Artigo | Stopping Cross Sections for Protons Across Different Phases of Water
Dos autores F. Matias, N. E. Koval, P. de Vera, R. Garcia-Molina, I. Abril, J. M. B. Shorto, H. Yoriyaz, J. J. N. Pereira, T. F. Silva, M. H. Tabacniks, M. Vos e P. L. Grande.
Publicado em Physical Review Letters.
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Trabalho conta com os docentes Tiago Fiorini da Silva e Manfredo Tabacniks (IFUSP) como coautores e foi selecionado como sugestão do editor no último número da PRL ( Vol. 135, #14, de 03/10/25).
De acordo com o pesquisador Tiago Fiorini, "O trabalho aborda como prótons perdem energia ao atravessar diferentes fases da água, líquida, sólida e vapor, tema fundamental tanto para o avanço de aplicações, como a terapia com prótons no tratamento do câncer, quanto para o entendimento de processos astrofísicos. Utilizando uma abordagem baseada em teoria do funcional da densidade dependente do tempo (TDDFT), os autores demonstraram que a água líquida e o gelo amorfo apresentam comportamento equivalente na desaceleração de prótons, o que abre novas possibilidades experimentais e computacionais."
Abstract:
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 protons 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 nonperturbative 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 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.
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