Electronic-mediated nuclear stopping power in proton irradiated water ice

TL;DR

This study reveals a novel electronic-mediated nuclear stopping mechanism in proton-irradiated water ice, involving energy transfer between electronic and nuclear subsystems, explaining previously unexplained experimental observations.

Contribution

It introduces a new understanding of proton stopping in water ice by demonstrating the interplay of electronic and nuclear effects through advanced simulations.

Findings

Identifies a new electronic-mediated nuclear stopping mechanism.

Shows a significant isotopic effect in stopping power.

Aligns with and explains long-standing experimental results.

Abstract

Traditionally, it has been assumed that the stopping of a swift ion travelling through matter can be understood in terms of two essentially independent components, i.e. electronic vs. nuclear. Performing extensive Ehrenfest MD simulations of the process of proton irradiation of water ice that accurately describe not only the non-adiabatic dynamics of the electrons but also of the nuclei, we have found a stopping mechanism involving the interplay of the electronic and nuclear subsystems. This effect, which consists in a kinetic energy transfer from the projectile to the target nuclei thanks to the perturbations of the electronic density caused by the irradiation, is fundamentally different from the atomic displacements and collision cascades characteristic of nuclear stopping. Moreover, it shows a marked isotopic effect depending on the composition of the target, being relevant mostly for light water as opposed to heavy water. This result is consistent with long-standing experimental results which remained unexplained so far.