original sources

arXiv2026

Sensitivity of silicon-to-water dose conversion and Bragg-peak metrics to stopping-power datasets in proton dosimetry

Accurate proton dosimetry requires consistent stopping-power data for detector-to-water conversion and Monte Carlo radiation transport. We quantify the sensitivity of water-to-silicon stopping-power ratios, converted dose-to-water distributions, and Bragg-peak metrics to the stopping-power dataset for a 67.5 MeV pristine proton beam in water. PHITS simulations used SRIM-2013, PSTAR/NIST, ATIMA, and TDDFT-Penn stopping powers up to 10 MeV, together with a common SBETHE-based extension at higher energies. The water-to-silicon stopping-power ratio showed relative entrance-to-distal variations of 17.40%$-$22.10%. Conversion of normalized PTW silicon-diode percentage-depth-ionization data yielded relative percentage-depth-dose curves with a common maximum at 36.86 mm, consistent with the experimental Bragg-peak depth of (36.81 $\pm$ 0.15) mm. The converted curves were approximately 3% below the reference throughout the entrance and plateau regions, while deviations of up to 2.1% occurred near the Bragg peak. Direct PHITS calculations predicted Bragg-peak depths of 36.575$-$36.675 mm; only the TDDFT-Penn result lay within the quoted experimental uncertainty. These results show that stopping-power treatment affects the magnitude of the converted dose more strongly than the Bragg-peak position does, and that it should be harmonized or explicitly included in uncertainty budgets for proton-beam calibration, commissioning, quality assurance, and Monte Carlo validation.

physics.med-ph↗

arXiv2025

Stopping cross-section for protons across different phases of water

Accurately quantifying the energy loss rate of proton beams in liquid water is crucial for the precise application and improvement of proton therapy, whereas the slowing down of proton in water ices also plays an important role in astrophysics. However, precisely determining the electronic stopping power, particularly for the liquid phase, has been elusive so far. Experimental techniques are difficult to apply to volatile liquids, and the availability of sufficient reliable measurements has been limited to the solid and vapor phases. The accuracy of current models is typically limited to proton energies just above the energy-loss maximum, making it difficult to predict radiation effects at an energy range of special relevance. We elucidate the phase differences in proton energy loss in water in a wide energy range (0.001-10 MeV) by means of real-time time-dependent density functional theory combined with the Penn method. This non-perturbative model, more computationally-efficient than current approaches, describes the phase effects in water in excellent agreement with available experimental data, revealing clear deviations around the maximum of the stopping power curve and below. As an important outcome, our calculations reveal that proton stopping quantities of liquid water and amorphous ice are identical, in agreement with recent similar observations for low-energy electrons, pointing out to this equivalence for all charged particles. This could help to overcome the limitation in obtaining reliable experimental information for the biologically-relevant liquid water target.

physics.med-ph↗

arXiv2024

Deeper-band electron contributions to stopping power of silicon for low-energy ions

This study provides accurate results for the electronic stopping cross-sections of H, He, N, and Ne in silicon in low to intermediate energy ranges using various non-perturbative theoretical methods, including real-time time-dependent density functional theory, transport cross-section, and induced-density approach. Recent experimental findings [Ntemou \textit{et al.}, Phys. Rev. B {\bf 107}, 155145 (2023)] revealed discrepancies between the estimates of density functional theory and observed values. We show that these discrepancies vanish by considering the nonuniform electron density of the silicon deeper bands for ion velocities approaching zero ($v \to 0$). This indicates that mechanisms such as ``elevator'' and ``promotion,'' which can dynamically excite deeper-band electrons, are active, enabling a localized free electron gas to emulate ion energy loss, as pointed out by [Lim \textit{et al.}, Phys. Rev. Lett. {\bf 116}, 043201 (2016)]. The observation and the description of a velocity-proportionality breakdown in electronic stopping cross-sections at very low velocities are considered to be a signature of the deeper-band electrons' contributions.

physics.chem-ph↗

arXiv2024

Modeling of Proton Interaction with Organic Polymers: Implications for Cancer Therapy and Beyond

This comprehensive study delves into the intricate interplay between protons and organic polymers, offering insights into proton therapy in cancer treatment. Focusing on the influence of the spatial electron density distribution on stopping power estimates, we employed time-dependent density functional theory (TDDFT), coupled with the Penn method. Surprisingly, the assumption of electron density homogeneity in polymers is fundamentally flawed, resulting in an overestimation of stopping power values at energies below 2 MeV, approximately. Moreover, Bragg's rule application in specific compounds exhibited significant deviations from experimental data in the Bragg peak region, challenging established norms.

physics.atom-ph↗